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    Circuit protection is a frequently discussed topic, and the various types of circuit protection differ due to the various problems in the circuit. Short-circuit, overload, grounding, and lightning strikes are the most common faults in power supply systems. To ensure the safe and dependable operation of the power supply system, protection devices must be installed to monitor the working conditions of the power supply system, detect faults in time, and cut off the power supply of the faulty equipment, preventing the accident from spreading. In general, the protection circuit is made up of various relays, signal indicating devices, and other components. This blog provides an in-depth discussion on several circuit protections. Below is an introduction video about short circuit protection. DIY Short Circuit (Overcurrent) Protection   Catalog   I Introduction to circuit protection II Switching power principle and characteristics      2.1 Operational principle of switching power      2.2 Characteristic of switching power III DC Switching power supply protection      3.1 Overcurrent protection circuit      3.2 Overvoltage protection circuit      3.3 Soft start protection circuit        3.4 Overheat protection circuit IV Conclusion FAQ   I Introdcution to circuit protection The operation of electronic equipment can not be separated from electricity, so DC switching power supply which can control the electricity is playing a more and more important role. And it has entered various fields of electronics and electrical equipment: SPC exchange, communication, electronic testing equipment power supply and controlling equipment power supply, which are widely used DC switching power supply.  Meanwhile, with the development of many high-tech technologies, including high-frequency switching technology, soft-switching technology, power factor correction technology, synchronous rectifier technology, intelligent technology, surface installation technology, etc., switching power supply technology is constantly innovating. This provides a wide range of development for DC switching power supply.  DC current diagram   But the circuit is complex to control in the switching power supply, the transistor and the integrated device have poor resistance to electricity and thermal shock, which brings great inconvenience to the user in the process of using. In order to protect the safety of switching power supply itself and load, the overheat protection, over-current protection, over-voltage protection and soft start protection circuit are designed according to the principle and characteristics of DC switching power supply.   II Switching power principle and characteristics 2.1 Operational principle of switching power DC switching power supply is composed of input part, power conversion part, output part and control part. The power conversion part is the core of the switching power supply. It performs conversion which needed for the output on the high-frequency and unstable DC. It is mainly composed of switching transistor and high frequency transformer. Figure 1. DC Switching power supply principle Figure 1 shows the schematic diagram and equivalent schematic block diagram of DC switching power supply, which is composed of full wave rectifier, switching tube V, excitation signal, fly-wheel diode Vp, energy storage inductance and filter capacitance C. In fact, the core part of DC switching power supply is a DC transformer. 2.2 Characteristic of switching power   In order to meet the needs of users, the world's major switching power supply manufacturers are committed to the simultaneous development of new and highly intelligent components, especially by reducing the loss of the secondary rectifier. In order to improve the magnetic properties under high frequency and high magnetic flux density, power ferrite (Mn-Zn) materials have been developed. At the same time, the application of SMT technology in the field of switching power supplies has also made considerable progress. The components are arranged on both sides of the circuit board to ensure that the switching power supply is light, small and thin. Therefore, high frequency, high reliability, low power consumption, low noise, anti-interference and modularization are the development trends of DC switching power supplies. However, DC switching power supplies also have disadvantages. The DC switching power supply switch has serious interference, and its ability to adapt to harsh environments and sudden failures is weak. There is still a certain gap in microelectronics technology in developing countries. Specifically, the production technology of resistors and capacitors and the technology of magnetic materials are compared with those of some technologically advanced countries. Therefore, the manufacture of DC switching power supplies is very difficult. In most parts of the world, maintenance is difficult and the cost is high. III DC Switching power supply protection Based on the characteristics of DC switching power supply and the actual electrical condition, in order to make DC switching power supply work safely and reliably in bad environment and sudden fault, this paper designs a variety of protection circuits according to different conditions. 3.1 Overcurrent protection circuit   Figure 2. Input Overcurrent protection circuit In DC switching power supply circuit, in order to avoid short circuit and overflow damage to protect the regulator tube in the circuit, the basic method is that, when the output current exceeds a certain value, the regulator tube is in the reverse bias state, thus the circuit current is cut off automatically. As shown in Fig. 2, the over-current protection circuit consists of transistor BG2 and divider resistor R4, R5. When the circuit works normally, the base potential of BG2 is lower than that of emitter through the partial voltage interaction between R4 and R5, and the emitter junction bears reverse voltage. So the BG2 is in the cutoff state (equivalent to open circuit), which is used to stabilize the voltage. But the voltage stabilizing circuit has no effect. When the circuit is short circuit, the output voltage is zero and the emitter of BG2 is equivalent to grounding, then the BG2 is in the state of saturation conduction (equivalent to short circuit), so that the regulator tube BG1 base and emitter are close to short circuit, and in the cut-off state, the circuit current is cut off to achieve the purpose of protection.   3.2 Overvoltage protection circuit The overvoltage protection of switching regulator in DC switching power supply includes input overvoltage protection and output overvoltage protection. If the voltage of the unstabilized DC power supply (such as batteries and rectifiers) used by the switching regulator is too high, it will cause the switching regulator to fail to work properly and even damage the internal devices. Therefore, it is necessary to use the input overvoltage protection circuit in the switching power supply. Fig. 3 is a protection circuit composed of transistors and relays, in which the voltage of the input DC power supply is higher than the breakdown voltage of the zener diode, at this condition, current flows through resistor R, making diode T conducts. Following these electrical actions, relay operates and common closed contact disconnected, inputting current. The polarity protection circuit of the input power supply can be combined with the input overvoltage protection to form the polarity protection identification and overvoltage protection circuit. Figure 3. Input overvoltage protection circuit 3.3 Soft start protection circuit The circuit of switching power supply is complex, the input end of switching regulator is usually connected with small inductance and large-capacitance input filter. At start-up instant, the filter capacitor flows through a large surge current that can be several times the normal input current. Such a large surge current melts the contacts of the normal power switch or the relay and melts the input fuse. In addition, surge current can also damage capacitors, shorten their life, cause premature damage. To this end, a current-limiting resistance should be connected in the circuit, through this current-limiting resistance to charge the capacitor. In order not to consume too much power by the current limiting resistance, and avoid affecting the normal operation of the switching regulator, therefore a relay is used to connect it automatically after the transient process is finished, which makes the DC power supply directly to the switching regulator. This is called the "soft start" circuit of DC switching power supply. Figure 4. Soft start-up protection circuit When the power supply is switched on, capacitor C is charged by input voltage through rectifier bridge (D1 ~ D4) and current-limiting resistance R1 to limit the surge current. The inverter works normally when the capacitor C is charged to about 80% rated voltage. The trigger signal of thyristor is generated by auxiliary winding of main transformer, which makes thyristor switch on and short circuit current-limiting resistance R1, and the switching power supply is in normal operation state. In order to improve the accuracy of the delay time and prevent the relay operation from shaking and oscillating. The delay circuit can replace the RC delay circuit by the circuit shown in figure 4(b). 3.4 Overheat protection circuit The high integration and light weight of switching regulator in DC switching power supply greatly increase the power density per unit volume, so if the internal components of the power supply do not have a corresponding increase in the temperature of its working environment, it will inevitably make the circuit performance damaged and components life service shortened prematurely. Therefore, overheating protection circuit should be installed in high power DC switching power supply. Figure 5. Overtemperature protection circuit In this paper, the temperature relay is used to detect the internal temperature of the power supply device. When the inside of the power supply device is overheated, the temperature relay operates, which makes the alarm circuit of the whole machine in the state of alarm and realizes the protection of the overheating of the power supply.  As shown in Fig. 5 (a), the P type control gate thermal thyristor is placed near the power switch transistor in the protection circuit. According to the characteristics of the TT102 (the on-on temperature of the device is determined by the Rr value, the larger the Rr is, The lower the conduction temperature), when the temperature of the power tube or the temperature inside the device exceeds the allowable value, the thermal thyristor is switched on and the LED is lighting to give an alarm. If cooperate with photoelectric coupler which can make whole machine alarm circuit operation, protecting switch power supply.  The circuit can also be designed as shown in Fig. 5 (b) to protect the power transistor from overheating. The base current of the switching transister is bypassed by the TT201 of the N type control gate thermal thyristor, and the switch tube is cut off, also the collector current is cut off, and the overheating is prevented. IV Conclusion This blog mainly discusses various protection methods of internal devices in DC switching power supply, and introduces some concrete circuits. For a given DC switching power supply, it is very important for the security and reliability of the power supply device whether the protection circuit is perfect and set up to work necessarily. Because the protection scheme and circuit structure of switching power supply are diverse, reasonable protection scheme and circuit structure should be chosen for specific power supply devices. In practical application, several protection methods are usually used to form a perfect protection system to ensure the normal operation of DC switching power supply.   FAQ   1. What is the purpose of circuit protection? The basic goals of circuit protection are to 1) localize and isolate the condition or fault and 2) prevent and minimize any unnecessary power loss. There are several types of abnormal conditions that may occur throughout a building's life, in which an electrical system must be designed to correct or overcome.   2. What protective devices are used in circuits? Fuses, MCBs, RCDs, and RCBOs are all devices used to protect users and equipment from fault conditions in an electrical circuit by isolating the electrical supply.   3. How do you protect a circuit design? The most basic device is a fuse, a type of low resistance resistor that acts as a sacrificial device to provide over current protection, of either the load or source circuit. A fuse protects the circuit, but once it's utilized, it's kaput.   4. What are the two main circuit protection devices? The two types of circuit protection devices discussed in this chapter are fuses and circuit breakers. A fuse is the simplest circuit protection device. It derives its name from the Latin word "fusus," meaning "to melt." Fuses have been used almost from the beginning of the use of electricity.   5. What is a DC switching power supply? A Switching DC power supply (also known as switch mode power supply) regulates the output voltage through a process called pulse width modulation (PWM). The PWM process generates some high frequency noise, but enables the switching power supplies to be built with very high power efficiency and small form factor.   6. What are the differences between linear DC power supply and switching power supply? Linear power supplies deliver DC by passing the primary AC voltage through a transformer and then filtering it to remove the AC component. Switching power supplies feature higher efficiencies, lighter weight, longer hold up times, and the ability to handle wider input voltage ranges.   7. Can I use a switching power supply to drive a DC motor? A simple unregulated analog power supply may be easier and be able to supply the large starting under load current more that the switching one. DC motors are not too fussy about the supply, and will usually run quite well on unfiltered DC.   8. Do I need a switching power supply? The switching power supply implies higher efficiency due to the high switching frequency, enabling it to use a smaller, less-costly high-frequency transformer as well as lighter, less-costly filter components. Switching power supplies contain more overall components, therefore are usually more expensive.   9. What are the 3 types of power supply? There are three subsets of regulated power supplies: linear, switched, and battery-based. Of the three basic regulated power supply designs, linear is the least complicated system, but switched and battery power have their advantages.   10. What is a switching mode power supply used for? Switched-mode power supplies are used to power a wide variety of equipment such as computers, sensitive electronics, battery-operated devices and other equipment requiring high efficiency.    

Regarding the design of a micropower isolated power supply for the two-wire transmitter, we must know what is the transmitter first. When the output of the sensor is a specified standard signal, it is called a transmitter. A sensor, usually composed of sensitive elements and conversion elements, is a floorboard for a component or device that can be measured and converted into a usable output signal according to certain rules. And the common types are power transmitters, current-voltage transmitters, and so on.How to Build a FM Radio Transmitter CatalogI. Brief Introduction to Internal Micro-power Supply DesignII. Overall DesignIII. Constant Current Voltage Stabilizing CircuitIV. DC/CD in CircuitV. Isolated Power Source WindingVI. ConclusionFAQ I. Brief Introduction to Internal Micro-power Supply Design The design of an internal micro-power supply is very important when developing a low-power intelligent two-wire transmitter. Firstly, in order to satisfy the power supply of the micro-controller, A/D, D/A, and communication circuit, the intelligent transmitter with microprocessor needs more power than that of an ordinary 4~20mA one), and its power supply efficiency of the internal power supply must be higher.  In addition, for capacitive sensors and thermocouples, it is necessary to consider the case of grounding or the possibility of the sensor earthing. So the input and output of the designed transmitter circuit must be isolated, only this way can guarantee the normal operation of the follow-up control system and the ability of anti-common-mode interference.  Since the external circuit provides the maximum working current of 4mA for the two-wire transmitter system, specific requirements like this bring great difficulties and challenges to the design of the power supply of the system. Adopting a full integrated circuit, the isolated two-wire transmitter power supply with micro-input power has the advantages of simple structure, stable performance, and low cost. And it takes the 12~35V DC as the input power, designing the simple input circuit of the constant current and stable voltage front end, fixing the consumption of 315mA current, and providing two sets of isolated 3V power supply. In this case, the not isolated imputing group with maximum 5mA load capacity and the isolated imputing group with maximum 3mA load capacity, which can meet the requirements of input and output isolating two-wire transmitters for power supply.  II. Overall Design Fig.1 is a schematic diagram of the power supply. It consists of three main parts: 315mA/812V constant current voltage stabilizing circuit composed of U1, R1, and Z1; DC/DC converter circuit composed of U2 as the core; and a set of isolated power supply composed of L2 and U3. The system is designed to be concise and highly integrated, and all selected components can work at -40 ~ 85 ℃, which can ensure the reliable application of the power supply to field transmitters.Fig.1 Schematic Diagram of Power Supply III. Constant Current Voltage Stabilizing Circuit As a power supply to the two-wire transmitter, the maximum working current is 4mA. The transmitter with this power supply needs some low zero output indication, so the general system power supply standard is usually below 315mA, meanwhile, this type of power supply must have constant current characteristics to meet the operating requirements of the two-wire transmitter. And there are many ways to design constant-current sources. The design in Fig.2 adopts the three-terminal adjustable voltage stabilizer LM317L to design a constant-current source. LM317L is a three-terminal adjustable voltage stabilizer, and its application is as follows in Fig.2. Its basic application as a standard regulator is shown in Fig.2 (a), where a steady pressure difference is generated between the output and adjustment terminal, the typical value is 1125V, so its output voltage is VO=1125 (1+Ra/Rb). Because of the stable pressure difference of LM317, it is often used to design the constant-current source. Fig.2 (b) is a typical application circuit, which generates a current of I=1125 / R, consulting Fig.1; the R1 value in the design is 360Ω, so you can obtain a constant current of about 315mA.  Considering the working voltage range of the subsequent DC/DC chip is 4~11V and the actual out the power supply, a voltage stabilizer Z1 with 812V is used to parallel the voltage stabilizing function while providing a stable inlet voltage for U2. It requires that the U2 total current consumption is less than 314mA and Z1 must be the high-quality voltage stabilizer with the breakdown current less than 011mA (Philips products can be used, the lowest static stable current is only dozens of μA). Fig.2 Typical Application of LM317LThe D1 of the front end of the circuit is an anti-inversion diode( as shown in Fig.1), generally using 1N4148. The fuse is the PTC device self-recovery fuse, its parameter is 100mA/ 60V, which ensures that the external power supply will not be affected when the power supply fails. The field transmitter is the final application of the power supply. Its changing ambient temperature is in a wide range, so the temperature drift must be taken into account. The main temperature drift of the power supply is the constant current drift, which is caused by the temperature drift of the reference voltage difference of LM317L and the temperature drift of the constant current resistance R1. In reality, the temperature drift can be neglected when the temperature coefficient is below 5*10-6/℃.  The relationship between the reference pressure difference and temperature coefficient of LM317L is shown in Fig.3: The temperature effect is obvious in the temperature range of - 40-85%, thus compensation must be made in the high precision application. In intelligent transmitter systems, in order to correct sensors and compensate circuits, temperature sensors are commonly designed in the transmitter circuits, because the practical applications of power supply are aimed at intelligent transmitters. But the digital thermometric chip, like LM75 or TC77, does not design a special hardware compensation, while a software compensation algorithm provided when applying power supply to deal with temperature drift.  Fig.3 LM317L Benchmark Temperature CurveAs shown in Fig.3, the curve of the relationship between the reference pressure difference and temperature of LM317L is approximate to a simple cubic polynomial function. It only needs to design a compensation function for the reverse Y-axis, and the system is calibrated at 20 ℃ as the basic compensation. The specific compensation formula is ΔI=A (t-20)2+B (t-20) in which “t” is the ambient temperature. The coefficients A and B can be derived from the reference voltage temperature curve provided by the LM317L chip manual, the simplest method is to obtain two binary linear equation groups for solving A and B by taking two points of -20 ℃ and 60 ℃. In this way, it is easy to obtain an approximate function of the compensation curve with a good fitting degree, and the effect of compensated temperature drift can be neglected basically. The biggest difficulty of power supply design is that the input power is very small, thus the isolated feedback mode with high power consumption should be avoided in the design of the isolation terminal, and the open-loop auxiliary side should be used in the actual circuit. The specific process is using MAX639 to design the core circuit of DC/DC, which realizes the high power efficiency conversion. For example, when the input of 315mA is supplied, it can supply the circuit with a current much larger than that of 315mA, thus solving the need for a large current in an intelligent system. According to the requirements of the system, the core chip must have the advantages of low power consumption, high efficiency, wide input voltage range, and simple peripheral devices. The DC/DC chip in Fig.1 is MAXIM's MAX639, which is a step-down converter chip. Its main features are wide input voltage range (4~115V), high conversion efficiency (up to 90%) and low static current (10 μ A); fixed output or an adjustable output. IV. DC/CD in Circuit The circuit is designed for adjustable output and the output is set to 3V. Output current: Io=（Vi Ii η）/Vo, Vi is the input voltage; Ii is the input current, and η is the conversion efficiency and Vo is the output voltage. In the circuit, Vi=812V, Ii=315mA,η= 90%, Vo=3V, getting an approximation Io=816mA without considering the isolating side output, this output current is already a relatively large supply capacity in the low-power system. But the calculation of the above Io is only theoretical, if you want to make the circuit operate reliably under the condition of micro-input power such as 315mA/812V, and to obtain more than 90% conversion efficiency, it is necessary to design the circuit very carefully. The reliable operation of DC/DC is restricted by many conditions, the necessary condition is providing sufficient start-up pulse current. A 10μF tantalum electrolytic capacitor C2 in parallel to Z1 provides an operation guarantee, also it can effectively avoid the interference of DC/DC work on the constant current of LM317. The inductance L1 plays a decisive role in the conversion efficiency of DC/DC. The algorithm provided by the MAXIM manual is L1=50/I0, μH is the unit of L1 and A is the unit of I0. In the practical circuit, the value of L1 is 4mH, which can ensure the circuit work stably under the maximum output power, and it can keep the high conversion efficiency at the same time. what should be emphasized is that if L1 is small, the conversion efficiency of the circuit will be reduced, the starting current will increase and even can not operate. If L1 is larger, the output capacity will decrease and the DC/DC circuit will oscillate. To ensure the stability of the circuit, DC / DC chip has a high requirement for output capacitor C3, the most important is that its equivalent series resistance ESR must be smaller, and it must have enough capacity at the same time. So a 10μF tantalum electrolytic capacitor with excellent performance is used in the circuit design, which can guarantee a stable output. The DC/DC chip is the core of the circuit, and the actual circuit layout has a great influence on the performance of the circuit, especially on the output ripple. The unreasonable layout design of the circuit board will even bring extra parasitic oscillation in the output, so much more attention should be paid to the design. Thus the most important principle is that the ends of C2 and LI lead should be as close as possible to the MAX639 pin, and the grounding pins of C2, D2, MAX639, R3, and C3 should be as close as possible to each other, linking with thick wires. The setting input voltage of DC/DC is 812V, which is guaranteed by Z1. If the actual transmitter requires a lower power supply, Z1 can choose a lower stable voltage, which makes the whole power supply require a lower input voltage. The low threshold of the inlet voltage is 12V; if Z1 selects 612V, the threshold voltage can be reduced to 10V. V. Isolated Power Source Winding The main feature of the circuit is to provide an isolated power supply winding, which uses the method of "stealing" electricity on the DC/DC output energy storage inductor. In Fig.1, the L2 is the power supply coil for this isolated power supply. Because the isolating power supply is a secondary coil loaded on the energy storage coil of DC/DC, and its structure is an open loop, therefore its output stability is relatively poor. In order to obtain satisfactory results, it is necessary to consider the whole design from different angles.First of all: determine its output power. Because of the method of "stealing" electricity from the energy storage coil, its output power is limited and can only be smaller than the original side output power. The output of this set of isolated power supply is mainly supplied by sensor conversion circuit, front-end A/D converter, and isolated circuit in the application of specific transmitters. And the power consumption of analog measuring circuits of differential capacitance sensors, thermocouple sensors, and thermal resistance sensors reaches μA level. The front-end A/D is usually multi-integral or Σ-Δ, the power consumption is less than 1 mA, and the whole low power dissipation optoelectronic isolation can be below 1mA. Therefore, isolated windings provide 3mA that can meet the actual needs. It has been calculated that the maximum output of the circuit is 816mA without the secondary winding, so it is obvious that the 3mA current can be supplied in the case of the secondary winding. Secondly: Avoid working / hibernating rotation for devices with high power consumption. The isolation winding adopts an open-loop structure, and the change of load on the primary side directly affects the stability of the secondary side, so it is required that the power consumption stability of the original circuit system should be guaranteed as much as possible when the circuit is used in practice. What’s more, the circuit can provide the maximum 5mA current for the original edge and can fully meet the requirements of the commonly used low-power MCU control system without the use of sleep mode. In this way, the maximum system running speed can be obtained. Finally:  the low-voltage difference linear regulator and the DC/DC converter should be used in the design. The isolated power winding mainly supplies power to the front-end small-signal analog circuit, therefore, the quality of the power supply requires high. Noise reduction and voltage stabilization treatment of low voltage output converted by DC/DC through low dropout linear regulator(LDO), which can not only improve the efficiency of power supply but also meet the requirement of small ripple voltage. Specifically, LDO uses MAX1726 chip, its working current is the only 2μA, the output is 313V; The output amplitude before voltage stabilization depends on the output power of the original edge and the inductance of L2, the experiment confirmed that L2 is 3mH. When the primary current varies between 3~5mA and the secondary current is 2mA, the voltage fluctuates between 318V and 418V before the voltage stabilizes, which meets the input requirements of the LDO voltage stabilizer. VI. Conclusion The isolated power supply of two-wire transmitter is stable and reliable, and can meet various complex requirements of the use of two-wire transmitter. It has the characteristics of wide temperature range, wide input voltage range, high output efficiency, high integration, good isolation performance, small volume and low cost. And this power supply has been applied to the integrated intelligent temperature transmitter, after a long period of field test, finding that it has excellent performance and can fulfill the requirements of the isolated two-wire transmitter completely. FAQ 1. What does a transmitter do?In the Telecommunications world, a Transmitter is a device that produces radio waves radiating from an antenna. In the world of process control, a Transmitter is a device that converts the signal produced by a sensor into a standard instrumentation signal representing a process variable being measured and controlled. 2. What is called transmitter?In electronics and telecommunications a transmitter or radio transmitter is an electronic device which produces radio waves with an antenna. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. 3. What is transmitter and its types?Pressure transmitters are divided into three types: Absolute Transmitter: This transmitter take vacuum pressure as its base, and then measures process pressure. Gauge Transmitter: This type measures process pressure with the location's atmospheric pressure as a base. 4. What are the main features of transmitter?Some of the main features which make the transmitter complex are higher clock speed, higher transmit power, directional antennas and need for a linear amplifier. 5. What is transmitter frequency?A radio transmitter or just transmitter is an electronic device which produces radio waves with an antenna. Radio waves are electromagnetic waves with frequencies between about 30 Hz and 300 GHz. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. 6. What is the difference between transmitter and antenna?A transmitter is a different kind of antenna that does the opposite job to a receiver: it turns electrical signals into radio waves so they can travel sometimes thousands of kilometers around the Earth or even into space and back. Antennas and transmitters are the key to virtually all forms of modern telecommunication. 7. What is difference between transmitter and transducer? Transducers and transmitters are virtually the same thing, the main difference being the kind of electrical signal each sends. A transducer sends a signal in volts (V) or millivolt (mV) and a transmitter sends a signal in milliamps (mA). 8. What is transmitter PLC?Transmitters are also referred to as stationary instruments and convert measurement parameters into an electrical signal that is then sent to a BMS ( Building Management System), PLC ( Programmable Logic Controller), SCADA ( Supervisory Control and Data Acquisition). 9. What is the pressure transmitter?A Pressure Transmitter is an instrument connected to a Pressure Transducer. The output of a Pressure Transmitter is an analog electrical voltage or a current signal representing 0 to 100% of the pressure range sensed by the transducer. 10. Which oscillator is used in transmitter?Crystal oscillators are the most common type of linear oscillator, used to stabilize the frequency of most radio transmitters, and to generate the clock signal in computers and quartz clocks. You May Also LikeThe 3W PowerSpot transmitter for Power Over-the-air from PowercastBuild a Remote RC Firecracker and Firework lgniter Using RF Transmitter4 Channel 2 Core Twisted Pair Remote Controller Using PT2262

Warm hints: The word in this article is about 3000 words and reading time is about 12 minutes.     This article would introduce you different kinds of power supply circuits.   Catalog   I. Circuit Arrangement of Switching Power Supply II. The Principle of the Input Circuit and the Common Circuits 2.1 Principle of AC Input Rectifier Filter Circuit 2.1.1 Lightning Protection Circuit 2.1.2 Input Filter Circuit 2.1.3 Rectifier Filter Circuit 2.2 Principle of DC Input Filter Circuit 2.2.1 Input Filter Circuit 2.2.2 The Anti-surge Circuit III. Power Conversion Circuits 3.1 The Working Principle of MOS Tube 3.2  Common Schematic Diagram 3.3 Working Principle 3.4 Push-pull Power Conversion Circuit 3.5 Power Conversion Circuit with Transformer Driver IV. Output Rectifier Filter Circuit 4.1 Forward Rectifier Circuit 4.2 Flyback Fectifier Circuit 4.3 Synchronous Rectifier Circuit V. Principles of Steady-voltage Loop 5.1 Schematic Diagram of Feedback Circuit 5.2 Working Principles VI. Short Circuit Protection Circuits 6.1 Current-limiting Circuit 6.2 Short Circuit Protection for Low-power Circuit 6.3 Short Circuit Protection for Medium-power Circuit 6.4  Common Current-limiting, Short-circuit Protection Circuit 6.5 Current Transformer Sampling Current Protection Circuit VII. Output Current Limiting Protection VIII. Output Overvoltage Protection Circuits 8.1 SCR Trigger Protection Circuit 8.2 Optocoupler Protection Circuit 8.3 Output Voltage Limiting Protection Circuit 8.4 Output Overvoltage Lockout Circuit IX. Power Factor Correction Circuit (PFC) 9.1 Schematic Diagram of PFC Circuit 9.2 The Working Principles X. Input Under-voltage and Overvoltage Protection 10.1 Schematic Diagram 10.2 The Working Principles FAQ       I. Circuit Arrangement of Switching Power Supply   The main circuit of the switch-mode power supply is composed of an input EMI filter, rectifier filter circuit, power conversion circuit, and PWM controller circuit, output rectifier filter circuit. The auxiliary circuits include the input & output Undervoltage protection circuit, the output overcurrent protection circuit, the output short circuit protection circuit, and so on.   The block diagram of switching power supply circuit arrangement is as follows:   FIG.1 Block diagram of switching power supply circuit arrangement   II. The Principle of the Input Circuit and the Common Circuits   2.1 Principle of AC Input Rectifier Filter Circuit 2.1.1    Lightning Protection Circuit When there is a lightning strike, the circuit composed of MOV1, MOV2, MOV3, F1, F2, F3, and FDG1 is used to provide protection against the resulting high voltage introduced into the power supply through the electrical grid.   When the voltage applied to the two ends of the piezoresistor exceeds its operating voltage, the resistance value will decrease, making the high voltage energy be consumed on the piezoresistor; if the current is too large, the F1, F2, and F3 will burn out to protect the following circuits. 2.1.2     Input Filter Circuit The double Pi filter network composed of C1, L1, C2 and C3 is mainly used to suppress the electromagnetic noise and clutter signal of the input power supply to prevent its interference to the power supply, and also to prevent the interference of the high-frequency clutters generated by the power supply itself to the electrical grid. The C5 will start to be charged when the power is turned on, producing a large instantaneous current, which is called surge current, but with an RT1 (thermistor) it can be effectively prevented. Because the instantaneous energy is all consumed on the RT1, after a certain time the resistance of RT1 will decrease as the temperature rises (RT1 is a negative temperature coefficient device) and the energy consumed by RT1 will be very small at this time, to make sure the following circuits work normally.     2.1.3   Rectifier Filter Circuit After the AC voltage is rectified by BRG1 and filtered by C5, a purer DC voltage can be obtained. If the C5 capacity becomes smaller, the output AC ripples increase with it.     2.2 Principle of DC Input Filter Circuit FIG.3 The schematic of rectifier circuit   2.2.1   Input Filter Circuit The double Pi filter network composed of C1, L1and C2 is mainly used to suppress the electromagnetic noise and clutter signal of the input power supply to prevent its interference to the power supply, and also to prevent the interference of the high-frequency clutters generated by the power supply itself to the electrical grid. C3 and C4 are Safety Capacitors and the L2, L3 are Differential Mode Inductors.   2.2.2   The Anti-surge Circuit This anti-surge circuit is composed of R1, R2, R3, Z1, C6, Q1, Z2,  R4, R5, Q2, RT1 and C7. At the instant of switch-on, Q2 does not conduct due to the presence of C6, and the current forms a loop through the RT1. Q2 turns on when the voltage on C6 is charged to Z1's steady voltage value. If C8 leaks or the following circuits are short-circuited, the voltage drop generated by the instantaneous current at the instant of switch-on on RT1 causes the Q1 conducted, so that Q2 does not have a gate voltage and does not conduct, making the RT1 burnt out in a very short time to protect the following circuits.   III. Power Conversion Circuits   3.1   The Working Principle of MOS Tube At present, the most widely used insulated gate FET is MOSFET, which uses the electroacoustic effect that occurs on the semiconductor surface to work, making it also known as surface field effect transistor. Because its gate is in a nonconducting state, the input resistance can be greatly increased up to 105 ohms. The MOSFET uses the gate-source voltage to change the amount of charge induced on the semiconductor surface to control the drain current.   3.2   Common Schematic Diagram FIG.4 Schematic of power conversion circuit    3.3  Working Principle The buffer composed of R4, C3, R5, R6, C4, D1, and D2 are connected in parallel with the MOS transistor switches, so that the voltage stress of the switch transistor and EMI are reduced, without secondary breakdown occurring. When the switch Q1 is turned off, the primary coil of the transformer is prone to generate peak voltages and spike currents. These components are combined to absorb the peak voltage and current well. The peak current signal measured from R3 participates in the duty cycle control of the current operating cycle and is therefore the current limit of the current operating cycle. When the voltage on R5 reaches 1V, the UC3842 stops working and switch Q1 turns off immediately.   The junction capacitances CGS and CGD in R1 and Q1 together form an RC network. The charge and discharge of the capacitor directly affects the switching speed of the switch. If R1 is too small, it will cause oscillation and electromagnetic interference will be great. If R1 is too large, the switching speed of the switching tube will be reduced. Z1 usually limits the GS voltage of the MOS transistor to less than 18V, thus protecting the MOS transistor.   The gate-controlled voltage of Q1 is a saw wave. The larger the duty cycle is, the longer the Q1 conduction time is, the more energy the transformer stores. When Q1 is turned off, the transformer releases energy through D1, D2, R5, R4, and C3 and at the same time, it also achieves the goal of resetting the magnetic field, which prepares the transformer for the next storage and transfer of energy. According to the output voltage and current, the IC adjusts the duty cycle of 6-pin sawtooth wave, thus stabilizing the output current and voltage of the complete machine.   C4 and R6 are voltage surge absorption loops.   3.4  Push-pull Power Conversion Circuit Fig.5 Schematic diagram of push-pull power conversion circuit Q1 and Q2 will be turned on in turn.   3.5  Power Conversion Circuit with Transformer Driver FIG.6 Schematic diagram of power conversion circuit with transformer driver T2 is the transformer driver, T1 is the switch-mode transformer, TR1 is the current loop .   IV. Output Rectifier Filter Circuit   4.1   Forward Rectifier Circuit FIG.7 Schematic diagram of forward rectifier circuit T1 is a switch-mode transformer, its primary and secondary sides are in a same phase. D1 is a rectifier diode, D2 is a flyback diode and R1, C1, R2 and C2 form a despiker circuit. L1 is a freewheeling inductor and C4, L2, and C5 form a π filter.   4.2  Flyback Fectifier Circuit FIG.8 Schematic diagram of flyback fectifier circuit T1 is a switch-mode transformer, and the primary and secondary sides are opposite. D1 is a rectifier diode, and R1 and C1 form a despiker circuit. L1 is a a freewheeling inductor, R2 is adummy load and C4, L2 and C5 form a π type filter.   4.3   Synchronous Rectifier Circuit FIG.9 Schematic diagram of synchronous rectifier circuit Working principle: When the upper end of the secondary winding of transformer is positive, the current through C2, R5, R6 and R7 makes Q2 turned on and form a loop. Q2 is the rectifier and the Q1 gate is turned off due tothe reverse bias. When the lower end of second wingding is positive, the current through C3, N4 and R2 makes Q1 conducted as a freewheeling diode. The Q2 gate is turned off due to the reverse bias. L2 is a freewheeling inductor, C6, L1 and C7 form a π filter and R1, C1, R9 and C4 form a despiker circuit.   V.  Principles of Steady-voltage Loop   5.1  Schematic Diagram of Feedback Circuit FIG.10 Schematic diagram of feedback circuit 5.2  Working Principles When the output U0 is increased, the voltage of pin 3 of U1 chip is increased either after dividing voltage with these sampling resistors R7, R8, R10 and VR1, until exceeding the reference voltage of pin 2 of U1 chip, it begins to output a high level, turning the Q1 and photoelectric triode on, and lighting the optocoupler OT1 and LED. Accordingly, the potential of pin 1 of UC3842 becomes lower and therefore decreases the duty cycle of pin 6 of U1 chip and U0.    On the contrary, when the output U0 is decreased, the voltage of pin 3 of U1 chip is decreased either until it exceeds the reference voltage of pin 2 of U1 chip, it begins to output a low level, Q1 and photoelectric triode are not conducting, and optocoupler OT1 and LED do not shine. Accordingly, the potential of pin 1 of UC3842 becomes higher and therefore increases the duty cycle of pin 6 of U1 chip and U0. Repeatedly, so that the output voltage remains stable. Regulating VR1 can change the output voltage.   Feedback loop is an important circuit that affects the stability of switching power supply. If the feedback resistors and capacitors are wrong, missed or false soldered, self-excited oscillations will occur, resulting in fault phenomena, such as abnormal waveforms, oscillations within empty or full load condition and unstable output voltage.   VI. Short Circuit Protection Circuits   6.1  Current-limiting Circuit In the case of short circuit at the output end, PWM control circuit can limit the output current within a safe range. There are many ways to  realize the current limiting. When the current limiting circuit does not work in short circuit, all we can do is to add additional circuits.   6.2  Short Circuit Protection for Low-power Circuit FIG.11 Schematic diagram of low-power short-circuit protection circuit When the output circuit is shorted, the output voltage disappears, the optocoupler OT1 does not turn on, the voltage of pin 1 of UC3842 rises to about 5V, and the partial voltages of R1 and R2 exceed the TL431 reference, making it conductive, the VCC potential of pin 7 of UC3842 is pulled down, and the IC stops operating. After UC3842 stopped working, the potential of pin 1 disappeared, TL431 did not conduct, and the potential of UC38427 increased, making UC3842 restart, and go round and begin again, until the short-circuit phenomenon disappears, then the circuit automatically returns to normal operation.   6.3  Short Circuit Protection for Medium-power Circuit FIG.12 Schematic diagram of medium-power short-circuit protection circuit When the output is short-circuited, the voltage of pin of UC3842 rises. When the potential of pin 3 of U1 chip is higher than that of pin 2, the comparator inverts the output high level of pin 1 to charge C1. When the voltage across C1 exceeds the pin 5 reference voltage, the pin 7 of U1 chip outputs low level. The voltage of pin 1 of UC3842 begins to be lower than 1V and UC3842 stops working, making the output voltage be zero, and go round and begin again, until the short-circuit phenomenon disappears, and the circuit begins to work normally. R2 and C1 are charge and discharge time constants respectively, and the short circuit protection will not work if the resistance is not correct.   6.4  Common Current-limiting, Short-circuit Protection Circuit FIG.13 Schematic diagram of protection circuit 1 When the output circuit is short-circuited or overcurrent, the primary current of the transformer increases, the voltage drop across R3 increases, the voltage at pin 3 increases, and the duty cycle of pin 6 of UC3842 increases. When the voltage at pin 3 exceeds 1V, the UC3842 turns off and without output.   6.5  Current Transformer Sampling Current Protection Circuit The current transformer sampling current protection circuit which has low power consumption but high cost, and the circuit is often complicated. FIG.14 Schematic diagram of protection circuit 2 The larger the output current is (the extreme case refers to short circuit), the higher the voltage sensed by the TR1 secondary coil. When the voltage of pin 3 of UC3842 exceeds 1 volt, the UC3842 stops working. Go round and begin again, until the short-circuit or overload disappears, the circuit recovers itself.   VII. Output Current Limiting Protection FIG.15 Schematic diagram of protection circuit 3 The above is a common output current limiting protection circuit, and its working principle is as follows:   When the output current is too high, the voltage across the RS (manganese copper wire) rises, the voltage of pin 3 of the U1 chip is higher than the reference voltage of pin 2. Pin 1 of the U1 chip outputs a high voltage, which makes Q1 turned on, and the optoelectronic effect occurs on the optocoupler, the voltage of pin 1 of UC3842 is reduced, together with the output voltage, to achieve the goal of overload protection or current limiting.     VIII. Output Overvoltage Protection Circuits   The role of the output overvoltage protection circuit is to limit the output voltage to a safe value when the output voltage exceeds the design value.    When an internal voltage regulator loop of a switching power supply fails or an overvoltage occurs due to a user's improper operation, an overvoltage protection circuit is used to protect against damage to downstream electrical equipment.   The most commonly used overvoltage protection circuits are as follows:   8.1  SCR Trigger Protection Circuit FIG.16 Schematic diagram of protection circuit 4 As shown above, when the output of Uo1 rises, the Zener diode (Z3) breaks down and it is pulled into conduction, letting the control terminal of the Silicon Controlled Rectifier reach the trigger voltage, so the SCR turns on and the Uo2 is shorted to ground. Then the overcurrent or short circuit protection circuit will work and stop the operation of the entire power supply circuit. When the overvoltage condition on the output terminals is eliminated, the trigger voltage of the control terminal of the thyristor is discharged to the ground through R, and the thyristor returns to the off state.   8.2  Optocoupler Protection Circuit FIG.17 Schematic diagram of protection circuit 5A FIG.18 Schematic diagram of protection circuit 5B As shown in the above figure, when an phenomenon of overvoltage occurs in the Uo, the Zener breaks down and conducts current through the optocoupler (OT2) and R6 to the ground, lightening the light-emitting diode of the photocoupler, which causes the phototransistor of the photocoupler to conduct. The base of Q1 is turned on and the voltage of pin 3 of UC3842 is reduced, turning off the IC and the entire power supply while Uo is zero, and go round and begin again.   8.3  Output Voltage Limiting Protection Circuit FIG.19 Schematic diagram of protection circuit 6 The output voltage limiting protection circuit is shown in the diagram. When the output voltage rises, zener and optocoupler are on, and the base of Q1 turns on either due to a driving voltage according. The voltage of pin 3 of UC3842 rises and the output drops. When the zener is not conducting, the voltage of pin 3 of UC3842 drops and the output voltage rises. As time goes by, the output voltage will be stable within a range (depending on the zener's value).   8.4  Output Overvoltage Lockout Circuit FIG.20 Output overvoltage lockout circuit A FIG.21 Output overvoltage lockout circuit B The working principle is shown in Figure A is that when the output voltage Uo rises, the Zener and optocoupler turn on, and then go with the base of Q2, because of which the base of Q1 is on due to the drop of voltage.   Q2 is on all the time after the voltage of Vcc is through R1, Q1, and R2, making the pin 3 of UC3842 always be conducted with high level and therefore stop working.   In Figure B, the voltage of pin 3 of the U1 chip raises due to big rises of Uo, and pin 1 outputs a high level. Because of the presences of D1 and R1, the pin 1 of U1 chip is always on and outputs a high level, so it is always low and then it stops working. Is it positive feedback?     IX. Power Factor Correction Circuit (PFC)   9.1 Schematic Diagram of PFC Circuit FIG.22 Schematic diagram of PFC circuit 9.2  The Working Principles The input voltage is rectified by an EMI filter composed of L1, L2, L3, and so on and a BRG1, one part of which is then fed into the PFC inductor and another part of which is fed into the PFC controller as the sampling of the input voltage to adjust the duty cycle of the control signal before divided by R1 and R2, that is to change them on and off time of Q1 and to stabilize the output voltage of PFC.   L4 is a PFC inductor that stores energy when Q1 is on and releases energy when Q1 is switched off. D1 is the start diode. D2 is the PFC rectifier diode, and C6, C7 are filtered. One part of the PFC voltage is sent to the downstream circuit, and another part of it is fed into the PFC controller as the sampling of the output voltage before divided by R3 and R4, to adjust the duty cycle of the control signal and to stabilize the output voltage of PFC.     X. Input Under-voltage and Overvoltage Protection   10.1  Schematic Diagram FIG.23 Schematic diagram of input undervoltage and overvoltage protection circuit   10.2  The Working Principles The input under-voltage and overvoltage protection principles of the switching power supply of AC input and DC input are almost the same. The sampling voltages of the protection circuits all come from the same input filtered voltage.   The sampling voltage is divided into two ways, one way is fed into pin 3 of the comparator after divided by R1, R2, R3, and R4. If the sampling voltage is higher than the reference voltage of pin 2, then pin 1 of the comparator will output a high level to control the main controller and make the main controller turned off, so there is no power output. The other way is fed into pin 6 of the comparator before it is divided by R7, R8, R9, and R10.   If the sampling voltage is lower than the reference voltage of pin 5, then pin 7 of the comparator will output a high level to control the main controller and make it turned off, so there is no power output.   How To Make a Switching Power Supply     FAQ   1. What are the 3 types of power supply? There are three subsets of regulated power supplies: linear, switched, and battery-based. Of the three basic regulated power supply designs, linear is the least complicated system, but switched and battery power have their advantages.   2. What is meant by switch mode power supply? A switch mode power supply is a power converter that utilises switching devices such as MOSFETs that continuously turn on and off at high frequency; and energy storage devices such as the capacitors and inductors to supply power during the non-conduction state of the switching device.   3.What are the advantages and disadvantages of switch mode power supply? Advantages & disadvantages of switch mode power supply (SMPS) a. The switch mode power supply has a smaller in size. b. The SMPS has light weight. c. It has a better power efficiency typically 60 to 70 percent. d. It has a strong anti interference. e. SMPS has wide output range. f. Low heat generation in SMPS.   4. What is a DC switching power supply? A Switching DC power supply (also known as switch mode power supply) regulates the output voltage through a process called pulse width modulation (PWM). The PWM process generates some high frequency noise, but enables the switching power supplies to be built with very high power efficiency and small form factor.   5. What is the difference between a switching power supply and a linear power supply? Linear power supplies deliver DC by passing the primary AC voltage through a transformer and then filtering it to remove the AC component. Switching power supplies feature higher efficiencies, lighter weight, longer hold up times, and the ability to handle wider input voltage ranges.   6. Do I need a switching power supply? The switching power supply implies higher efficiency due to the high switching frequency, enabling it to use a smaller, less-costly high-frequency transformer as well as lighter, less-costly filter components. Switching power supplies contain more overall components, therefore are usually more expensive.   7. Is a switching power supply regulated? A switch mode power supply regulates an output voltage with pulse width modulation (PWM). This process creates high-frequency noise but it provides a high-efficiency rating in a small form factor. ... The low DC voltage is finally converted into a steady DC output with another set of diodes, capacitors, and inductors.   8. How do I know if my power supply is regulated? You can generally stick one probe into the middle of the connector, and hold the other against the outside. With a few exceptions, the middle is positive, so use the red lead there, and use the black lead on the outside shell. Regulated supplies, without any load, should measure very close to the target voltage of 12v.   9. Can I use a switching power supply to drive a DC motor?   A simple unregulated analog power supply may be easier and be able to supply the large starting under load current more that the switching one. DC motors are not too fussy about the supply, and will usually run quite well on unfiltered DC.   10. Are switch mode power supplies any good? Switch mode power supplies, SMPS provide improved efficiency & space saving over traditional linear supplies, but care has to be taken to ensure noise on the output is low. Switch mode power supplies are widely used because of the advantages they offer in terms of size, weight, cost, efficiency and overall performance.   You May Also Like: Transformers Basics: Construction, Types, Materials and Design Modeling and Control of Full Bridge Push-Pull Bi-Directional DC/DC Converter Review and Application of Electronic skin How to Drive Thermostat by Using Solid State Relay

Warm hints: The word in this article is about 3000 words and  reading time is about 10 minutes.   The transformer is a static electrical device, mainly composed of an iron core (or magnetic core) and coil. The coils have two or more windings, of which the ones connected to the power are called primary coils, and the rest are called secondary coils. Transformers are widely used in electrical equipment such as household appliances, electronic equipment, switching power supply, and so on. Circuit symbols commonly used T as the beginning of the number, for example, T01, T201.    This article covers the construction, functions, classification, and design of transformers and materials used for building magnetic cores in transformers.     Catalogs   I. The Composition of Transformer II. The Construction and Functions of Transformer III. High-frequency Transformer Design Program 3.1 Program structure 3.2 Matters needing attention when doing the core material   selection 3.3 Ferrite magnetic material requirements IV. Power Transformer Classification V. Principle and method of Transformer Design FAQ   I. The Composition of Transformer 1）The primary side 2）The secondary side 3）Magnetizing inductance 4）Leakage inductance 5）Open-circuit or short-circuit measurement of the primary side leads to the  Magnetic inductance and the leakage inductance turns ratio respectively:  K=Np/Ns=V1/V2   II. The Construction and Functions of Transformer 1) Electrical isolation 2) Energy storage 3) Voltage change for same power input.   III. High-frequency Transformer Design Program   3.1 Program structure (1) Core material (2) Core structure (3) Core parameters (4) Transformer Winding Parameter (5) package assembly (6) Temperature rise check   (1) Core material Soft magnetic ferrite is widely used in switching power supply because of its own characteristics. It has the advantages of high resistivity, low AC eddy current losses, low price, and easy to be machined into magnetic cores of various shapes. The disadvantages are low working magnetic flux density, low permeability, large magnetostriction, and high sensitivity to temperature changes. Which kind of soft magnetic ferrite material can satisfy the design requirement of a high-frequency transformer more fully, only when it is carefully considered and the transformer design can reach the high-cost performance.   (2) Magnetic core structure The factors considered in the selection of magnetic core structure are as follows: reducing magnetic leakage and leakage inductance, increasing the area of coil heat dissipation, which is beneficial for shielding and makes it easier to wind coils, more convenient to wire for assembly and so on.   The magnetic leakage and leakage inductance are directly related to the magnetic core structure . If the magnetic core does not need air gap, then a enclosed ring-like or square type magnetic core may be used as far as possible.   (3) Magnetic core parameters In the design of core parameters, special attention should be paid to the operating flux density only limited by the magnetization curve, but also by the losses, and also related to the working mode of power transmission. When the flux changes in one direction, there is ΔB=Bs-Br, which is not only limited by the saturation flux density but also mainly by the losses (Losses cause temperature rise, which in turn affects magnetic flux density). The operating flux density Bm=0.6～0.7ΔB.   An air gap can decrease Br and therefore increase the flux density ΔB. The exciting current can be increased after using an air gap opening, but the core volume can be decreased either. For the two-way operation of magnetic flux, the flux density ΔB is twice the maximum operating flux density Bm, that is ΔB=2Bm. In bidirectional operating mode, we should pay attention to the problem of transformer DC magnetic bias due to the inequality of volt-second areas of positive and negative excitation variation, which is caused by different reasons. A small air gap will be needed in the core, or a DC capacitor can also be added to the circuit design.   Magnetic properties of ferromagnetic materials Magnetic hysteresis loops of the core   (4) Coil parameters Coil parameters include: turns, conductor section (diameter), wire form, winding arrangement and insulation. The conductor section (diameter) depends on the current density of winding, using taking 2.5～4A/mm2. When doing some choosing of section conductor diameter don’t forget to take the skin effect into consideration and do regulations necessary after some temperature rise tests of the transformer.   General winding arrangements: the primary winding is close to the core and the secondary windings & feedback windings are gradually arranged outward. The following two winding arrangements are recommended:   1) If the voltage of the original windings is high (for example, 220V) and meanwhile that of the secondary windings is low, a more appropriate arrangement is the secondary winding being close to the core, and then goes the feedback winding, the original winding is arranged on the outermost ends, which is advantageous to the insulation arrangement of the original winding to the core;   2) If we want to increase the coupling between the primary and secondary windings, we can make half of the original windings be close to the core, then goes the feedback winding and secondary winding, and the other half of the original winding being the outermost ends, which is an arrangement advantageous to reduce the leakage inductance.   (5) Assembly structure The assembly structure of high-frequency power transformers are divided into horizontal and vertical types. If you'd like to select the planar core, sheet magnetic core and thin-film magnetic core, then a horizontal-type assembly would do you good.   (6) Temperature rise tests The temperature rise tests can be carried out by calculation and sample test. The temperature rise is lower than the allowable temperature rise above 15 degrees, the current density and the cross-section of the wire are appropriately increased. Appropriately increase the current density and decrease the cross-section of the wire, and do the exact opposite if temperature rise exceeds the allowable value, such as increasing the diameter or enlarging the core if necessary, to increase the area of coil heat dissipation.       3.2 Matters needing attention when doing the core material selection (1) Soft ferrite, due to its low price, good adaptability, and high performance at high frequency, has been widely used in switching power supply.   (2) Soft ferrite is commonly divided into two series: Mn-Zn ferrite and Ni-Zn ferrite. The Mn-Zn ferrite is composed of Fe2O3，MnCO3，ZnO and so on, which is widely used in all kinds of filters, inductors, transformers, and so on below 1MHz. The Ni-Zn ferrite is composed of Fe2O3，NiO，ZnO and so on, which is widely used in all kinds of adjustable inductor windings, anti-jamming magnetic beads, antenna matching devices, and so on above 1MHz.    (3) Mn-Zn ferrite is the most widely used core in switching power supply, and the selection of its material depends on its use. The core for the input filter part of the power supply is mostly high-conductivity magnetic core, and its material number mostly is R4K～R10K, that is, the ferrite core of relative permeability is about 4000~10000, but the main transformer and output filter are magnetic materials with high saturation flux density, where Bs is about 0.5T (5000GS).     3.3 Ferrite magnetic material requirements   Ferrite magnetic materials for switching power supply shall meet the following requirements:   (1) High saturation flux density Bs and low residual flux density Br   The residual flux density Bs has a certain influence on the transformer and winding results. Theoretically speaking, the number of turns of transformer windings can be reduced and the copper loss can be reduced because of the high Bs. In practical applications, there are different types of circuits of high-frequency converters in switching power supply.    For transformers, their operations can be divided into two categories:   1) Bipolar: The circuit topologies include half-bridge, full-bridge, push-pull, etc. In the primary winding of the transformer, the excitation current is equal and opposite in direction during the positive and negative half-cycles. Therefore, the magnetic flux changes in the magnetic core of the transformer are symmetrically moved up and down. The maximum variation range of B is  ΔB=2Bm, and the DC component of the magnetic core is basically canceling out.   2) Unipolar: The circuit topologies include single-ended forward, single-ended flyback, etc. The transformer primary winding adds a unidirectional square wave pulse voltage in one cycle (this is the case for single-ended flyback). The magnetic flux density varies from the maximum Bm to the residual flux density Br in the unidirectional-excitation transformer core. If we decrease the Br and increase the saturation flux density Bs, then the △B will be increased, and the turns and copper loss will also be reduced.   (2) Transformers or inductors are divided into three categories according to their topology:   1) An DC-filter inductor's magnetic core only works in one quadrant, the topologies of this operating state including Boost, Buck, buck/boost inductors, single end flyback converter transformer, forward and all push-pull converters and output filter inductors.   2) The core of the transformer in the forward converter also works in one quadrant, but the transformer needs to magnetic reset.   3) The core of the transformer with push-pull topology is in bidirectional alternating magnetization. These kinds of converters include push-pull, half-bridge and full-bridge converters, AC filter inductors, and so on.   (3) Low power loss at high frequency   The power loss of ferrite not only affects the power output efficiency but also leads to the heating of the magnetic core and waveform distortion.   The heating problem of the transformer is very common in practical applications, which is mainly caused by copper loss and core loss of the transformer. If the selected Bm is too low and the turns of winding are too many, it will cause the winding to heat up and transfer the heat to the core at the same time, and vice versa.   When selecting the ferrite material, we must make the power loss change with temperature characterized by a negative temperature coefficient. This is because if the core loss is the main heating, making the transformer temperature rise up, which then will lead to a further increase of core losses, thus it will form a vicious circle and eventually make the power tube, transformer, and other components burn down. Therefore, in the researches of power ferrite at home and abroad, we must solve the problem of negative temperature coefficient of magnetic material power loss itself, which is also a remarkable feature of magnetic materials having met the requirements for power supply applications, such as PC40 from Japanese company TDK and R2KB from China manufacturers and so on.   (4) A relatively moderate permeability   (5) How we choose the appropriate relative permeability?    Well, this depends on the switching frequency of your actual circuit, mostly 2000, meanwhile its applicable frequency must be below 300kHz, and sometimes can be a little higher, but the maximum will not be higher than 500 kHz.   (6) A relatively high Curie temperature   Curie temperature is the temperature at which a magnetic material loses its magnetic properties, generally above 200 ℃. However, the actual operating temperature of the transformer should not be higher than 80℃, at which the saturation flux density Bs will drop to 70% of that at the normal temperature when the temperature is above 100℃. That is, the saturation flux density of the core will drop more seriously when the operating temperature is too high. Furthermore, when the temperature is higher than 100℃, the power loss has been experiencing a positive temperature coefficient, which will lead to a vicious circle. For R2KB2 materials, the temperature corresponding to the allowable power consumption has reached 110℃ and the Curie temperature is up to 240℃, which meets the requirements of high-temperature use.     IV. Power Transformer Classification Power transformers are divided into three categories according to their topology: (1) Flyback transformers; (2) Forward transformers; (3) Push-pull transformers (full-bridge/half-bridge converters)   The appropriate topologies for various core structures are shown in the following table:   Core structureTypes of converter circuitFlybackForwardPush-pullE cores++0Planar E Cores-+0EFD Cores-++ETD Cores0++ER Cores0++U Cores+00RM Cores0+0EP Cores-+0P Cores-+0Ring Cores-++    "+"=fit; "0"=normal; "-"=unfit Summary of High frequency transformer core.XLS V. Principle and Method of Transformer Design   (1) There are two main ways to design transformer: Area Product (AP) Method AP: The product of core effective cross section Ae and Area of window Aw PT-The calculation power of the transformer Ae-Core effective cross section Aw- Area of window Ko-Core window utilization coefficient, typically 0.4 Kf-Waveform coefficient, usually square wave being 4 and sine wave being 4.44 Bw-The operating magnetic intensity of core FS-Switching frequency Kj-Current density coefficient, usually 395A/cm2 X-Core structure coefficient     (2) According to the area product (AP) method, the general steps of designing transformer are as follows: 1. Select the core material to calculate the apparent power of the transformer; 2. Determine the core cross section AP and select the core size according to AP value; 3. Calculation of the primary side inductance and the number of turns; 4. Calculation of the length of air gap; 5. Calculating the line diameter according to the current density and the secondary side RMS current. 6. Determine whether the copper loss and iron loss meet the requirements (eg allowable loss and temperature rise)   Selecting the flyback topology, the basic parameters of the power supply are as follows: Input voltage: 175-264 VAC Output voltage: 21V Output current: 3A Output power P0=63W Frequency set at 60Khz Duty cycle set at 0.45 initially   1) Select the core material to determine the apparent power PT of the transformer   and select the PC40 material here considering the cost factor and check the PC40 data to get Bs=0.39T, Br=0.06T. In order to prevent the core from becoming saturated instantly, a certain margin is reserved. Let Bm= ΔBmax*0.6=0.198T, and pick up the 0.2T. For flyback topology, the transformer apparent power PT is:   2) Calculating AP values with Excel tables   Where, J is the current density, usually 395A/cm2, and Ku is the effective use coefficient of copper window, usually 0.2～0.4, now we set Ku as 0.4.    Based on the figure above, we select the core EE3528 due to its being greater than the calculated AP value, with the following parameters: Ae: 84.8mm2 AP：1.3398cm4 Wa：158mm2 AL：2600nH/H2 In order to adapt to the abrupt load current, the power supply is designed in critical mode and the critical current is: I0B=0.8×I0=2.4A     3) Calculation of the primary side inductance and the number of turns (A) Minimum input voltage Vimin=ViACmin*1.2=210V (B) Turns ratio n=[Vimin/(V0+Vf)]*[Dmax/(1-Dmax)] n=[210V/(21V+1V)*[0.45/(1-0.45)] n=7.8 (C) Peak secondary current ^IsB=2*IoB/(1-Dmax) ^IsB=2*2.4A/(1-0.45) ^IsB=8.72A (D) Secondary inductance Ls=(V0+Vf)*(1-Dmax)*[1/(Fs*1000)]/^IsB*1000000 Ls=(21V+1V)*(1-0.45)*[1/(60Khz*1000)]/8.72A*1000000 Ls=23.58Uh (E) Primary inductance Lp=n*n*Ls Lp=7.8*7.8*23.58uH Lp=1434uH   Primary and secondary peak currents (F) Calculation of peak secondary current in continuous mode ^Isp=Io/(1-Dmax)+(^IsB/2) ^Isp=3A/(1-0.45)+(8.72A/2) ^Isp=9.81A (G) Calculation of peak primary current in continuous mode ^Ipp=^Isp/n ^Ipp=9.8A/7.8 ^Ipp=1.257A (H) Calculating the turns of the primary and secondary auxiliary windings a) Number of turns in the primary side Np=Lp*^Ipp/(^B*Ae) Np=1434uH*1.257A/(0.2*84.8) Np=106.28T After rounding: Np=106T b) Number of turns in the secondary side Ns=Np/n Ns=106T/7.8 Ns=13.58T After rounding: Ns=14T c) Number of feedback turns Nv=(Vcc+Vf)/[(V0+Vf)/Ns] Nv=(14.5V+1V)/[(21V+1V)/14T] Nv=9.87T After rounding: Nv=10T   To avoid core saturation, an appropriate air gap is added to the magnetic loop, the calculation go as follows: The number of turns may need to be corrected by the air-gap flux edge effect.   4) There are two ways to calculate the wire diameters of the primary, secondary and auxiliary windings: Effective current of original side diameter: Iprms=Po/^n/Vimin Iprms=63W/0.8/210V Iprms=0.375A (A) Calculating the area of bare wire (B) Calculating the wire diameter (current density J to take 4A/mm2) Using two 0.18mm-diameter wires wound around or AWG #28 a single strand The secondary diameter: Use four wires with a diameter of 0.25mm (AWG #31) and wind around. Calculation of Skin Depth: The diameter of multi-strand parallel winding must be less than or equal to dwH, in single wire winding, however, if the diameter exceeds the dWH value,  the multi-strand wire winding should be taken into account.   5) Calculation of copper loss Pcu and iron loss Pfe (total transformer loss Ploss) (A) Calculating the loss of primary and secondary windings.  Where, MLT is the average turn length of magnetic core (B) Calculating the allowable total loss Ploss and allowable iron loss at efficiency η (C) According to the loss curve of iron core, the actual loss (iron loss per unit weight and actual iron loss) is obtained by: The Ploss is the loss of the whole circuit, including diode/MOSFET losses and other losses, the actual losses Pfe must be much smaller than the calculated one, so here is only for reference. (D) Calculating the loss per unit area by Φ=Ploss/As If the temperature rise caused by Φ is less than 25 degrees, then the design is wonderful.   6) Calculating the BW The working flux density BW should be below Bs-Br within the design specifications, that is Bw<Bs-Br, to avoid saturation of the core.   FAQ   1. What is the use of transformer? Transformers are employed for widely varying purposes; e.g., to reduce the voltage of conventional power circuits to operate low-voltage devices, such as doorbells and toy electric trains, and to raise the voltage from electric generators so that electric power can be transmitted over long distances.   2. What are the 3 types of transformers? There are three primary types of voltage transformers (VT): electromagnetic, capacitor, and optical.   3. What is the basic principle of transformer? A transformer consists of two electrically isolated coils and operates on Faraday's principal of “mutual induction”, in which an EMF is induced in the transformers secondary coil by the magnetic flux generated by the voltages and currents flowing in the primary coil winding.   4. Does a transformer convert AC to DC? A transformer is built to transfer the energy from one circuit into another circuit by way of magnetic coupling. ... An alternating current creates a magnetic flux in the core on its way through the first winding, inducing the voltage in the others. It can convert high and low voltages, it cannot convert AC to DC.   5. What are the main parts of transformer? There are three basic parts of a transformer: a. an iron core which serves as a magnetic conductor, b. a primary winding or coil of wire and. c. a secondary winding or coil of wire.   6. What are the classification of transformer? Depending upon the type of construction used, the transformers are classified into two categories viz.: (i) Core type, and (ii) Shell type. Depending upon the type of service, in the field of power system, they are classified as: (i) Power transformers, and (ii) Distribution transformers.   7. Can a transformer work on DC? As mentioned before, transformers do not allow DC input to flow through. This is known as DC isolation. This is because a change in current cannot be generated by DC; meaning that there is no changing magnetic field to induce a voltage across the secondary component.   8. How do you convert a transformer? This conversion is made by winding two separate conductors around a common iron core. Applying an alternating voltage to the primary conductor produces current which sets up a magnetic field around itself. This is known as mutual inductance.   9. What are two components of no load current in transformer? The no-load current of a transformer consists of two components: The Magnetization Current iM is the current required to produce the flux in the transformer core. The Core-loss Current ih+e is the current required to make up for hysteresis and eddy current losses.   10. Which type of transformer core is most efficient? SHELL CORE. The most popular and efficient transformer core is the SHELL CORE, as illustrated in figure (4). As shown, each layer of the core consists of E- and I-shaped sections of metal. These sections are butted together to form the laminations.   You May Also Like: Analysis of Calculation Theory for Transformer Temperature Rise Some suggestions about protecting transformers Learn Some Basic Knowledge about Capacitor Voltage Transformer      

Maxim Integrated is a company specializing in semiconductor interface, digital signal processor, analog signal chain, communication IC, power supply and battery management, etc. In the past twenty years, Maxim has developed ICs with high reliability, working in the extended temperature range for industrial applications. Now, they also offer products with current and voltage protection, reducing the devices' demand for space and power consumption with excellent performance indicators. CatalogsI MAX7409 / MAX741O / MAX7413 / MAX7414II MAX847 / MAX769III MAXl674 / MAXl675 / MAXl676IV MAX3875V MAX2105VI MAX3690VII MAX4539 / MAX4540VIII MAX7400 / MAX7403IX MAXl710X MAX668 / MAX669XI MAX254BXIII MAX2663 / MAX2671 / MAX2673Intro Integrated circuits (ICs) are a keystone of modern electronics, in this article we will disguss some kinds of ICs in Maxim Integrated. They are the heart and brains of most circuits. They are the ubiquitous little black "chips" you find on just about every circuit board. Unless you’re some kind of crazy, analog electronics wizard, you're likely to have at least one IC in every electronics project you build, so it's important to understand them, inside and out.An IC is a collection of electronic components ——resistors, transistors, capacitors, etc. ——all stuffed into a tiny chip, and connected together to achieve a common goal. They come in all sorts of flavors: single-circuit logic gates, op amps, 555 timers, voltage regulators, motor controllers, microcontrollers, microprocessors, FPGAs…the list just goes on-and-on.Embedded computing is based on microcontroller design and provides fixed function operation control. Embedded computing originated from industrial control applications, and has been widely used in consumer electronics, medical treatment, and even communications. Maxim provides real-time clock, security authentication, interface IC and sensor solutions for these markets,which makes it an important supplier in the industry.  What is IC chip and how does an IC work I Space and power saving 5th order filter IC---MAX7409/MAX741O/MAX7413/MAX7414New 5th order Bessel, Butterworth Switched-Capacitor Low Pass Filters series products, uMAX-8 pins and DIP package. MAXIM's proprietary uMAX package, which is 80% smaller than the 8-pins DIP package, makes it the industry's smallest 5-order switched capacitor filter. MAX7409/MAX7410 works at +5V, MAX7413/MAX7414 works at +3V and both devices draw only 1.2mA of supply current. Low price, small size and low power consumption make this kind of filter extremely suitable for price sensitive portable devices requiring DAX post-filtering or anti-aliasing applications.The MAX7409/MAX7413 Bessel filters have the characteristics of low overshoot, fast establishment and linear phase response, and the MAX7410/MAX7414 Butterworth filters have the flatest band-pass response. The four kinds of chips are all fixed frequency response, and the design tasks of filter is simplified to selecting clock frequency.The angular frequency can be tuned from 1Hz to 15 kHz by the clock at a rate of 100 times the clock/rotation angle. Two modes of clock operation, one is a self-contained clock of an external capacitor, another is an external clock which could strictly control the cut-off frequency. They have a very low output misalignment (±4 mV) and can be further regulated via an offset adjustment pin. Figure 1. Typical application circuit of MAX7409/MAX741O/MAX7413/MAX7414 II Power management ICs for communication equipment---MAX847/MAX769The MAX847/MAX769 DC-DC converter produced by MAXIM Company of USA has the characteristics of low voltage operation, high conversion efficiency and synchronous rectification. It is suitable for the low power digital radio communication system with 1 to 3 batteries, such as two-way paging, GPS receiver and so on, ensuring the cut-in voltage is as low as 0.87V and the quiescent current is 37 μA (the outage current is 2 μA).The built-in synchronous rectifier eliminates the external Schottky diode, meanwhile the conversion efficiency is increased to 90% , and for MAX847, an output current exceeding 50mA may be provided when power is supplied with a single battery. When two batteries are supplied, the MAX769 with function of boost/buck conversion could provide an output current over 90mA. Both chips can digitally adjust the output voltage through a serial interface compatible with SPI, which ranges from 1.8 V to 4.9 V whit an adjustable interval of 100 mV. The no-load current is only 13 μA.The MAX769 is similar to the MAX847 except that it contains a buck/boost DC-DC converter (for 2-cell or 3-cell inputs) rather than a boost-only converter (for 1-cell inputs). Both MAX847 and MAX769 include a multichannel ADC for battery monitoring. Three low noise Linear Regulator outputs for various uses (3V analog, 2.85V logic, and 1V receiver.  Both chips are 28-pin QSOP packaged. Figure 2. Typical application circuit of MAX847 Figure 3. Typical application circuit of MAX769 III Compact and efficient DC-DC converter IC with very low power supply current---MAXl674/MAXl675/MAXl676The MAX1674/MAX1675/MAX1676 DC-DC converter chip can provide up to 94% conversion efficiency. They available in small 8 or 10-pin uMAX package, and the static current is only 16 μA. The built-in synchronous rectifier not only improves efficiency but also eliminates the using of  external Schottky diodes, resulting in smaller dimensions and lower costs.The MAX1674 has a current-limiting of 1A, and the MAX1675 has a current-limiting of 0.5A, allowing the use of very small inductors. The MAX1676 has an optional current-limiting and minimizes the EMI due to an elimination of inductive oscillations. All chips have built-in N channel MOSFET with 0.3Ω and with a pin-selectable output voltage of 3.3V or 5V. The output voltage can also be adjusted in the range of 2 V to 5.5 V using the divider resistance. The input voltage ranges from 0.7 V to VOUT and the cut-in voltage can be as low as 1.1 V. Other features include: efficiency up to 94% when the output current is 200mA, built-in low voltage detection and 0.1 μA shutdown mode. IV Clock recovery and data retiming IC---MAX3875MAX3875 is a compact, low power clock recovery and data retiming chip for 2.488GbpsSDH／SONET systems. The fully integrated PLL can extract the synchronous clock from the serial NRZ input data which is retimed by the recovery clock. The clock and data output of the chip are compatible with the differential PECL and the additional 2.488Gbps serial input is used for loopback test of the system. It can also provide unlock monitoring signal of a TTL level.MAX3875 can be used as regenerator or terminal receiver in 0C-48／STM-16 transmission system. Insert jitter characteristics are higher than any SONET/SDH specification. The single supply is from 3.3V to 5V and when power is 3.3V, the power loss is less than 400mW in the full temperature range from -40 ℃ to 85 ℃.MAX3875 is available in 32-pin TQFP package.Figure 4. Typical application circuit of MAX3875 V Digital DBS direct-conversion tuner IC---MAX2105It is designed for the application of Direct Broadcast Satellite (DBS) TV set-top box. Compared with the structure based on intermediate frequency, the cost of the system is greatly reduced because of the use of direct frequency conversion structure. MAX2105 is supplied by a single power supply of 5V and the input signal frequency ranges from 950MHz to 2150MHz, tuned directly from L band to baseband by broadband I/Q down converter.The MAX2105 internal circuit includes a low noise amplifier with AGC, two down conversion mixers, an oscillating buffer with a 90° orthogonal generator, a prescaler and a baseband amplifier. The range of AGC gain adjustment is 41 dB, and the minimum power of input signal is -60 dB. Since the range of AGC gain adjustment is reduced, MAX2105 can use high gain external LNAs to obtain better noise coefficient, and can also provide a automatic baseband drift correction.MAX2105 is available in 28-pin SO package.Figure 5. Typical application circuit of MAX2105 VI SDH/SONET 8:1 serializer with clock synthesis and TTL inputs---MAX3690The MAX3690 serializer is powered by 3.3V only with a 200mW power consumption. Ideal for converting 8-bit-wide, 77Mbps parallel data to 622Mbps serial data in SDH / SONET system. Other applications include Add/Drop Multiplexers, Digital Cross-Connects.The clock and data input of MAX3690 is TTL logic level, serial data output is 3.3V PECL logic level. A fully integrated PLL synthesizes an internal 622Mbps serial clock from a low-speed crystal reference clock (77.76MHz, 51.84MHz, or 38.88MHz). An unlocked output of a TLL level can be used to indicate whether the PLL is working properly.MSX3690 is available in 32-pin TQFP packages.Figure 6. Functional diagram of MAX3690 VII Single 8-channel and dual-4 channel multiplexer ICs with precision resistance networks---MAX4539/MAX4540The single-8 channel MAX4539 and the dual-4 channel MAX4540 are a kind of multiway switch with calibration function (calibrating multiplexer), which is suitable for system self-testing and precision type MAX4540. Their built-in precision resistive partial voltage networks can provide accurate reference voltage of V+／2、5／8(V+ -V-)、15VREF/4096 and 4081VREF/4096 (Where VREF is external reference voltage).The MAX4539/MAX4540 have enable inputs and address latching. When power supply working at 5V or ±5V, the digital input has a 0.8V/2.4V logic threshold that guarantees compatibility with TTL/CMOS.The MAX4539/MAX4540 are available in small 20-pin DlP, S0, and SSOP packages, both of which can operate in a single supply of +2.7V to 12V or a duplicate supply of ±2.7V to ±6V. The on resistance (maximum 100 Ω) of the same device matches within 12Ω, and Each switch can handle Rail-to-Rail analog signals.The off leakage current is 1nA at TA = +25°C and 10nA at TA = +85°C.Functional diagram of MAX4539Figure 8. Functional diagram of MAX4540 VIII 8th-Order, lowpass, elliptic, switched-capacitor filters---MAX7400／MAX7403MAX7400/MAX7403 is a newly developed 8th-order, lowpass, elliptic, switched-capacitor filters by MAXIM Company of USA. The cut-off frequency ranges from 1Hz to 10kHz, and only draw 2mA of supply current. With a single power supply of 5 V, it is ideal for low power anti-aliasing and post-filtering of D/A converters. They feature a shutdown mode that reduces the supply current to 0.2μA.MAX7400 devices provide a sharp roll-off with a 1.5 transition ratio and 80 dB of stop-band rejection, while the MAX7403 devices provide a sharper roll-off of 1.2 transition ratio and 58 dB of stop-band rejection. For the both filters, the low output offset of ±4 mV can be adjusted via an offset adjustment pin.The internal switching operation of the filter can be controlled by an internal clock of an external capacitor or an external control to obtain a more accurate angular frequency. The fixed frequency response greatly simplifies the design, which only needs to set the clock frequency according to the desired angular frequency. MAX7400 and MAX7403 filters are available in 8-pin SOIC and plastic DIP packages.Figure 9. Typical application circuit of MAX7400/MAX7403 IX High-speed, digitally adjusted step-down controllers fornotebook CPUs---MAXl710The MAX1710/MAX1711 step-down controllers are intended for core CPU DC-DC converters in notebook computers. They feature a triple-threat combination of ultra-fast transient response, high DC accuracy, and high efficiency needed for leading-edge CPU core power supplies. Maxim's proprietary Quick-PWMTM quick-response, constant-on-time PWM control scheme handles wide input/output voltage ratios with ease and provides 100ns "instant-on" response to load transients while maintaining a relatively constant switching frequency.High DC precision is ensured by a 2-wire remote-sensing scheme that compensates for voltage drops in both the ground bus and supply rail. An on-board, digital-to-analog converter (DAC) sets the output voltage in compliance with Mobile Pentium Ⅱ CPU specifications. The MAX1710 achieves high efficiency at a reduced cost by eliminating the current-sense resistor found in traditional current-mode PWMs. Efficiency is further enhanced by an ability to drive very large synchronous-rectifier MOSFETs.Single-stage buck conversion allows these devices to directly step down high-voltage batteries for the highest possible efficiency. Alternatively, 2-stage conversion (stepping down the +5V system supply instead of the battery) at a higher switching frequency allows the minimum possible physical size. MAXl710 is available in Small 24-Pin QSOP Package.Figure 10. Typical application circuit of MAX7400/MAX1710 X Boosting DC-DC controllers with power levels of 20W---MAX668/MAX669The MAX668/MAX669 constant-frequency, pulse-width modulating (PWM), current-mode DC-DC controllers are designed for a wide range of DC-DC conversion applications including step-up, SEPIC, flyback, and isolated-output configurations. Power levels of 20W or more can be controlled with conversion efficiencies of over 90%. The 1.8V to 28V input voltage range supports a wide range of battery and AC-powered inputs. An advanced BiCMOS design features low operating current (220µA), adjustable operating frequency (100kHz to 500kHz), soft-start, and a SYNC input allowing the MAX668/MAX669 oscillator to be locked to an external clock.DC-DC conversion efficiency is optimized with a low 100mV current-sense voltage as well as with Maxim's proprietary Idle ModeTM control scheme. The controller operates in PWM mode at medium and heavy loads for lowest noise and optimum efficiency, then pulses only as needed (with reduced inductor current) to reduce operating current and maximize efficiency under light loads. A logic-level shutdown input is also included, reducing supply current to 3.5µA.The MAX669, optimized for low input voltages with a guaranteed start-up voltage of 1.8V, requires boot-strapped operation (IC powered from boosted output). It supports output voltages up to 28V. The MAX668 operates with inputs as low as 3V and can be connected in either a bootstrapped or non-bootstrapped (IC powered from input supply or other source) configuration. When not bootstrapped, it has no restriction on output voltage. Both ICs are available in an extremely compact 10-pin µMAX packages.Figure 11. Typical application circuit of MAX669Figure 12. Functional diagram of MAX668/MAX669 XI Low cost and small size RS-232 transceiver---MAX254BMAX254B is a complete electrically isolated RS-232 interface developed by MAXIM Company in USA. It is suitable for the system with demanding cost and size. It is mainly aimed at equipment in which noise, high transient voltage and highland potential damage or communication interference maybe occur.  XII High-performance laser driver---MAX3867The MAX3867 is a complete, single +3.3V laser driver for SDH/SONET applications up to 2.5Gbps. The device accepts differential PECL data and clock inputs and provides bias and modulation currents for driving a laser. The synchronizing input latch can be bypassed if a clock signal is not available.An automatic power control (APC) feedback loop is incorporated to maintain a constant average optical power over temperature and lifetime. The wide modulation current range of 5mA to 60mA and bias current of 1mA to 100mA are easy to program, making this product ideal for use in various SDH/SONET applications.The MAX3867 also provides enable control, a programmable slow-start circuit to set the laser turn-on delay, and a failure-monitor output to indicate when the APC loop is unable to maintain the average optical power. The MAX3867 is available in a small 48-pin TQFP package as well as dice.Figure 13. Functional diagram of MAX3867 XIII High linearity upconverters---MAX2663／MAX2671／MAX2673The MAX2663/MAX2671/MAX2673 miniature, low-cost, low-noise upconverters are designed for low-voltage operation and are ideal for use in portable consumer equipment. Signals at the IF input port are mixed with signals at the local oscillator (LO) port using a double-balanced mixer. These upconverters operate with IF input frequencies between 40MHz and 500MHz, and upconvert to output frequencies as high as 2.5GHz.These upconverters offer a wide range of supply currents and output intercept levels to optimize system performance. Supply current is essentially constant over the specified supply voltage range. Additionally, when the devices are in a typical configuration with VSHDN-bar=0, a shutdown mode reduces the supply current to less than 1μA.The MAX2663/MAX2671 family of upconverters are offered in the space-saving 6-pin SOT23 package. For applications requiring balanced IF ports, choose the MAX2673 upconverters in the 8-pin μMAX package.Figure 14. Typical application circuit of MAX2663／MAX2671／MAX2673   

A high-output-power balanced power amplifier is designed with power-combining architecture for satellite communication terminals. The power-combining architecture introduces a ±45° phase shift in the output matching network of two amplifiers, which makes the balanced power amplifier more tolerant to load mismatch and less sensitive to load variation. This balanced power amplifier is implemented with InGaP/GaAs HBT process. Under the band of 1.5 GHz to 1.7 GHz and the supply voltage of 5 V, the measured results show that 32 dB of the gain, 38 dBm of the saturated output power and 43% of power added efficiency (PAE) are achieved, and a good radio frequency performance can be maintained under load mismatch conditions. Power Amplifier ( PA ) Basics and fundamental tutorial on radio frequency   Catalog Ⅰ Introduction of Power Amplifier 1.1 Background of power amplifier 1.2 Application of power amplifier in   power combination scheme 1.3 High power balanced power amplifier Ⅱ Design and Analysis of balanced Power   Amplifier 2.1 Design of Integral circuit 2.2 Circuit Analysis Ⅲ Test result Ⅳ Conclusion FAQ     Ⅰ Introduction of power amplifier 1.1 Background of power amplifier In recent years, with the development of economy, satellite communication and navigation systems are widely used in electronics and automobile industry,and the demand for power amplifiers of handheld terminal transmitters is increasing.These power amplifiers require greater power output and better stability to meet the performance requirements of satellite communications and navigation systems. Therefore, it is of great significance to study the practical and reliable high power integrated power amplifier used in the handheld terminal of satellite communication and navigation system. The traditional single-terminal multi-stage integrated power amplifier is not only low in output power, due to the influence of its own semiconductor physical characteristics and the limitations of processing technology, heat dissipation, impedance matching, etc, but the output power will also decrease rapidly with the increase of frequency. In order to improve the output power, the power combination technology is a practical and easy method to implement. At the same time, the balanced power amplifier is widely used in the power synthesis scheme because of its insensitive load and wider bandwidth than the single-ended power amplifier.    1.2 Application of power amplifier in power combination scheme In reference, a high linearity and high efficiency power amplifier is realized by balanced synthesis method. The power amplifier has the advantages of flat gain characteristics and more stability than the corresponding single-ended amplifier in a wide band. However, the introduction of orthogonal 3dB couplers at the input and output ends makes the power amplifier require more discrete devices, which is not conducive to miniaturization and integration. In reference, a novel balanced synthesis architecture was used to design a load insensitive power amplifier.This kind of power amplifier adds ±45 °phase shift network to the upper input and lower output terminals, and finally combines the two power channels through the Wilkinson synthesizer at the output end. This design not only achieves high efficiency and linearity, but also has good stability when the load changes. It is widely used in 3G WCDMA mobile phone terminals. However, the introduction of Wilkinson synthesizer also brings many disadvantages, such as large insertion loss, increasing integration cost and complexity. In reference, on the basis of reference, the ±45°phase shift network in the output end of the power amplifier is improved and optimized, the Wilkinson synthesizer is removed either, which makes the power amplifier insensitive to the load change while achieving high efficiency and high linearity.This design reduces the integrated devices, reduces the cost, and is widely used in modern 3G smart phone terminals.   1.3 High power balanced power amplifier Based on the comprehensive consideration of output power and stability, a high power balanced power amplifier based on InGaP/GaAs HBT process, operating in the 1.5-1.7 GHz band, is designed in this article. The test results show that the balanced power amplifier has high output power and power addition efficiency (PAE), and the circuit can still maintain good RF performance when the load mismatches. Ⅱ Design and analysis of balanced power amplifier 2.1 Design of Integral circuit  Due to the superior linearity and high efficiency of HBT process in RF IC design, a balanced power amplifier working in 1.5-1.7 GHz band is designed by using InGaP/GaAs HBT process in this article. The overall circuit structure is shown in figure 1. The balanced power amplifier circuit includes the same upper and lower branch amplifiers, and the input and output matching circuits of ±45°phase-shifting networks. In order to obtain a higher gain, the upper and lower branches are designed using a three-stage power amplifier structure, in which the first stage works in a class A to obtain a high linearity; in order to take into account the linearity and efficiency of the overall power amplifier, the second and third stages work in Class AB.   Figure 1. A balanced power amplifier circuit   In order to achieve a good compromise between efficiency and linearity, the biasing circuit adopts self-adaptive linearizing bias.By adding one inductor and one capacitance to the input matching circuit of the upper and lower branches, the balanced power amplifier generates ±45°phase shift to the input signal, thus realizing that the upper and lower channels of the amplifier work in an orthogonal state. A LC resonant network with a resonant frequency of 2Ω0 is added to the output matching, where Ω0 is the fundamental frequency, which is equivalent to getting a load of second harmonic short circuit at the same time, thus realizing the suppression of the second harmonic. The structure is similar to that of F power amplifier, and is beneficial to obtain higher efficiency. The main characteristic of the circuit in this article is that the output matching circuit of the upper and lower branches added a ±45°phase shift network, the upper branch adds a -45°phase shift network with a low pass filter structure, and the lower branch adds a +45°phase shift network with a high pass filter structure. The balanced power amplifier designed by this synthetic structure has the advantages of small space usage, simple structure and easy implementation. At the same time, it can make the balanced power amplifier more tolerant to load mismatch and insensitive to the change of load.   2.2 Circuit Analysis When the balanced power amplifier is in operation, the input signal is coupled to the A node through the blocking capacitor, and two signals are separated from the A node into the upper and lower branches respectively, because the three-stage amplifier in the upper and lower branches is exactly the same, they sharing an equal input impedance, so the power of the two signals separated at the A node is equal. The separated signals are transmitted to the input end of the amplifier through the opposite 45°phase change of the upper and lower branches respectively, and then the orthogonal signals are amplified by the three-stage amplifier of the upper and lower branches. The orthogonal signal of the upper and lower branches undergoes an opposite phase shift of 45° in the output matching network, so the same signal with the same phase and the same amplitude is realized at point B, and the output power of point B is the sum of those of the two amplifiers, finally the balanced power amplifier can obtain higher output power. The balanced power amplifier is equivalent to the three-port network shown in figure 2. Because the upper and lower branch of amplifiers are exactly the same,it can be considered that the amplifiers of the upper and lower branches have the same output reflection coefficient ΓPA. After passing through ±45°phase shift network, we can obtain ΓPAе −j2ΔΦ and ΓPAе +j2ΔΦ respectively. Therefore, the equivalent output impedance of the upper and lower branches viewed from the ab surface to the left in figure 2 is respectively as follows:   The equivalent output impedance ZL of the network viewed from the terminal to the left can be obtained in parallel by ZL1 and ZL2: The output reflection coefficient of node B is: By substituting formula (1)-(3) into equation (4) and simplifying, the output reflection coefficient of the balanced power amplifier is as follows: When ΔΦ=45°, you have: It is shown that the output reflection coefficient and VSWR of the balanced power amplifier are twice as much as that of the single branch power amplifier. Therefore, when the load mismatch occurs, the load mismatch tolerance of the balanced power amplifier is higher than that of the single-branch power amplifier after the ±45°phase shift output matching network is introduced. Figure 2. Circuit equivalent diagram In order to analyze the performance of the balanced power amplifier in the case of load mismatch, the equivalent circuit of figure 2 is simulated and analyzed. When the load mismatch (such as VSWR=3:1), the load impedance (normalized) of the upper and lower branch amplifiers varies with the phase ψ of the reflection coefficient Γ, as shown in figure 3. By comparing the load impedance of the upper and lower branches, it can be seen that they have a phase difference of 180°. Because of the change of the load impedance of the upper and lower branches, the corresponding current is changed, and the phase difference of 180°occurs between the two. The collector of the two third-stage amplifiers of the balanced power amplifier is single power supply, so the current of the upper and lower branches compensates each other, resulting in little change in the total current, as shown in Figure 4. Therefore, when the load mismatch of the balanced power amplifier occurs, the change of working current is relatively small, that is, not sensitive to the change of load. The load insensitive effect of using this balancing architecture is similar to that of classical balanced power amplifier which is realized by using orthogonal 3 dB coupler. Figure 3. Changes in the load of the structure (normalized) when VSWR=3:1 In the case of terminal mismatch (VSWR=3:1), the single end circuit architecture and the present balanced architecture are compared as shown in Fig. 5 with the same output power of 38 dBm. It can be seen from figure 5 that the output power of the single-ended circuit architecture fluctuates greatly with of the phase ψ of the reflection coefficient Γ, while the output power of the balanced architecture in this article is relatively flat. At the same time, compared with the circuit architecture without phase shift, the in-phase circuit architecture has more advantages than the single-ended circuit architecture, but the output power of the balanced architecture is the flattest and can work stably. Figure 4. Changes of current of the structure (normalized) when VSWR=3:1 Figure 5. Comparison with the output power (normalized) changes in three kinds of circuits when VSWR=3:1   Ⅲ Test result  In this post, the balanced power amplifier is fabricated by InGaP/GaAs HBT technology. The three-stage amplifier and bias circuit with upper and lower branches are realized in the chip with an DIE area of 0.9 mm×0.8 mm. The choke inductor, input matching and output matching circuit are realized out of the chip. Considering the heat dissipation of the power amplifier, the whole thing is integrated on the Fr4 substrate with an area of 8 mm×8 mm. Figure 6 is the physical diagram of the circuit.The working voltage of the balanced power amplifier is 5 V and the total static current is about 310 mA. Using Agilent's network analyzer E5071C to measure the small signal S parameters S21, S11, S22 of the balanced power amplifier, as shown in figure 7: S21 > 31 dB (in the band of 1.5 GHz-1.7 GHz with a variation of less than 1 dB) S11 < -12 dB S22 < -10 dB The test results show that the design has good small signal performance. Using Agilent's signal generator N5182A and spectrometer N9030A to build the test platform, inputting continuous wave (CW) and the performance of the balanced power amplifier is measured at 1.5,1.616 and 1.7 GHz, as shown in figure 8. It can be seen from the diagram that the gain of the balanced power amplifier in the frequency band is about 32 dB, the in-band gain flatness is ±0.3 dB, the saturation power is more than 38 dBm/6.3 WN, and the power additional efficiency is greater than 43 dB. At the same time, according to the gain curve of each frequency point, the balanced power amplifier has good AM-AM characteristic and 1dB compression point is about 37 dBm. The third order intermodulation distortion (IMD3) and the fifth order intermodulation distortion (IMD5) of the balanced power amplifier are measured by using a two-tone signal with a deviation of 2 MHz, as shown in figure 9. The results show that the balanced power amplifier has good linearity. In general, the balanced power amplifier not only has high gain, high output power and high efficiency, but also has good linearity.  Figure 6. Chip physical diagram Figure 7. S parameter test results Figure 8. Test performance in frequency band when CW signal is input In order to verify the tolerance of the balanced power amplifier to the load mismatch and the load insensitivity, and the balanced power amplifier can still work properly when VSWR=20:1, a microwave manual tuner is connected to the output of the power amplifier. And when the working frequency is 1.616 GHz, the input power Pin=10 dBm and voltage standing-wave ratio VSWR=3:1, the output power of the balanced power amplifier changes with the reflection coefficient phase, as shown in Figure 10. The figure shows that the output power is about 35.7 dBm, with a range of ±0.7 dBm. Therefore, the performance of the balanced power amplifier is stable when the load is mismatched to a certain extent. Figure 9. Test performance of IMD3 and IMD5 Figure 10. Changes of output power when VSWR=3:1 Ⅳ Conclusion In this post, a high power balanced power amplifier is designed by using the balance architecture, the chip area is 8 mm×8 mm by using InGaP/GaAs HBT process and the total static current is about 310 mA at a operating voltage of 5V. When the CW signal is input, the gain can be up to 32 dBm in the band of 1.5-1.7 GHz, the saturation output power psat is 38 dBm, and the additional power efficiency is 43%. Beyond that, it can still work stably when the load mismatches. This balanced power amplifier is practical, reliable and safe, and can be used in handheld terminal of the satellite communication and navigation system.   FAQ     1. What is a power amplifier used for? The function of a power amplifier is to raise the power level of input signal. It is required to deliver a large amount of power and has to handle large current. The base of transistor is made thicken to handle large currents.   2. How does a power amplifier work? The power amplifier works on the basic principle of converting the DC power drawn from the power supply into an AC voltage signal delivered to the load. Although the amplification is high the efficiency of the conversion from the DC power supply input to the AC voltage signal output is usually poor.   3. Does a power amp make a difference? A better amp will make your speakers play louder and sound better, but it won't make bad speakers sound like good speakers. Many speakers have a "maximum wattage rating" on the back. ... High-end amplifier companies make amps with more than 1,000 watts, and you could plug in a $50 speaker into it with no problem.   4. What is power amplifier circuit? A power amplifier circuit is used to drive the loads like speakers with minimum output impedance. ... In this mode the output is an inverted amplified signal which is at low power. Two Darlington power transistors are arranged in a class AB configuration to amplify the power level of this signal.   5. How do you make a power amp circuit? Amplifier power gain and design. As power is the voltage multiplied by the current in a circuit, the power gain can simply be expressed as the product of the two. It is also possible to use the voltage and current levels to provide gain expressed in dB, but any changes in impedance must be accounted for.   6. What is balanced amplifier? A balanced amplifier has two amplifying devices that are run in quadrature. That is, they are operating 90 degrees apart in transmission phase. ... Balanced amplifiers may more immune to load pull effects than in-phase power combining schemes, because the two reflection coefficients are seen 180 degrees out of phase.   7. What is the difference between amplifier and power amplifier? The crucial difference between a voltage amplifier and a power amplifier is that a voltage amplifier increases the voltage level of the applied input signal.   8. Why do we need power amplifier? The function of a power amplifier is to raise the power level of input signal. It is required to deliver a large amount of power and has to handle large current. The base of transistor is made thicken to handle large currents.   9. What power amplifier do I need? Generally you should pick an amplifier that can deliver power equal to twice the speaker's program/continuous power rating. This means that a speaker with a “nominal impedance” of 8 ohms and a program rating of 350 watts will require an amplifier that can produce 700 watts into an 8 ohm load.   10. Does a power amp improve sound quality? No, amplifiers don't improve sound quality. They just increase the signals to required levels. However if amplifiers have equaliser or other signal processing facility, they can make it sound different and possibly more suitable for listening pleasure. But again that is the work of signal processing part of amplifier.