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IntoductionAn operational amplifier, or op-amp for short is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op-amp produces an output potential that is typically hundreds of thousands of times larger than the potential difference between its input terminals, and is a voltage amplifying device designed to be used with external feedback components such as resistors and capacitors between its output and input terminals. They are used extensively in signal conditioning, filtering or to perform mathematical operations such as add, subtract, integration and differentiation.In this video, the basic introduction of the Operational Amplifier (Op-Amp) has been given and different characteristics of ideal and real Op-amp (General Purpose 741 Op-Amp) has been discussed. CatalogIntroductionⅠ Operational Amplifier Basics1.1 Amplification Principle1.2 Balance Resistor1.3 Feedback Resistor in Parallel with a Capacitor 1.4 Pulling Down Resistor and Pulling Up the Capacitor1.5 Parasitical Resistor as an Integrator1.6 Parasitical Resistors and Capacitors1.7 Balance Resistor Failure1.8 Magnification, Input Impedence, Voltage1.9 Open Loop Gain1.10 Virtual ShortⅡ Op Amp ApplicationⅢ Op Amp SamplingⅣ Op Amp Reference VoltageⅤ Importance of Op AmpⅠ Operational Amplifier BasicsWhen using op amp, there will be more problems confusing us, what are they? Listing all of them is impossible, but we can seek the core of these problems, which are the following lists.1.1 Amplification PrincipleThere are many types of op amps with many functions, and their circuits are inconsistent, but the internal block diagrams are basically the same. It consists of three parts: input stage, intermediate stage, and output stage. The input stage consists of a differential amplifier circuit that uses circuit symmetry to improve overall circuit, and the main function of the intermediate voltage amplifier stage is to increase the voltage gain. It can be composed of one or more stages of amplifying circuits; the output stage has a voltage gain of 1, but can provide a certain amount of power, and the circuit consists of two power supplies V+ and V-. The entire amplifier circuit is designed with two inputs P and N, and one output O. The voltages of the three terminals are represented by Vp, Vn, and Vo, respectively. The two ends of P and N are respectively called the non-inverting input terminal and the inverting input terminal, which means that when the P terminal is added with the voltage signal Vp (Vn = 0), it is obtained at the output end. The voltage Vo is in-phase with Vp, when the voltage signal Vn (Vp = 0) is applied to the N terminal, the output voltage Vo obtained at the output is inverted from Vp.The operational amplifier is actually a differential amplifier. Look at its structure, two transistors are connected back to back to share the crossing current source. One of the transistors is the positive input of the op amp and the other is the inverting input. The positive input is amplified and sent to a power amplifier circuit to amplify the output. Thus, if the voltage at the forward input rises, the output naturally becomes larger. If the voltage at the inverting input rises, the reverse current is large, and the forward current is small, because the inverting tertiary tube and the forward tube share a same current source.1.2 Balance ResistorGenerally, there is a balance resistor in the inverting / non-inverting amplifier circuit. What is the role of this balance resistor?(1) Provide a suitable static bias for the transistors inside the chip.The internal circuit of the chip is usually directly coupled, and it can automatically adjust the static operating point, but if an input pin is directly connected to the power supply or the ground, its automatic adjustment function can not work normally. Because the voltage of the ground cannot be raised by the inside transistors, and the voltage of the power supply cannot be reduced, which causes the chip to fail to meet the conditions of virtual short and virtual open.(2) Eliminate the influence of the static base current on the output voltage, and the value should be balanced with the equivalent resistance value of the external DC of the two input terminals.(3) In non-inverting op amp circuit, if it not connecting a balance resistor, the op amp will be burned, because the resistor acts as a voltage divider. 1.3 Feedback Resistor in Parallel with a Capacitor What is the role of the feedback resistor in parallel with a capacitor when using non-inverting op amp?(1) The feedback resistor and capacitor form a high-pass filter, so that local high-frequency amplification is particularly noticeable.(2) Prevent self-excitation. 1.4 Pulling Down Resistor and Pulling Up the CapacitorWhat role does the role of pulling down resistor and pulling up the capacitor at the input of the op amp play?To get positive feedback and negative feedback, depending on the specific circuit connection. For example, if the input voltage signal and the output voltage signal are taken to the input, the partial output signal passes through the balance resistor to obtain a new voltage value, that is, shunting the input voltage to make the input voltage smaller, and this is a negative feedback. Since the signal output from the signal source is always constant, the output signal can be corrected by negative feedback. 1.5 Parasitical Resistor as an IntegratorWhat is the function of the resistor RF connected to the op amp as an integrator at the two ends of the integrating capacitor?Adjust resistance to prevent the output voltage from running out of control. 1.6 Parasitical Resistors and CapacitorsWhy are resistors and capacitors connected in series at the input of the op amp?Regardless of the type of op amp, it consists of transistors or MOS transistors. In the absence of an external components, the op amp is a comparator actually. When the voltage of the non-inverting terminal is high, it will output a level similar to the positive voltage, and vice versa, but this op amp does not seem to have much use. Only when the external circuit is formed to generate the feedback will make the real op amp function. 1.7 Balance Resistor FailureWhat is the consequence of the balance resistor doesn't work well in non-inverting amplifier circuit?(1) The non-inverting end is unbalanced. For example, there will be an output although the input is 0. When the input signal is output, the output value is always larger (or smaller) than the theoretical output value by a fixed number.(2) The error caused by the input bias current cannot be eliminated. 1.8 Magnification, Input Impedence, VoltageWhat is the amplification factor and input impedence of an ideal integrated operational amplifier? What is the voltage between the non-inverting input and the inverting input?The magnification is infinite, the input impedance is infinitesimal, and the voltage is almost the same (the voltage is not 0V, for example, the non-inverting end is 10V and the inverting end is 9.99V). 1.9 Open Loop GainWhy is the open loop gain of an ideal op amp infinite?1) The actual open loop gain of the op amp is very large, so imagine it as infinity and derive the virtual ground from it.2) Deriving virtual ground is not only an inverting amplifier for the negative feedback connection, because there is no virtual ground for positive feedback.The open-loop gain of the op amp is infinite, when design the circuit, the closed-loop gain can be independent of the open-loop gain, and only depends on the external components. It is to use the large open loop gain in exchange for the stability of the closed loop gain.3) Assuming that the gain is small, the difference between the voltages applied across the op amp is relatively large for an output voltage. If it is connected to a negative feedback state, the voltage across the op amp will be different, causing amplification.We all know that the op amp’s output voltage Vo is equal to the difference Vid between the non-inverting input voltage and the inverting input voltage, multiplied by the op amp’s open-loop gain A, that is, Vo = Vid * A = (VI + - VI-) * A ( 1 ). Since the output voltage of the op amp does not exceed the supply voltage in practice, it is a finite value. In this case, if A is large, (VI+ - VI-) is necessarily small; if (VI+ - VI-) is small enough, then we can actually treat it as 0, at this time,  there will be VI+ = VI-, that is, the voltage at the non-inverting input of the op amp is equal to the voltage at the inverting input. This is what we call “virtual short”. Note that they are not really connected together, and there is resistance between them.In the above discussion, how did we get the result of “virtual short”? Our starting point is the formula (1), which is based on the characteristics of the op amp. Then, we made two important assumptions, one is that the output voltage of the op amp is limited, and it not exceed the power supply voltage; the second is that the open loop gain A of the op amp is large. The A of a normal op amp usually reaches 106 or 107 or even larger, but the actual open loop gain of the op amp is also related to its working state. For example, if the op amp is not working in the linear area, the value A may be small, so second assumption is conditional.Therefore, we know that when the open loop gain A of the op amp is large, the op amp can have a virtual short. But it is one of the possibilities, and it is not suitable for every op amp in any case to say their inputs are virtual short, in other words, virtual short can only be achieved in circuits under certain conditions.The conditions of virtual short:a. The open-loop gain of operational amplifier should be large enough.b. There should be a negative feedback circuit. From the above we know when we need to analyze the virtual short in the circuit. In reality, condition (1) is true for most op amps, and the important point is to look at the work area. If it is a circuit drawing, judge by calculation; if it is an actual circuit, it is reasonable to use the instrument to measure amplifier output voltage.There is also a situation related to virtual short called “virtual ground”, that is, there is a virtual short when the input is grounded. Some books say that virtual short will be exist under deep negative feedback conditions, but in reality, the op amp is more likely to work in the linear region under this situation. But this is not absolute, when the input signal is too large, the op amp with deep negative feedback will still be saturated. Therefore, it should be judged to be the most reliable with the output voltage value. 1.10 Virtual ShortAdd the input signal directly to the non-inverting input, and the inverting input is grounded through the resistor. Why is U-= U+ = Ui≠0? Is it not a virtual short? What are the conditions that the virtual ground exists?(1) In the non-inverting amplifier circuit, the output affects by the feedback, so that U(+) automatically tracks U(-), so they will be close to zero. It seems that the two ends are short circuit, so it is called virtual short.(2) Due to the virtual short phenomenon and the high input resistance of the op amp, the current flowing through the two input terminals is small, approaching 0. This phenomenon is called virtual open, which is derived from virtual short.(3) The virtual ground is in the inverting op amp circuit, the (+) terminal is grounded, and the (-) is connected to the input and feedback network. Due to the virtual short, U(-) and U(+) are very close, which is said to be virtual ground.(4) About the conditions: the virtual short is an important feature of the closed-loop (negative feedback) operating state of the non-inverting amplifier circuit; the virtual ground is an important feature of the inverting amplifier circuit in the closed-loop operating state. Ⅱ Op Amp ApplicationWhen a operational amplifier is connected as a non-inverting amplifier, the potentials of the two inputs are the same. If the waveform of the input is measured, it will be the same. This is like a common-mode signal. In fact, there are still small differential mode signal on the two inputs, but the differential mode signal can not be measured by the general instrument. As a result, the virtual short artificially increases the common-mode signal at the two inputs, which poses a challenge to the performance of the operational amplifier. Why is an op amp used like this?(1) The common mode signal of the non-inverting amplifier is much larger than the inverting amplifier, and strict to the common mode rejection ratio.(2) For single-ended input, the equivalent common-mode value is half of the input value, whether non-inverting or inverting input. However, since the input impedance of the non-inverting amplifier is usually larger than the inverting amplification, the anti-interference ability is a little poor.As mentioned above, when the inverting input is performed, the voltage at the inverting terminal is almost zero, so the differential influence on the tube collector voltage that has only one tube change. When the input is in phase, the voltage at the inverting terminal is equal to the non-inverting terminal voltage, so the common mode voltage and the input voltage are equivalent. That is to say, the collector voltage of the differential tube has variable quantity that changes in the same direction when the two tubes have portions that change in different directions at the same time, which is the common mode output voltage. It is added in phase with the voltage of one of the tubes. Therefore, it is easy to cause the tube to become saturated (or cut off), fortunately, the amplification of the common mode voltage is only tens of thousands of parts of the differential mode amplification.However, this does not mean that the common mode rejection suppression ratio of the differential mode input and the common mode input of the amplifier is different. It should be that the non-inverting input is added with a common mode signal equivalent to the input volume, so it should be careful to use non-inverting amplification mode when the input signal is large. Ⅲ Op Amp SamplingWhy is the amplifier circuit composed of operational amplifiers generally sampling the inverting input mode?(1) The significant difference between the inverting input and the non-inverting input mode is:When inverting input, because there is a balanced resistor connected to the ground at the same phase, and there is no current on this resistor (because the input resistance of the op amp is extremely large), this non-inverting terminal is approximately equal to the ground potential, and  the potential at the non-inverting terminal is extremely close to the inverting terminal, so there is a virtual ground at the inverting end. The advantage of having a virtual ground is that there is no common mode input signal, even if the common mode rejection ratio is not high, there is no common mode output. The non-inverting input mode has no virtual ground. When a single-ended input signal is used, a common-mode input signal is generated. Even if an operational amplifier with a high common-mode rejection ratio is used, there is still a common-mode output. Therefore, it is best to use the inverting input method.(2) The positive phase is the oscillator, and the inverting can stabilize the amplifier and access the negative feedback.(3) From the principle point of view, it is possible to connect to the same analog circuit. However, the signal (differential mode signal) that is amplified during the actual application tends to be small, thus it is necessary to pay attention to suppressing noise (usually expressed as a common mode signal). In the same way, the amplification circuit has a poor ability to suppress the common mode signal, and the signal that needs to be amplified is submerged in the noise, which is not conducive to post processing. Therefore, an inverting proportional amplification circuit with better suppression capability is good.Ⅳ Op Amp Reference VoltageSome op amps will have an output even if no voltage is input after power-on, and the output is not small, so VCC/2 is often used as the reference voltage.The output is output signal without any input, this is called the input offset voltage Vos, which is caused by the asymmetry of the design structure of the op amp. It is a very important performance indicator of the op amp. The op amp commonly used VCC/2 as the reference voltage is because the op amp is in a single power supply state. At this time, the real reference of the op amp is VCC/2, so a DC offset of VCC/2 is often provided at the positive terminal of the op amp. When having positive and negative dual power supply, it is often referenced to the ground.The selection of op amps requires attention to many things. Under less stringent conditions, it is often necessary to consider the operating voltage, output current, power consumption, gain bandwidth product, and price of the op amp. Of course, when using it under special conditions, different factors must be considered in practice. Ⅴ Importance of Op Amp(1) If the voltage on both inputs of the op amp is 0V, the output voltage should also be equal to 0V. But in fact, there is always some voltage at the output, that is, the offset voltage Vos. If the offset voltage at the output is divided by the noise gain of the circuit, the calculated result is called the input offset voltage or the input reference offset voltage. The Vos is considered to be a voltage source in series with the inverting input of the op amp. A differential voltage must be applied to both inputs of the amplifier to produce a 0V output.(2) The input impedance of an ideal op amp is infinite, so no current flows into the input. However, a real op amp using a bipolar junction transistor (BJT) in the input stage requires some operating current, which is called bias current (IB). There are usually two bias currents: IB+ and IB-, which flow into the two inputs, respectively. The range of IB values is large, with bias currents of lower at 60fA for special op amps and up to tens of mA for some high-speed op amps.(3) The power supply voltage range required for the first single-chip op amp to operate normally is ±15V. Today, op amps are moving toward low voltages due to increased circuit speeds and power supplies from low-power sources such as batteries. Although the op amp’s voltage specifications are usually specified as symmetrical two-pole voltages ±15V, these voltages do not necessarily require a symmetrical voltage or a two-pole voltage. For an op amp, as long as the input is biased in the active region (within the common-mode voltage range), the ±15V supply is equivalent to a +30V/0V supply, or a +20V/-10V supply. The op amp does not have a ground pin unless the negative voltage rail is grounded in a single-supply application.The input voltage swing of high speed circuits is smaller than that of low speed devices. The higher the speed of the device, the smaller its geometry, which means the lower the breakdown voltage. Due to the low breakdown voltage, the device must operate at a lower supply voltage. Today, op amps typically have a breakdown voltage of around ±7V, so high-speed op amps can work at a supply voltage of ±5V, and they can also operate at a single supply voltage of +5V.For general-purpose op amps, the supply voltage can be as low as +1~8V. These op amps are powered by a single power supply, but this does not mean that a low supply voltage must be used. Because the terms single supply voltage and low voltage are two related and independent concepts. Frequently Asked Questions about Operational Amplifiers Problems1. How can you tell if an op amp is blown?Re: how to tell whether an op amp is burned out? measure the DC voltage at the +input. then measure the DC voltage at the output. if the results are significantly different, the opamp is most likely shot. 2. How do I know if my op amp is broken?measure the DC voltage at the +input. then measure the DC voltage at the output. if the results are significantly different, the opamp is most likely shot. if they are the same, the opamp is most likely ok and the problem is something else. 3. What errors you have to consider with real operation amplifiers?These errors include input bias current, input offset current, input offset voltage, CMRR, PSRR, and finite input impedance. In reality, all these errors will occur at the same time. 4. How do op amps fail?The common failures I have seen including with comparators involve either the output being shorted or open to one supply or the input differential pair or input protection circuits being damaged causing excessive input bias current and/or input offset voltage which usually ends up pinning the undamaged output. 5. Why do op amps fail?The common failures I have seen including with comparators involve either the output being shorted or open to one supply or the input differential pair or input protection circuits being damaged causing excessive input bias current and/or input offset voltage which usually ends up pinning the undamaged output.

Ⅰ AbstractIn portable electronic devices such as mobile phones, notebook computers, and small video cameras, lithium-ion batteries have developed rapidly due to their sound performance, such as high working voltage, large specific energy, long cycle life, low self-discharge rate, no memory effect and so on, which are compared with traditional NiCd batteries and NiMH batteries.Figure 1. Lithium-ion Movement in Li-ion BatteryCatalogⅠ AbstractⅡ Charging Characteristics of Lithium BatteriesⅢ Performance Description of Several Different Charging States3.1 On Standby3.2 Precharging3.3 Constant Current3.4 Constant VoltageⅣ Charging Process Analysis4.1 High Voltage Constant Current Mode4.2 Low Voltage High Current Mode4.3 High Voltage High Current ModeⅤ Li-ion Battery Charging Security5.1 Common Sense in the Daily Use of Batteries5.2 Charging RulesⅥ One Question Related to Lithium-ion Battery and Going Further6.1 Question6.2 AnswerThe charge and discharge of lithium-ion batteries do not transfer electrons through traditional methods, but energy changes occur through the entry and exit of lithium ions in the crystals of layered materials. Under normal charge and discharge conditions, the in and out of lithium ions cause changes in the interlayer spacing, but will not cause damage to the crystal structure, so lithium-ion batteries can be regarded as an ideal reversible battery. During charging and discharging, lithium ions come and go between the positive and negative electrodes of the battery, and they shake between the positive and negative electrodes like a rocking chair.Lithium-ion Battery Charging BasicCharging batteries is common for people's daily life, as we all know, Li-ion batteries play a very important role in our social life with their excellent performance, in order to get longest service life, proper charging of Li-ion batteries is essential. Li-ion battery charging mode is voltage limit and constant current, which is controlled by IC chip. The typical charging method is: detect the voltage of the battery to be charged firstly, if its voltage is lower than 3V, pre-charge is required necessarily, and the the charging current is 1 ≤ 10 of the set current. After the voltage rises to 3V, then transferring into the standard charging process. The standard charging process is: having constant current charging with set current. When the battery voltage rises to 4.20V, it is changed to constant voltage charging mode, and the charging voltage is kept at 4.20V. At this time, the charging current gradually decreases till the current drops to 1/10 of the set charging current, the charging ends.The charging process of a Li-ion battery can be divided into three processes: trickle charging (low voltage precharging), constant current charge, and constant voltage charge. Ⅱ Charging Characteristics of Lithium BatteriesFigure 2. Typical Charge ProfileAs can be seen from the above figure, the charging current and voltage of the lithium battery are dynamically changed, which is determined by the chemical content of the lithium battery itself. Therefore, it is necessary to configure the performance of the charging IC according to the charging characteristics of the lithium battery itself to achieve a correct, safe and efficient use of the lithium battery. The "lithium-ion battery charging current" in the daily expression is for the charging current of fast charging. As a dynamic process, the optimal charging current of the lithium battery is actually divided into three stages. Ⅲ Performance Description of Several Different Charging StatesFigure 3. Li-ion Battery Process3.1 On StandbyThe standby state is handled in the following cases:1) The input voltage is lower than the minimum operating voltage of the circuit.2) After the battery voltage is approach to the limit.3) Using external switch to turn offmanagement IC to stop charge.Voltage and current characteristics in standby mode: The charging IC has no charging voltage output, and the IC input current is in the uA level, which can reduce power loss. 3.2 PrechargingAs shown in above figure. Optimal current during precharging: that is, when the initial/no-load voltage of the lithium battery is lower than the prechargeing threshold, it needs a pre-charging stage. For a single lithium-ion battery, this threshold is generally 3.0V, in the phase, the precharge current is about 10% of the current in the constant current charging phase. 3.3 Constant CurrentAs shown in the figure above, when the battery voltage is greater than the preset voltage threshold and less than the maximum voltage of 4.2V, the IC will charge the battery with the maximum charging current set by the external resistor. When the battery voltage is equal to the maximum charging voltage (near 4.2V), the charge stop.The best current for constant current charging: when stay in constant current stage, the voltage gradually rises, then enter the fast charging phase. Most of the constant current charging current is set between 0.5 and 1.0C, and the best set is 0.8C, because the battery can be full charged about two hours without consider other factors. The case is a good balance between charging time and charging safety.Several problems that should be paid attention to when batteries at constant current charging:1) In this state, the IC is in the state of maximum charging current, and the loss at this time is also the largest. The linear voltage drop loss calculation is L = (Vin-Vout) × Iout, it is necessary to pay attention to the maximum operating temperature of the IC.2) The increasing temperature due to the highest charging current, the IC will automatically reduce the maximum charge current, and this is why the charging current drops during overheating. 3.4 Constant VoltageThe maximum charging voltage portion shown in the above figure, when it is detected that the battery voltage is equal to or close to the battery charging voltage, at this time, the charging mode will be stepped down with a constant charging voltage of 4.2V. When it is detected that the charging current is less than 1/10 of the maximum set current, charging will stop. Charging current during constant voltage charging: In the case of a single-cell lithium-ion battery, as the battery voltage rises to 4.2 V, the constant current charging ends and the constant voltage charging stage begins. In order to achieve the best performance, the voltage stabilizer tolerance should be better than +1%.At this stage, the voltage is keeping constant and the current is reduced, and this current reduction is a sequential decrement process. Most lithium battery protection selects 0.1C as the termination current, which means that the charging process enters the end state. Once charging is finished, the charging current drops to zero. The problem to be noted in this state is that the battery can be automatically turned off when the battery is charged to the highest setting voltage. At the same time, when the overvoltage protection of the IC is in the abnormal battery state, it can be automatically locked. Unlike nickel batteries, continuous trickle charging is not recommended. Because it will cause plate plating effect to the lithium metal, making batteries failure.The core of the best charging current of lithium battery is the current design of constant current charging. It should be emphasized that most portable lithium batteries should be designed to charge 0.5C~0.8C. For example 1400mAh capacity of iPhone battery(capacity mAh= current mA × time /h), choosing 0.7C, that is, Apple’s charging current is about 1A, so that most of the batteries between 0.5C~0.8C you can choose.When charging, the voltage of the battery should be detected first. If the voltage is lower than 3V, pre-charging should be performed first. When the charging current is 1/10 of the set current, 0.05C is selected generally. After the voltage rises to 3V, it enters the standard charging process. The standard charging process is constant current charging with set current. Till the battery voltage rises to 4.20V, it is changed to constant voltage charging, and the charging voltage is kept at 4.20V. At this time, the charging current gradually decreases, and when the current drops to 1/10 of the set charging current, the charging ends.Generally, the charging current of the lithium battery is set between 0.2C and 1C. The larger the current, the faster the charging, and the greater the heat of the battery. Moreover, when lies in excessive current charging, the capacity is not full, because the electro-chemical reaction inside the battery takes time. Ⅳ Charging Process Analysis Figure 4. Charging Characteristics of Lithium-ion Battery 4.1 High Voltage Constant Current ModeIn general, the charging process of the mobile phone is to first reduce the 220V charging voltage to the 5V charger voltage, and the 5V charger voltage reduce to the 4.2V battery voltage. During the entire charging process, if the voltage is increased, heat is generated, therefore, the charger will heat up and the phone will heat up. Moreover, the greater the power consumption, the greater the damage to the battery. 4.2 Low Voltage High Current ModeWhen the voltage is constant, the current can be increased by using a parallel circuit. Under this situation, the smaller the volume shared by each circuit after parallel shunting, each circuit has the smaller load damage, so as to the phones charging process. 4.3 High Voltage High Current ModeThis method increases the current and voltage at the same time, so that from the previous formula P=UI, we can know that this method is the best way to increase the power, but it will generate more heat when the voltage is increased. In this way, the more energy is consumed, but the voltage and current are not freely increased without limitation.The maximum charging current of a lithium battery is strictly determined by the structure of the battery. Therefore, the specifications of the lithium battery manufacturers are not consistent, some are set to 0.6C, and the highest current specification for portable lithium batteries is 1C.  Of course, the current design of pre-charging and constant voltage charging cannot be ignored. In the two processes, if the initial voltage is not lower than the pre-charging threshold of 3.0V, there is no pre-charging process. In general, there is a process to check batteries charging voltage that is beneficial to keep the long-term use of lithium batteriess.Ⅴ Li-ion Battery Charging Security5.1 Common Sense in the Daily Use of BatteriesMisunderstanding: “Battery activation”, charging for more than 12 hours in the first three times.For the “activation” problem of lithium batteries, many sayings are: charging time must be more than 12 hours, and repeat three times in order to activate the battery. This statement that “the first three charges have to be charged for more than 12 hours” is obviously a continuation of nickel batteries (such as nickel cadmium and nickel hydride), in other words, this kind of statement can be said to be misinformation of the other batteries. After a sample survey, it conformed that a considerable number of people have confused the charging methods of the two batteries. Lithium-ion battery activation does not require a special method, they will be activated naturally in the normal use.The charge and discharge characteristics of lithium and nickel batteries are very different. All the professional technical data reviewed emphasize that overcharge and overdischarge can cause huge damage to lithium batteries, especially liquid Li-ion batteries. Therefore, charging is preferably performed in accordance with standard methods, especially for ultra-long charging of more than 12 hours. For example, the charging method described in the mobile phone manual is a standard charging method suitable for the mobile phone. It is not suitable to charge for a long time, also the battery is completely dischargedand thenThe lithium battery phone or charger will automatically stop charging when the battery is fully charged. There is no so-called “turbulent” charging over 10 hours for nickel battery chargers. If the lithium battery is fully charged, it will not be charged anymore continuously.Over-time charging and power off completely will cause over-charging and over-discharging, which will cause permanent damage to the positive and negative electrodes of lithium-ion batteries. At the molecular level, over-discharge will cause the anode carbon to release lithium ions excessively causing the layer structure collapses, and overcharging will hardly plug too much lithium ions into the negative carbon structure, and some of the lithium ions will no longer be released. Regular deep charge and discharge for battery calibrationLi-ion batteries generally have a management IC and a charge control IC. The management IC has a series of registers, which contain values such as capacity, temperature, ID, state of charge, and discharge times. These values will gradually change during use, so the main function of the “The batteries should be fully charged and discharged when used once a month or so” is to correct the improper values in these registers. 5.2 Charging RulesThe following rules should be noted when charging and discharging lithium ion batteries:Figure 5. Typical Li-ion Battery Discharging DiagramCharge currentItmust limited for li-ion batteries. Typically the maximum value is 0.8C, but lower values are more usually set to give some margin. Charge temperature  Itshould be monitored. The cell or battery must not be charged when the temperature is lower than 0°C or greater than 45°C. Short circuit protectionItis required to prevent damage or explosion as a result of short circuits. Over-voltage protectionItis required to prevent a voltage that is too high being applied across the battery terminals. Over-charge protectionItis required to stop the Li-ion charging process when voltage per cell rises above 4.30 volts. Reverse polarity protectionItis needed to make sure the battery is not charged in the wrong direction as this could lead to serious damage or even explosion. Over-discharge protectionItis required to prevent the battery voltage falling below about 2.3V dependent upon the manufacturer, when battery voltage less than 2.3V will make battery damage irreversibly. Over temperature protectionIt is necessary to prevent the battery operating in a high temperature, because heating will age batteries and reduce their service life. if the temperature rises too high. Temperatures above 100°C can cause irreparable damage.Ⅵ Questions Related to Lithium-ion Batteries1. How many years does a lithium ion battery last?three yearsThe typical estimated life of a Lithium-Ion battery is about two to three years or 300 to 500 charge cycles, whichever occurs first. One charge cycle is a period of use from fully charged, to fully discharged, and fully recharged again. 2. What is the difference between a lithium battery and a lithium ion battery?Lithium batteries feature primary cell construction. This means that they are single-use—or non-rechargeable. Ion batteries, on the other hand, feature secondary cell construction. This means that they can be recharged and used over and over again. 3. Why are lithium ion batteries bad for the environment?Recycling Lithium-IonUnwanted MP3 players and laptops often end up in landfills, where metals from the electrodes and ionic fluids from the electrolyte can leak into the environment. Because lithium cathodes degrade over time, they cannot be placed into new batteries. 4. Is there a better battery than lithium ion?Zinc-air batteries can be considered superior to lithium-ion, because they don't catch fire. The only problem is they rely on expensive components to work. 5. What is the best way to charge a lithium ion battery?Simple Guidelines for Charging Lithium-based BatteriesTurn off the device or disconnect the load on charge to allow the current to drop unhindered during saturation.Charge at a moderate temperature.Lithium-ion does not need to be fully charged; a partial charge is better.

CatalogⅠ What is Biosensor?Ⅱ Principle of Biosensors Ⅲ Characteristics of Biosensors Ⅳ Types of Biosensors  4.1 Acoustic Biosensor  4.2 Optical Biosensor  4.3 Magnetic Biosensor  4.4 Electrochemical Biosensor  4.5 Optical Fiber Nano BiosensorⅤ FAQⅠ What is Biosensor?Biosensor is an instrument that is sensitive to biological substances and converts its concentration into an electrical signal for detection. Biosensor has the function of receiver and converter. Because enzyme membrane, mitochondrial electron transport system particle membrane, microbial membrane, antigen membrane and antibody membrane have the selective recognition function to the molecular structure of biomaterials and only have the catalytic activation function to specific reactions, so biosensors have very high selectivity. The disadvantage is that the biofilm is not stable.Biosensors are mainly used in clinical diagnosis, treatment monitoring, fermentation industry, food industry, environment and robotics. Biosensor is an interdisciplinary subject combining bioactive materials(Enzyme, protein, DNA, antibody, antigen, biofilm, etc)with physical and chemical transducers. It is an advanced detection method and monitoring method necessary for the development of biotechnology, and it is also a rapid and microanalysis method at the molecular level. In the 21st century, in the development of the knowledge economy, biosensor technology will be a new growth point between information and biotechnology. It will have a wide application prospect in clinical diagnosis, industrial control, food and drug analysis(including biopharmaceutical research and development), environmental protection, biotechnology, biochip and other research in the national economy. All kinds of biosensors have the following common structures: including one or several related bioactive materials(Biofilm) and physical or chemical transducers(sensors) that can convert the signals expressed by bioactivity into electrical signals. The two are combined to reprocess the biological signals with modern microelectronics and automatic instrument technology to form a variety of usable biosensor analysis devices, instruments and systems.Ⅱ Principle of Biosensors The substance to be measured enters into the bioactive material through diffusion, and after molecular recognition, biological reaction occurs. The information generated is then transformed into a quantitative and treatable electrical signal by the corresponding physical or chemical transducer, and then amplified and output by the secondary instrument, the concentration of the substance to be measured can be known.Ⅲ Characteristics of Biosensors     （1）The biosensor uses the immobilized bioactive substance as the catalyst, and the expensive reagent can be reused many times, which overcomes the shortcomings of the high cost of enzyme analysis reagent and complicated chemical analysis in the past.    （2）Strong specificity only reacts to a specific substrate, and not affected by color and turbidity.     （3）The analysis speed is fast, and the results can be obtained in one minute.    （4）High accuracy; general relative error can reach 1%.    （5）The operating system is simple and easy to realize automatic analysis.    （6）Low cost; only a few cents per measurement in continuous use.     （7）Some biosensors can reliably indicate the oxygen supply and by-products in the microbial culture system. In the process of production control, much complex information can be obtained only by the comprehensive action of physical and chemical sensors. At the same time, they also pointed out the direction of increasing the yield of products.Ⅳ Types of BiosensorsAccording to the classification of life substances used in biosensors, biosensors can be divided into microbial sensors, immune sensors, tissue sensors, cell sensors, enzyme sensors, DNA sensors, etc. According to the principle of sensor detection, it can be divided into a thermosensitive biosensor, FET biosensor, piezoelectric biosensor, optical biosensor, acoustic channel biosensor, enzyme electrode biosensor, mediator biosensor, etc.According to the type of interaction between sensitive substances, it can be divided into two types: affinity type and metabolism type. 4.1 Acoustic BiosensorAcoustic biosensor is a kind of sensor to detect the change of acoustic frequency caused by the substance to be detected. Among them, quartz crystal microbalance（QCM） biosensor has been studied most. In the piezoelectric crystal of quartz crystal microbalance biosensor, AT mode is often used to form two parallel metal((Au，Ag，Pt，Ni，Pd etc.)) membrane electrodes on both sides of the crystal by ion beam deposition. (At cutting means that the cutting surface is 25.15 ° to the main optical axis of quartz crystal.  At this moment, the temperature coefficient of crystal resonance is close to zero at room temperature)The recognition molecules are fixed on the surface of the membrane electrode. Because of their specificity, the recognition molecules combine with the molecules to be detected, causing the quality change of the electrode surface, thus changing the oscillation frequency of the quartz crystal. If the nanoparticles are modified on the molecules to be detected, the quality of the molecules to be detected will be significantly improved, and the detection signal will also be enhanced. Ward et al. Labeled the antibody with nano colloidal particles, and combined it to the surface of quartz crystal by antibody antigen immunoassay.  Because the modified colloidal particles(The diameter of sol particles is 5 "100nm) improved the quality of the labeled molecules, according to Sauerbrey equation, the oscillation frequency of quartz crystal was correspondingly increased, so the detection signal was amplified, the detection sensitivity was improved, and the detection lower limit was also reduced.4.2 Optical BiosensorNano metal particles can be used for optical resonance detection. Bauer et al. Fixed nano-metal particles on the surface of conductive materials by antigen-antibody or protein receptor binding methods. Due to the interaction of reflection dipoles of nanoparticles, the resonance of reflected light is enhanced. The materials to be detected can be detected by detecting resonance signals. Nanoparticles can also be used to locate tumors. Fluorescein labeled recognition factors bind to tumor receptors, and then the size and location of tumors can be displayed in vitro. Nano metal particles can also be used as a general fluorescent annihilation group. Maxwell and other scientists labeled gold nanoparticles and fluorescence excitation groups at both ends of oligonucleotide probe molecules respectively. The probe formed a "hairpin" structure due to complementary bases, and the proximity of fluorescence excitation group and gold nanoparticles resulted in excitation fluorescence annihilation. When the probe combined with specific target DNA, its conformation changed, and the gold nanoparticles and fluorescence excitation groups were separated, so as to excite Fluorescence. The principle can be used for real-time fluorescence detection of nucleic acids and single base mutation polymorphism detection.4.3 Magnetic BiosensorMagnetic nanoparticles have important application value in biological detection and drug analysis. By using magnetic materials to label biomolecules and molecular recognition technology, complex operations such as sample mixing, separation and detection can be realized. Scientists label molecules with magnetic materials, and realize the separation and detection of samples under the magnetic field gradient. Richardson et al. Used magnetic counter to detect magnetic labeled molecules by magnetic immunoassay.  In addition, the distribution and position of magnetic particles in vivo can be measured in vitro after the identification factor is labeled with nanomagnetic particles and combined with the target recognition device on the tumor surface, so as to locate the tumor. Chemla and other scientists used paramagnetic nanoparticles and a microscope based on high-temperature transient DC superconducting quantum interface device (SQUID) to propose a novel rapid detection technology for biological samples. Firstly, the magnetic particles of the fixed antibody are suspended in the solution, and then the magnetized nanoparticles are generated under the instantaneous magnetic field pulse.  When the magnetic field disappears, the particles tend to be free distribution, because the particles without the antibody are Brownian motion, so there is no detection signal; while the nanoparticles with the target molecule move in the way of Neel relaxation, resulting in a slowly attenuated magnetic signal, The substance to be detected can be analyzed by the signal collected by the squid. This technology can directly detect the labeled molecules without separating the nanoparticles which are not combined with the molecules to be detected, which shortens the detection time and improves the detection efficiency.4.4 Electrochemical BiosensorColloidal gold is the most common metal nanoparticles, which can be used to mark biomolecules, thus realizing signal detection and amplification; in addition, it can also be widely used in TEM, SEM characterization and paper strip color. Many literatures also reported the signal amplification of colloidal gold in various biosensors. Gonzalez Garcia and other scientists used colloidal gold labeling and electrochemical methods to study the interaction between biotin and avidin.  By modifying biotinylated albumin on the electrode surface and then reacting with avidin labeled by colloidal gold with a diameter of 10 nm, scientists found that the current response caused by colloidal gold was linearly related to the concentration of avidin(2.5×10-9mol/L "2.5×10–5mol/L). Nanoparticles have an excellent specific surface area, which can be used to immobilize biomolecules, increase the number of fixed molecules, and achieve signal amplification. Singh and other scientists used the sol-gel method to synthesize silicon nanoparticles with a diameter of 20 nm or 200 nm. Acetylcholinesterase immobilized on the surface of nanoparticles can be used to make organophosphorus pesticide biosensor.  Because of its high specific surface activity, combined with the detection of ion-sensitive field effect tube, the metal nanoparticles with rapid response can be used as the carrier of catalyst, which can greatly improve the performance of catalyst. Enzyme colloidal gold is fixed on the surface of the electrode and can be used for the electrochemical detection of H2O2, glucose, xanthine and hypoxanthine. Xu et al. Modified the surface of the screen-printed carbon electrode with colloidal gold, combined with immunity and horseradish peroxidase (HRP) to make H2O2 biosensor. The results showed that the electrocatalytic performance and current response of HRP were significantly improved, the linear range of signal was greatly improved(0.8μM"1.0mM), and the detection limit was also reduced to 0.4 μ M.4.5 Optical Fiber Nano BiosensorCompared with other types of biosensors, fiber-optic nano biosensors are not only small in size and high insensitivity, but also free from electromagnetic interference and do not need reference devices. It can enter the interior of cells and measure the changes of structure and cytoplasm in vivo. （1）Optical fiber nano fluorescence biosensorKopelman was the first to use a fluorescent fiber-optic nanosensor to detect the pH value in the microenvironment. Its working principle is to fix the fluorescent agent at the head of the optical fiber. When the fluorescent agent reacts reversibly with the proton, the optical property of the liquid changes.  According to the change of the fluorescence intensity, the pH value can be determined. The optical fiber processing method is as follows: the optical fiber is drawn into a fiber probe with a head diameter of 100nm "1000nm by a fiber drawing instrument, and aluminum is plated on the surface of the optical fiber by a vacuum evaporator to prevent light from leaking during transmission. Then, the exposed optical fiber head is silanized, and the surface is modified into an active surface containing hydroxyl or amino group, and the antigen or antibody of the molecule to be detected is fixed and identified.  Finally, the light The fiber head is combined with a pH selective fluorescent dye polymer. The response time of the nano sensor is 250ms, and it can detect the ion concentration of μ M. These characteristics are suitable for the detection of single cell and subcellular structure, such as the detection of pH value of mouse embryonic cell fluid. （2）Optical fiber nano immune biosensorOptical fiber nano immunosensor is a kind of sensor which applies optics and photonics technology to immunoassay. It can convert the amount of antigen or antibody to optical signal by using the characteristic that antigen and antibody can combine specifically. This kind of sensor combines the advantages of traditional immunoassay, optics and biosensor technology, and has high specificity, sensitivity and stability.  At the same time, the fiber-optic nano immune sensor only uses nano products on sensitive components, so it not only retains many advantages of the original but also makes it suitable for the measurement of single cells. Dinh et al. Have successfully developed an optical fiber nano immunosensor for the detection of BPT (benzopyrene tetrol, a biomarker of DNA damage related to exposure to carcinogenic benzo [α] pyrene). They first made quartz fiber with a diameter of 10nm "100nm with a fiber drawing instrument, then silanized the fiber head, modified the fiber head with BPT antibody, and then plated the whole length of the fiber (except the modified fiber head) with silver to prevent light from leaking out.  Finally, cell puncture and detection experiments were carried out on a single cell operated micromanipulator/microinjector, they used photomultiplier PMT to record the fluorescence produced by the binding of BPT and antibody, and detected the content of BPT in cells by measuring the change of fluorescence intensity. The minimum detection limit of the sensor can reach 10 – 21mol. Ⅴ FAQ1. What is the principle of piezoelectric biosensors?Piezoelectric Biosensors are also known as Acoustic Biosensors as they are based on the principle of sound vibrations i.e. acoustics. When a mechanical force is applied to a piezoelectric biosensor, they produce an electrical signal. The biological elements are attached to the surface of the piezoelectric biosensor. 2. What are the different types of biosensors?• Electrochemical Biosensors.• Magnetic Biosensors.• Thermometric Biosensors.• Acoustic Biosensors.• Optical Biosensors. 3. How does a basic biosensor work?The term ‘biosensor’ is short for ‘biological sensor.’ The device is made up of a transducer and a biological element that may be an enzyme, an antibody or a nucleic acid. The bio element interacts with the analyte being tested and the biological response is converted into an electrical signal by the transducer. 4. What are the main components of biosensors?A biosensor typically consists of a bio-receptor (enzyme/antibody/cell/nucleic acid/aptamer), transducer component (semi-conducting material/nanomaterial), and electronic system which includes a signal amplifier, processor & display. Transducers and electronics can be combined, e.g., in CMOS-based microsensor systems. 5. How do you classify biosensors?Biosensors can be classified according to the transduction methods they utilize (Fig. 4). Most forms of transduction can be categorized in one of five main classes: electrochemical, electrical, optical, piezoelectric (mass detection methods) and thermal detection. 6. What are wearable biosensors?Wearable systems are devices that allow physicians to overcome the limitations of technology and provide a response to the need for monitoring individuals over weeks or months. Wearable Biosensors typically rely on wireless sensors enclosed in bandages or patches or in items that can be worn. 7. What is an amperometric biosensor?Amperometric biosensors are self-contained integrated devices based on the measurement of the current resulting from the oxidation or reduction of an electroactive biological element providing specific quantitative analytical information. 8. What is voltammetric biosensor?Cyclic Voltammetry (CV) Voltammetry belongs to a category of electro-analytical methods, through which information about an analyte is obtained by varying potential and then measuring the resulting current. It is, therefore, an amperometric technique. 9. What is the electrochemical biosensor?An electrochemical biosensor is a self-contained integrated device, which is capable of providing specific quantitative or semi-quantitative analytical information using a biological recognition element (biochemical receptor) which is retained in direct spatial contact with an electrochemical transduction element. 10. What are Piezoelectric Biosensors?Piezoelectric biosensors are a group of analytical devices working on the principle of affinity interaction recording. A piezoelectric platform or piezoelectric crystal is a sensor part working on the principle of oscillations change due to a mass bound on the piezoelectric crystal surface. 

Introduction Diodes are widely used in electronics, such as rectification in power supply, as detection and mixing, etc. in communications, and are often used in voltage regulation and protection in various circuits (such as freewheeling diodes, TVS and so on). Due to the wide variety and versatility, the following is an analysis of the simple application of Schottky diodes in digital circuits.In this video, the Schottky diode has been explained.CatalogIntroductionⅠ Schottky Diodes CharacteristicsⅡ Schottky Diode Applications2.1 As Dual Power Supply2.2 As AND Gate2.3 As OR GateⅢ Schottky Diode ParametersⅣ Example AnalysisⅠ Schottky Diodes CharacteristicsThe Schottky diode is structurally different from the PN junction diode. It is made of an anode metal (a barrier layer made of a material such as molybdenum or aluminum), SiO2 (electric field eliminating material), and N- epitaxial layer (arsenic material), the N-type silicon substrate, N+ cathode layer, and the cathode metal, which are as shown in the following figure. A Schottky barrier is formed between the N-type substrate and the anode metal. When a forward bias is applied to both ends of the Schottky barrier (anode metal is connected to the positive electrode of the power supply, and the N-type substrate is connected to the negative electrode), the Schottky barrier layer is narrowed, and the internal resistance becomes small. On the contrary, when a reverse bias is applied across the Schottky barrier, it becomes wider and its internal resistance becomes larger. Figure 1. Schottky Diode Structure Ⅱ Schottky Diode ApplicationsThe problem with Schottky diodes is that the withstand voltage is relatively low and the reverse leakage current is large. At present, the general condition of the Schottky diode used in the power conversion circuit is that the withstand voltage is below 150V, the average current is below 100A, and the reverse recovery time is between 10 and 40ns. Therefore, Schottky diodes are ideal device for use in high frequency and low voltage circuits.2.1 As Dual Power SupplyAt present, in the electronic design with the main controller, the real-time clock (RTC) is basically used, and the RTC needs an additional button battery to support, to avoid information lost after the system is powered off. And meanwhile, after the system is started, in order to extend the battery life, the main system is often supplied with power. Therefore, RTC often requires dual power supply, and the diode can be used for power isolation due to its single-conductivity. Taking the small-signal Schottky diode BAT54C as an example, the forward voltage drop is only 0.24v (the forward current is 0.1mA), and the RTC current consumption is uA-level, after adding the Schottky diode to isolate power supply to save info security.2.2 As AND GateAs shown in the figure below, n Schottky diodes form the AND gate of the n input. As long as there is a signal output logic 0 in A1~An, the Output is logic 0, only all signals in A1~An output logic 1, Output can output logic 1. That is, the phase sum of the signals A1~An is realized. Since the chip signal input stage is basically high-resistance in the digital circuit, the overall current of the AND gate circuit composed of the Schottky diode is uA-level, and the Schottky diode voltage drop is extremely small. In the case of it, the flat can still meet the design requirements.  Figure 2. Schottky Diode as AND Gate2.3 As OR GateAs shown in the figure below, n Schottky diodes form an n-input OR gate. As long as there is a signal output logic 1 in A1~An, Output outputs a logic 1. Only all signals in A1~An output logic 0, and Output can output logic 0. That is, the phase sum of the signals A1~An is realized.  Figutre 3. Schottky Diode as OR Gate Ⅲ Schottky Diode ParametersNote: Because Schottky diodes are used differently in different electronic circuits, we also need to consider the following parameters when using them.1）Forward voltage drop VFVF is the forward voltage drop when the diode is forward conducting. The greater the current through the diode, the larger the VF, in addition, the higher the diode temperature, the smaller the VF.2）Reverse saturation drain current IRIR refers to the current flowing through the diode when a reverse voltage is applied to the diode. The Schottky diode has a large reverse leakage current, therefore, selecting a Schottky diode with a smaller IR.3）Rated current IFIt refers to the average current value calculated from the allowable temperature rise when the diode is in a long time operation.4）Maximum surge current IFSMExcessive forward current that is allowed to flow. It is not a normal current, but an instantaneous current, which is quite large.5）Maximum peak inverse voltage VRMEven if there is no reverse current, as long as the reverse voltage is continuously increased, the diode will be damaged sooner or later. This reverse voltage is not the instantaneous voltage, but the reversed voltage that is added repeatedly. Since the rectifier is supplied with an alternating voltage, its maximum value is a specified important factor. And the maximum reverse peak voltage VRM refers to the maximum reverse voltage that can be applied to avoid breakdown. At present, Schottky's highest VRM value is 150V.6）Maximum DC reverse voltage VRVR is the value when the DC voltage is continuously applied. For DC circuits, the maximum DC reverse voltage is important to determine the allowable and upper limits.7）Maximum operating frequency FMDue to the junction capacitance of the PN junction, when the operating frequency exceeds a certain value, its unidirectional conductivity will deteriorate. And Schottky diodes have high FM values up to 100 GHz.8）Reverse recovery time TrrWhen the operating voltage changes from a forward voltage to a reverse voltage, the ideal operation of the diode is that the current can be instantaneously turned off. In fact, it usually takes a little delay. The amount that determines the current cut-off delay is the reverse recovery time. Although it directly affects the switching speed of the diode, it does not mean that this value is small. That is, when the diode is suddenly reversed by conduction, the reverse current is greatly attenuated to a time required to approach IR. This indicator is important when the high-power switch is operating in the high-frequency state.9）Maximum dissipation power PWhen a current flows through the diode, it absorbs heat and raises its temperature. In reality, the external heat dissipation condition also has a great influence on P. Specifically, the voltage applied across the diode is multiplied by the current flowing through and the reverse recovery loss. Schottky Diode Symbols Ⅳ Example AnalysisIn digital circuit design, it is often necessary to make simple phase, or phase inversion of some signals. If the logic chip such as the 74 series is directly used, not only the layout area is greatly increased, but also the wiring is not flexible. The use of small-signal Schottky diodes and OR gates is more flexible and easy to use. The following figure shows a simple two-way reset circuit. JTAG generating a reset signal needs to reset the master, and the external reset button also needs to reset the master when pressed. If the JTAG reset and button reset directly to the reset pin of the master, it may cause damage to the JTAG emulator. For example, when the reset button is pressed, the JTAG output reset pin will be directly lowered. The phase and circuit are formed by the Schottky diode BAT54A , and the signal outputs do not affect each other. The following figure allows the master to reset as long as the JTAG output logic 0 or pressing the button reset output logic 0.Figure 4. Schottky Diode BAT54A ApplicationIf it is to be used as a non-gate, a triode can be used. Of course, the triode is widely used in electronics, such as a switching device in a digital circuit, as a current drive, level shifter, and the like. Frequently Asked Questions about Small Signal Schottky Diodes1. What is the Schottky diode and how it works?A typical diode combines p-type and n-type semiconductors to form a p-n junction. In a Schottky diode metal replaces the p-type semiconductor. This metal can range from platinum to tungsten, molybdenum, gold, etc. When metal is combined with an n-type semiconductor an m-s junction is formed. 2. What does small signal mean?A small signal is an AC signal (more technically, a signal having zero average value) superimposed on a bias signal (or superimposed on a DC constant signal). This resolution of a signal into two components allows the technique of superposition to be used to simplify further analysis. 3. Which statement is correct for Schottky diode?Explanation: The majority charge carriers in a Schottky diode are electrons not holes. Explanation: Due to the metal-silicon junction there are no stored charges hence, no reverse recovery time, due to which the switching is faster. 4. What are the two important features of a Schottky diode?We have seen here that the Schottky Diode also known as a Schottky Barrier Diode is a solid-state semiconductor diode in which a metal electrode and an n-type semiconductor form the diodes ms-junction giving it two major advantages over traditional pn-junction diodes, a faster switching speed, and a low forward bias.

Ⅰ. IntroductionIn electronics, an operational amplifier is a circuit unit with a very high amplification factor. In the actual circuit, usually combined with the feedback network to form a certain functional module. It is an electronic device with a special coupling circuit and feedback. The output signal can be the result of mathematical operations such as addition, subtraction or differentiation, integration, etc, thus it was used in analog computers to implement mathematical operations.CatalogⅠ. IntroductionⅡ. Non-inverting Amplifiers and Inverting Amplifiers   2.1 Terminology   2.2 Non-inverting Amplifier Circuit   2.3 Inverting Amplifier CircuitⅢ. Note: Input ImpedanceⅣ. Amplifier GainⅤ. Differences between Inverting & Non-Inverting Amplifiers   5.1 Facts Consideration   5.2 Differences SummaryⅥ One Question Related to Amplifier and Going Further   6.1 Question   6.2 AnswerAn op amp is a functional unit that can be implemented in discrete devices or in semiconductor chips. With the development of semiconductor technology, most of the op amps exist in the form of a single chip, but there are many types of op amps, which are widely used in the electronics industry. The op amp can be simply viewed as a high-gain direct-coupled voltage amplifying unit with one signal output port (Out) and two high-impedance inputs, non-inverting input and inverting input, so op amps can be used to make the non-inverting, inverting, and differential amplifiers.Difference between Inverting and Noninverting Amplifier Ⅱ. Non-inverting Amplifiers and Inverting Amplifiers2.1 TerminologyAn operational amplifier in an electronic circuit has a non-inverting input and an inverting input. The same polarity of the input and the output is a non-inverting amplifier, on the contrary, it is an inverting amplifier. And the inverting amplifier circuit has a function of amplifying the input signal and inverting the output. 2.2 Non-inverting Amplifier CircuitWhen a positive phase is received, a positive phase is output, whereas the negative phase is output. The phases of non-inverting end and the output end are the same. In other words, the signal is applied to the non-inverting input of the op-amp, and it is not inverted at the output when compared to the input. Figure 1. Non-inverting Amplifier(A signal applied keeps its polarity at the output, and a positive input remains a positive output.)Vin and V-Virtual are short circuit in the figure, where Vin=V-……aBecause of the virtual open circuit, there is no current to the inverting input, the current through R1 and R2 is equal, and the current is set to I, which is obtained by Ohm's law:I=Vout/(R1+R2)……bVin equal to the partial voltage on R2, where Vin=I*R2……cBy a, b, c, where Vout=Vin*(R1+R2)/R2 2.3 Inverting Amplifier CircuitWhen the positive phase is received, the negative phase is output, whereas the positive phase is output. And the non-inverting end and the output end are keeping inverting relation. An inverting amplifier provides the same function as the common emitter and common-source amplifier.Figure 2: The grounding of the op amp is 0V, the inverting end and the non-inverting end are short circuit, so it is also 0V. The input resistance of the inverting input is very high, while it is virtual open. So that there is almost no current injection and outflow, then R1 and R2 are equal to a series connection, the current flowing through each of the components in a series circuit is the same, that is, the current flowing through R1 and the current flowing through R2 are the same. Figure 2. Inverting Amplifier(The polarity of a signal is reversed at the output, and a negative input becomes a positive output.)Current flowing through R1: I1=(Vin-V-)/R1………aCurrent flowing through R2: I2=(V--Vout)/R2……bV-=V+=0………………cI1=I2……………………dBy solving the above algebra equation, we can get the result:Vout=(-R2/R1)*ViThe inverting amplifier circuit has the function of amplifying the input signal and inverting output, which is a negative feedback technique. Negative feedback returns a portion of the output signal to the input. The reason why the inverting amplifier can only connect the signal to the inverting input is because the negative feedback can be formed only in this way, otherwise it will not work in the linear amplification region.When inputting from both ends simultaneously, the size and phase are the same, that is the common mode signal, and the theoretical output is zero. Ⅲ. Note:  Input ImpedanceThe input impedance of the non-inverting input is high, and the input impedance of the inverting input is low. The input impedance of the non-inverting input is basically determined by the bias resistor connected in parallel with the non-inverting terminal, and the resistance can be very large. When the inverting input is connected, the feedback resistor is connected between the inverting terminal and the output terminal, and the resistance is small, so the input impedance of the inverting input is relatively low.1. The magnitude of the input resistance of the non-inverting amplifier does not affect the input impedance, and the inverting amplifier input resistance is approximately equal to the input impedance.2. When the input impedance is required to be high, the non-inverting amplifier should be selected.3. If the input impedance is not required to be large, the non-inverting or inverting can be selected at this time. When the phase is not considered strictly, the inverting amplification is preferred because it only has the differential mode signal.4. The CMRR of the inverting amplifier is better when the CMRR is decisive.Inverting amplifier, the input common mode of the op amp is almost constant, the common mode amplification is not reflected to the output, and the input common mode of the op amp in the non-inverting amplifier changes with the input signal, the common mode amplification of the op amp will be reflected Output. Therefore, the CMRR of the inverting amplifier is better when the CMRR of the op amp is decisive. Ⅳ. Amplifier GainBasic Inverting Amplifier Made with an Op-ampNon-inverting AmplifierInverting AmplifierGAIN (AV) = 1+(R2 / R1)Example:if R2 is 1000 kilo-ohm and R1 is 100 kilo-ohm the gain would be :1+ (1000/100) = 1 + 10 or GAIN (AV) = 11If the input voltage is 0.5v the output voltage would be : 0.5 X 11 = 5.5vGAIN (AV) = -R2 / R1Example:if R2 is 100 kilo-ohm and R1 is 10 kilo-ohm the gain would be :-100 / 10 = -10 (Gain AV)If the input voltage is 0.5v the output voltage would be : 0.5v X -10 = -5v Ⅴ. Differences between Inverting & Non-Inverting Amplifiers5.1 Facts ConsiderationIt can be seen that comparing them is from the following aspects: input and output impedance, common mode anti-interference.1. The input impedance of the non-inverting amplifier is equal to the input impedance of the op amp, and they are close to infinity. The input resistance of the non-inverting amplifier does not affect the input impedance; and the input impedance of the inverting amplifier is equal to the resistance of the series resistor of the signal to the input. Therefore, when the input impedance is required to be high, the non-inverting amplifier should be selected.2. The input signal range of the non-inverting amplifier is limited by the op amp's common-mode input voltage range, while it is not the case with the inverting amplifier. Therefore, if the input impedance is required to be low and the phase is free, the inverting amplification is preferred because it only has a differential mode signal. And the anti-interference ability is strong, thus a larger input signal range can be obtained.3. In the design where the same magnification is required, try to select a resistor with a small value, which can reduce the influence of the input bias current and the influence of the distributed capacitance. If you are more concerned about power consumption, you have to compromise on the resistance.4. Determine if an input signal is a non-inverting input or an inverting input. If the input resistance of the amplifier circuit is required to be large, the non-inverting input amplifier circuit should be used because the increase of the input resistance of the amplifier circuit will affect the voltage gain. When the inverting input resistance is increased, the voltage gain of the circuit is reduced, and the voltage gain is also affected by the internal resistance of the signal source. Therefore, when designing the inverting input amplifying circuit, sometimes the input resistance and the voltage gain is difficult to balance. If the bias resistor or the voltage divider is appropriately increased, the input resistance of the amplifier circuit can be increased, and the voltage gain has little or no effect on the voltage gain, which requires a better understanding of the circuit.Figure 3. Integrated Circuit Using Op-amp5.2 Differences SummaryThe integrated amplifier can be connected to the non-inverting or to the inverting amplifier. Is it better to select non-inverting amplification or inverting amplification? Let's look at the difference between them.1）non-inverting amplifiera. AdvantagesThe input impedance is equal to the input impedance of the op amp, which close to infinity.b. DisadvantagesThe amplifying circuit has no virtual ground, so it has a large common mode voltage, and the anti-interference ability is relatively poor. So that the op amp requires a higher common mode rejection ratio, and another disadvantage is that the amplification factor can only be greater than one.2）inverting amplifiera. Advantages The potential of the two input terminals is always approximately zero (the non-inverting terminal is grounded, and the inverting terminal is virtual-grounded), in addition, only the differential mode signal exists, and the device has strong anti-interference ability.b. Disadvantages The input impedance is small, which is equal to the resistance of the series resistance of the signal to the input.3) The gain calculation of the two are different, and their phases are opposite. Ⅵ One Question Related to Amplifier and Going Further6.1 QuestionWhat are non-inverting amplifiers used for?6.2 AnswerThe non-inverting amplifier configuration is one of the most popular and widely used forms of op amp circuit and it is used in many electronic devices. The op amp non-inverting amplifying circuit provides a high input impedance along with all the advantages gained from using an op amp. Frequently Asked Questions about Difference between Inverting and Noninverting Op Amp1. Which is better inverting or noninverting amplifier?Inverting op-amps provide more stability to the system than non-inverting op-amp.In case of inverting op-amp negative feedback is used that is always desirable for a stable system. 2. What are the advantages of non inverting amplifier over inverting amplifier?The advantages of the non-inverting amplifier are as follows: The output signal is obtained without phase inversion. In comparison to the impedance value of the input at the inverting amplifier is high in the non-inverting amplifier. The voltage gain in this amplifier is variable. 3. What is an inverting amplifier used for?The inverting amplifier is an important circuit configuration using op-amps and it uses a negative feedback connection. An inverting amplifier, like the name suggests, inverts the input signal as wells as amplifies it. 4. Where are non-inverting amplifiers used?The non-inverting amplifier configuration is one of the most popular and widely used forms of operational amplifier circuit and it is used in many electronic devices. The op amp non-inverting amplifier circuit provides a high input impedance along with all the advantages gained from using an operational amplifier. 5. Why are inverting amplifiers better than non inverting?Inverting op-amps provide more stability to the system than non-inverting op-amp.In case of inverting op-amp negative feedback is used that is always desirable for a stable system.

The transformer is an essential part of electrical equipment. So it is necessary to know and master the basic knowledge of it. Is a necessary skill of every electric design. Catalog I. What is a Transformer? II. How does Transformer Works? III. What types of transformer are there? IV. What are the components of the transformer? V. What are the losses of transformers in operation? How to reduce them? VI. What is the nameplate of the transformer? What are the main technical   data on the nameplate? VII. How to choose a transformer? VIII.Why transformer cannot run when overload? IX. What kinds of tests should be done for transformers in operation? FAQ I. What is a Transformer? The transformer is a device that uses the principle of electromagnetic induction to change the AC voltage. The main components are primary coil, secondary coil, and core (magnetic core). The main functions are voltage conversion, current conversion, impedance transformation, isolation, voltage stabilization (magnetic saturation transformer), and so on. It can be divided into a power transformer and special transformer (furnace transformer, rectifier transformer, power frequency test transformer, voltage regulator, mine transformer, audio transformer, intermediate frequency transformer, high-frequency transformer, impulse transformer, instrument transformer, electronic transformers, reactors, voltage, and current transformer, etc.) The role of the core is to strengthen the magnetic coupling between the two coils. In order to reduce the eddy current and hysteresis loss in the iron, the iron core is formed by the superposition of the painted silicon steel sheet; there is no electrical connection between the two coils, and the coils are wound by insulated copper wire (or aluminum wire). One coil connected to the AC power supply is called the primary coil (or the primary coil) and the other coil is the secondary coil connected to electrical appliances. The actual transformers are very complicated, so there may be problems that exist to concern, such as copper loss (coil resistance heating), iron loss (core heating), magnetic flux leakage (air-closed magnetic induction line), and so on.  To simplify the discussion, an ideal transformer is introduced. An ideal transformer requires some necessary conditions: ignoring the flux leakage, ignoring the resistance of the primary and secondary coils, ignoring the loss of the iron core, and ignoring the no-load current (the current in the primary coil which supplies the secondary coil). For example, the power transformer is close to the ideal condition when it is running at full load (the output with a rated power of the secondary coil). The transformer is a static electrical appliance made by the principle of electromagnetic induction. When the primary coil of the transformer is connected to the AC power supply, the core produces an alternating flux, which is represented by φ. The φ in the primary and secondary coil is the same, and φ is also a simple harmonic function, and φ = φ msinωt. According to Faraday's law of electromagnetic induction, the induction electromotive force in the primary and secondary coils is e1=-N1d φ/dt, e2=-N2d φ /dt. N1, N2 is the number of turns of the secondary coil. From the diagram, we can see that U1=-e1, U2=e2(the primary coil physical quantity is represented by the subscript 1, the secondary coil physical quantity is indicated by the subscript 2), and the complex-effective value is U1=-E1=jN1 ω Φ, U2=E2=-jN2 ω Φ, and makes transformer ratio k=N 1 /N 2. From the upper formula, we can get U1 /U2=-N1 /N2=-k. that is, the voltage effective value of the transformer to that of two coils, which is equal to its coil-voltage ratio, and the phase difference of the voltage of two coils is π. Further More Based On Above Mentioned U1/U2=N1/N2 Under the condition that the no-load current can be neglected, there is I1 /I2=-N2 /N1, that is, the effective value of the coil's current is inversely proportional to the number of turns, and the phase difference is π. On the contrary, under the condition of no-load current, I1/ I2=N2/N1 The power of the ideal transformer is equal to that of the subsoils, that is P1=P2. It shows that the ideal transformer itself has no power loss. But there is always a loss in the actual transformer, and its efficiency is η= P2 /P1, for example, although power transformer efficiency is very high, can reach over 90%, still has a little loss. In an AC circuit, the equipment that increases or decreases the voltage is called a transformer. The transformer can transform any voltage into the value we need at the same frequency to meet the requirements of transmission and distribution. For example, the power generated by a power plant has a lower voltage level, which must be increased the voltage to transmit to a far distance, and the power area must reduce the voltage to a suitable voltage level for power equipment and daily use. II. How does Transformer Works? This video gives a detailed animated illustration on the working of electrical Transformers. Here the basic working principle and construction of transformer, step-up transformer, step-down transformer, transformer winding and core construction are well illustrated. Transformers are based on electromagnetic induction. It consists of an iron core made of silicon steel sheet (or silicon steel sheet) and two sets of coils around the core. The core and the coil are insulated from each other without any electrical connection. The coils connected to one side of the transformer and the power supply are called primary coils (or primary sides), and the coils that connect transformers and electrical equipment are called secondary coils (or secondary sides).  When the primary coil of the transformer is connected to the AC power supply, the changing magnetic field line in the core appears. Because the secondary coil is wound on the same iron core, the magnetic field line cuts the secondary coil, and the inductive electromotive force must be generated on the secondary coil, finally, the voltage at both ends of the coil generated. Because the magnetic line is alternating, the voltage of the secondary coil is also alternating. And its frequency is exactly the same as the frequency of the power supply. It is proved by the theory that the voltage ratio between the primary coil and the secondary coil is related to the turns of coils. It can be expressed as follows: Primary coil voltage / secondary coil voltage = primary coil turns / secondary coil turns, the higher the number of turns, the higher the voltage. Therefore, it can be seen that the turns of the secondary coil are less than the primary coils, that is, a step-down transformer, otherwise, it is a step-up transformer. III. What types of transformer are there? According to the number of phases, there are single-phase and three-phase transformers;  according to thefunction, there are power transformers, special power transformers, voltage regulating transformers, measuring transformers (voltage transformers, current transformers), small power transformers (for small power equipment), safety transformers;  according to the structure, there are core type and shell type; according to the coil, there has double winding and multi-winding transformers, auto-transformer; according to the cooling mode, oil-immersed type and air-cooled type transformers. IV. What are the components of the transformer? Transformer components are mainly composed of iron core, coil, also have other parts, such as oil tank, oil pillow, insulating sleeve and splice, etc. What’s the function of transformer oil? The functions of transformer oil are:  (1) insulation;   (2) heat dissipation;  (3) elimination of arc. What is autotransformer? The autotransformer has only one set of coils, and the secondary coils are tapped from the primary coils, and its electricity can transmitted. It not only has electromagnetic induction, but also the transmission of electricity. There are fewer silicon steel sheets and fewer copper wires in this kind of transformer than in ordinary transformers, often used to voltage regulator. How voltage regulator works? The voltage regulator is constructed the same as the autotransformer, but the iron core is made into a ring coil. The secondary coil tap uses a sliding brush contact to make the surface of the ring along the contact slip in a circular way to achieve voltage regulation smoothly. What is the current relationship between the primary coil and the secondary coil of the transformer? When the transformer operates with load, the current change of secondary coil will cause the corresponding change of primary coil current. According to the principle of magnetic potential balance, it is deduced that the current of the primary and secondary coil is inversely proportional to the number of turns of the coil, the current is small with more turns, and the current with less turns is large. The following formula can be expressed: primary coil current / secondary coil current = secondary coil turns / primary coil turns. What is the voltage change rate of a transformer? The voltage change rate of the voltage regulator is one of the main indexes of transformer performance. When the transformer supplies power to the load, the voltage at the load end of the transformer will inevitably decrease. Comparing the reduced voltage value with the rated voltage value, the percentage is the rate of voltage change. It can be expressed by the formula: voltage change rate = [(secondary rated voltage-load terminal voltage) / secondary rated voltage] ×100%. Generally, for the normal power transformer, when connected to the rated load, the voltage change rate is 4% to 6%. How to ensure that the transformer has a rated voltage output? Too high or too low voltage will affect the normal operation and service life of the transformer, so the voltage must be adjusted. The method of voltage regulation is to draw out several taps in the primary coil and connect them to the tap beginning, which changes the number of turns of the coil by turning the contact. In addition, the required rated voltage can be obtained by rotating the position of the tap switch. It also needs to note that voltage regulation usually occurs after the load of the transformer is cut off. What kind of small transformers are usually used? Where are they applied? Small transformers refer to single-phase transformers with a capacity below 1k VA, mostly used as power transformers for electrical equipment control, electronic equipment and safe lighting equipment. V. What are the losses of transformers in operation? How to reduce them? The loss of transformer in operation includes two parts. (1) One is caused by the iron core. When the coils are electrified, the magnetic field lines are alternating and cause eddy current and hysteresis loss in the core.  (2) Another loss is caused by the resistance of the coil itself. When the primary and secondary coils of the transformer have current passing through, some electrical energy may lose. The sum of iron loss and copper loss is the transformer loss, which is related to transformer capacity, voltage, and equipment utilization. Therefore, in the selection of transformers, the capacity of the equipment and the actual usage should be as consistent as possible, in order to improve the utilization rate of the equipment, pay attention not to make the transformer lies in light load operation. VI. What is the nameplate of the transformer?  The nameplate of the transformer should indicate the transformer's performance, technical specifications, and use occasions to meet the needs of the user. The main technical data usually selected are as follows: (1) The number of rated capacity. The output capacity of the transformer is rated. For example, the rated capacity of a single-phase transformer is Uline × I line, and the capacity of a three-phase transformer is also the U line × I line. (2) Rated voltage volts. Indicate the terminal voltage of the primary coil and the secondary coil (when the load is not attached). Note that the terminal voltage of the three-phase transformer refers to the line voltage U-line value. (3) Rated current amperes. It means LineI current value that allows long-term passage of primary and secondary coils at rated capacity and allowable temperature rise. (4) Voltage ratio. It is the ratio between primary coil rated voltage and secondary coil rated voltage. (5) Line connection mode. Single-phase transformers have only a set of coils of high and low voltage, only for single-phase use, and three-phase transformers have Y/△type. In addition to the above technical data, there are transformer rated frequency, phase number, temperature rise, impedance percentage of the transformer, etc. VII. How to choose a transformer?  First of all, it is necessary to investigate the power supply voltage of the place where the electricity is used, the actual power load of the user, and the conditions of the place where it is located, and then select one by one according to the technical data indicated by the nameplate of the transformer, generally from the capacity and voltage of the transformer. Considering the current and environmental conditions, the capacity selection should be based on the capacity, nature, and service time of the user's power equipment to determine the required load, and then select the transformer capacity. In normal operation, the power load of the transformer should be about 75% ~ 90% of the rated capacity of the transformer. When the actual load of the transformer is less than 50%, the small capacity transformer should be used, and the large transformer should be replaced immediately if the rated capacity of the transformer is greater than that of the transformer. At the same time, when selecting the transformer to determine the primary coil voltage of the transformer according to the line power supply and the voltage value of the secondary coil according to the electrical equipment, it is best to select the low-voltage three-phase four-wire power supply system. This can provide a power supply for the entire operation. For the selection of current, attention should be paid to that the load can meet the requirements of the motor when it starts (because the starting current of the motor is 4 ~ 7 times larger than that of the sinking operation). VIII. Why transformer cannot run when overload? Overload operation refers to the transformer operating in excess of the currency specified on the nameplate. Overload is divided into normal overload and accident overload. The former refers to the increase of power consumption under the normal power supply, and it often makes transformer temperature rise, impels transformer insulation to age, and reduces service life. Therefore, transformer overload is not allowed. In special cases, the overloading of transformers in a short period of time should not exceed 30% of the rated load in winter, and not more than 15% in summer. For the latter, the accident overload and allowable time requirements are as follows: Multiple of Rated LoadReasonable Time of Overload Multiple of Rated Load Reasonable Time of Overload Indoors Outdoors 1.30 2 hours 1 hour 1.60 30 minutes 15 minutes 1.75 15 minutes 8 minutes 2.00 7.5 minutes 4 minutes IX. What kinds of tests should be done for transformers in operation? In order to ensure the normal operation of the transformer, the following tests should be carried out regularly. (1) Temperature test. Whether the transformer is running normally, the temperature is very important. The regulations stipulate that the upper oil temperature shall not exceed 85℃(that is, the temperature rise is 55℃). General transformers are equipped with special temperature measuring devices. (2) Load measurement. In order to improve the utilization rate of transformers and reduce the loss of electric energy, it is necessary to determine the real power supply capacity of transformers in the operation of transformers, the measurement is usually carried out during the current peak period and is measured directly with a clamp ammeter. The current value shall be 70%~ 80% of the rated current of the transformer. (3) Voltage measurement. The regulation requires that the voltage range should be within ±5% of the rated voltage. If beyond this range, taps should be used to adjust the voltage to reach the specified range. Voltmeters are generally used to measure the terminal voltage of the secondary coil and the terminal voltage of the user. (4) Insulation resistance measurement. In order to keep the transformer in normal condition, insulation resistance must be measured to prevent insulation aging and accidents. When measuring the transformer, the transformer should stop running and the insulation resistance of the transformer should be measured by using the tramegger. The resistance measured should not be less than 70 percent of the previously measured value. When using tramegger, the low-voltage coil may adopt a voltage grade of 500 volts. 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. 11. What is the power factor of transformer? The power factor of a distribution transformer is between (0.75 to 0.80) when secondary is connected to u.p.f loads. 12. Why do we need Transformers? Transformers help improve safety and efficiency of power systems by raising and lowering voltage levels as and when needed. They are used in a wide range of residential and industrial applications, primarily and perhaps most importantly in the distribution and regulation of power across long distances. 13. What is the difference between a step up transformer and a step down transformer? A transformer that increases the voltage from primary to secondary (more secondary winding turns than primary winding turns) is called a step-up transformer. Conversely, a transformer designed to do just the opposite is called a step-down transformer. 14. Are transformers dangerous? There is no established evidence that the exposure to magnetic fields from powerlines, substations, transformers or other electrical sources, regardless of the proximity, causes any health effects. 15. Why transformer rating is in kVA not in kW? Copper losses (I²R) depends on current which passing through transformer winding while Iron losses or core losses or Insulation losses depends on Voltage. ... That's why the transformer rating may be expressed in VA or kVA, not in W or kW.