Introduction As we all know, Resistors play a important role in limiting current in the circuit. Among then, pull-up resistors and pull-down resistors are often mentioned and frequently used in electronics. The pull-up is to clamp the uncertain signal to a high logical level through a resistor, which acts as a current limiter; while the pull-down resistor clamps the uncertain signal to a low logical level. Because there are only two states of high level and low level in digital circuits, it is uncertain at the initial stage of digital signals. Pull-up/ Pull-down Resistor - Explained ( with calculation ) Catalog Introduction Ⅰ Why Pull-down and Pull-up Resistor? Ⅱ Pull-up & Pull-down Resistor Circuits Ⅲ What the Role of Pull-up and Pull-down Resistor? Ⅳ Pull-up & Pull-down Resistor Applications Ⅴ How to Select Pull-up & Pull-down Resistors? Ⅵ FAQ Ⅰ Why Pull-down and Pull-up Resistor? Pull-up and pull-down resistors are often applied when interfacing a switch or some other input with a microcontroller or other digital gates. That is, in the initial stage of digital circuit power-on, because the high logical level and low level of the output state are uncertain, in order to make the circuit state normally, a pull-up resistor or pull-down resistor is needed to stabilize the uncertain circuit state. The low logical level is connected to GND inside the IC, and the high level is connected to the super resistance inside the IC.The pull-up resistor connects with the status port of the power supply. Simply put, the high voltage is applied to this point, where the potential will increase. The pull-down resistor means that the resistor is connected to the negative pole, and there is also the case of digital grounding. When the input port signal changes due to different circuit forms, the change will be fed back to the output port, so that the output port acquires a state that should have been completed, but the input port has no signal at this time and keep the original state.According to the above understanding, many people may feel awkward. Take an example from daily life, when you use the key to open the door, people enter but the door is not closed, at this time, you can add a switch to make the door close automatically. Figure 1. Schematic of Pull-up Resistor at Positive Input The above schematic diagram explains why the positive pole and the input terminal resistor can high the level. The two resistances of the port are assumed to be equivalent. We can get that the voltage of the port is 2.5V according to Ohm's law. By connecting the pull-up resistor (red part), the voltage of the port rises at this time, calculate the port voltage. Among them, 10K is connected in parallel with the later connected 1K, and the resistance must be greater than or equal to 1K, which is equivalent to the series relationship between 1K and the 10K resistor below, but the passing current is actually the same. Finally, the voltage of the two 10K resistors increases, and the terminal voltage also increases.The pin connected to the IC and power (or ground) is not necessarily a pull-down resistor. When this happens, many people may think that the red part of the figure is also a pull-down resistor. However, it is not connected in series with any pin or ground. In fact, it is used for circuit startup resistor, not pull-up/pull-down resistor. For the pull-up/pull-down resistors, it is only for the input port and the output port. Although some circuits will connect the pull-up and pull-down resistors to the redundant ports for stability, not all the resistors are connected to one pin of the IC all the time, and the other pin is connected to power or ground to represent the pull-up and pull-down resistors.   Ⅱ Pull-up & Pull-down Resistor Circuits Look at the following analyses to figure out what are pull-up resistor and pull-down resistor in circuits. Pull-up resistors are used to ensure that a wire is pulled to a high logical level in the absence of an input, while pull-down resistors ensure the voltage between VCC and a microcontroller pin is actively controlled. Just check the details below. Figure 2. OC(TTL) Circuit，OD(COMS) Circuit When the I/O port of the IC is in high level, the impedance between the node and GND is very large, which can be understood as infinite. At this time, it is connected to VCC through a pull-up resistor (such as 4.7K ohm, 10K ohm resistor), and the voltage divider of the pull-up resistor is almost negligible. When the I/O port node is in low level, it can be directly connected to GND. At this time, VCC and GND are connected through the pull-up resistor, and the current passing through is very small, which can be ignored.The level value are relative to the ground level, so you should refer to the ground level value. See if those pins are connected to the ground, it has nothing to do with whether they are connected to peripheral devices.Connect a 10K ohm or 4.7K ohm pull-up resistor between the node and +5V to pull up the potential of this node. Often this node requires a single-chip microcomputer or other controller to control it (and this node is connected to I/O). If you simply want to make this node a high level, and the output impedance is very large, you can directly connect the power supply, but if the microcontroller wants to make this node low, that is, the node is grounded inside the microcontroller, so that the 5V power supply and the ground are short-circuited.In addition, when this node is required to be at a high level, the impedance between this node and the ground is generally very large. For example, with an impedance of 100K ohms, when connect a 10K ohm pull-up resistor, the voltage at this point is 100KΩ/(100K +10K)*5V=4.5V, so it can also get a high level.When the node is required to be low level, just connect it to the ground, and there is a 10K resistor between the power supply and the ground, so that it will not be short-circuited. When it is low, there is a loop formed by a load between the power supply and the ground. Sometimes this node will be connected with a resistor in series. Because the current flows to the place with low impedance, the current will flow to the ground through the resistor connected to the power supply instead of Flow to this resistance connected to the node, because the resistor connected to this node has a high impedance, so the potential at this point is in low level.It can be considered that, for the I/O port of the IC, controlling the high and low levels inside the IC is equivalent to controlling the O/O port to be connected to its internal GND or a very large resistor, such as 100K ohms. When the I/O port is the low level (0V), inside the IC, the pin that controls the O/O port of the IC chip is connected to GND.When the I/O port is at a high level, such as 5V, the I/O port pin is connected to a very large resistor in the chip, such as 100K ohms, and sometimes another one is connected in series at the I/O node. A resistor with a small resistance value, such as 68 ohms, because the current flows to a place with low impedance, when the I/O port and GND inside the chip are connected to a low level, the pull-up resistor and the GND inside the chip form a loop.At this time, the current at the I/O port node will flow to the GND inside the chip, because a small resistance resistor is connected in series at the node, which is high resistance relative to GND, so the current will not flow through this series resistor.Using a pull-down resistor, when the I/O port is in a high-impedance state, the pull-up resistor can keep it in a high-level state. That is, when the I/O port is in the high-impedance state, using a pull-down resistor to connect this port to GND. The high-impedance state has a large resistance value, which can be understood as disconnection, in fact, it is actually a large resistor inside the chip. The resistors are connected and pulled to the ground, so there is no current and the level value is 0. It can only work unless a high level value is given to this pin. Figure 3. Pull-up and Pull-down Resistor in MCU   Ⅲ What the Role of Pull-up and Pull-down Resistor? As for the purpose of pull-up & pull-down resistors, generally speaking, the pull-up resistor increases the current, and the pull-down resistor is used to absorb the current.1) Increase the voltage level.When the TTL circuit drives the CMOS circuit, if the output high level of the TTL circuit is lower than the lowest high level of the CMOS circuit, then it is necessary to connect a pull-up resistor to the output terminal of the TTL to increase the value of the output high level. The OC gate circuit must add a pull-up resistor to increase the high-level value of the output.2) Increase the drive capability of the output pin.In order to enhance the drive capability of the output pins, pull-up resistors are often used on some single-chip pins.3) The N/A pin (the pin not connected) should be anti-static and anti-interference.On the CMOS chip, in order to prevent damage caused by static electricity, the unused pins cannot be left floating. Generally, a pull-up resistor is connected to reduce the input impedance, provide a leakage path, and improve the anti-electromagnetic interference ability of the bus. Because the pin is left floating, it is easier to receive electromagnetic interference from the outside world.4) Resistance matchIn the long-line transmission, the resistance mismatch can easily cause the reflected wave interference. In addition, the pull-down resistor makes the resistance match, which can effectively suppress the reflected wave interference.5) Preset space state/default potentialPull-up or pull-down resistors are connected to some CMOS input terminals to preset the default potential. When these pins are not used, these input terminals are pulled down to low level or pulled up to high level. The state when idle on the bus such as I2C is obtained by the pull-up and pull-down resistors.6) Improve the noise tolerance of the chip input signal.If the input terminal is in a high-impedance state, or in a floating state, a pull-down or pull-down resistor needs to be added at this time, so as to avoid the random level. Similarly, if the output terminal is in a passive state, a pull-down or pull-down resistor needs to be added. For example, the output terminal is only the collector of a transistor, thereby improving the noise tolerance of the chip input signal and enhancing the anti-interference ability through a pull-up resistor or pull-down resistor. Figure 4. Pull-up/ Pull-down Resistor   Ⅳ Pull-up & Pull-down Resistor Applications When to use pull-up or pull-down resistors? Look at the following cases explained.1) If a pull-up & pull-down resistor is used for the input signal pin, the usual function is clamping the signal to a certain level to prevent the signal line from appearing in an uncertain state. In practical applications, the 10K ohm resistor is the most used pull-up resistor. Whether to use a pull-up resistor or a pull-down resistor depends mainly on the needs of the circuit system itself. For example, for a highly effective enable control signal, we hope that the circuit system be in an invalid state after power-on, and then a pull-down resistor will be used.Assuming that the enable signal is used to control the motor, if it is left floating, the signal line may be triggered falsely to a high level by other noise interference after power-on (or during operation), resulting in undesired rotation of the motor, and a pull-down resistor can be added at this time. Correspondingly, for the active-low reset control signal (RST#), if we want to be in an inactive state after power-on reset, a pull-up resistor should be used.2) Most chips with logic control functions (such as single-chip microcomputers, FPGAs, etc.) will integrate pull-up or pull-down resistors. Users can choose whether to turn on or not according to their needs. STM32 microcontroller GPIO mode includes pull-up or pull-down.3) According to the resistance value of the pull-up resistor, we can also divide it into strong or weak pull-up/down. The pull-up resistors integrated in the chip are usually weak pull-up (larger resistance), the smaller the pull-up resistance, the stronger the level capability (strong pull), and the stronger the ability to resist external noise (that is, if the unwanted interference noise is to change the strong pull signal level, the required energy must be strengthened accordingly ), but the smaller the pull-up resistance, the greater the corresponding power consumption, because the normal signal requires more energy to change the state of the signal line. In terms of energy consumption, both pull-up /down resistors are the same.4) There is no strict definition of how many ohms are the boundary between strong pull and weak pull. Generally, the pull-up resistors we use are weak pulls, so we can still use external control signals to pull up/down the signal lines as needed.The extreme of the strong pull resistance is the zero, that is, the signal line can directly connected to the power supply or ground.5) There are more knowledge points involved when the pull-up resistor is used as an output (or input and output), but the essential function is also to clamp the level. The most common output pull-up resistor appears in the open collector (OC) Or open drain (OD) structure pin.6) The current sink capability and current source capability are also called the drive capability of the chip pins. For any given chip, the pin drive capability is limited. If the load driven by the pin is large, it may cause the output level to be incorrect (the predetermined level cannot be output).7) OC (OD) pin output structure is different (OC structure exists in the transistor, and OD structure exists in the field effect transistor FET). The output of most comparator chips is an OD/OC output structure, and the signal pins of many chips or modules that feed back the system status are also in this structure, so that users can pull up the level to the corresponding level according to the actual needs of the circuit system. With the power supply voltage VCC, the level conversion can be omitted. Figure 5. Pull up Resistor with Example   Ⅴ How to Select Pull-up & Pull-down Resistor? When select pull-up & pull-down resistors, you can consider the following three aspects:1) Considering power saving, sink current capability of the chip should be large enough, the resistance is large and the current is small.2) It is necessary to ensure sufficient drive current, so the resistance is small and the current is large.3) For high-speed circuits, excessive pull-up resistors may have smooth edges.Considering the above three points comprehensively, the resistance value is usually selected between 1K and 10K. The same principle applies to pull-down resistors.   Ⅵ FAQ 1. What is pull-down and pull-up resistor?A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. A pull-down resistor connects unused input pins (OR and NOR gates) to ground, (0V) to keep the given input LOW.   2. What is difference between pull up and pull-down resistor?A pull-up resistor connects unused input pins (AND and NAND gates) to the dc supply voltage, (Vcc) to keep the given input HIGH. A pull-down resistor connects unused input pins (OR and NOR gates) to ground, (0V) to keep the given input LOW.   3. When to use pull-up or pull-down resistors?Pull-up and pull-down resistors are often used when interfacing a switch or some other input with a microcontroller or other digital gates. Most microcontrollers have built-in programmable pull-up and/or pull-down resistors, so fewer external components are needed.   4. What is the function of a pull-up resistor?In electronic logic circuits, a pull-up resistor or pull-down resistor is a resistor used to ensure a known state for a signal. It is typically used in combination with components such as switches and transistors, which physically interrupt the connection of subsequent components to ground or to VCC.   5. What is the purpose of pull-down resistor?What is Pull-down Resistors. Similarly to pull-up resistors, pull-down resistors ensure the voltage between VCC and a microcontroller pin is actively controlled when the switch is open. However, instead of pulling a pin to a high value, such resistors pull the pin to a low valued instead.   6. How do you calculate pull-down resistors?To calculate the pull-down resistor value, it's slightly different from the pull-up resistor value. Knowing that current is 100uA, we'll take 0.5v as our pull-down voltage since the input is 0.8v. Thus, applying our R = V/I once again, but this time we don't have to minus, so our formula remains constant.   7. Why does I2C need pull-up resistor?As discussed in the I2C Basics module, the resistors that are commonly seen on I2C circuits sitting between the SCL and SDA lines and the voltage source are called pull up resistors. ... A pull up resistor is used to provide a default state for a signal line or general purpose input/ouput (GPIO) pin.   8. Which port has no built in pull-up resistor?Input/Output (I/O) pin − All the circuits within the microcontroller must be connected to one of its pins except P0 port because it does not have pull-up resistors built-in.   9. What is pull up and pull down in Arduino?Introduction: Understanding the Pull-up/Pull-down Resistors With Arduino. ... With a pull-up resistor and with the button unpressed you make a logic state ON and with the button pressed you make a logic OFF. With a pull - down resistor and a pressed button you make an ON logic state and OFF logic state when its unpressed.   10. What happens if the pull up resistor for an I2C signal is too small?Too small of a value will once again prevent the output drivers from sinking enough current to pull the pin all the way down to 0.

Introduction The audio power amplifier, also called power amp, is a sound-producing device that reconstructs the input audio signal on the output element. The reconstructed signal volume and power level must be idea, effective and low distortion. The audio frequency range is about 20Hz to 20000Hz, so the amplifier must have a good frequency response in this range. Depending on the application, the power level varies greatly, from the milliwatt level of earphones to the several watts of TV or PC audio, to the tens of watts of home stereo and car audio, to the more powerful home and commercial audio, even the system’s hundreds of watts are large enough to meet the sound requirements of the movie theater or auditorium. Catalog Introduction Ⅰ What is Audio Power Amplifier? Ⅱ Types of Audio Power Amplifiers 2.1 Class A Power Amplifier 2.2 Class B Power Amplifier 2.3 Class AB Power Amplifier 2.4 Class D Power Amplifier Ⅲ Audio Power Amplifiers Comparisons Ⅳ Audio Power Amplifier Circuit Architecture Ⅴ Typical Audio Amplifier Circuits Examples Ⅵ FAQ Ⅰ What is Audio Power Amplifier? Audio power amplifier is one of the important components of multimedia products and is widely used in the field of consumer electronics. Linear audio power amplifiers have always dominated the traditional audio amplifier market due to their low distortion and good sound quality. With the popularization of portable multimedia devices such as mobile phones, tablet PC, and notebook computers, the efficiency and volume of linear power amplifiers can meet the requirements of the market, for example, class D power amplifiers have become more and more popular for their advantages such as high efficiency and small size.The development of audio amplifier has experienced three generations of electron tube (vacuum tube), bipolar transistor and field effect tube. The tube audio amplifier has a mellow tone, but it is bulky, with the disadvantages of high power consumption, extremely unstable, and poor high-frequency response. Bipolar transistor audio amplifiers have bandwidth, large dynamic range, high reliability, long life, and high-frequency response, but its static power consumption and on-resistance are very large, so it is difficult to improve its efficiency. The FET audio amplifier has the same mellow tone as the electronic tube, and its dynamic range is wide, and more importantly, its on-resistance is small, which can achieve very high efficiency. audio power amplifier" width="410" height="250" /> Figure 1. Hi-Fi Audio Power Amplifier Ⅱ Types of Audio Power Amplifiers There are many types of audio power amplifiers, and more than ten modes of it commonly used, such as Class A, Class B, Class AB, Class C, Class D, Class E, Class F, Class G, Class H, and Class S, but only four types suitable for audio applications: Class A, Class B, Class AB and Class D. 2.1 Class A Power Amplifier The main feature of the Class A power amp is: The operating point Q of the amplifier is set near the midpoint of the load line, and the transistor is turned on during the entire cycle of the input signal. The amplifier can work in a single tube or push-pull state. Since the amplifier works in the linear range of the characteristic curve, transient and alternating distortion are small. The circuit is simple and the debugging is convenient. Class A power amplifiers only need one transistor to provide current to the load, and the conduction angle is 360°C during a complete signal cycle. This kind of power amplifier has low distortion, but often requires a large static current and is low in efficiency. Theoretically, the maximum working efficiency of a class A power amplifier is 25%, so a heat sink is required when working. 2.2 Class B Power Amplifier Class B power amplifier is composed of two complementary transistors. In a complete signal cycle, each amplifier tube will be turned on in one half cycle and turned off in the other half cycle, that is, the conduction angle is only 180°C. Because it has no static current, it has a higher efficiency. In theory, the maximum efficiency of a Class B power amplifier can reach 78%. However, when the input signal is close to zero, the amplifier tube has a critical conduction state, resulting in crossover distortion. 2.3 Class AB Power Amplifier Class AB power amplifier inserts two diodes into the input end of the Class B power amplifier. When the input is close to zero, the amplifier tube has been slightly turned on, so that the conduction angle of each amplifier tube is greater than 180°C and less than 360°C. It overcomes the crossover distortion of Class B power amplifiers, and the efficiency is between Class A and Class B power amplifiers, based on a common structure of traditional linear power amplifiers. However, the medium output voltage is usually far away from the power supply voltage, and a lot of power consumption is consumed in the transistor. Therefore, even a well-designed amplifier, its efficiency is still low. 2.4 Class D Power Amplifier Class D (digital audio power) power amplifier is a kind of input analog audio signal or PCM digital information into PWM (pulse brightness modulation) or PDM (pulse density modulation) pulse signals, which is used to control the amplifier power switching devices turn on/off audio power amplifiers, also known as switching amplifiers. It has the outstanding advantage of high efficiency.The output stage of the Class D power amplifier consists of two complementary power tubes. Driven by the high-frequency control pulse signal, the power tubes work in the on-off state. One is turned on and the other is turned off. Therefore, the amplifier does not require static power consumption, that is, it has a very high efficiency. In theory, the efficiency of Class D power amplifiers can reach 100%, but in fact it is over 80%, which is 2 to 3 times that of traditional linear power amplifiers.The digital audio power amplifier also looks like a one-bit power digital-to-analog converter. The amplifier is composed of four parts: input signal processing circuit, switching signal forming circuit, high-power switching circuit (half-bridge and full-bridge) and low-pass filter (LC). In electronics, Class D amplifiers use a very high frequency switch circuit to amplify the audio signal. DIY Class D Audio Amplifier Class D amplifiers have the following advantages:1) It has a high efficiency, usually above 85%.2) Small size, which can save a lot of space than analog amplifier circuits.3) Connection without crack noise.4) Have low distortion and good frequency response curve. Few peripheral components, easy to design and debug.   Ⅲ Audio Power Amplifiers Comparisons 1) Class A, B, and AB amplifiers are analog amplifiers, and class D amplifiers are digital amplifiers. 2) Class B and Class AB push-pull amplifiers have higher efficiency and less distortion than Class A amplifiers, and their transistors consume less power and have better heat dissipation. However, Class B amplifiers will have poor switching characteristics during the transition between transistor on and off states or cause alternate distortion due to improper selection of circuit parameters. 3) The Class D amplifier has high efficiency and low distortion, a good frequency response curve, and fewer peripheral components. 4) Class AB amplifier and Class D amplifier are the basic circuit forms of audio power amplifiers at present. Figure 2. Amplifier Circuit Example Ⅳ Audio Power Amplifier Circuit Architecture The purpose of audio amplifier is to reproduce the audio input signal with high efficiency and low distortion on the sound output element at the required volume and power level. The frequency range of the audio signal is 20 Hz to 20000 Hz, so the audio amplifier must have a good frequency response. Audio amplifiers usually consist of preamplifiers and power amplifiers.PreamplifierThe amplitude of the audio signal source signal is generally very small and cannot directly drive the power amplifier. Therefore, they must be amplified to a certain condition first, which requires the use of a preamplifier. In addition to the signal amplification function, it can also have functions such as volume adjustment, tone control, loudness control, and channel equalization.Power amplifierThe power amplifier is referred to as the power amplifier for short, and its purpose is to provide the load with a large enough current drive capability to achieve power amplification. Class D power amplifier works in the on-off state. In theory, it does not require static current and has high efficiency.The topological structure of a typical Class D power amplifier circuit is shown in Figure 2: It consists of a triangle wave generator, a comparator, a power output stage and an LC low-pass filter. Figure 3. Class D Power Amplifier Circuit Figure 2 is a schematic diagram of the working principle of a Class D power amplifier. The sine wave audio input signal and the triangular wave signal with a much higher frequency are modulated by the comparator to obtain a PWM modulation signal whose duty cycle is proportional to the amplitude of the input signal. It pushes the output power tube to work in the on-off state. The output end of the tube obtains an output signal with a constant duty cycle. The amplitude of the output signal is the power supply voltage and has a strong current drive capability. After signal modulation, the output signal contains both the input signal and the fundamental component of the modulated triangle wave, as well as their higher harmonics and combinations. After LC low-pass filtering, the high-frequency components in the output signal are filtered out, and a low-frequency signal with the same frequency and amplified amplitude as the original audio signal is obtained on the load.   Ⅴ Typical Audio Amplifier Circuits Examples The following is a brief introduction of AN7115 audio power amplifier circuit. Figure 4. AN7115 Audio Amplifier Circuit AN7115 has an output power of 2.1W and a noise output of 3mV under the conditions of V=9.0V, THD=10%, and RL=8Ω.Limit parameters: Vcc=13V, power dissipation (without radiator) is 1.2W, and 2.25W with a radiator. Working temperature: -20℃ to 70℃, suitable for small portable radio recorders and audio equipment as power amplifiers. TDA2030 adopts V-shaped 5-pin single in-line plastic package structure. According to the shape of the pin, it can be divided into H-type and V-type. This integrated circuit is widely used in car stereo radio and tape recorders and mid-power audio equipment. It has the characteristics of small size, high output power, low distortion, etc., and has an internal protection circuit. Circuit characteristics are as followed: Figure 5. TDA2030 Audio Power Amplifier Circuit 1) Very few external components.2) The output power is large, Po=18W (RL=4Ω).3) The use of ultra-small package (TO-220) can increase the assembly density.4) The boot impact is minimal.5) It contains various protection circuits, so it is safe and reliable to work. The main protection circuits include: short circuit protection, thermal protection, ground wire coupling open circuit, power supply polarity reverse connection (Vsmax=12V), and load discharge voltage kickback, etc. Figure 6. Mini Audio Power Amplifier Ⅵ FAQ 1. What is audio power amplifier?An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high enough for driving loudspeakers or headphones. Audio power amplifiers are found in all manner of sound systems including sound reinforcement, public address and home audio systems and musical instrument amplifiers like guitar amplifiers.   2. How do audio amplifiers work?An amplifier takes an input signal from a source, such as a laptop, turntable or CD player, and creates a larger copy of the original signal before it's sent to the speakers. It gets the power to do this from your mains electricity, which is sent directly to the power supply within the amplifier.   3. What does an audio power amplifier do?An audio power amplifier (or power amp) is an electronic amplifier that amplifies low-power electronic audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high enough for driving loudspeakers or headphones.   4. What is the most powerful audio amplifier?Classic audio brand McIntosh has announced its most powerful integrated amplifier. The fully loaded, hybrid MA12000 Integrated Amplifier is McIntosh's most powerful integrated amplifier ever offering 350W per channel.   5. Do you need amplifier for speakers?Powered speakers do not need an amplifier. They have an amplifier already installed in them which is why they are called 'powered speakers' to begin with. Depending on the speakers' input options, you can hook them up to different audio sources without the need for a separate amplifier.   6. Does an amplifier improve sound quality?Amplifiers ideally amplify audio signals linearly and, therefore, do not technically improve or worsen sound quality. However, less-than-ideal amplifiers, amp settings and amplifier-speaker combinations may worsen sound quality. Amps are nevertheless needed to drive speakers and headphones properly.   7. Why do I need a power amplifier?Some users prefer to separate input switching and AV processing from the task of providing power for, and connection of, loudspeakers through separate AV preamp/processors and power amplifiers. ... A separate preamp and power amp results in more equipment and cable clutter.   8. Which is better power amplifier or integrated amplifier?A preamplifier / power amp does generally offer better quality; while flat output has become common place, keeping your switching circuitry separate from your amplification and having two separate power supplies can reduce the internal interference that can be introduced into your signal.   9. What is a home audio amplifier?A home theater amplifier (also known as an audio-visual receiver or simply an AVR) is a powerful piece of kit that combines amplifiers and digital signal processors to convert output from a range of source devices into high quality sound and video. In short, it is the hub of a home theater set up.   10. What is the most powerful audio amplifier?Classic audio brand McIntosh has announced its most powerful integrated amplifier. The fully loaded, hybrid MA12000 Integrated Amplifier is McIntosh's most powerful integrated amplifier ever offering 350W per channel.   11. What is the purpose of an audio amplifier?The goal of audio amplifiers is to reproduce input audio signals at sound-producing output elements, with desired volume and power levels—faithfully, efficiently, and at low distortion.   12. What do you mean by audio amplifier?Any electronic device that increases the power of an electrical signal whose vibrations are confined to the audio frequency range—the range that can be perceived by the human ear—is an audio amplifier.

Introduction A resistor is a passive two-terminal electrical component. After it is connected to the circuit, the resistance is fixed, which can limit the current through the branch connected to it. On one hand, the resistance that cannot be changed is called a fixed resistor, on the other hand, the resistances of potentiometers or variable resistors are changeable. The main physical characteristic of a resistor is to transform electrical energy into thermal energy. It can also be said that it is an energy-consuming element, because internal energy is generated when current passes through it. Figure 1. Use Resistor in Circuit Catalog Introduction Ⅰ Functions of Resistor Ⅱ Three Basic Principles for Resistor Selection Ⅲ The Role of Resistors in Transistor Circuits 3.1 Why Should a Resistor Be Added to the Base of the Transistor? 3.2 Pull-down Resistor in Transistor Circuits Ⅳ FAQ Ⅰ Functions of Resistor In short, the function of resistance is to limit current, divide current, divide voltage, and convert electric energy into internal energy (heating) in the circuit. According to Ohm's law, through calculations, resistors in parallel and series connections can be used to achieve the desired current and voltage. Also there are different resistors and switches combined to produce voice-activated switches, photosensitive switches, infrared switches and so on. How to Use Resistors in circuits? 1) Limit CurrentIn order to prevent the components connected in series from being burnt out by the excessive current and to ensure the normal operation of the electrical appliances, a variable resistor can usually be connected in series in the circuit.2) Current DiversionThe resistor is connected in parallel to the component or circuit that needs to be shunted, and the voltage does not change. The function of this resistor is to divide current.3) Voltage DiversionGenerally, electrical appliances are marked with a rated voltage value. If the power supply is higher than it, the electrical appliance cannot be directly connected to the power supply for a normal operation. In this case, a resistor with suitable resistance can be connected in series in the circuit to share a part of the voltage, therefore the electrical appliance can work at the rated voltage. At this time, the role of the resistor is to divide the voltage.4) Provide Bias VoltageIn the transistor circuit, the resistor is connected between the base of it and the working voltage. At this time, the power supply provides a bias voltage to the base through the resistor, and the resistance can determine the bias voltage. The role of the resistor in the circuit at this time is to provide a bias voltage.5) Negative FeedbackUsed in the resistance between the base and collector of the transistor, then the feedback branch of the negative feedback circuit is formed in the circuit. At this time, the resistor plays a negative feedback role in the circuit.6) OscillationResistor and capacitor form an RC circuit, which can be combined in parallel and in series.7) Damping EffectConnecting a resistor in parallel in the LC resonant circuit can reduce the Q value, at this time, resistor plays a damping effect.8) DecouplingThe use of resistors in multi-stage amplifier circuits can prevent harmful low-frequency interference, which play a decoupling effect.9) Convert Electrical Energy into Internal Energy (Heating)When the current passes through the resistor, it will convert all (or part) of the electrical energy into internal energy, which will generate heat. This principle is often used in electric stoves and heaters in our lives.10) Convert Current into VoltageWhen current flows through the resistor, a voltage will be generated across the resistor. As shown in the figure below, the collector load resistor R2 plays this role, converting the current flowing through the resistor R2 into a voltage and outputting it from U0. Figure 2. Resistor Circuit   Ⅱ Three Basic Principles for Resistor Selection 1) Choose resistors that are manufactured by a certification body that implement high-level standards.2) Choose resistors produced by manufacturers with functional advantages, quality advantages, efficiency advantages, price advantages, and service advantages.3) Choose a manufacturer that can meet the above-mentioned requirements in the model catalog.   Ⅲ The Role of Resistors in Transistor Circuits 3.1 Why Should a Resistor Be Added to the Base of the Transistor? First of all, we must understand the basic principle of the transistor. It is a current-controlled element, which is different from the MOFET, a voltage-controlled element. The transistor has three working areas: cut-off area, amplification area and saturation area. Take NPN transistor as an example, the voltage difference（UBE）of BE is about 0.6V (the actual size depends on the model of the component). When UBE＜0.6V , the transistor is off; when UBE=0.6V, the transistor is in the amplification or saturation region. Figure 3. Schematic Diagram of the NPN Transistor Current When the transistor is in the amplification area, the added resistance between the base and VCC is a bias resistance. The following explains why the base should be added when the transistor is used as a switch. What is the difference between transistor and MOSFET circuits when adding a resistor.The following figure is the most commonly used circuit diagram of NPN transistors. The common input terminal is the I/O port of the microprocessor (microcontroller, DSP, ARM, etc.). Figure 4.  NPN Transistor Take the microcontroller I/O port with 0/5V input as an example. Why must a resistor be connected in series with the base? Can it work without a resistor? Here the resistor is a current control element. When the transistor is in an amplified or saturated state, the voltage of the UBE is 0.6V, and the base current can be calculated according to the input voltage U. The calculation formula is Ib=(U-0.6 )/R1. It can also be seen from the formula that if the current limiting resistor R1 is not connected, when the input voltage is greater than 0.6V, the base current will be very large to burn the tube.Moreover, the resistor cannot be used casually. It needs to be calculated according to the input voltage and the characteristics of the tube. For example, the amplification factor β of the transistor is 50, the maximum current of the collector is 500mA, and the input voltage is 5V. If the design requires the transistor to be in a saturated state, then Ic=500mA, Ib=Ic/β=10M=mA, where the current-limiting resistance R1=(5V-0.6V)/Ib=430Ω. If it is required to input 5V, the collector current is about 200mA, then Ib=Ic/β=200mA/50=4mA can be calculated, finally the current-limiting resistance R1=(5V-0.6V)/Ib=1075Ω (1K can be selected Standard resistance). Note: The above figure is used to explain the example, but it is not very reliable. A more reliable connection method should be to connect a large resistor (such as 10K, or 20K) between the base and the ground. When there is no input, pull the base down quickly to ensure that the tube is in a stable cut-off state.If the NPN transistor in the figure above is replaced with an N-channel MOS tube, the principle is the same. When a high level is input, the tube is turned on, and when a low level is input, the tube is turned off. Figure 5. MOSFET Circuit Since the MOSFET is a voltage-controlled device, the current of the gate (G) is very small and can be ignored, so it can work normally without connecting the resistor R1.The figure after remove the resistor is shown in the below: Figure 6. MOSFET Circuit without Resistor Note: In actual applications, a resistor is generally connected in series to improve reliability. The product reliability is very important. Without current-limiting resistor, when the MOS is   damaged by voltage breakdown, the components on the control terminal will be affected easily, especially the processor, is easily damaged by high current. 3.2 Pull-down Resistor in Transistor Circuits 🔺For TransistorsThe transistor is a current-type driving component, so a current-limiting resistor is connected to the base, generally less than 10K, and the typical values are 3.3K, 4.7K, 5.1K, 6.8K, etc. What is the function of this pull-down resistor?The following figure shows the transistor 8050 switching circuit. The transistor will be turned on when the I/O port outputs a high level, and the transistor will not be turned on. If the I/O port does not output a high level, the base will always be pulled low without a 68K pull-down resistor, that is to say it is in the cut-off state. The circuit may be in an unstable state, especially when it is initialized at the moment of power-on. It is easy to generate noise and easily cause the transistor to malfunction, especially for some general input/output ports. Therefore, this resistor is actually a bias resistor, which makes the base to be pulled down when there is no driving signal, making the circuit more reliable. Figure 7.  Pull-down Resistor in Transistor Circuit Although the pull-down resistor can make the circuit more reliable, tit cannot be too large or too small. If the resistance too large, the base current will not be enough to drive the transistor. On the contrary, if it is too small, the bias voltage will be less than the transistor conduction voltage. In general, this resistance is not more than 100K.Sometimes we see that a capacitor is connected in parallel with this resistor. In fact, this is generally designed in high-speed signal switching circuits. Adding a capacitor can improve performance, as shown below: Figure 8.  RC Circuit 🔺For MOSFETUnlike transistors, MOS transistors are voltage-controlled components, which are driven by voltage. We all know that there is parasitic capacitance between the two pins of MOS transistors. In fact, the key of MOS transistors’ conduction is the charging and discharging of capacitors. Therefore, for the N-type MOS, it will be turned on when Vgs is greater than a certain value, but for the P-type MOS, it will be turned on when the value of Vgs is less than a certain value.Therefore, due to the capacitive effect between the three pins, when the MOS is constantly turned off, the parasitic capacitance voltage can be properly discharged, which is similar to the role of a bleeder resistor and is a kind of protection for the MOS. Figure 9.  MOSFET Circuit Ⅳ FAQ 1. What is the function of the resistor?A resistor has the ability to reduce voltage and current when used in a circuit. The main function of a resistor is to limit current flow. Ohm's law tells us that an increase in a resistors value will see a decrease in current.   2. How do resistors work?A conductor has low resistance, while an insulator has much higher resistance. Devices called resistors let us introduce precisely controlled amounts of resistance into electrical circuits. ... A resistor works by converting electrical energy into heat, which is dissipated into the air.   3. Why do you need resistors?A resistor controls the flow of the electrical current within a circuit. ... Resistors are essential to many electoral circuits, and they can be applied to a myriad of different applications. Protect against voltage spikes. Resistors also protect components against voltage spikes.   4. What role do resistors play in electronic devices?A resistor is a passive two-terminal electrical device that resists the flow of current. It is probably the simplest element in an electronic circuit. It is also one of the most common components as resistance is an inherent element of nearly all electronic circuits. They are usually color-coded.   5. What is a good example of a resistor?A few examples include limiting electric current, voltage division, heat generation, matching and loading circuits, gain control, and setting time constants. They are commercially available with resistance values over a range of more than nine orders of magnitude.   6. What happens if I use a higher ohm resistor?The cases where using a higher value resistor will damage a circuit exist, but are a bit less usual than the cases where it may simply produce a weaker result than desired, or a different frequency response than desired.   7. What is a resistor simple explanation?A resistor is an electrical component that limits or regulates the flow of electrical current in an electronic circuit. Resistors can also be used to provide a specific voltage for an active device such as a transistor. ... The most common type in electronic devices and systems is the carbon-composition resistor.   8. What happens when a resistor blows?Blowing Up a Resistor. By applying too high a voltage to a resistor, the resistor will draw too much current. This causes excessive power to be dissipated in the resistor which makes it go up in flames and a cloud of smoke as this video shows.   9. How is a resistor connected in a circuit?Resistors are said to be connected in “Series”, when they are daisy chained together in a single line. Since all the current flowing through the first resistor has no other way to go it must also pass through the second resistor and the third and so on.   10. Do resistors change voltage?The larger the resistor, the more energy used by that resistor, and the bigger the voltage drop across that resistor. Ohm's Law can be used to verify voltage drop. In a DC circuit, voltage equals current multiplied by resistance. V = I R.

For so many years, tube amplifier has always been a “controversial” component in the electronic field, people are attracted by its premium sound quality but discouraged by its price.   Today we are going to talk about tube amplifiers, to understand what this device is, why its price is so much higher than other amplifiers, what are its advantages and disadvantages compared with other amplifiers, and so on. Catalog I. What is a Tube Amplifier? II. Pros and Cons of Tube Amplifier? III. How Does the Tube Amplifier Work? IV. Tube Amplifier VS Solid State Amplifier? V. Tube Amplifier VS Transistor Amplifier? VI. Things Needing Attention While Using a Tube Amplifier VII. Why is Tube Amplifier So Expensive? Is It Worth It? VIII. How to Extend the Life of   the Tube Amplifier?    FAQ I. What is a Tube Amplifier? The tube amplifier is one of the earliest electrical signal amplifiers.   The cathode electron emission part, the control grid, the acceleration grid, and the anode (panel) lead enclosed in a glass container (generally a glass tube) are welded to the tube base.   The electric field is used to inject an electronic modulation signal into the control grid in the vacuum, and the signal data of different parameters after signal amplification or feedback oscillation is obtained at the anode.   Tube amplifiers were used in electronic products such as televisions and radio amplifiers in the early days. In recent years, they have been gradually replaced by amplifiers and integrated circuits made of semiconductor materials. However, in some high-fidelity audio equipment, tube amplifiers with low noise and high stability coefficient are still used. II. Pros and Cons of Tube Amplifier? Pros: 1. The tube amplifier has a large input dynamic range and a fast conversion rate.   2. Electronic tube amplifiers mostly use discrete components, manual wiring, and welding, which are low in efficiency and high in cost. This is especially obvious in developed countries.   3. The open loop index of the tube amplifier is better than that of the transistor amplifier. It does not need deep negative feedback and can work stably without adding phase compensation capacitors, so its dynamic index is better.   4. The sound quality of the tube amplifier is generally soft and pleasant. More specifically, the low-frequency sound of the tube amplifier is soft and clear, and the high-frequency sound is slender and clean. The performance of human voice is its strong point.   5. The treble of the tube amplifier is smoother, has enough air, and has a sound coloring that quite a few people like. The soft and slightly fuzzy sound is very beautiful.   6. The tube amplifier mainly causes even-numbered second harmonics. This harmonic component is very pleasing, just like adding rich overtones and beautifying the sound.   Cons: 1. The service life of the tube amplifier is relatively low, and some technical indicators will drop significantly after one to two thousand hours of use.   2. The tube amplifier consumes high power and often works in Class A state, which reduces the efficiency. However, there are basically no harmful sound quality factors such as transient intermodulation distortion, switching distortion and crossover distortion.   3. The tube amplifier is not at all superior to the transistor amplifier in terms of weight, efficiency, and lifespan.   4. In use, the tube amplifier should have good ventilation and heat dissipation. Overheating of the temperature will inevitably shorten the life of the tube amplifier, so it is necessary to keep the temperature of the tube amplifier as low as possible.   5. Vibration is not good for tube amplifiers, so it is important to take anti-vibration measures to avoid vibration as much as possible. III. How Does the Tube Amplifier Work? This is a basic overview of some of the components of a tube guitar amp and how they work, without getting too technical. IV. Tube Amplifier VS Solid State Amplifier? A solid-state amplifier converts an electrical signal into an audio wave using transistor circuitry. Instrumental amplifiers have two amplification stages: the preamp stage at the beginning of the circuit and the power amp stage at the end.    The physical difference between a solid-state amp and a tube amp is that a solid-state machine employs electronic transistors for amplification, whereas a tube amp employs vacuum tubes (also known as valves). Transistors differ from tubes in that they do not deform pleasantly when pushed to their limits.   The key difference between tube amplifier and solid state amplifier is: solid-state amplifiers are ideal for guitarists that require a lot of power (a.k.a a loud, clean, undistorted signal). However, without any natural distortion, an electric guitar can sound brittle. As a result, solid-state amplifiers are more popular among bassists and keyboard players than guitarists. Compared with tube amp, solid-state amp has several advantages: 1.    They are less expensive. Almost all solid-state amplifiers are less expensive than tube amplifiers. They have fewer parts and the ones they do have are reasonably inexpensive.  2.    They are less bulky. Weight can be an issue if you're a gigging musician who needs to transport an amp around town. Tube amplifiers are almost always heavier than solid-state amplifiers. This is due to the circuitry necessary to operate the glass tubes, not the glass tubes themselves (which are hollow). 3.    They require less maintenance. Tube amplifiers need routine maintenance. Most gigging guitarists replace their power tubes once a year and their preamp tubes every two years. Solid-state amplifiers, on the other hand, do not require part switching. They can function for decades with all of their original components. V. Tube Amplifier VS Transistor Amplifier? A transistor amplifier, as the name implies, is used to amplify power, voltage, or current signals. It has a common emitter amplifier, a common collector amplifier, and a common base amplifier. This is the most basic. There are also differential, push-pull, and so on. The audio is actually a power (transistor) amplifier. The difference between transistor amplifier and tube amplifier: 1. Working characteristics and circuit structures are different Transistor amplifiers work under low voltage and high currents. The working voltage of transistor power amplifiers is within tens of volts, and the current reaches several amperes or tens of amperes. In the circuit design, direct-coupled (OCL, BTL, etc.) non-output transformer circuits are mostly used. The output power can be very large, up to several hundred watts, and the various electrical properties are very high. The tube amplifier works under high voltage and low current conditions. The screen voltage of the final power amplifier tube can reach 400-500V or even thousands of volts, and the current flowing through the electron tube is only tens of milliamps to hundreds of milliamps. The input range is too large and the conversion rate is fast. Most of the tube amplifiers use discrete components, manual wiring, and welding, which are low in efficiency and high in cost. Transistor amplifiers mostly use a combination of transistors and integrated circuits, and printed circuit boards are widely used, with high efficiency, stable soldering quality, and high electrical performance indicators. 2. Power reserve and anti-overload ability are different The dynamic range of the high-fidelity amplifier should be 120dB, so as to meet the needs of the sound from the slightest to the peak of the climax, the amplifier output is not clipped, so the amplifier must have sufficient power reserve. If the dynamic range of the audio voltage is 3:1, since the power is proportional to the square of the voltage, the power dynamic range is 9:1. That is to say, a power amplifier with a power of 90W can only be turned on to 10W to achieve high-fidelity playback. Therefore, the transistor amplifier needs a large power reserve to avoid overload distortion. Once the ground is loaded, its distortion will almost rise in a vertical line, which can damage the transistor in severe cases. The anti-overload capability of the tube amplifier is far stronger than that of the transistor amplifier. In case of overload, the peak of the music signal only becomes slippery than the normal waveform, and the sound is not deformed much. For transistor amplifiers, clipping will occur at this time, and the sound quality will deteriorate significantly. 3. Efficiency, life, and cost are different Tube amplifiers are not superior to transistor amplifiers in terms of weight, efficiency, and lifespan. The service life of the electron tube is relatively low, and some technical indicators will drop significantly after one to two thousand hours of use. The lifetime of transistors and integrated circuits is much longer. In addition, the tube amplifier consumes high power and often works in the Class A state, which reduces the efficiency. However, there are no harmful sound quality factors such as transient intermodulation distortion, switching distortion, and crossover distortion. In terms of cost, for the same grade of amplifiers, tube amplifiers are generally significantly higher than transistor amplifiers. The main reasons are the high cost of electronic tubes and output transformers, and the production process of electronic tube power amplifiers is not easy to automate, and the production efficiency is low. 4. Different sound quality The sound quality of the tube amplifier is significantly better than that of the transistor amplifier. Transistor power amplifiers have a sense of overwhelming when listening to high and medium and high frequencies, and less low frequencies. Transistor power amplifiers sound hard, especially low-frequency sounds are not soft enough, and high-frequency sounds are sharp and dry. Sometimes it sounds like there is crossover distortion in the high-frequency range. These phenomena become more obvious when the frequency increases and the volume is louder. However, the transistor amplifier has large dynamics and high speed, which is especially suitable for music with greater dynamics. As for the sound effects of guns and lightning, it is certainly better than a tube amplifier. Generally speaking, the sound quality of the tube amplifier is soft and pleasant. Specifically, the low-frequency sound of the tube amplifier is soft and clear, and the high-frequency sound is slender and clean. The performance of the human voice is its strong point, and therefore it is more valuable. All in all, the choice of amplifier varies from person to person. If you like orchestral music, especially chamber music and vocals, then tube amplifiers should be your first choice. If you like jazz, rock, and modern music, then transistor amplifiers are the choice. VI. Things Needing Attention While Using a Tube Amplifier? 1.    The tube amplifier must be used under the limit parameters. Although it can still work normally under the limit parameters, the life of the tube amplifier will be shortened quickly. Therefore, the tube should be used under the rated parameters. 2.    The location of the components in the device should be conducive to the heat dissipation of the tube amplifier. To control the temperature of the tube case of the tube amplifier, the allowable temperature of the glass case of various tube amplifiers is different. For example, the allowable limit temperature of the power output tube during operation does not exceed 90°C in principle. 3.    Except for the high-reliability tube amplifier with a special structure that can work at higher accelerations, other receiver amplifier tubes can only withstand small shocks for a short time. Therefore, pay attention to the shock absorption of the tube when using it. 4.    When using small tubes (thumb-finger type) and other tubes without tube bases (but with tube needles), use tube sockets specified by the Ministry of Electronics Industry. Prevent cracking or damage to the glass shell. When plugging and unplugging the tube, its direction should be perpendicular to the plane of the tube base. When inserting an electronic tube, prevent damage to the normal position of the contact reed in the socket socket of the tube socket, and avoid using the empty foot of the tube socket as a connecting pad. 5.    When using an indirectly heated tube amplifier, the potential difference between the cathode and the filament must not exceed the specified limit. For this reason, a dedicated filament transformer is often used for power supply. In order to eliminate the effect of leakage current instability, under the condition of not hindering the operation of the circuit, a shunt resistance of about several ohms can be connected between the cathode and the filament. VII. Why is Tube Amplifier So Expensive? Is It Worth It? In short, tube amplifiers are costly because they use pre and power tubes as their primary amplification source. Each tube costs approximately $50 and can have up to four of them in a single unit. Second, these amplifiers have more expensive components, larger casings, and more complicated circuitry than solid-state amplifiers.   Whether tube amplifiers are "worth it” or not, well, that’s more of a subjective question.   If your goal is to build a pristine audio chain that cleanly reproduces the input signal you give it, a tube amplifier is definitely not worth it. By spending extra money to put a tube in your signal chain, you are intentionally distorting the sound.   Note that modern high end A/D/A conversion equipment (which aims for perfect signal reproduction) never uses tubes. The marketing pitch on tube equipment is that it does change the sound that you give it. Don't buy a tube amplifier unless that is what you want.   Now, if your goal is not to amplify signal accurately, but rather to make a sound that you personally find pleasing, a tube may yield some benefits.   You can listen to some tube amps at different levels to decide what you personally prefer. Does this make a tube amp worth it? Bear in mind that there are many ways of creating harmonic distortion (in the analog domain, or emulated with digital techniques), and many are cheaper than tubes, which are expensive to produce.   The high cost of tubes is not a function of the fact that it was difficult to engineer their particular audio qualities. The way tube amplifiers color audio is a historical function of the fact that engineers were not able to compensate for the changes they introduce.   Many people have now decided that this is a valuable property - but the production of tubes is becoming relatively more expensive as demand for them diminishes and they require specialty, limited-run manufacturing (compared to transistors, demand for which is growing).   In all, thinking from your practical needs before jump into any conclusion, whether tube amplifier is worth it or not, there’s no absolute answer to this question. VIII. How to Extend the Life of the Tube Amplifier?    The problem of short life of the tube amplifier is often criticized, but this is often not a problem of the tube amplifier itself, but a defect in the circuit design and a problem in use. It should be noted that a good quality tube amplifier must have a correctly designed circuit, sufficient heat dissipation, and thoughtful shock absorption.   In use, the tube amplifier must have good ventilation and heat dissipation. Overheating of the temperature will inevitably shorten the life of the tube, so the tube amplifier should be kept as low as possible.   Vibration is not good for tube amplifiers, so it is important to take anti-vibration measures to avoid vibration as much as possible. If these two can be achieved, the service life of the tube amplifier can be at least doubled. For this reason, there should be a proper space around the tube amplifier equipment, especially above it, in order to have good convection ventilation, if possible, a fan can be used to help dissipate heat.   When the cathode of the tube amplifier has not reached the required temperature, the high-voltage power supply is immediately applied, and its cathode will be damaged, which will also shorten the life of the tube amplifier.   Therefore, if the tube amplifier equipment has a preheating device, it must be used. For example, first turn on the filament low-voltage power supply to preheat, and then turn on the high-voltage power supply. If there is no preheating device, don't rush to connect the input signal, you can turn the volume down to the minimum, wait for 20-30 minutes to warm up the machine before using it.   If the indirectly heated rectifier tube is used to supply the high voltage of the whole machine, it just provides a simple and effective high voltage delay. In addition, do not switch the power supply frequently during normal use.   Of course, if the tube amplifier circuit is designed correctly and the wrong use is avoided, the tube amplifier will not "die young". It should be normal for the tube amplifier to use thousands of listening hours.   The most common mistakes in circuit design are: 1. The potential difference between the filament and the cathode of the tube amplifier is too high 2. The screen or screen grid voltage of the tube amplifier is applied to the maximum value 3. The filament voltage of the tube amplifier is too low or too high 4. Improper installation position of the tube amplifier causes the electrode to overheat and the high-voltage power supply does not have a delay device, etc.   Therefore, these problems should be avoided when designing the circuit to effectively extend the service life of the tube amplifier. FAQ 1. Why is a tube amp better? Tubes, like analog recordings, have a more full-bodied sound than transistor gear. There's a "roundness" to tube sound that solid-state gear never equals. Tubes are less forgiving about mismatches, so to get the best out of a tube amp it must be used with just the right speaker. 2. What is tube amplifier used for? Tube amplifiers, or tube amps as they're commonly called, are tiny electronic or electromagnetic components that are used to boost electric current in devices to improve their performance. It's what makes your hearing aid pick up sounds through a microphone from all around you. 3. Are tube amps worth it? In many cases, tube amps do not require the amount of maintenance that they have a reputation for. As long as you properly take care of your gear, owning a tube amp is simple and very well worth it for the tone. 4. How long should a tube amp warm up? 20 to 30 minutes. As a rule of thumb, your tube amp needs to be warmed up for 20 to 30 minutes at least before you can start playing your guitar. 5. Why are tube amps louder? When tubes are driven outside their linear region, for the first 12db or so of overdrive the harmonics that they produce trick the human ear into thinking that the sounds are getting louder, when in fact the sound is getting progressively more distorted. 6. How does a tube amplifier work? The power transformer and rectifier work together as an electron pump which pulls electrons out of the amp circuit creating a positive voltage (electron scarcity = positive voltage). The amplifier's electronics need DC to amplify. The amp is powered by DC but the guitar signal moving through the amp is AC. 7. What's the difference between a tube amp and a regular amp? The physical difference between a solid-state amp and a tube amp is that a solid-state machine derives amplification from electronic transistors, while a tube amp uses vacuum tubes (also known as valves). ... Solid-state amps are great for players who want maximum headroom (a.k.a a loud, clean, undistorted signal). 8. Which is better tube amp or solid state? Tube amps are generally more expensive in initial cost and to operate (because you need to replace the tubes occasionally), and solid-state amps are generally less delicate and more reliable. Many players, however, feel that tube amps yield a warmer, more musical tone and more musical-sounding distortion. 9. How often should a tube amp be serviced? 15 years. If its a well made amp, recap every 10 or 15 years, retube as needed. Fenders might go many years without needed a power tube replaced. 10. How many watts do I need in a tube amp? 100 watts. You'll need a solid state amp that has around 100 watts, or a valve amp that has around 50 watts. This will usually give you enough volume that you can be heard over the drummer, without having to push your amp's volume too hard so that the distortion becomes overbearing.

In this article, we will present you a comprehensive introduction to solid state relay, covers from its definition, characteristics, structure, pros and cons, and some problems you might encounter with during using SSR and so on. Catalog I. What is a Solid State Relay? 1.1 Brief Introduction 1.2 Structure of Solid State Relay 1.3 Characteristics of Solid State Relay 1.4 Difference Between Solid State Relay & Normal   Relay II. Pros and Cons of Solid State Relay III. Common Problems of Solid State Relays IV. Maintenance Method of Solid State Relay V. Application of Solid State Relay FAQ I. What is a Solid State Relay? 1.1 Brief Introduction The solid state relay (SSR) is a non-contact switch composed of microelectronic circuits, discrete electronic devices, and power electronic power devices. It is a component of a full electronic circuit combination. It depends on the electromagnetic and optical characteristics of semiconductor devices and electronic components. Its isolation and relay switching functions.   This video tells briefly what solid state relay is. Compared with the traditional electromagnetic relay, the solid-state relay is a relay without machinery and no moving parts, but has essentially the same functions as the electromagnetic relay.   Solid state relays are widely used in industrial automation control, such as electric furnace heating systems, familiar control machinery, remote control machinery, motors, solenoid valves and signal lights, flashers, stage lighting control systems, medical equipment, photocopiers, washing machines, fire protection systems, etc. It works reliably, has no contact, no spark, long life, no noise, no electromagnetic interference, fast switching speed, and achieves the purpose of directly driving a large current load with a tiny control signal. 1.2 Structure of Solid State Relay The solid state relay is composed of three parts: input circuit, isolation (coupling) and output circuit.   1. Input circuit: According to the different types of input voltage, the input circuit can be divided into three types: DC input circuit, AC input circuit and AC/DC input circuit. Some input control circuits are also compatible with TTL/CMOS, positive and negative logic control and inverting functions, and can be easily connected with TTL and MOS logic circuits.   For a control signal with a fixed control voltage, a resistive input circuit is used. The control current is guaranteed to be greater than 5mA. For the control signal with a large variation range (such as 3~32V), a constant current circuit is used to ensure reliable operation of the current greater than 5mA within the entire voltage variation range.   2. Isolation and coupling The input and output circuits of solid state relays can be isolated and coupled in two ways: photoelectric coupling and transformer coupling: photoelectric coupling usually uses photodiodes-phototransistors, photodiodes-bidirectional light-controlled silicon controlled thyristors, photovoltaic cells, to achieve control side and load side Isolation control; high-frequency transformer coupling is a self-excited high-frequency signal generated by the input control signal is coupled to the secondary, detected and rectified, and processed by a logic circuit to form a drive signal.   3. Output circuit The power switch of the SSR is directly connected to the power supply and the load side to realize the on-off switching of the load power supply. Mainly use high-power transistors, unidirectional thyristors (or SCR), bidirectional thyristors (Triac), power field effect transistors (MOSFET), and insulated gate bipolar transistors (IGBT).   The output circuit of solid state relay can also be divided into DC output circuit, AC output circuit and AC/DC output circuit. According to the load type, it can be divided into DC solid state relay and AC solid state relay. Bipolar devices or power FETs can be used for DC output, and two thyristors or one bidirectional thyristor are usually used for AC output. The AC solid-state relays can be divided into single-phase AC solid-state relays and three-phase AC solid-state relays. AC solid-state relays can be divided into random AC solid-state relays and zero-crossing AC solid-state relays according to the timing of turn-on and turn-off. 1.3 Characteristics of Solid State Relay The solid state relay is a non-contact electronic switch with isolation function, and there are no mechanical contact parts during the switching process. Therefore, in addition to the same functions as electromagnetic relays, solid state relays also have logic circuit compatibility, vibration resistance and mechanical shock resistance, unlimited installation location, and good moisture, mildew and corrosion resistance. It also has excellent performance in explosion protection and prevention of ozone pollution. It also has the characteristics of low input power, high sensitivity, low control power, good electromagnetic compatibility, low noise and high operating frequency.   (1) The SSR has no internal mechanical parts, and the structure adopts a fully sealed method of perfusion. Therefore, the SSR has the advantages of vibration resistance, corrosion resistance, long life and high reliability, and its switch life is up to 10.1 million times; (2) Low noise: AC SSR adopts zero-crossing trigger technology, so the voltage rise rate dv/dt and current rise rate di/dt value are effectively reduced on the line, so that the SSR has minimal interference to the mains during long-term operation; (3) Its switching time is short, about 10ms, which can be used in higher frequency occasions; (4) It adopts photoelectric isolation between its input circuit and output circuit, and the insulation voltage is above 2500V; (5) Its input power consumption is very low, compatible with TTL and COMS circuits; (6) Its output terminal has a protection circuit; (7) Strong load capacity. 1.4 Difference Between Solid State Relay & Normal Relay Ordinary relays are generally composed of relay coils and static and dynamic contacts. The movable contact is actuated by the electromagnetic attraction force of the relay coil to realize the connection and disconnection of the circuit. So there is mechanical movement. When the current reaches a certain level, the contacts will spark. Ordinary relays are cheap and simple in structure, but sparks and mechanical movements during operation will have a certain impact on its life.   The advantages of ordinary relays are: simple drive, good isolation, and good short-term overload tolerance. The disadvantages of ordinary relays are: large size (heavy), slow response speed (up to ms level), and large power consumption to drive the relay.   The comparison between traditional relays and solid-state relays, as there are many types involved, the following is a comparison between electromagnetic relays and corresponding solid-state relays to illustrate their differences:   1. Structural difference: Electromagnetic relays work by using the suction force generated by the circuit in the input circuit between the electromagnet core and the armature; solid-state relays use electronic components to perform their functions without mechanical moving components, and the input and output are isolated.   2. Difference in working mode: Electromagnetic relay uses the principle of electromagnetic induction to control the on-off of the circuit through the power of electromagnet. Therefore, when DC is used to connect the coil, the contacts can pass AC and DC; solid state relays rely on the electrical, magnetic and optical characteristics of semiconductor devices and electronic components to complete their isolation and relay switching functions. Therefore, they are divided into DC input-AC output type and DC Input-branch output type, AC input-AC output type, AC input-DC output type.   3. Differences in working status: Electromagnetic relays make use of the suction force generated between the armature to make and break the circuit. Therefore, the action response is slow, noisy, and life is limited; solid state relays have fast response, operate without noise, and have a long life.   4. Operating environment: In the influence of temperature, humidity, atmospheric pressure (altitude), sand and dust pollution, chemical gas and electromagnetic interference, electromagnetic relays are generally inferior to solid state relays.   5. Electrical performance difference: Compared with the corresponding solid-state relay, the electromagnetic relay is simple to drive, but has large power consumption, good isolation, good short-term overload tolerance, and is not as good as the latter in high-current and high-power situations. And when controlling the circuit with frequent action, the life of the electromagnetic relay is not as long as the latter.   In short, traditional relays and solid state relays have their own advantages. The latter is more and more popular because of its reliable operation, no contacts, no sparks, long life, no noise, no electromagnetic interference, and fast switching speed.   II. Pros and Cons of Solid State Relay Pros: (1) Long life and high reliability: SSR has no mechanical parts and solid components to complete the contact function. Because there are no moving parts, it can work in a high impact and vibration environment. Because of the components that make up the solid state relay The inherent characteristics determine the long life and high reliability of solid state relays.   (2) High sensitivity, low control power, and good electromagnetic compatibility: The solid state relay has a wide input voltage range and low drive power, and is compatible with most logic integrated circuits without the need for buffers or drivers.   (3) Fast switching: Because solid-state relays use solid-state devices, the switching speed can range from a few milliseconds to several microseconds.   (4) Electromagnetic interference: The solid state relay has no input "coil", no arc ignition and rebound, thus reducing electromagnetic interference. Most AC output solid state relays are a zero-voltage switch, which is turned on at zero voltage and turned off at zero current, reducing the sudden interruption of the current waveform, thereby reducing the switching transient effect.   Cons: (1) After the solid state relay is turned on, the tube voltage drop is large, and the forward voltage drop of the thyristor or two-phase thyristor can reach 1~2V, and the saturation voltage drop of the high-power transistor is also between 1~2V. Generally, the on-resistance of the power FET is also larger than the contact resistance of the mechanical contacts.   (2) The semiconductor device can still have a leakage current of several microamperes to several milliamperes after it is turned off, so ideal electrical isolation cannot be achieved.   (3) Due to the large pressure drop of the tube, the power consumption and heat generation after the turn-on are also large, the volume of the high-power solid-state relay is much larger than the electromagnetic relay of the same capacity, and the cost is also higher.   (4) The temperature characteristics of electronic components and electronic circuits have poor anti-interference ability and poor radiation resistance. If effective measures are not taken, the working reliability of solid state relays will be reduced.   (5) Solid state relays are more sensitive to overload and must be protected by fast fuse or RC damping circuit. The load of the solid state relay is obviously related to the ambient temperature. As the temperature rises, the load capacity will drop rapidly. III. Common Problems of Solid State Relays When the solid state relay is open and there is voltage at the load terminal, there will be a certain amount of leakage current at the output terminal. Care should be taken to prevent electric shock when using or designing. When solid state relays fail to be replaced, products with the same original model or technical parameters should be used as much as possible to match the original application circuit to ensure the reliable operation of the system. Among all, overheat, overcurrent and overvoltage are always the common problems you might encounter when using a solid state relay.   overheat When the SSR is turned on, the component will withstand the dissipation power of P=V (tube pressure drop) × I (load), where the effective value of V and the effective value of I are the effective values of the saturation voltage drop and the operating current, respectively.   The load capacity of the solid state relay is greatly affected by the ambient temperature and its own temperature rise. It must be based on the actual working environment conditions and strictly refer to the allowable case temperature rise (75°C) at the rated working current. Reasonably select the size of the radiator or reduce the current for use. During installation and use, ensure that it has good heat dissipation conditions, otherwise it will cause loss of control due to overheating, and even cause product damage.   Generally speaking, under 10A, an instrument base plate with good heat dissipation conditions can be used, and a product with a rated working current above 10A should be equipped with a radiator.   Below 30A, use natural air cooling. When the continuous load current is greater than 30A, the instrument fan must be used for forced air cooling. Products above 100A should be equipped with a radiator and a fan for forced cooling.   When installing, pay attention to the good contact between the bottom of the relay and the radiator, and consider applying a proper amount of thermal grease to achieve the best heat dissipation effect.   For example, when the relay is working at high temperature for a long time (40℃~80℃), the user can consider derating according to the curve data of the maximum output current and ambient temperature provided by the manufacturer to ensure normal operation.   Reasons for overheating of solid state relays: When the solid state relay is working normally, there is a certain power loss on its internal chip. This power loss is mainly determined by the product of the output voltage drop of the solid state relay and the load current, and is consumed in the form of heat.   Therefore, the quality of heat dissipation directly affects the reliability of the solid state relay, and the excellent thermal design can avoid failure and damage caused by poor heat dissipation.   Overcurrent and overvoltage When the relay is in use, the internal output thyristor of the SSR solid state relay will be permanently damaged due to overcurrent and load short circuit. You can consider adding a fast fuse and an air switch to the control loop for protection (the product output protection should be selected when selecting the relay, built-in Varistor absorption circuit and RC buffer can absorb surge voltage and improve dv/dt tolerance).   Fast fuse and air switch are general overcurrent protection methods. Fast fuse can be selected according to 1.2 times of rated working current, generally small capacity fuse can be used. Pay special attention to load short circuit, which is the main cause of damage to SSR products.   For inductive and capacitive loads, in addition to the internal RC circuit protection, it is recommended to use a varistor in parallel at the output as a combined protection. The area of the metal zinc oxide varistor (MOV) determines the absorption power, and the thickness determines the protection voltage value.   For AC 220V SSR, select MYH12-430V varistor; 380V select MYH12-750V varistor; for larger capacity motor transformer, select MYH20 or MYH2024 varistor with large current capacity. The selection principle is to use 500V-600V varistors for 220V, and 800V-900V varistors for 380V. IV. Maintenance Method of Solid State Relay 1. When selecting solid state relays used on printed circuit boards with low current specifications, since the lead terminals are made of high thermal conductivity materials, the soldering should be carried out under the conditions of a temperature less than 250℃ and a time less than 10S. If the surrounding temperature is considered, If necessary, derating can be considered. Generally, the load current should be controlled within 1/2 of the rated value.   2. Selection of solid state relays for various load surge characteristics   The controlled load will generate a large inrush current at the moment of switching on. Because the heat is too late to dissipate, it is likely to damage the SSR's internal thyristor.   Therefore, the user should analyze the surge characteristics of the controlled load when selecting the relay, and then select the relay. The relay can withstand this surge current under the premise of ensuring steady-state operation. When selecting, refer to the derating factor of various loads in Table 2 (at normal temperature).   If the selected relay needs to work in the occasions with more frequent work, high life and reliability requirements, it should be multiplied by 0.6 on the basis of Table 2 to ensure reliable work.   Generally, follow the above principles when selecting, and when low voltage requires low signal distortion, you can choose a DC solid-state relay that uses a field effect tube as an output device; for example, for AC resistive loads and most inductive loads, you can choose a zero-crossing relay. Extend the life of loads and relays, and also reduce their own radio frequency interference. For phase output control, random solid state relays should be used.   3. The influence of ambient temperature   The load capacity of solid state relays is greatly affected by the ambient temperature and its own temperature rise. During installation and use, ensure that it has good heat dissipation conditions. Products with a rated operating current of more than 10A should be equipped with a radiator, and products with a rated operating current of more than 100A should be equipped with a radiator. Equipped with a radiator and a fan for forced cooling. When installing, pay attention to the good contact between the bottom of the relay and the radiator, and consider applying a proper amount of thermal grease to achieve the best heat dissipation effect.   For example, when the relay is working at high temperature for a long time (40℃~80℃), the user can consider derating according to the curve data of the maximum output current and ambient temperature provided by the manufacturer to ensure normal operation.   4. Overcurrent and overvoltage protection measures   When the relay is used, the internal output thyristor of the SSR solid-state relay will be permanently damaged due to overcurrent and load short-circuit. Consider adding a fast fuse and air switch to the control loop to protect it (the product output protection should be selected when choosing the relay, built-in Varistor absorption circuit and RC buffer can absorb surge voltage and improve dv/dt tolerance); RC absorption circuit and varistor (MOV) can also be connected in parallel at the output of the relay to achieve output protection. The selection principle is to use 500V-600V varistors for 220V, and 800V-900V varistors for 380V.   5. Relay input circuit signal   When in use, when the input voltage is too high or the input current is too large and exceeds its specified rated parameters, consider connecting a voltage divider resistor in series at the input end or a shunt resistor in parallel at the input port, so that the input signal does not exceed its rated parameters value.   6. In specific use, the control signal and load power supply should be stable, and the fluctuation should not be greater than 10%. Otherwise, voltage stabilization measures should be taken.   7. Keep away from electromagnetic interference and radio frequency interference sources during installation and use to prevent the relay from malfunctioning and out of control.   8. When the solid state relay is open circuit and there is voltage at the load terminal, there will be a certain amount of leakage current at the output terminal. Pay attention to it when using or designing.   9. When the solid state relay is replaced by failure, try to choose the product with the same original model or technical parameters to match the original application circuit to ensure the reliable operation of the system. V. Application of Solid State Relay The dedicated solid-state relay can have short-circuit protection, overload protection and overheat protection functions, and the combination logic solidification package can realize the intelligent module required by the user, which can be directly used in the control system.   Solid state relays have been widely used in: (1) Computer peripheral interface equipment, constant temperature system, temperature adjustment, electric furnace heating control, motor control, numerical control machinery, remote control system, industrial automation device; (2) Signal light, dimming, flasher, lighting stage lighting control system; (3) Instruments, medical equipment, photocopiers, automatic washing machines; (4) Automatic fire-fighting, security systems, as well as the switch of power capacitors for power factor compensation of the power grid, etc. In addition, solid state relays are widely used in chemical, coal, and other occasions that require explosion-proof, moisture-proof, and corrosion-proof. FAQ 1. What is solid state relay and how it works? A solid state relay (SSR) is an electronic switching device that switches on or off when an external voltage (AC or DC) is applied across its control terminals. It serves the same function as an electromechanical relay, but has no moving parts and therefore results in a longer operational lifetime. 2. What is the difference between a relay and a solid state relay? The main difference between solid state relays and general relays is that there is no movable contacts in solid state relay (SSR). In general, solid state relays are quite similar to the mechanical relays that have movable contacts. ... SSR provide high-speed, high-frequency switching operations. 3. How fast is a solid state relay? The SSR output is activated immediately after applying control voltage. Consequently, this relay can turn on anywhere along the AC sinusoidal voltage curve. Response times can typically be as low as 1 ms. The SSR is particularly suitable in application where a fast response time is desired, such as solenoids or coils. 4. Do solid state relays get hot? All solid state relays develop heat as a result of a forward voltage drop through the junction of the output device. Beyond a point, heat will cause a lowering (or derating) of the load current that can be handled by the SSR. ... Loads greater than 4 Amps will require heat sinks. 5. What causes solid state relay failure? What are the main causes and solutions of the Solid-state Relays (SSR)'s failures? If an inrush current exceeds the rated making current of the SSR due to the high inrush current of loads such as motors and lamps, SSR output elements are damaged. Consider using an SSR with a higher capacity. 6. Can a solid state relay switch DC? Solid state relays can be designed to switch both AC or DC currents by using an SCR, TRIAC, or switching transistor output instead of the usual mechanical normally-open (NO) contacts. 7. How do you test a solid state relay with a multimeter? Using Multimeter:  1. Set the multimeter in continuity test mode. 2. Place the probes of the multimeter on the coil terminals. 3. If the multimeter beeps (or show any sign of continuity), the coil is electrically closed (good). 4. If the multimeter does not beep, the coil is open & damaged. The relay needs to be replaced. 8. How reliable are solid state relays? Solid-state relays are the preferred choice for system reliability because they have no moving parts or contacts. Over time, the plating on the contacts inside EMRs can erode. This erosion can cause the contacts to weld shut; therefore they no longer open/close properly, and the relay has to be replaced. 9. Is a solid state relay a transistor? Solid-State Relay: A sort of hybrid between a conventional relay and a transistor, these relays switch a load using an LED activated by the control circuitry. The LED activates a light-activated MOSFET that controls the load. 10. How do I know if my solid state relay is bad? Solid-state relays should be checked with an ohmmeter across the normally open (N.O.) terminals when control power is off. The relays should be open, switched to OL, and closed (0.2 , the internal resistance of the ohmmeter) when control power is applied. 11. How do I choose a solid state relay? When selecting a Solid State Relay, consider: Current rating, as a general rule consider using the relay at no more than 70% of its rated current. Electrical environment,. i(In harsh electrical environments, consider a relay with an line voltage rating above the application line voltage.) 12. Do solid state relays need a diode? 2 Answers. The control side of solid state relays is usually just a LED, sometimes two LEDs back to back, and sometimes with integrated resistor. ... If the relay is on the same board as whatever is driving it, then no inductive kickback diode is needed. It's no different than driving any other on-board LED. 13. Do solid state relays leak voltage? Solid State relays have leakage. If you want to repeatedly switch something on / off, use them. But when you want the SSR to be fully off, say after pressing an off switch, a mechanical relay should be across the load to take it off the SSR. ... The SSR control is attached to the atmega328 through a 200ohm resistor.

This article is a collection of 5 frequently asked questions about blower motor resistor. Catalog I. What is a Blower Motor Resistor? II. How Does the Blower Motor Resistor Work? III. How Do I Know If My Blower Motor Resistor is Bad or Broke? IV. How to Test a Blower Motor Resistor? V. Can I Fix the Blower Motor Resistor by Myself? FAQ I. What is a Blower Motor Resistor? The blower motor resistor is the blower motor component that regulates the speed. When you raise the thermostat on the air conditioner, the resistor sends a signal to the blower motor to speed up and blow more air. When you turn it down, the opposite happens. It is an electronic component that sends electronic pulses corresponding to the information you send through the adjustment dial. The electrical signal increases or decreases, which affects the overall motor speed of the fan. As far as electrical systems are concerned, they are simple, but as you might see, if something interrupts the flow of power, problems can occur.   Behind these vents in the dashboard, there is a blower motor that starts when you need heating or air conditioning. Usually, it is located in the dashboard on the other side of the steering wheel. You can't see it because it is inside the vehicle, but there it is.   A digital speed controller controls a variable speed motor. The controller typically receives a digital input from the speed switch or HVAC control head. The control head then sends a command to the motor controller to adjust the speed to the driver's requirements.   The motor controller rapidly pulses the ground circuit on and off to achieve the desired speed. So a half-speed driver request will result in the blower motor controller pulsing the ground connection off twice as often as when the fan is running at full speed.   The blower motor resistor or control module is often positioned within one of the ducts in the HVAC system, close to the blower motor, in most modern vehicles. This is done so that the resistor or control module can be cooled by passing air. A blower motor resistor was fitted on the firewall of some older vehicles, with access from under the hood.  II. How Does the Blower Motor Resistor Work? This video will give a detailed explanation of blower motor circuit to help you better understand how eactly it works. III. How Do I Know If My Blower Motor Resistor is Bad or Broke? There are a few indications that your car's blower motor resistor has failed. Because the symptoms may overlap with difficulties in other systems in your vehicle, you may require the assistance of a specialist to help you diagnose them. These are some of the most typical warning signs. (1)  No air. As simple as it may sound, one of the most noticeable indicators to look for is a lack of air moving through the vents when trying to get the heater or air conditioner to function. If nothing comes out when you turn the knob or press the button and it's intended to start blowing air, it's a good clue that the blower motor resistor has failed. This can be a sign of a variety of different issues, so don't take it as a given if this is the only signal you're receiving.   (2)  High speeds only. As previously stated, a blower motor resistor is not required in two situations. When the fan is totally turned off or when it is running at high power. Because the current does not need to be modulated at high power, it bypasses the resistance. So, if you discover that your heat and air conditioning can only switch from being completely off to being on at high power, it's almost certain that you have a broken blower motor resistor.   (3)  Low speeds only. When your fan only works at low speed, this may be a signal of poor blower motor resistance as well. However, when there is a wiring problem between the blower motor resistor and the blower motor itself, it may only work at low speeds.   (4)  The fan will not turn off. If you can't turn off the fan no matter what you do, and no matter how you try to go up, down, or turn off the fan, the fan is constantly running, which means that the blower motor resistor cannot properly regulate the current.   (5)  The blower motor works under certain settings, but does not work under other settings. The blower motor should have a series of settings, from low to high, which can be set in a variety of intermediate ranges. If you find that some of these intermediate settings are working and some of them do nothing at all, it probably means that there is a problem with the switch, and how the switch sends a signal about your settings to the blower motor resistor blower motor.   (6)  Smoking vents. This is an unusual signal of a faulty blower motor resistor, though it is not unheard of. If there is a short around the blower motor resistor and wires begin to melt, the fan may spew smoke from those melting wires back into your car's cabin.   A solid rule of thumb is that if smoke starts flowing in via your car's vents, you should pull over immediately and figure out what's wrong. If it isn't the blower motor resistor, it could be something more serious, and you should get it checked out as soon as possible.   (7)  Burning Smell. Similarly to the smoking vent issue, it is not always as dangerous as actual smoke billowing into the car's cabin, but you will detect the distinct burning smell that indicates that some metal or plastic is overheated somewhere in the vehicle. This is frequently associated with one of the other signals we've already mentioned above. IV. How to Test a Blower Motor Resistor? Blower motor resistor test V. Can I Fix the Blower Motor Resistor by Myself? Whether you can repair the blower motor resistor yourself obviously depends on how much you know about blower motor resistors and general car maintenance. If you are reading a guide on blower motor resistance and its functions, you may not be familiar with them. Therefore, we recommend that you do not try to fix this problem yourself, as this is not a beginner-level fix.   This is not to say that you cannot replace the blower motor resistance yourself, but it will be a complicated task. But we provide you with some basic methods to diagnose and repair some simple blower motor problems, for reference only. For specific steps, please consult professionals or check related videos on youtube.   (1) The blower only works in high speed. This is a sure sign of a bad blower motor resistor, not a faulty speed switch. Change the resistor.   (2) The blower only works in low speed. Check for a blown fuse or a faulty high-speed relay. Replace the high-speed relay with a relay of the same part number. Check the fuse for the high speed relay's control side as well. Verify that the high speed relay's ground side is good.   (3) Repeated failures of the blower motor resistor Check for full airflow at the vents. If airflow appears to be restricted or lower than typical, a blocked cabin air filter is to blame. Examine the cabin air filter. If everything is ok, look for debris on the evaporator or heater. When the airflow is reduced, the blower motor resistor overheats and fails. Reduced airflow forces the blower motor to work harder and draw more current, which might result in repeated blower motor resistor failures. FAQ 1. What does a resistor do on a blower motor? Blower resistors are resistors which are used to control the fan speed of automotive blowers. The fan speed can be changed either by switching the blower resistor resistance mechanically, using a rotating lever, or electronically by the air conditioning system. 2. Can I bypass blower resistor? Blower resistors are resistors which are used to control the fan speed of automotive blowers. The fan speed can be changed either by switching the blower resistor resistance mechanically, using a rotating lever, or electronically by the air conditioning system. 3. What can cause a blower motor to stop working? In a situation where the motor doesn't work on any speed, the most likely causes are: a blown power supply fuse, a bad motor ground connection, bad motor speed control module or a failed motor. On all systems, a failed blower motor is least likely. ... Start by checking the blower fuse and HVAC controller fuse. 4. How do you test a blower motor resistor with a multimeter? Place one lead of the Ohmmeter on terminal 1 of the resistor. Place the other lead on terminal 2 and check against specifications. If this circuit is open, showing infinity on the Ohmmeter, the blower resistor must be replaced. Move the lead from terminal 2 to terminal 3 and check this reading against specifications. 5. Is the blower motor resistor supposed to get hot? Yes that resistor will get very hot. Most people don`t know this but it is faster to defrost the windshield on low or medium fan speed due to that resistor putting off heat. Also that resistor needs to be cooled off with the air flow or it will burn up . 6. What is the function of a blower motor resistor? A blower motor resistor is an adjustable resistor. This electrical component is used to control the air conditioning system of a vehicle. It is the part that controls the fan speed of the fan motor according to settings that can be changed by turning the knob to the left or right, thereby increasing or decreasing the resistance of the electric current flowing to the rotating fan motor connected to the fan. 7. Where is the blower motor resister? A blower motor resistor, typically located beneath the passenger side dashboard, contains three resistors, or sets of terminals designed to generate voltage in proportion to electrical current. 8. How do you replace a blower motor resistor? Safety Tip: Always wear safety glasses when working on your motor. Wear other personal protective equipment (PPE) when necessary, for example latex gloves or closed toe shoes. 1.Remove the negative battery terminal.2.Locate the blower motor resistor on the passenger side under the dash board. It is mounted to the the blower housing near the blower motor.3.Disconnect the electrical connector to the blower motor resistor.4.Remove the screws or bolts to the blower motor resistor and remove the resistor.5.Installation is the reverse of the removal. 9. Can you test a blower motor resistor? Yes. Set your multimeter to Diod or continuity and place leads on either side of the resistor. If no tone and infinite resistance it is bad. If tone but no resistance it is bad. If you have continuity to ground, something has shorted to ground look for heat damage. If you have tone and resistance it is good.  10. Why does a blower motor resistor keep going out? If you are constantly blowing that part. You ether have the motor pulling to much amps. If it is home unit it could also be a inline control board cap.