Introduction Capacitors are now commonly used as decoupling capacitors, DC blocking capacitors, or as matching capacitors due to their characteristics of blocking DC while passing AC. But in practical applications, DC can charge the capacitor and pass through it. Is this contrary to its characteristics? Why can DC charge the capacitor? Here we will discuss this issue in details. Charging and Discharging of Capacitor -RC Circuit Catalog Introduction Ⅰ Capacitor Charging Principle Ⅱ Why Capacitor Charges in DC? Ⅲ Capacitor Transient and Steady-state Processes Ⅳ Capacitor Circuit Analysis and Calculations Ⅴ FAQ Ⅰ Capacitor Charging Principle A capacitor is a component that can store electrical energy. As one of the most commonly used electronic components, the simplest capacitor is composed of plates at both ends and an insulating dielectric (including air) in the middle. After being energized, the plates are charged to form a voltage (potential difference), but due to the insulating material in the middle, the entire capacitor is non-conductive. However, this situation is under the premise that the critical voltage (breakdown voltage) of the capacitor is not exceeded. In fact, any substance is relatively insulating. When the voltage across the substance increases to a certain level, the substance can conduct electricity. We call this voltage breakdown voltage.It is the same for the capacitor. After the capacitor is broken down, it is not an insulator. In an AC circuit, because the direction of the current changes with time as a certain function. The process of charging and discharging a capacitor takes time. At this time, a changing electric field is formed between the plates, and it is also a function of time. So current passes between capacitors in the form of an electric field.Capacitors are similar to batteries in that they also have two electrodes. Inside the capacitor, the two electrodes are connected to two metal plates separated by a dielectric. When the capacitor is connected to the power supply, under the action of the electric field force, the free electrons of the capacitor plate connected to the positive electrode of the power supply will move to the negative electrode. The positive electrode is positively charged due to the loss of negative electrons, and the negative electrode is negatively charged due to its negative electrons. In addition, the charges on the positive and negative plates are equal, with opposite signs.The directional movement of the charge forms a current. Due to the repulsion of the same charges, the current is the largest at first, and then gradually decreases. During the charge movement, the charge stored in the capacitor plate continues to increase, and the charge stops moving when the voltage between the two plates of the capacitor is equal to the power supply voltage. That is, the current I=0, the switch is closed, and the positive and negative plates of the capacitor are neutralized through the connection of the wires. When the switch is closed, the positive charge of the positive pole of the capacitor can be moved to the negative pole and neutralized. When the charge gradually decreases, the current decreases, and the voltage gradually decreases to zero. Ⅱ Why Capacitor Charges in DC? Why is there a charging current that lasts for a period of time when using DC to charge a capacitor? At this time, the circuit is equivalent to an open circuit, there is no continuous current without a loop, and the capacitor charging has time, not instantaneously, so the instantaneous current is not the answer. Having a potential difference, how does a circuit without a closed loop produce a charging current that lasts for a period of time? Figure 1. Transition Process When Charging the Capacitor The voltage across the capacitor is not allowed to change suddenly. So when the power is turned on, the voltage across the capacitor is equal to zero, and then the voltage rises exponentially until it enters a steady state. The capacitor after entering the steady state is equivalent to an open circuit. In fact, the capacitor can block the constant direct current and disconnect when it fully charged in the circuit. According to the leakage resistance of the capacitor, the charge can be stored in the capacitor for a long period of time.When Usr is instantly added to the resistor-capacitor circuit, because the voltage across the capacitor is not allowed to change suddenly, the capacitor is equivalent to being short-circuited at this time. So at time 0, the current flowing through the capacitor and resistor R is .Then the capacitor began the charging process, and the current became smaller and smaller. After 5 times the RC time, the capacitor charging is basically over and the current is reduced to zero. Since then, it has entered a steady state. The RC(τ) here is called the time constant.We know that resistance is equal to the ratio of voltage to current, that is, R=U/I. We also know that the capacitance C is equal to the ratio of the electric quantity Q to the voltage U, and the electric quantity Q is equal to the product of the current I and the time t .It turns out that the product of resistance and capacitance is time. The unit of resistance is ohms and the unit of capacitance is farads, so the unit of time is seconds.In Figure 1, when the capacitor is charged, the voltage across it is .We find Uc when t=0, 1RC, 2RC, 3RC, 4RC, and 5RC, as follows: It can be seen that when time t=0, the voltage across the capacitor is equal to zero; when t=5RC, the voltage across the capacitor is almost equal to the input voltage.Let's look at the current flowing through the capacitor, its expression is as follows: When t=5RC, where .It can be seen that the current at this time is almost equal to zero. Therefore, the transient process and steady-state process of the capacitor must be clearly distinguished. Ⅲ Capacitor Transient and Steady-state Processes 1) There are transient and steady-state processes in the capacitor charging circuit.2) At the beginning of capacitor charging, it must be considered that the voltage across the capacitor does not allow sudden changes, which is an important principle.3) The transient process generally ends after 5τ.4) For Figure 1, at the moment of the transient start, the capacitor voltage Uc is equal to zero, and the current Ic is equal to the maximum value. We know from Ohm's law that the equivalent resistance of the capacitor is equal to zero . Usually we say that the capacitance at this time is equal to the short circuit i. In the steady state at the end of the transient, the capacitor voltage Uc is equal to the input voltage Usr, and the capacitor current Ic=0. According to the Ohm's law that the equivalent resistance of the capacitor is equal to infinity . At this time, the capacitance is equivalent to an open circuit.5) If the input signal voltage is a short pulse, the capacitor can transmit the signal to the load; if the input signal is a constant voltage, the capacitor will only respond during a short transition, and then block the input signal; if the input signal is an AC signal, which is exactly in the middle of the above two situations.The higher the frequency of the AC signal, the easier it is to pass through the capacitor. We call this feature a high-pass filter function. Although the AC signal can pass through the capacitor, there will be a certain amount of clipping. This shows that the capacitor has the function of isolating DC in the steady state, and a high-pass characteristic. So we can further analyze, any circuit with capacitor and inductor, we must analyze the circuit according to the transient state and the steady state, in order to get the correct analysis result. Ⅳ Capacitor Circuit Analysis and Calculations The analysis is available from the figure below: Figure 2. Output Voltage Usc If set Usr=10Vdc, the capacitance is equal to 10 microfarads, and the resistances R1 and R2 are both 1 kiloohm, then how to analyze the value of Usc?Step 1: Determine the time constant of the capacitor. Figure 3. Usr in Short-circuit Connection From the analysis of the above figure, it can be seen that the time constant is 20 milliseconds , and the time for 5 times the time constant is 0.1 seconds.Step 2: Let's calculate the specific value of Usc.When Usr in Figure is just established, the capacitor voltage drop is equal to zero, so there is .After 5τ, the capacitor is full of voltage, and its value is Uc=Usr, so Usc=0, .When charging starts, t=0, When the time has passed 0.1 second, we have , and the Usc at this time is almost equal to zero. Now, let's connect R1 and C in parallel, and see what happens: Figure 4. R1 and C are Connected in Parallel We see that if Usr in the figure is short-circuited, R1 and R2 are connected in parallel, so the time constant is At the beginning of Usr power on, C is equivalent to a short circuit, and Usr is directly loaded on both ends of the resistor R2, so at this time Usc=UseWhen the circuit enters a steady state, Usc is equivalent to the partial pressure of Usr by resistors R2 and R1, namely Based on this, we can derive the following equation: .In the above formula, the first term on the right side of the equal sign is the change in capacitor voltage, which reflects the transition process. The second term on the right side of the equal sign is the final steady-state voltage.Substitute the parameters, and calculate the time constant first: .In other words, when the time is 5τ, that is, 25 microseconds, the output voltage tends to stabilize. The final value is .It is still 5V, but the transition process is only 25 microseconds, which is much shorter than the previous 0.1 second. Ⅴ FAQ 1. When a capacitor is charging in a DC circuit?At this point, the electric field between the plates cancels the effect of the electric field generated by the battery, and there is no further movement of charge. Thus, if a capacitor is placed in a DC circuit then, as soon as its plates have charged up, the capacitor effectively behaves like a break in the circuit. 2. What happens to the current in a DC circuit once a capacitor is charged?For a capacitor charge Q = capacitance C multiplied by voltage V. This quite simply means that a rate of change of voltage gives rise to a current. If the voltage is rising linearly with time, the capacitor will take a constant current and once the voltage stops changing the current is zero. 3. Does current flow in a DC circuit while a capacitor is charging?Yes. For DC circuits, when a capacitor is charged or discharged, current is flowing into and out of it. For AC circuits, a capacitor can act almost like a "resistor" but instead it is called reactance. But alas, current does flow through the capacitor. 4. Do capacitors charge with AC or DC?When DC current is applied to a circuit with only resistance and capacitance, the capacitor will charge to the level of the applied voltage. Since DC only flows in one direction, once the capacitor is fully charged there is no more current flow. 5. Can we use capacitor in DC?Capacitors can be used in many different applications and circuits such as blocking DC current while passing audio signals, pulses, or alternating current, or other time varying wave forms. ... At DC a capacitor has infinite impedance (open -circuit), at very high frequencies a capacitor has zero impedance (short-circuit). 6. Can a capacitor be charged by DC?When capacitor is connected to dc voltage source, capacitor starts the process of acquiring a charge. This will built up voltage across capacitor. Once capacitor has acquire enough charge, current starts flowing and soon capacitor voltage reaches at value approximately equal to dc source voltage. 7. Why does AC pass through capacitor but not DC?Capacitors have two parallel metallic plates placed close to each other and there is a gap between plates. A capacitor blocks DC but it allows AC. ... Therefore the electrons flowing in one direction (i.e. DC) cannot pass through the capacitor. But the electrons from AC source seem to flow through C. 8. What happens when capacitor is connected to DC?When capacitors are connected across a direct current DC supply voltage, their plates charge-up until the voltage value across the capacitor is equal to that of the externally applied voltage. ... Then the Capacitance in AC circuits varies with frequency as the capacitor is being constantly charged and discharged. 9. Why capacitor is used in DC circuit?Capacitors are useful to reduce the voltage pulsation. When the high voltage is applied to the parallel circuit, the capacitor is charged, and on the other hand, it is discharged with the low voltage. While electricity flowing out is alternating current, most of electronic circuits work with direct current. 10. Why do capacitors block DC current?We know that there is no frequency i.e. 0Hz frequency in DC supply. If we put frequency “f = 0″ in the inductive reactance (which is AC resistance in capacitive circuit) formula. If we put XC as infinity, the value of current would be zero. That is the exact reason why a capacitor block DC. 11. How is a capacitor charged in a DC circuit?When used in a direct current or DC circuit, a capacitor charges up to its supply voltage but blocks the flow of current through it because the dielectric of a capacitor is non-conductive and basically an insulator. ... At this point the capacitor is said to be “fully charged” with electrons. 12. Which capacitor is used in DC circuit?Decoupling capacitor is used, where we have to decouple the two electronics circuits. In other words, the noise generated by one circuit is grounded by decoupling capacitor and it does not affect the performance of other circuit. 13. Can you charge a capacitor with DC current?A DC voltage source is used to charge a Capacitor. When the DC voltage source is outputting more than the DC voltage source can charge, the Capacitor will charge up. Capacitors will charge up to 9 volts if they are connected to a 9-volt battery. 14. What happens if DC is applied to capacitor?When capacitors are connected across a direct current DC supply voltage, their plates charge-up until the voltage value across the capacitor is equal to that of the externally applied voltage. ... Then the Capacitance in AC circuits varies with frequency as the capacitor is being constantly charged and discharged. 15. Can we charge capacitor with DC current?When capacitor is connected to dc voltage source, capacitor starts the process of acquiring a charge. This will built up voltage across capacitor. Once capacitor has acquire enough charge, current starts flowing and soon capacitor voltage reaches at value approximately equal to dc source voltage.
Introduction The audio power amplifier is a device used to drive the speaker to produce sound, thereby reproducing the sound. It is used in all electronic products that produce sound, which amplifies the smaller audio signal, increases its power, and then outputs it. Pre-amplification mainly used for small signals, and amplifies the voltage of the input audio small signals by using a non-inverting amplifier circuit to obtain the input required by the latter stage. The latter stage mainly amplifies the power so that it can drive the resistor to obtain the required audio. Making an Audio Power Amplifier Catalog Introduction Ⅰ What is Power Amplifier Distortion? Ⅱ Types of Audio Power Amp Distortion 2.1 Harmonic Distortion (THD) 2.2 Intermodulation Distortion (IMD) 2.3 Transient Distortion 2.4 AC Interface Distortion Ⅲ Conclusion Ⅳ FAQ Ⅰ What is Power Amplifier Distortion? Distortion is the phenomenon that the input signal and the output signal change in the amplitude proportional relationship, phase relationship and waveform shape. The distortion of audio power amplifiers is divided into electrical distortion and acoustic distortion. The former is caused by the circuit, and the latter is caused by the speaker of the sound reproduction device. The types of electrical distortion are: harmonic distortion, intermodulation distortion, and transient distortion. The acoustic distortion is mainly the distortion of the AC interface. According to the nature, there are nonlinear distortion and linear distortion.Linear distortion refers to the change in the amplitude and phase relationship between signal frequency components, and only the amplitude and phase distortion of the waveform appear. The characteristic of it is that no new frequency components are generated. Figure 1. Linear Distortion Non-linear distortion means that the signal waveform has been distorted and new frequency components have been generated. Ⅱ Types of Audio Power Amp Distortion The main points of distortion produced by audio power amplifiers are as follows: 2.1 Harmonic Distortion (THD) 🔸What is THD?This distortion is caused by non-linear components in the circuit. After the signal passes through these components, new frequency components (harmonics) are generated, which affect the original signal. The characteristic of this distortion is the input signal waveform inconsistent with the shape of the output signal. That is, the waveform is distorted. The following is a specific analysis.Harmonic distortion refers to the more harmonic components of the output signal than the input signal. It is caused by a system that is not completely linear. The sum of all additional harmonic levels is called total harmonic distortion, which is related to frequency. Generally speaking, at a frequency of 1000Hz, the distortion is the smallest. So many products confirm the distortion at this frequency as a indicator.Harmonic distortion is actually the distortion of the sound when the speaker reproduces the sound due to the resonance phenomenon that occurs during the working process of the speaker. Although only the fundamental frequency signal in the speaker is the original sound signal, due to the inevitable resonance phenomenon (the second, third and even multiple harmonics are generated on the basis of the original sound wave), there is no longer only the fundamental frequency signal in the sound signal, but also includes harmonics and their frequency multiplier components. These frequency multiplied signals will cause distortion when the speaker is playing. For ordinary speakers, a certain harmonic signal component is allowed, but it must be a prerequisite that it does not have a large impact on the sound fundamental frequency signal output.The total harmonic distortion usually expressed as a percentage. Generally speaking, the smaller the value, the better. Generally speaking, the THD value of high-quality equipment is very low (less than 0.002%), but there are exceptions. Many electronic tube devices have very high THD, but transistor devices must have low THD because their excess harmonics can make the sound uncomfortable. 🔸How to Calculate THD? In the above formula, G represents the effective value of the harmonic component. It will be replaced by I when expressing current and U when expressing voltage as required. The value of H is given in each standard related to the limit. According to the above definition, THD does not include interharmonics, and there is a fixed upper limit of harmonics. In the above formula, Q is the total effective value, and Q1 is the fundamental effective value, which can represent the voltage or the current. According to the above definition, THD includes interharmonics and DC components. 🔸How to Reduce THD?The main ways to reduce harmonic distortion are: 1) Apply an appropriate amount of negative feedback. 2) Choose amplifiers with high characteristic frequency, low noise figure and good linearity. 3) Increase the power reserve of the power supply and improve the filtering performance of it. 2.2 Intermodulation Distortion (IMD) 🔸What is IMD?This distortion is usually produced by active devices in the circuit (such as transistors and tubes). Two or more signals of different frequencies pass through an amplifier or speaker to produce beats and form new frequency components. The magnitude of the distortion is related to the output power. Since these newly generated frequency components have no similarity with the original signal, the less intermodulation distortion is also easy to be noticed by the human ear. 🔸How to Calculate IMD?The excitation signal used in the measurement technique of IMD is more than a single simple sinusoidal signal. In the fields of professional audio, broadcasting and consumer audio, two sine waves are used as excitation signals to measure it. When any two sine signals with frequencies of F1 and F2 are applied to the nonlinear device, the original two sine waves will be generated plus countless IMD terms, that is, countless combined frequency components, as shown in the following formula: mF1±nF2Where m and n are any positive integers. The order of any particular IMD value is the sum of m and n. The order of some terms are listed below:F1-F2 2nd order (even order)F1+F2 2nd order (even order)2F1-F2 3rd order (odd order)F1-2F2 3rd order (odd order)2F1+F2 3rd order (odd order)3F1-F2 4th order (even order)3F1+2F2 5th order (odd order)…….The above "odd" and "even" refer to whether m+n is odd or even.The measurement method of IMD is actually the measurement of harmonic voltage components, and its formula is:Where, F1 is high frequency, F2 is low frequency. 🔸How to Reduce IMD?Methods to reduce intermodulation distortion: 1) Use electronic frequency division to limit the working bandwidth of the amplifier circuit or loudspeaker, thereby reducing the generation of beats. 2) Choose a tube or circuit structure with good linearity. 2.3 Transient Distortion Transient distortion is an important indicator of modern acoustics. It reflects the ability of the power amplifier circuit to keep track of transient signals, so it is also called transient response. This kind of distortion makes music lack level or transparency, and there are two forms of expression: 🔸A. Transient Intermodulation Distortion (TIM)When inputting a pulsed transient signal, the output terminal cannot get the proper output voltage immediately due to the capacitance in the circuit, and the negative feedback circuit cannot get a timely response. The amplifier is in an open loop state at this moment, making the output instantaneous. Clipping occurs due to overload. This clipping distortion is called transient intermodulation distortion, and it is more serious on transistor machines.Transient intermodulation distortion is a dynamic indicator of the power amplifier, which is mainly caused by the deep negative feedback inside the power amplifier. It will affect the sound quality of the stone machine and cause "transistor noise" and "metal noise".The main methods to reduce this distortion are as follows: 1) The TIM can be eliminated by controlling the gain within the delay time of the negative feedback amplifier. 2) Multistage negative feedback can be used, so it is not easy to cause TIM due to fast feedback time and short path.3) Take well anti-interference measures. 🔸B. Distortion Caused by Too Low Conversion RateAs mentioned above, high-level input pulses cause the amplifier to clip and then cause transient intermodulation distortion. Will low-level input pulses cause distortion? It depends on the response time of the amplifier. Because the response time of the amplifier is too long, the change of the output signal of the amplifier cannot keep up with the rapid change of the input signal. The transient distortion is caused by the low conversion rate. It reflects the response speed of the amplifier to the signal. This low-distortion amplifier has very good sound quality resolution, layering and positioning. 2.4 AC Interface Distortion The distortion of the AC interface is caused by the back EMF of the speaker (the electric potential generated by cutting the magnetic lines of force when the speaker sounds vibration) feedback to the circuit.The improving methods are:1) Reduce the output impedance of the circuit.2) Choose a suitable speaker to make the damping coefficient more reasonable.3) Reduce the internal resistance of the power supply. Ⅲ Conclusion For different types of audio power amplifiers, due to the differences the circuit itself, their sound is different. Transistor power amplifiers are affected by odd harmonic distortion and transient intermodulation distortion, and the sound will be cold, straightforward, burr or metallic. The sound of the tube amplifier is warm, thick, and stretched. So far, the electronic tube is still the active amplifier device with the best linearity and the smallest native distortion, and the transistor cannot be compared. But in fact, the total harmonic distortion (THD) of the tube power amplifier is several orders of magnitude larger than that of the transistor power amplifier. This is because it is difficult to add sufficient negative feedback to improve the linearity of the tube power amplifier. Most of these non-linear distortions are even harmonics that are pleasing to the ears, but they make people feel pleasant to the ears. The transistor power amplifier uses a large loop deep negative feedback to significantly improve the linearity. Due to the stability requirements, a compensation capacitor is introduced as the main pole. However, it may cause a problem of poor transient response. With the advancement of technology, the sound quality of integrated chip audio power amplifiers is getting closer and closer, even surpassing the above two types of power amplifiers, and it also has obvious advantages in terms of volume, cost, and scope of application. Ⅳ FAQ 1. What is power amp distortion?The short answer is that power amp distortion derives from overloading/distorting an amplifier's power section. After the preamp portion of an amplifier is 'done' with the signal, it is then passed on to the phase inverter and out to the amp's power tubes. 2. Why is my amp distortion?You can create distortion by merely increasing the volume of your guitar and setting the input gain high enough on your amplifier. This combination of volume and preamp gain will create distortion as explained above, the gain exceeding the voltage capacity, causing the sound waves to clip. 3. Is amp distortion better than pedal distortion?Distortion pedals are considered more versatile with more parameters to shape your ideal sound. Their downfall is that some cheap pedals can sound unnatural. In contrast, the majority valve amp distortion provides a more, smoother, and overall, more well-rounded distortion. 4. How do I adjust the distortion on my amp?Turn knobs marked "gain" or "overdrive" all the way up. Turn other volume knobs down to get the loudness you want. Once you've proved you can get heavy distortion, dial things back to find the tone you want. Some amps won't distort at low volumes. 5. Do amps have built in distortion?The answer to the question do all guitar amps have distortion is no; not all guitar amps have distortion. In fact, there are different categories you could place guitar amps in depending on how they generate their distortion. 6. Does preamp reduce distortion?Preamp distortion generally offers higher gain than power amp distortion and is more compressed and smoother, with higher sustain at lower volume levels. ... In general, vintage-style amps sound best when driven into power amp distortion — depending on the amp, its preamp may not even be able to distort. 7. Do tube amps need distortion pedals?Most tube amps won't need a distortion pedal, digital or otherwise. When an amp has both a dirty (gain) and a clean channel, this allows you to dial your distorted tones along with whatever clean sound you might want to use. 8. Can you use a distortion pedal without an amp?Most modern multi-effects pedals have a jack where you can plug in any speakers or headphones. This means you can play an electric guitar without an amp by using a multi-effects pedal. Simply plug your guitar into a suitable multi-effects pedal and plug headphones or speakers into the pedal. 9. What amp is good for distortion?Top 5 Amps for Creating Clean and Distortion Sounds1) Orange Micro Terror2) Blackstar HT1R3) Peavey Vypyr VIP 14) Fender Champion 205) Marshall MG50CFX 10. Why is my audio distorted?The most common reason for distortion is an input overload like the microphone overload mentioned above. Mic'ing an instrument, or even a vocal, is more than sticking a microphone right up to the sound source. ... A distorted sound can be resolved by placing a greater distance between the sound source and the microphone.
Introduction As a beginner, what the functions of capacitors in a circuit? A Capacitor is a passive electronic component that stores and releases the energy. Its unique characteristic is blocking direct current while allowing alternating current to pass. The main functions of capacitors are based on these characteristics. The use of capacitors is also based on this. Here are collecting 20 questions about capacitor use in electronics enclosed with details. Let you have a more comprehensive understanding of the use of capacitors. How Capacitors Work? 20 Questions about the Role of Capacitors in Circuits Help you learn about capacitors functions in 30 minutes. These questions forcus on how capacitors work, where capacitors are used, why capacitors are used, the different types. 1) What is the function of a capacitor connected in parallel with the positive and negative terminals of the voltage source?When cap used in a rectifier circuit, it has a good filtering effect. When the voltage is alternating, the voltage at both ends cannot be changed suddenly due to the charging effect of the capacitor, which ensures the stability of the voltage. When cap used as a battery power supply, it is equivalent to short-circuiting the battery's AC signal, avoiding the increase in battery internal resistance and parasitic oscillation of the circuit due to the battery voltage drop. 2) A capacitor in series or in parallel can achieve the effect of coupling in the circuit. What is the difference between whether there is a capacitor in the circuit?In the AC multi-stage amplifying circuit, because of the different gains and powers of each stage, the DC working offset values of each stage are different. If the levels are directly coupled, it will cause the bias values of all levels to be mixed and unable to work normally. The “Pass AC, Block DC” characteristic not only solves the coupling of inter-stage exchanges, but also isolates the inter-stage biased value intermixing. 3) The two coupling capacitors in the basic amplifying circuit, the positive pole of the capacitor and the DC positive pole are connected to pass the AC and block the DC. Can the reverse connection also have this function?If the connection is reversed, the electrolytic capacitor will leak, which will change the DC operating point of the circuit and make the amplifying circuit abnormal or unable to work. 4) What is the role of the capacitor in the resistance-capacitance coupling amplifier circuit?Block the DC signal so that the static operating points of adjacent amplifying circuits are independent of each other and do not affect each other. 5) Can the analog circuit amplifier do not have a coupling capacitor? The theory in amplifier circuit adds a coupling capacitor between the transformer secondary coil and the transistor. Turn the output of the former stage into the input of the latter stage, so that two stages do not affect. The former stage is alternating current, so does the latter stage, so there no mutual influence.The former stage is indeed alternating current, but the latter stage is alternating current superimposed direct current. The transistor needs a DC bias. If there is no capacitor to block the DC, the coil of the transformer will bypass the DC bias of the transistor (because the inductor passes DC). 6) In the basic amplifier circuit, can the coupling capacitor be non-polar?In the basic amplifying circuit, the coupling capacitor depends on the frequency. When the frequency is high, a non-polar capacitor is needed. It is characterized by relatively stable, high withstand voltage, small size and capacity. Its biggest use is to block direct current and pass alternating current. Coupling capacitor is widely used in high-frequency alternating current paths, bypass, resonance and other circuits. (high-pass)When the frequency is low, since the capacitance of the non-polar capacitor is relatively low, the capacitive reactance is relatively increased, so it is necessary to use a polar electrolytic capacitor. Because of the electrolyte inside, the capacity can be made large, allowing low-frequency alternating current to pass. However, because of the organic medium between the internal two poles, the withstand voltage is limited. Non-polar capacitor is mostly used in circuits such as low-frequency AC paths, filtering, decoupling, and bypassing. (low-pass) 7) In a battery-powered circuit, why does the capacitor charging and discharging have the delay effect?Capacitors accumulate electric charge. During the charging process, the voltage rises slowly, while discharging vice versa. During charging, at the beginning, the voltage across the capacitor is zero, as the time goes by, the voltage gradually rises to the voltage you set to control the switching of the circuit. Of course, the discharging process can also be used to achieve this. The delay time is related to capacitor capacity, capacitor leakage, charging resistance, voltage, and sometimes the load resistance is also taken into consideration. 8) The resistance-capacitance coupling amplifier circuit can only amplify AC signals, but cannot amplify DC signals?Capacitor is an electronic component that blocks DC and AC. Therefore, the resistance-capacitance coupling amplifier circuit can only amplify AC signals. A direct coupling amplifier circuit is used to amplify DC signals. 9) How to tell the coupling capacitor and the bypass capacitor in the amplifying circuit?The negative pole of the coupling capacitor is not grounded, but is connected to the input of the next stage, and the negative pole of the bypass capacitor is grounded. 10) How to choose coupling capacitor for the multi-stage AC amplifier circuit?Generally ceramic capacitors can be done, and tantalum capacitors can be used if the performance is good. According to the frequency range of your input signal, capacitance of 103,104 can be used for high frequencies, and also electrolytic capacitors of about 22uF can be used for lower frequency AC signals. 11) The amplifying circuit adopts direct coupling, and the feedback network is a pure resistor network. Why is the circuit only possible to produce high-frequency oscillation?The oscillation comes from the phase shift of the closed loop reaching 180 degrees and the loop gain at this time is greater than zero. Using a pure resistor network as a feedback network will definitely not have phase shift, which comes from the open loop circuit of the amplifier only. Using a direct-coupled open-loop amplifier, there will be no capacitive elements between stages that will cause phase shifts, but the capacitor inside the transistor or MOS tube will cause it. These capacitances are all fF, the maximum is pF. The resonant frequency of the circuit composed of these capacitors and the equivalent resistance of the circuit is quite high. Therefore, the amplifier adopts direct coupling, with a pure resistor feedback network, which can only produce high-frequency oscillations. 12) How to estimate the output resistance of the first-stage amplifier and the input resistance of the second-stage amplifier? When the amplitude of the signal source is too large, what will happen at the output of the two-stage amplifier? Shake the input end of the amplifier and observe the output end to see what appears? why?A. The input resistance of the second stage amplifier is the output resistance of the first stage amplifier. B. Have distortion. C. Cause clutter due to human body induction. 13) How to use the charge and discharge of capacitors to understand filtering, decoupling and bypassing?Capacitors block DC and pass AC. Blocking DC is easy to understand, but passing AC is not easy to understand. As long as you understand it, you can understand filtering, decoupling and bypass.Capacitors are charging and discharging, but the direction of alternating current changes alternately. The magnitude of the amplitude also changes periodically. The entire changing image is a sine curve.The capacitor is connected to the AC circuit, and due to the periodic change of the AC voltage, it is also periodically changes. There is a charging and discharging current in the line. This charging and discharging current has the same shape as the voltage except that the phase is 90 degrees ahead of the voltage, which is equivalent to the AC passing through the capacitor.The alternating current passing through the resistance consumes electric energy (heating) on the resistor. However, the capacitor only exchanges energy with the power supply. The power supply sends energy to the capacitor when charging, and the capacitor returns the electrical energy to the power supply when discharging. Therefore, the power generated by multiplying the voltage by the current here is called reactive power.What needs to be clear is that when the capacitor is connected to an AC circuit, the flowing electrons (current) do not really rush through the insulating layer, but generate current in the circuit. This is because in the circuit, reverse discharge and forward charge are in the same direction, the forward discharge and reverse charge either. Understand that the capacitor is connected to AC, then the AC component is bypassed to the ground, and also the filtering is completed. 14) How to use bypass capacitor, filter capacitor and decoupling capacitor respectively?These three types of capacitors are actually used for filtering, but they are used in different circuits, so their names and usages are different.Filter capacitor, this is the capacitor we usually use after power rectification. It is a capacitor that rectifies the AC of the rectifier circuit into a pulsating DC and smoothes it by charging and discharging. This type of capacitor is generally an electrolytic capacitor with a large capacity.Bypass capacitors are used to filter out the high frequency components in the input signal. They are mainly used to filter high frequency clutter. Usually, ceramic capacitors and polyester capacitors are used. The capacity is small and is at the picofarad level.The decoupling capacitor takes the interference of the output signal as the filtering object. It is equivalent to the battery and uses its charge and discharge so that the amplified signal will not be interfered by the sudden change of the current. Its capacity depends on the frequency of the signal and the degree of ripple suppression. 15) Regarding the function of the capacitor, under what circumstances use the coupling capacitor and under what circumstances use the filtering capacitor?After the alternating voltage is applied to the two ends of the capacitor, it will continue to charge and discharge with the alternating frequency of the current. At this time, there is an alternating current of the same frequency in the circuit, which is the passing characteristic of the capacitor.When the frequency is appropriate, the capacitor can be regarded as a path to the circuit, and the AC output of the previous stage can be transmitted to the subsequent circuit through the capacitor.For direct current, it is isolated, because when the voltage at both ends is charged to be equal to the circuit voltage, there will be no more charging current.When acting on the transmission of front and rear AC signals, it is coupling, and when acting on filtering out fluctuation components and useless AC components, it is filtering. 16) The capacitor filter of the rectifier circuit uses its charge and discharge, but sometimes the filter uses the capacitor to have a different capacitive reactance to the non-pass frequency signal, such as a bypass capacitor. So which point is used when analyzing capacitor filtering?The theoretical explanation of using capacitor characteristic is more general, and the theory using capacitive reactance is more in-depth. The role of capacitor is to use its charge and discharge characteristics, depending on what components you want to filter out. Use large capacitors to filter low frequencies and a small capacitor for high frequency. In theory, the filtering in the low-frequency rectifier circuit and the bypassing in the high-frequency circuit are the same, and the difference is the capacitive reactance. 17) After the filter capacitor is fully charged, it will discharge the back circuit and then in cycle?Such a working process in the circuit, capacitor is related to the frequency of the signal. First of all, it depends on what you want to put the capacitor in the circuit. When used as a filter, it filters out a certain frequency signal to the ground. For example, the capacitors at the front end of the chip power supply are decoupling. The phenomenon you mentioned is like the filter capacitor before the voltage regulator is turned off and the filter capacitor of the switching power supply. 18) What is the specific coupling of capacitors? Is there any difference compared with filtering?Coupling refers to the process of signal transmission from the first stage to the second stage, and usually refers to AC coupling when it is not specified. Decoupling refers to taking further filtering measures on the power supply to remove the influence of mutual interference between the two levels of signals through the power supply. The coupling constant refers to the time constant corresponding to the product of the coupling capacitance value and the second-stage input impedance value.Decoupling has three purposes: D.Remove the high-frequency ripple in the power supply, and cut off the high-frequency signal of the multi-stage amplifier through the crosstalk path of the power supply.E.When the large signal is working, the circuit's demand for the power supply increases, causing the power supply fluctuations, here decoupling reduces the impact of power fluctuations on the input stage/high voltage gain stage during large signals.F. Form a floating ground or floating power supply, and complete the coordination of various parts of the ground or power supply in a complex system.The high-frequency switching noise generated by the active device during switching will propagate along the power line. The main function of the decoupling capacitor is to provide a local DC power supply to the active device to reduce the noise on the board and to guide it to the ground. 19) How to distinguish whether the capacitor in the circuit is a filter capacitor or a bypass capacitor?The filter capacitor is in the power circuit; the bypass capacitor is in the signal circuit.In fact, their function is basically the same. The filter capacitor: Bypasses or filters out the pulsating current components and plays the role of charging and discharging. Bypass capacitor: Filter or bypass high frequency or low frequency components in the circuit. 20) Is the coupling capacitor a decoupling capacitor?It is completely different. The coupling capacitor is for signal transmission, and the decoupling capacitor is for reducing interference.
IntroductionThe Temperature Sensor, a measuring instrument, uses various physical properties of a substance to convert the thermal quantity into the physical quantity, including expansion, resistance, capacitance, electromotive force, magnetic properties, frequency, optical characteristics and thermal noise. Many materials and components change with temperature, so there are quite a few materials that can be used as temperature sensors. Here are four temperature sensors in detail.Temperature Sensors ExplainedCatalogIntroductionⅠ Temperature Sensor Types Overview1.1 What is Thermocouple?1.2 What is Thermistor Sensor?1.3 What is Resistance Temperature Detector (RTD)?1.4 What is IC Sensor?1.5 Temperature Sensor Cons and ProsⅡ How to Test: Measuring IndexesⅢ FAQⅠ Temperature Sensor Types OverviewThere are many types of temperature sensors, which can be divided into contact type and non-contact type according to the measurement method; thermistor and thermocouple according to the characteristics of sensor materials and electronic components.The contact temperature sensor needs to maintain thermal contact with the measured medium, so that the two can perform sufficient heat exchange to reach the same temperature. This type of sensor mainly includes resistance type, thermocouple, PN junction temperature sensor and so on. The non-contact temperature sensor does not need to be in contact with the measured medium, but achieves the purpose of temperature measurement through the heat radiation or convection of the measured medium.Here is a detailed introduction to the commonly used four: Thermocouples, Thermistors, Resistance Temperature Detector (RTD), IC Sensor.Figure 1. Temp Sensors (Resistance Changes with Temperature)1.1 What is Thermocouple?Thermocouples are the most commonly used temperature sensors in measurement. Its main advantages are wide temperature range and adaptability to various atmospheric environments, and it is strong, low in price, does not require power supply, and is also the cheapest. The thermocouple consists of two different metal wires connected at one end. When one end of the thermocouple is heated, there is an electric potential difference in the thermocouple circuit, and the measured electric potential difference can be used to calculate the temperature.Figure 2. Metal JunctionsThe thermocouple sensor has two contacts. The measurement end (sometimes called the hot end) is where the two metals connect. The reference junction (also called the cold end) is connected to the measurement circuit. When there is a temperature difference between two ends, an mV signal proportional to the temperature difference is generated. The mV value increases with increasing temperature. The relationship between mV and temperature is non-linear.The thermocouple connector can be constructed by connecting the thermal junction to the outer sheath for grounding or ungrounding (insulating from the sheath). A grounded thermocouple responds faster, but the thermocouple will contact the processing voltage. Therefore, it is important to isolate the measurement circuit to prevent the formation of ground loops and to avoid measurement errors.Figure 3. Thermocouple for Temperature MeasurementInside the temperature component, the thermocouple is usually embedded in magnesium oxide (MgO) and a metal sheath, then insert it into the thermowell or protective tube. This helps protect the sensor from environmental pollution. When magnesium oxide is contaminated with water and salt, even thermocouples that are not grounded will eventually be grounded.As above mentioned, the relationship between voltage and temperature is nonlinear, so it is necessary to make a second measurement for the reference temperature (Tref), and use the test equipment software or hardware to process the voltage-temperature conversion inside the instrument to finally obtain the thermocouple temperature (Tx). Thermocouple is the simplest and most versatile temperature sensor, but its sensitivity is relatively low, which is easy to be affected by environmental interference signals, and the temperature drift of the preamplifier. So it is not suitable for measuring small temperature changes, that is, it is not suitable for high-accurate measurement and application.In actual use, the thermocouple measuring circuit can measure any temperature except 0°C. The measuring circuit must measure the temperature of the cold junction and restore the temperature to 0°C. This kind of electrical compensation is called cold junction compensation (or reference junction compensation). Most thermocouple measurement circuits do this.If the application requires a thermocouple instead of a thermistor, a higher-grade thermocouple is better. In addition, their cost difference is small, and high-quality wire can provide higher stability.🔺Table 1: Thermocouple Types and Application RangesThermocouple TypeApplication Range (℃ / ℉)E95-900℃ (200-1650℉)J95-760℃ (200-1400℉)K95-1260℃ (200-2300℉)N95-1260℃ (200-2300℉)R870-1450℃ (1600-2640℉)S980-1450℃ (1800-2640℉)T0-350℃ (32-660℉) 1.2 What is Thermistor Sensor?The main component of the thermistor sensor is the thermistor, which absorbs heat radiation around.Thermistors are made of semiconductor materials, mostly with a negative temperature coefficient, that is, the resistance decreases with increasing temperature. Temperature changes will cause large resistance changes, so it is the most sensitive temperature sensor. However, the linearity of the thermistor is extremely poor and has huge effects with the production process. So the manufacturer cannot give a standardized thermistor curve.The thermistor is very small and responds quickly to temperature changes. But it needs to use a current source, and its small size also makes it extremely sensitive to self-heating errors.Figure 4. Thermistor SensorThe thermistor measures the absolute temperature on the two lines, with better accuracy, but it is more expensive than a thermocouple, and the measurable temperature range is also smaller than that of a thermocouple. A commonly used thermistor has a resistance value of 5kΩ at 25°C, and a temperature change of 1°C causes a resistance change of 200Ω. Note that the lead resistance of 10Ω only causes a negligible error of 0.05°C. It is very suitable for current control applications that require fast and sensitive temperature measurement. Small size is benefit for applications with space requirements, but care must be taken to prevent self-heating errors.Figure 5. Resistance-TemperatureThe thermistor also has its own measurement tips. With small size, it can quickly stabilize, and will not cause thermal load. However, it is not strong enough, and large currents can cause self-heating. Since the thermistor is a resistive device, any current source will cause heat on it due to power. Power is equal to the product of current squared and resistance. Therefore, a small current source must be used. If the thermistor is exposed to high heat, it will cause permanent damage. 1.3 What is Resistance Temperature Detector (RTD)?RTD is a precision temperature sensor, made of high-purity conductive metal (such as platinum, copper or nickel) or alloy. Its resistance increases with increasing temperature and decreases with decreasing temperature, similar to a thermistor. RTD is like a thermoelectric converter, converting temperature changes into voltage changes. By passing a constant temperature current through the temperature sensor, an output voltage that increases linearly with temperature can be obtained. The most suitable metal for RTD is a pure metal that remains stable within a given temperature range. The resistance-temperature change relationship is preferably linear. The larger the temperature coefficient (it is defined as the resistance change caused by unit temperature), the better, and it must be able to resist thermal fatigue and respond sensitively to temperature changes. A typical RTD has a protective sleeve and a probe. The protective sleeve is mainly used to protect the RTD from being damaged by the measured medium, which is usually made of stainless steel, carbon steel, inconel or cast iron, and its use temperature can reach 1100°C.Figure 6. Resistance Temperature Detector (RTD)It is currently the most accurate and stable sensor, and its linearity is better than thermocouples and thermistors. However, RTD is also a temperature sensor with slow response speed and more expensive price. So it is most suitable for applications that have strict requirements on accuracy, but speed and price are not critical. 1.4 What is IC Sensor?IC sensors can work in a temperature range of -55°C to +150°C, and precise one can operate at temperatures up to +200°C. It is commonly used in fitness tracking applications, wearable products, computing systems, data loggers, and automotive applications. The most common integrated IC temperature sensors are analog output devices, digital interface devices, remote temperature sensors, and those integrated ICs with thermostat functions.Figure 7. IC Sensors (Thermometer)Analog output devices (usually output voltage, but some also output current) are most like passive solutions when they need an ADC to process the output signal. Digital interface devices most often use a two-wire interface (I2C or PMBus) and have a built-in ADC. In addition to including a local temperature sensor, remote temperature sensors also have one or more inputs to monitor the remote diode temperature—they are most often placed in highly integrated digital ICs (for example, processors or field programmable gate arrays FPGA). When reached the temperature threshold, the thermostat can provide a simple alarm.Here are the details of two common types:🔺Analog Output Temperature SensorThe integrated sensor is made using silicon semiconductor integration process, so it is also called a silicon sensor or a monolithic integrated temperature sensor. It is a dedicated IC that integrates a temperature sensor on a chip and can take temperature measurement and then output analog signals. The main features of this sensor are single function (only measuring temperature), small temperature measurement error, low price, fast response speed, long transmission distance, small size, micro power consumption, etc., which are suitable for long-distance temperature measurement, control and measurement. What’s more, non-linear calibration doesn’t required, and the peripheral circuit is simple.🔺Digital Output SensorDigital temperature sensor is the product of microelectronics technology, computer technology and automatic test technology (ATE). The intelligent temperature sensor contains temperature sensor, A/D converter, signal processor, memory (or register) and interface circuit. Some products also come with multiplexers, central controller, random access memory and read-only memory. The characteristic of the intelligent temperature sensor is that it can output temperature data and related temperature control quantities, adapts to various microcontrollers (MCU). It realizes the test function through software on the basis of hardware, and its intelligent harmony also depends the level of software development.1.5 Temperature Sensor Cons and Pros🔺Table 2: Advantages and Disadvantages of thermocouples, RTDs, thermistors and IC sensors.CriteriaThermocoupleRTDThermistorIC SensorTemperature-250℃ to +750℃-100℃ to +500℃-267℃ to +2316℃-55℃ to +200℃AccuracyBestDepends on calibrationGoodGoodLinearityGoodWorstGoodBestSensitivityLessBestWorstGoodCircuityComplexDepends on accuracy/power requirementsComplexSimplestPower ConsumptionHigh when takingLow-highLowest Ⅱ How to Test: Measuring Indexes1) Measurement accuracy: 0.01 level2) Resolution 0.1uV and 0.1mΩ3) Scan switch parasitic potential: ≤0.4μV4) Temperature range: Water tank: (room temperature +5~95)°C; Oil tank: (95 ~ 300)°C; Low & constant temperature bath: (-80 ~ 100)°C; High temperature furnace: (300~1200)°C5) Temperature control stability: better than 0.01℃/10min (oil tank, water tank, low temperature constant temperature tank); 0.2℃/min (tube type verification furnace)6) Total uncertainty: For thermocouple verification, measurement uncertainty is better than 0.7 ℃, repeatability error <0.25 ℃; For thermistor verification, measurement uncertainty is better than 50 mk, repeatability error <10 mk7) Working power supply: AC220V±10%, 50Hz, and well protected grounding.8) High temperature furnace power: about 2kW9) Constant temperature bath power: about 2kW10) Power of microcomputer measurement and control system: <500 Ⅲ FAQ1. What is temperature sensor and how it works?How do temperature sensors work? They are devices to measure temperature readings through electrical signals. The sensor is made up of two metals, which generate electrical voltage or resistance once it notices a change in temperature. ... Temperature is the most common physical measurement type in industrial applications. 2. What happens when a temperature sensor goes bad?If the coolant temperature sensor goes bad it can send a false signal to the computer and throw off the fuel and timing calculations. ... This will cause the computer to think the engine is cold, even when it is not, and as a result will use more fuel than necessary. 3. Which temperature sensor is best?The most well-known are Pt100 (with a resistance of 100 ohms at 0°C) and Pt1000 (with a resistance of 1,000 ohms at 0°C). The Pt1000 offers better accuracy and a larger tolerance to long wire lengths than the Pt100. Compared to thermocouples, resistance sensors offer better accuracy and a more linear response. 4. What is the application of temperature sensor?Within our homes, temperature sensors are used in many electrical appliances, from our refrigerators and freezers to help regulate and maintain cold temperatures as well as within stoves and ovens to ensure that they heat to the required levels for cooking, air confectioners/heaters. 5. How do I know if my temperature sensor is bad?What Signs May Signal Your Coolant Temperature Sensor May Be Failing.Poor Fuel Economy.Irregular Temperature Readings.Black Smoke from Your Exhaust.Your Engine is Overheating.Your Check Engine Light is On. 6. How important sensors are nowadays?Intelligent sensor systems are omnipresent in our everyday lives. They provide security, save lives and improve our quality of life. As more and more areas of life are automated and networked, the importance of innovative sensor technologies will also increase in the future. 7. What should I consider when choose a temperature sensor?Several factors must be considered when selecting the type of sensor to be used in a specific application: temperature range, accuracy, response time, stability, linearity, and sensitivity. 8. What is the value range of a temperature sensor?The effective operating range is -50 to 250 °C for glass encapsulated thermistors or 150°C for standard thermistors. 9. What are the pros and cons thermocouple?Advantages and disadvantages of thermocoupleAdvantages of thermocouple: Simple working principle, Short response time, Low price, Wide temperature ranges, Rugged construction, Self-powered, Small size.Disadvantages of thermocouple: Nonlinearity, Accuracy, Interference can cause errors. Old technology, Needs calibration, Corrosion. 10. What is difference between PT100 and RTD?There is no difference a PT100 is a version of a RTD (resistance temperature detector). What is an RTD? A resistance temperature detector, also known as an RTD or resistance thermometer, is a type of temperature sensor. ... A PT100 sensor is the most common type of Resistance Thermometer (RTD).
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