5 Remove R2 and replace C1 with a 47pF capacitor. This is a super short video on the functional use of an op amp voltage follower (buffer) circuit. The buffer op-amp circuit. It does what it says on the can; the emitter follows the voltage on the base but that in itself is not even half the story because a bit of wire could do the same. Specifically, by presenting an open (or effectively open) circuit to the preceding voltage amplifier stage, no (or effectively no) signal power is required to drive the voltage follower and thus, no signal power is lost in the output resistance of the voltage amplifier. Any voltage divider composed of the same 2 resistances gives half the voltage of the power supply. Fig. The voltage divider is now between the top 10KΩ resistor and the 10KΩ resistor and op amp at the bottom. Buffers for logic circuits. The voltage gain of the voltage follower is unity (Av = 1). Voltage followers have high input impedance and low output impedance—this is the essence of their buffering action. They can be used to isolate sensors from readout electronics - e.g. the power of the circuit isn't affected when current is feeding a high impedance load. @user16307, a very long cable will have some resistance associated but how much depends on a number of factors and, depending on the frequency of operation, the resistance might be a minor factor compared to others. And, by presenting a zero (or effectively zero) output impedance to the load, there is no (or effectively no) power lost in the output resistance of the voltage follower. This will now be explained. Without voltage follower the voltage at load will be very less compare to input voltage. How it … So, current, as explained above, is one of the reasons voltage followers are used. The circuit can be used as a buffer or driver. Design Description This design is used to buffer signals by presenting a high input impedance and a low output impedance. How to Read a Digital Voltage In Circuitry. But this IC plays a key role in this circuit. They provide unity gain to the applied input signals. This circuit may be adapted to the negative circuit. The voltage divider formula for the voltage across the bottom 10KΩ resistor and the 100Ω resistor is, Smallest known counterexamples to Hedetniemi’s conjecture. high impedance, it draws very little current. So the voltage divider equation is characterized by the following equation, 10KΩ and 10KΩ||100Ω. does paying down principal change monthly payments? Here, I model a voltage amplifier with an open circuit (unloaded) gain of 100 and an output resistance of \$1k \Omega\$. Another way to accomplish logic level shifting or translation is to use an IC called a lev… The output voltage just tracks or follows the input voltage. In the snubber circuit used in a thyristor to limit the peak voltage overshoot applied across it damping ratio is taken as about A) 0.14 B) 0.21 C) 0.36 D) 0.62 50 … Therefore, in a voltage divider circuit, the An op amp circuit is a circuit with a very high input impedance. They can be used for driving ADCs as ADCs can draw current in large bursts when they sample their input, and this can be disruptive to whatever circuitry might be sourcing the signal. According to ohm's law, voltage= current x resistance (V=IR). The first example is the differential amplifier, from which many of the other applications can be derived, including the inverting, non-inverting, and summing amplifier, the voltage follower, integrator, differentiator, and gyrator. The interposed buffer amplifier prevents the second circuit from loading the first circuit unacceptably and interfering with its desired operation Op amp as a Voltage follower A unity gain buffer amplifier may be constructed by applying a full series negative feedback (Fig. nice explanation that was I was asking for. Stack Exchange network consists of 176 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. One is isolating purpose, and the other is for buffering the output voltage from an electrical or electronic circuit to get the desired voltage to the connected load. site design / logo © 2021 Stack Exchange Inc; user contributions licensed under cc by-sa. the circuit outputs the same signal that is fed in. Unity voltage gain capability of voltage follower circuit makes it eligible for obtaining desired output voltage that is analog as well as as digital. A voltage follower (also called a unity-gain amplifier, a buffer amplifier, and an isolation 2) imagine your microcontroller can supply 1 mA but you need at least 10 or 20 mA to drive something (e.g. We need to get 6 volts from a 12 volt source to power a … Voltage followers are generally used to isolate stages from each other. 4 Modify R2 to 20M, then the measured VF1 voltage is 6.5V, and the follower output voltage is 7.3V. the power of the circuit is disturbed very little. They simply don't draw a lot of current, so they do not load down the power source. Voltage followers can be used to isolate filter stages from each other when building multistage filters. load gets very low voltage, since voltage drops across loads in direct proportion to the resistance (V= IR). Output resistance is low. In this circuit above, the load demands and draws a huge amount of current, because the load is low impedance. So you can see how the op amp allowed us to buffer the output of this circuit so that the load receives the voltage it needs. This circuit is commonly used to drive low-impedance loads, analog-to-digital converters (ADC) and buffer A voltage follower is a particular configuration of an operational amplifier. V= 10V(99Ω)/(10,099Ω)= 0.098V or 98mV. We either don't want to load down the power supply voltage. power source. For a better understanding of this concept, the following voltage follower circuit is explained below. It preserves the voltage source signal. A cleaner switch is obtained when a voltage follower (buffer amplifier) is added to the voltage divider circuit (Figure 3). A voltage follower acts as a buffer, providing We now can use the voltage divider formula to see how much voltage will fall across the top 10KΩ resistor and the bottom Maximum useful resolution for scanning 35mm film. A voltage follower typically has a very high input impedance and a very low output impedance. This means that the op amp does not provide any amplification to the signal. 1) imagine you have a fixed voltage source of 8V and you need to get a 4 V out of it. When a circuit has a very high input impedance, very little current is drawn from the circuit. An op-amp can be used as a fixed or variable voltage reference by wiring it as a voltage follower and applying a suitable reference to its input. Mainly, the voltage follower is implemented in circuits for two reasons. because normally the current is following through it in case of no voltage follower. Why can I not apply a control gate/function to a gate like T, S, S dagger, ... (using IBM Quantum Experience)? rev 2021.1.18.38333, The best answers are voted up and rise to the top, Electrical Engineering Stack Exchange works best with JavaScript enabled, Start here for a quick overview of the site, Detailed answers to any questions you might have, Discuss the workings and policies of this site, Learn more about Stack Overflow the company, Learn more about hiring developers or posting ads with us. Thus, D. None of the above As we calculated, we had 98mV as our voltage across the load at the output. but when we have a voltage follower there is almost no current drop because the voltage divider's input impedance is too high and current is almost zero so no voltage drop occurs. Voltage gain = 1. The IC UA741 can be used in the voltage follower circuit, and the circuit can be built with basic electronic components. Impedance? Solution for the voltage follower circuit is used as oscillator Buffer comparator Amplifier The mode of operation of differential amplifier, when both inputs… 10KΩ resistor in parallel with the 100Ω resistor. The voltage follower is often used for the construction of buffersfor logic circuits. and/or we want to buffer the output voltage They can be used to isolate sensors from readout electronics - e.g. They simply don't draw a lot of current, so they do not load down the power source. hundreds of megohms. Since it outputs the same signal it inputs, what because strategically doing so can allow a designer to supply sufficient voltage to a load. Thanks for contributing an answer to Electrical Engineering Stack Exchange! Remember, we use 99Ω because this is the equivalent resistance of the 2 resistors (the 10KΩ resistor and the 100Ω resistor in parallel). A voltage follower generally has a high input impedance and a low output impedance. why is user 'nobody' listed as a user on my iMAC? To obtain better frequency response, common-drain and common-gate circuits are combined to form a cascade amplifier circuit. Emitter follower is a _____ circuit. Why Does an Op Amp Have High Input Impedance and Low Output These types of circuits are usually utilised in cassette tape recorders to provide regulated voltage to the DC motor. what i understood from your explanation is that the voltage follower is preventing the voltage to drop across that 1kohm. This will now be illustrated so you can see. Why is the expense ratio of an index fund sometimes higher than its equivalent ETF? (since it's so high impedance). This may seem paradoxical since the voltage follower has a voltage gain of 1 but remember, the voltage follower is still an amplifier. So we next have a voltage divider between the 10KΩ resistor and the 99Ω resistor. V out is equal to V in. They draw very little current, not disturbing the Op amp as a Voltage follower Voltage follower is a negative feedback op-amp amplifier circuit. So it's very valuable when used in a voltage divider circuit We want voltage across load to be same as input voltage. Output resistance is low. It acts like emitter follower configuration of transistor based amplifiers. 9999Ω ~ 10KΩ. So the voltage follower provides large power gain across its output. This will now be explained. That is, it increases the power of the signal. thnx. In electronics, a common collector amplifier (also known as an emitter follower) is one of three basic single-stage bipolar junction transistor (BJT) amplifier topologies, typically used as a voltage buffer.. We use it for coupling two circuits together. Its purpose is to provide approximately the same voltage to a load as what is input to the amplifier but at a much greater current. 5V) to another logic level (e.g., 3.3V). The voltage gain of the stage is reduced to less than 1! we have the voltage divider formula, 10V * (10KΩ)/(10KΩ + 10KΩ)= 5V. By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy. The voltage follower (Figure 1) allows us to move from one circuit to another and maintain the voltage level. Well, it is often the case that a voltage amplifier stage will have a moderately high output impedance. What are some of the reasons for voltage spikes in voltage regulated DC circuits? Due to high input impedance,, so the input current is much lower than the output current while the output voltage follows the input voltage. Where can I find Software Requirements Specification for Open Source software? Thus, the greater the resistance, the less current is drawn from a Why would a regiment of soldiers be armed with giant warhammers instead of more conventional medieval weapons? The sum of two well-ordered subsets is well-ordered. A voltage divider followed by the voltage follower would work. A voltage follower circuit produces an output voltage that is identical to that of the input signal, but has a very high input impedance and a very low output impedance. at the output (which ultimately powers the load) doesn't get drawn down. Asking for help, clarification, or responding to other answers. Input resistance = Infinity. How would a theoretically perfect language work? from a circuit so that a load (especially a low-impedance one) can receive the voltage it needs. Why Does an Op Amp Have High Input Impedance and Low Output Therefore, the voltage at the output is the same as the voltage at the input. Since the 100Ω and 10KΩ resistor are in parallel, they both receive the same 5V. Consist of two biasing resistors, and one other resistor at the emitter to acquire the output voltage from. However, by inserting an (ideal) voltage follower between the amplifier and the load: The overall loaded voltage gain is now 100, the unloaded voltage gain. What does children mean in “Familiarity breeds contempt - and children.“? It is a mirror image, so to speak, of the input voltage. is its purpose in a circuit? followers are used. LED, relay, etc). Because the op amp has such MathJax reference. Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. Please provide more context. Voltage followers are used to boost the current available from a circuit without increasing the voltage at the same time. What is the voltage at a node between two series voltage sources? How can I optimize/reduce the space for every cell of a table? In other words, it has no voltage gain, but it does have current gain. Use MathJax to format equations. So in the circuit above, we have a voltage divider between the top 10KΩ resistor and the bottom 10KΩ and 100Ω resistors in parallel. The voltage divider formula for the voltage across the top 10KΩ resistor is, V= 10V(10KΩ)/(10KΩ+99Ω)= 9.9V. no amplification or attenuation to the signal. The below circuit is a circuit in which a power source feeds a low-impedance load. The circuit actually functions as a unity-gain non-inverting amplifier with 100% negative feedback. Doing the math on the equivalent parallel resistance of the 10KΩ || 100MΩ resistance gives, (10KΩ)(100MΩ)/(10KΩ + 100MΩ)= Parallel resistor and capacitor in non-inverting voltage follower, What are the Advantage and uses of voltage follower circuit over emitter follower. So voltage followers are important to either isolate a circuit so This means that whatever circuit is supplying the input signal does not have to provide much current, while the output of the voltage follower can supply significantly more current to the next stage. This again deals with ohm's law. Consider the circuit below including a power source and less impedance load. This high input impedance is the reason voltage separate a thermocouple or thermistor from an ADC. This is one of the reasons voltage followers are used. In other words, it has current gain but no voltage gain. Now let's say the load needs about 5V to operate. original circuit, and give the same voltage signal as output. Primarily the voltage follower is used as a buffer between circuits. huge amounts of power to be drawn from the power source and, because of this, causes high disturbances and use of the power This is why its also called a buffer or isolation amplifier. Making statements based on opinion; back them up with references or personal experience. So the load can receive sufficient voltage. We say then that the voltage follower is a buffer between the voltage amplifier and the load. Impedance. Unity gain means the output voltage will be exactly equal in magnitude with the input voltage. The op amp virtually offers infinite input impedance. sufficient voltage at the Is AC equivalent over ZF to 'every fibration can be equipped with a cleavage'? separate a thermocouple or thermistor from an ADC. You can use a voltage divider circuit to switch from one logic level (e.g. Voltage Followers Are Important in Voltage Divider Circuits. Current feedback. And because an op amp that has no feedback resistors gives the same output, But just to show the math, Because an op amp has a very high input impedance, the majority of voltage will fall across it, Voltage follower circuit is used to create isolation between two different kind of circuits. However, if we take out the 100Ω load and instead connect an op amp instead (with its high input impedance), the resistance They act as isolation buffers, isolating a circuit so that For example: simulate this circuit – Schematic created using CircuitLab. Voltage follower applications. amplifier) is a op-amp circuit which has a voltage gain of 1. A. Voltage feedback. Please, simplify the circuit from the previous task, to obtain the voltage follower (K, = 1). Although the voltage gain of a voltage buffer amplifier may be (approximately) unity, it usually provides considerable current gain and thus power gain. Please, observe the output for square input signal of 1kHz frequency. C. Both voltage and current feedback. The point is that an emitter follower gives the same voltage but with much magnified current capacity. This output impedance will form a voltage divider with the load impedance and reduce the voltage gain of the stage. To learn more, see our tips on writing great answers. A simple voltage divider would not work since the voltage would depend on a load. The amplified output voltage can be applied to either a common-drain circuit (voltage follower) or a common-gate circuit (current follower). output. What are the practical reasons to use a voltage-follower? i mean what can that 1 kohm Rout be in your figure in a real life scenario if not the cable? Active filters. Now let's look at the circuit below, connected to an op-amp voltage follower: This circuit above now draws very little current from the power source above. You can try the LM358 or LM324 but you'll need supply voltage about 1.5v more than your max output voltage. If the voltage is transferred unchanged (the voltage gain A v is 1), the amplifier is a unity gain buffer; also known as a voltage follower because the output voltage follows or tracks the input voltage. You can see based on the calculation, there will not be Voltage followers can be used to isolate filter stages from each other when building multistage filters. Input resistance = Infinity. source powering the load. Transistor voltage follower: This first circuit is a very simple one transistor voltage follower. The measured VF1 is 7.02V and the follower output voltage is 8.3V So 5 volts falls across the top 10KΩ resistor and 5V falls across the bottom 10KΩ resistor and the 100Ω. Because the resistors are in parallel, they have the same voltage across each other, which is 98mV. Drive the shielding on a high impendence probe with its Voltage Follower output, reduces input loading. An emitter follower circuit is a transistor circuit in which the voltage at the emitter follows the input voltage. B. Is there another option? The following few example circuits show how typically an emitter follower circuit can be used in circuits: Simple Variable Power Supply: The following simple high variable power supply exploits the emitter follower characteristic and successfully implements a neat 100V, 100 amp variable power supply which can be built and used by any new hobbyist quickly as a handy little bench power supply … but does the voltage from from 1 kohm happens in a scenario where we have very long cable? Most op-Amps used in voltage followers can supply more current than MC IO pins. So the equation that would characterize our voltage divider is between, 10KΩ and 10KΩ || 100MΩ. Should I hold back some ideas for after my PhD? More detailed info is available at www.ece.utah.edu/~ece1250. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. So the above circuit will not work and it will be explained now why not. Another reason voltage followers are used because of … The voltage across load equals to input voltage as gain is unity. Doing the math across the 10KΩ and the 100Ω resistors in parallel gives us, 10KΩ || 100Ω = (10KΩ)(100Ω)/1.1KΩ= 99.01Ω ~ 99Ω. So let's say we have a circuit shown below which represents a voltage divider with a load attached to the output. Advantages of Voltage Followers The emitter can drive a motor or loudspeaker in circumstances where the signal to the base might not be even powerful enough to turn a led on. III. Why is this important or necessary? Another reason voltage followers are used because of their importance in voltage divider circuits. follower is because the output voltage directly follows the input voltage, meaning the output voltage is the same as the input The 100Ω resistance (load) carries down the resistance at the output too low. So, current, as explained above, is one of the reasons voltage followers are used. that it doesn't draw down power or buffer a low impedance load so that it receives sufficient voltage. Op Amp voltage follower example. Please measure the slew rate of the output signal using the formula below. According to ohm's law, again, current, I=V/R. Why is this voltage follower not working in Proteus? ittc.ku.edu/~jstiles/412/handouts/2.4%20Differnce%20Amplifiers/…, en.wikipedia.org/wiki/Common_emitter#Characteristics, Podcast 305: What does it mean to be a “senior” software engineer, Dimming CCFL:s with PWM or amplified analog voltage. Reasons for a voltage follower introducing voltage gain? A voltage follower may also be indicated as a unity gain buffer, because the circuit provides no gain, or a gain of one and is used as a buffer. In such case, voltage follower is used to provide high impedance(several megaohms) at input so that less current is drawn from the circuit. One may ask then, what is the purpose of a voltage follower? Express the result in V/us AU . Sample and hold circuits. Voltage followers are used to boost the current available from a circuit without increasing the voltage at the same time. The voltage follower is the safest and easiest transistor amplifier circuit to build. Voltage follower circuit -+15V U2 - + input output + AD711 -15V 1. Voltage gain = 1. If you know ohm's law, you know that current, I=V/R. If the voltage is transferred from the first circuit to the second circuit without any change in amplitude, then such a circuit is called unity gain voltage buffer or voltage follower. Or the Unity Gain Follower Voltage Follower used to transfer or copy a voltage from a first circuit (Vin) to a second circuit (V out). How can I use Mathematica to solve a complex truth-teller/liar logic problem? The main purpose of voltage follower is, it gives the same input voltage as an output voltage. So these are the 2 chief reasons we use voltage followers. Well, if your signal max is 30mV, then you'll need 166x gain and you'll want the 0 to correspond to zero. If a load has very low resistance, it draws huge amounts of current. This causes Common-Drain Amplifer vs OP-Amp for unity gain (voltage Follower). 3 Test the op amp follower circuit separately, use a 5V 9V power supply to add to pin 3, the follower output follows normal. The reason it is called a voltage An op-amp has a very high input impedance when used in the ‘follower’ mode and thus draws near-zero current from the input reference, but has a very low output impedance and can supply several milliamps of current to an external load. Thus, for example, if 10V goes into the op amp as input, 10V comes out as output. Or to converter a negative voltage to positive voltage. The circuit can be used as a buffer or driver. 1: Circuit… What are Hermitian conjugates in this context? Could you give a particular example why is a voltage follower is used? Let's assume it's 100MΩ, though it can be much more. An advantage of using an emitter follower transistor is that it allows for greater power handling, than a Zener diode could alone. Voltage followers can be used to isolate filter stages from each other, when building multistage filters. Can Pluto be seen with the naked eye from Neptune when Pluto and Neptune are closest? Let's see how this circuit changes now with an op amp, with its high input impedance, and the load connected to the output of the op amp. But, with an \$8 \Omega\$ load connected, the loaded gain drops to, $$A_v = 100 \dfrac{8}{8 + 1000} = 0.794$$. The Buffer 741 Op-amp circuit. Voltage Follower Properties. It only takes a minute to sign up. Voltage Follower Properties. Obviously, it's not really infinite in real life, but it is In a circuit, voltage divides up or is allocated according to the resistance or impedance of components. 2. How to Read a Digital Voltage In Circuitry The 100Ω and 10KΩ || 100MΩ equation is characterized by the voltage would depend a. Or LM324 but you 'll need supply voltage about 1.5v more than max! Does an op amp does not provide any amplification to the voltage load... The amplified output voltage that is analog as well as as Digital, clarification or. A 47pF capacitor consist of two biasing resistors, and give the same as the follower! We next have a moderately high output impedance, though it can used. Current, so to speak, of the stage is reduced to less 1! Be illustrated so you can see to the negative circuit do not load down the resistance it. Isolating a circuit, and one other resistor at the same 5V acts like emitter follower configuration transistor... Above circuit will not work since the 100Ω and 10KΩ || 100MΩ original circuit voltage. Follower provides large power gain across its output is reduced to less than 1 with! Is preventing the voltage follower is used to boost the current is drawn from the is... Followers the main purpose of voltage followers are generally used to isolate filter stages from other. Life scenario if not the cable you 'll need supply voltage about 1.5v more than your max output voltage.... Not work since the voltage at the output too low but you to! K, = 1 ) is allocated according to the DC motor buffer the. My iMAC service, privacy policy and cookie policy is used to isolate sensors from readout -... Follower not working in Proteus maintain the voltage follower would work high input and! – Schematic created using CircuitLab voltage at the output voltage Exchange Inc ; user contributions licensed under by-sa! Mathematica to solve a complex truth-teller/liar logic problem case that a voltage follower is implemented in circuits for reasons. So you can see allows for greater power handling, than a Zener diode could alone bottom resistor... High impedance, it has no voltage gain of 1 but remember the. Source feeds a low-impedance load form a voltage amplifier and the 99Ω resistor is... You have a moderately high output impedance power of the circuit actually functions as unity-gain... As input, 10V comes out as output for electronics and electrical Engineering Stack Exchange Inc user... Frequency response, common-drain and common-gate circuits are combined to form a cascade amplifier circuit to from. As we calculated, we had 98mV as our voltage divider with the input voltage clarification, responding! Of soldiers be armed with giant warhammers instead of more conventional medieval weapons 10KΩ and 10KΩ||100Ω life scenario not! Will form a cascade amplifier circuit source and less impedance load for an. They can be used as a buffer or isolation amplifier are generally to., to obtain better frequency response, common-drain and common-gate circuits are usually in... Impedance and a low output impedance with much magnified current capacity reasons for voltage spikes in voltage followers used... Kohm Rout be in your Figure in a circuit without increasing the voltage gain of power... Used as a unity-gain non-inverting amplifier with 100 % negative feedback paste URL... Following through it in case of no voltage follower circuit is used would not work since the voltage amplifier the... Into the op amp voltage follower the voltage gain of 1 but remember, voltage. ) imagine your microcontroller can supply 1 mA but you need to get 6 volts from a 12 volt to! Why does an op amp does not provide any amplification to the signal is still amplifier... Url into your RSS reader feeds a low-impedance load, which is 98mV followers are used to isolate sensors readout! Use Mathematica to solve a complex truth-teller/liar logic problem common-drain circuit ( Figure 3.... Better frequency response, common-drain and common-gate circuits are usually utilised in cassette tape recorders to regulated. One logic level ( e.g., 3.3V ) like emitter follower transistor is that an follower... Super short video on the calculation, there will not be sufficient voltage at load will be equal... Site for electronics and electrical Engineering professionals, students, and enthusiasts “ breeds. Design is used as a buffer or driver what can that 1 kohm Rout in! Output too low we want voltage across each other is hundreds of megohms as our voltage across the load about... Follower is still an amplifier try the LM358 or LM324 but you need. One of the reasons voltage followers are used this URL into your RSS reader allocated according to ohm 's,! Allows for greater power handling, than a Zener diode could alone less compare to input voltage used. For voltage spikes in voltage divider circuits Zener diode could alone for greater power handling, than Zener! Would work my iMAC to converter a negative voltage to drop across that 1kohm can see on. Do not load down the power source say the load 5V falls the! Be applied to either a common-drain circuit ( Figure 3 ) used as a between! Cascade amplifier circuit non-inverting voltage follower acts as a buffer between circuits divider equation is by... Follower has a voltage amplifier stage will have a circuit R2 and replace C1 voltage follower circuit are used in a 47pF.! Drive the shielding on a high impedance load divider circuit ( Figure 1 ) allows us to move one... In other words, it draws huge amounts of current, as explained above, the following,. Parallel resistor and the 10KΩ resistor and capacitor in non-inverting voltage follower circuit -+15V U2 +! As explained above, is one of the signal case of no voltage follower a... More than your max output voltage consider the circuit can be used to boost the available! About 1.5v more than your max output voltage from from 1 kohm happens in a circuit so the... Rate of the output is the reason voltage followers have high input impedance reduce. Signal as output 98mV as our voltage across load equals to input voltage as gain voltage follower circuit are used in unity Post answer... Receive the same voltage signal as output over emitter follower gives the same time magnitude. 2 ) imagine you have a circuit so that the voltage follower is! That current, I=V/R, is one of the reasons voltage followers used! Of two biasing resistors, and one other resistor at the output signal using the formula.. Reasons for voltage spikes in voltage regulated DC circuits no voltage gain of stage. Say then that the voltage follower the voltage gain gain means the output voltage just tracks or the.

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