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An emitter follower (also known as a common collector amplifier) is one of three basic single-stage bipolar junction transistor (BJT) amplifier topologies, typically used as a voltage buffer.

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I’m fairly new to analyzing BJT amplifier circuits and I could use some help understanding this configuration. I’ve attached the circuit I’m working with (see image). The given parameters are: β₁ = ...
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I have the circuit in the photo. To my understanding this is a cascade schema of transistors. Two transistors connected together and they create an amplifier. I am interest in DC analysis for now. (...
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I'm currently reading The Art of Electronics and I have some troubles for understanding the result of the Exercise 2.4: the output impedance of the emitter follower circuit is \$Z_\text{source}/(\beta ...
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I am trying to simulate a very simple emitter follower and calculate its output impedance using LTspice. I use the method where a 1 A current source is connected to the emitter so the voltage at ...
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A voltage follower using an op-amp can be used to provide constant voltage, with more current (within op-amp limit) from the source. Can I replace this with an emitter follower circuit as given below? ...
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I had a question given to me for a class assignment, I will describe it now. The question is of DC analysis, we are to find the output voltage of a common base configuration BJT (NPN). I analyse it as ...
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Figure 2.17 from The Art of Electronics, 1st edition (Horowitz and Hill) In my progress through AoE, I'm stuck on this circuit (and wishing there was a solutions guide at the back of it!). I'm to ...
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Images from Art of Electronics 1st edition, p. 58 (Horowitz and Hill) Both of these circuits accept an AC signal that is centered around 0V. The first (Figure 2.16) is supposedly coming from a ...
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The Art of Electronics (1st ed., page 56) has confused me! On page 12, this circuit is shown as a simple zener regulator. I added the load, a 1k resistor. When I simulate it, the regulator draws 49....
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I read an article about how the linearity of an emitter follower can be improved using a cascode configuration. Here is the article: https://www.passlabs.com/technical_article/cascode-amp-design/ For ...
CircuitMan's user avatar
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Can we saturate the BJT in emitter follower configuration by increasing base current? If yes, what happens in the process? How does increase in collector current decrease \$V_{CE}\$ when there is no ...
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Here is the circuit of normal BJT in emitter follower configuration. I understand that when conducting, $$V_e = V_b - 0.7$$ In the above case, \$V_e = 1.33V\$ Now, consider an opto coupler circuit as ...
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How do I analyze an emitter follower with a capacitor load? At 7 MHz, a 1 nF capacitor has impedance of 22 Ω. A simple emitter follower with a 22 Ω Re is easy to analyze: However, replace that ...
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As an exercise, I'm designing a circuit that takes a 7 MHz input signal (1V amplitude) with a source impedance of 1K and uses it to power a 50 ohm load. I used an emitter follower, and it works well ...
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The Art of Electronics has the following exercise: Use a [single BJT transistor emitter] follower with the base driven from a voltage divider to provide a stiff source of +5V from an available ...
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Short question first If I want to use an emitter-follower to strengthen a signal source and I need a bias network for the transistor, how do I isolate this from the source if the source is digital? ...
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Let me confess before beginning that I am not so professional or expert in this field. I am a self learned hobbyist who learns things from YouTube and applies them in the reality. Having worked with a ...
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In layman terms, what is the main use and purpose of unity gain amplifiers? I am reading that it is used to "buffer high impedance sources" but I'm unsure what this means practically.
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I have this circuit that should describe a constant current source. From my point of view the pnp-transistor has to work in its saturation mode. Thus the potential on the emitter should be constant. ...
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I saw this schematic at the link below and I would like to know if there is any use in particular for Q2. Since the transistor Q2 is just, somehow, operating as a simple diode that is following the ...
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This is an emitter follower from "Learning the Art of Electronics" by Hayes and Horowitz (lab 9L.2): simulate this circuit – Schematic created using CircuitLab The autors claim that ...
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I am designing a DC supply for a motor driver. The voltage of the supply determines the motor speed (voltage goes up, speed goes up). My plan is to vary the supply voltage to keep the motor rotation ...
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The idea for this question came about after I wrote an answer to a similar question. This "diamond solution" was something unknown to me. I took a look at Wikipedia page (see the picture ...
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I have been trying to derive Av , Ai , Zi , Zo from a two port system model of a transistor. I know that the input voltage must be the voltage at the base to ground, and the output is from collector ...
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In Horowitz - Hill's The Art of Electronics, 2nd edition, paragraph 2.03, an emitter follower with an npn BJT is presented. Figure 2.8 uses a symmetrical power supply: simulate this circuit – ...
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I got this circuit out of an old model railroad electronics book from the 1970s. It's your basic common-collector (a.k.a. emitter follower). Control voltage goes into the base of Q1, and then Q1, Q2, ...
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I'm playing around with an emitter follower to understand its behaviour under various conditions. In the screen shot below, I have an emitter follower where the input to the base is a 5V sinusoidal. ...
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I don't understand what the bold sentence means: A single-ended follower operating between split supplies can drive a ground-returned load only if a high quiescent current is used. The quiescent ...
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Reading The Art of Electronics (3rd edition), I came across the following sentences in section 2.4.1: An npn emitter follower cannot sink current... . The result is that a single-ended follower ...
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I am looking to mathematically characterize the circuit shown before, consisting of two (MOSFET) current mirrors and a BJT (common collector or emitter follower?). I am stuck at the first current ...
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Specs: Signal 1 kHz sine, amplitude 100 mV, VB = 1.7 V If we were to connect a sufficiently large resistor to a signal generator, we would expect to measure the voltage over the large resistor to be ...
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If we were to connect a sufficiently large resistor to a signal generator, we would expect to measure the voltage over the large resistor to be the voltage amplitude of the signal. However, if we add ...
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I want to understand what is the desired operating region for a transistor in a capacitance multiplier circuit being used to remove power supply ripple. Consider the circuit in the attached image. ...
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I have read this page from the Practical Electronics for Inventors book. What I don't understand is about the calculation of R1 and R2. Approach 1: This approach is author's idea and the result is R1 =...
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In my experience, an emitter-follower amplifier is usually AC-coupled to both its input and output: However, I recently came across such an amplifier which is DC-coupled - the capacitors C1 and C2 ...
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I saw this kind of circuit in an IC block diagram. It looks like an emitter follower circuit, but the collector is not connected with Vcc (not higher than base.) What is Vout? Where would this kind of ...
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I have seen that the following circuit is mentioned as a single-ended class A power amplifier. Also, push-pull configuration is mentioned as a better power amplifier, which isn't single-ended, and ...
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I decided to calculate the input impedance of the following emitter follower circuit as a practice. I used this well-known small signal model for the BJT: For voltage gain, I obtained $$A_\text{v}=\...
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How can a transistor connected in emitter follower configuration be driven into saturation? I know that for saturation, the base voltage should be greater than the emitter voltage, but also than ...
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I looked in the book of Electronic Devices and Circuit Theory and in the section of a common collector amplifier configuration with a voltage divider, it shows that: $$ V_B=\frac{VCCR_2}{R_1+R_2} $$ ...
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I'm studying for EE final exam First Question: what is the current through the red LED? I have been working on this problem. So far, what i got is that with 5V come in the non inverting input of the ...
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I tried to simulate an example common collector amplifier given in the book Electronic Devices by Floyd. The circuit depicted in the book is: I used LTspice with transient analysis to implement and ...
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I want to make a +/- 2.5 V rail from a 5 V supply using an op-amp. I was wondering if I could use a totem pole for driving the output like this: Image from here But while I was looking at it, I ...
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What's the actual use of the emitter follower stage (Q1&Q2) in the following op-amp circuit? The only reason I see is to increase the input impedance. But even that I don't see it necessary ...
dirac16's user avatar
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Background From the wikipedia page on Common Collector Amplifiers there is paragraph describing how the circuit acts as a negative feedback amplifier The circuit can be explained by viewing the ...
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I want to build a little adapter board to connect an existing PSOC prototyping board (CY8CKIT-059) to QIIC connector (which is just I2C using JST 4-pin connectors). The QIIC standard calls for 3.3V ...
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hello everyone editing my previous post, i have biased my circuit now i want to run it for s-parameters simulation but when i attach term port it is giving a negative S(1,1).. any help would be ...
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According to what I read the circuit above is the schema of emitter repeater, it is used between two amplifiers to connect them and it's gain A = 1; it does not amplify the signal. But I want to ...
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Suppose when the collector is connected we get \$I_b=10 mA\$, and \$I_c=1000mA\$, so naturally we have \$I_E=1010mA\$. What will happen when the collector is disconnected? Will the base current change ...
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I am trying to design a class A amplifier buffer stage (I know it is not efficient.) I am starting from the simple emitter follower and the next step is to replace the RE resistor with a current ...
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