# Questions tagged [emitter-follower]

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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### Emitter follower as single-ended power amplifier

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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### The advantage of using base biasing over emitter biasing?

Can someone please explain to me what is the advantage of using base biasing over emitter biasing. Why is a 'feedback resistor' used in base biasing?
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### Emitter follower and input impedance

I'm designing an active bandpass filter (using only BJTs, voltage sources, resistors and capacitors) with the following properties: Corner frequencies $8 ~ \text{kHz}$ and $800 ~ \text{kHz}$ (...
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### Op-amp with BJT circuit problem

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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### How to design a good common-collector amplifier?

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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### Op amp Power supply splitter with totem pole

I want to make a +- 2.5V rail from a 5V 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 noticed ...
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### Necessity of using emitter follower as the first stage

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 ...
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### Designing a stiff voltage source using an emitter follower

simulate this circuit – Schematic created using CircuitLab I am new to electronics, and I am trying to do Exercise 2.2, page 67 of The Art of Electronics. Use a follower with base driven ...
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### Emitter Follower / Common Collector as Negative Feedback Amplifier

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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### 3.3V LDO alternative using SOC analog output?

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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### What is emitter repeater?

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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### Emitter current

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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### Why do I have clipping in this emitter follower

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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### Limit base current on emitter-follower BJT

I'm using a BJT in emitter-follower configuration to control the current flowing through a high voltage load (170 V DC). The base is connected directly to an analog output of a BH2221FV DAC. During ...
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### Where voltage is lost in an emitter follower?

I'd wanted to know what happens in an NPN emitter follower with ${\delta}V=Vcc-Vee$. At which junction does voltage drop? May this drop be fatal to a transistor?
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### Art of Electronics 2nd edition p. 67, figure 2.8 — what causes the clipping?

I have been rereading this section and realized I always get hung up here. The idea of clipping happening because the emitter is not able to stay .6 or so volts less positive than the base is ...
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### calculating the the input impedance with the effect of ro

How could he calculate zb with the effect of resistance of ro? Here he calculated zb without the effect of ro and i have understood that.
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### How to improve emitter-follower efficiency?

I’m trying to wrap my head around the emitter follower. I’m currently using it to simulate a ~12V AC coming from a intercom ringer (about 700Hz). simulate this circuit – Schematic created using ...
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### How is the quiescent current and emmiter resistor determined on the driver and pre-drivers of a class-AB audio amplifier output stage

I am reading online about discrete audio amplifiers. I have learned about the input differential pair, the voltage amplifier stage, and now I'm learning about the output stage. I have learned that you ...
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### Need for ''stiff'' bias voltage in this emitter follower?

Here is my circuit: It is intended to drive headphones with low distortion, and be driven by fairly high impedance source (~500R). The trouble is maintaining a very high input impedance with high ...
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### In Emitter Follower BJT circuit Why the parallel resistance of the biasing resistors to be 1/10 of the Rin and not their series resistance?

Well In "Practical Electronics For Inventors" Book P.439 The Below Emitter follower circuit was introduced with the following explanation. The actual sizes of R2 and R1 should be such that ...
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### Transistor Noise A Concern In Emitter Follower

I'm looking at using a high voltage BJT as an emitter follower in a high voltage tube audio application (guitar amp). Unfortunately in the range of 200V, most BJTs are marketed as switching ...
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### Wiggle in the current source of an emittter follower amplifier

This has been bugging me for days. I still don't understand why the book says the current I through Q1 remains constant when there is a varying input signal at the base of Q1. Some peeps here also ...
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### Class A Emitter follower instantaneous power

I don't quite understand the explanation given in the book I'm reading. Why the maximum instantaneous power dissipated by Q1 is P=2Vcc*I at RL open? Also, why is the current ic1 constant I? Wouldn't ...
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### Emitter-Follower Class A amplifier

I was trying to solve a problem from SEDRA-SMITH book. I got stuck so I refer to the solution. When Studying how the author solved the problem I got even more confused. Let's refer first to the ...
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### re model of transistor

In which case shall I consider output resistance(ro)? I found that in case of re model for common emitter configuration we are considering output resistance(ro) but there is no (ro) in emitter ...
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### Maximising output amplitude

How can I modify this emitter follower circuit to get maximum amplitude output with no distortion? Re = 2.25k ohms, Rb1 = 57.3k ohms, Rb2 = 96.1 I currently have 0.96 gain Vcc is limited to 9V and ...
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### emitter follower output current

Is the output current of an emitter follower out of phase with input current? In the book Electronic devices and Circuit Theory, the current gain, Ai, is negative. It depends on direction on output ...
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### emitter follower biased by input signal?

For the standard emitter follower you typically need input coupling capacitors and a DC bias of roughly half the supply voltage however what if the input signal itself swings around half the supply ...
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### Why is the base resistance suggested to be one-tenth of the emitter resistance times beta?

This is a follow up question from Emitter follower biasing with voltage divider or the emitter follower design example in The Art of Electronics. Why is the recommended one-tenth ratio of base ...
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### How to calculate the reference voltage when a beta value is given?

I'm having trouble determine the value of the reference voltage. I don't know what's the beta used for. These is given: Vbe=Vd1=Vd2=0.75V for 1mA and beta=27 for all BJT. I did the following, but I'...
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### Input resistance of a BJT common-emitter amplifer

What's the input resistance of the circuit below? I think it is $R_{in}=R_B || r_\pi$, but I am not sure
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### Design an emitter-follower amplifier with bjt

I'm studying the emitter-follower configuration for bjt on the book "Practical Electronics for Inventors". On pag 439 there is an example related to the design of this system. In this problem it knows ...
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### Omitting ΔVbe in emitter follower KVL equations

In the forward active region, if we draw an emitter follower voltage variations as follows: It seems by using KVL we can say that: ΔVin = ΔVbe + ΔVe Now in many texts they omit ΔVbe and equate ...
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### Are base resistors of any use for a high-side NPN switch?

I "inherited" a small project from a person I don't know, and I'm navigating my way through it. It's a small gadget featuring a 7-segment LED display. I hear the device's original designer is more of ...
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### Design an emitter follower to operate in the audio range (20 Hz - 20 kHz)

I am now self-learning with the "Art of Electronics" book by Holowitz and Hill, and I encountered a problem understanding one example from the book. Here it is: And here is the explanation for the ...
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### Why is the input impedance of an emitter follower defined as $\Delta V_{B}/\Delta I_{B}$, as opposed to $V_{B}/I_{B}$?

In The Art of Electronics, chapter $2$:Transistors, page $65$, the author defined the input impedance $r_{in}$ of the emitter follower below as $r_{in}=\Delta V_{B}/\Delta I_{B}$. Why did ...
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### RC filter for emitter follower input

Please could someone explain how to compute the impedance with which to determine the frequency characteristics of the high-pass input filter in the following circuit? My question is prompted by an ...
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### Art of Electronics: Emitter-Follower Zout

I am a growing frustrated with the Art of Electronics. It is such an approachable book in Chapter 1, and then in Chapter 2 it seems like the authors wanted to make it more textbook-like and they ...
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### Emitter Follower as a Current Amplifier

Reviewing Basic amplifier stage properties, I found unanimously that a Current Amplifier has a Very Low (ideally zero) Input Impedance and a Very High (ideally infinite) Output Impedance. The Emitter ...
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### Is an op amp voltage follower better than one made with discrete (MOS)FETs?

Is there any advantage of the following op amp based voltage follower:- over one made with discrete MOSFET components such as:- other than component count?
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### The need for a current source in an emitter follower

What is the need for adding a current source ($I_\text{E}$) at the output of an emitter follower topology at the emitter leg of the transistor?
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### is it possible to boost up the current by keeping the voltage constant?

I have a source that can deliver 20mA and 4.5V (MAXIMUM). I need to boost the current to 1 A without using any further source. Also, the voltage should be maintained constant at 4.5V. is that ...