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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Common emitter amplifier with low impedance

The following schematic shows a common emitter amplifier driving a resistive load. The common emitter has a high output impedance, is it possible to use the amplification achieved with the common ...
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Operating Region for Transistor in Capacitance Multiplier

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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Why do two different approaches give different results about choosing resistances for voltage divider of emitter follower circuit?

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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Why would an emitter follower be DC-coupled to its input?

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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Is this a transistor emitter follower circuit?

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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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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Input impedance of emitter follower

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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Saturation for emitter follower

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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Common Collector Amplifier DC Analysis (why not get the VTH and RTH like in Thevenin's Theorem?)

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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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 +/- 2.5 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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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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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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Modulator design in ADS

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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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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6 answers
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What does this transistor circuit do?

I found a schematic which had this bit of circuitry between the +9 V (which apparently the author assumed to be > 9 V, more like 10-11 V) barrel connector and the +9 V supply rail. I tried to ...
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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 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 given ...
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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 9 V and a ...
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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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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 ...
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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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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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Emitter follower for parallel LED switch

I’m trying to confirm that the solution posted in https://electronics.stackexchange.com/a/60868 will work for my application. I have four yellow LEDs with a 2 V drop (yellow) and 30 mA max current I’d ...
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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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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 ...
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Emitter-coupled logic operation

For the operation of emitter-coupled logic and sedra smith book, 1) Compared to CMOS, why ECL is the faster logic family given that it requires so many transistors to propagate to output Y (T5 ...
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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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Loading effects of a signal source

I'm reading "The Art of Electronics" (3rd edition) by Paul Horowitz and Winfield Hill. In the 2nd chapter on BJT (page No. 79, section Emitter follower). The author says: ".. In general, the ...
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