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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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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56 views

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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49 views

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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43 views

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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37 views

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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35 views

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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83 views

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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228 views

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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40 views

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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43 views

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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32 views

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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75 views

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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113 views

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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68 views

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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53 views

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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76 views

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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103 views

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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170 views

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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2answers
375 views

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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3answers
542 views

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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1answer
138 views

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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194 views

Output resistance of emitter follower voltage regulator

How to calculate an output resistance of such circuit?
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How to select resistor for emitter follower when driving speaker?

simulate this circuit – Schematic created using CircuitLab The objective is to drive 1 watt into the speaker. R1 represents the output impedance of the previous common collector stage. Here's ...
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277 views

Emitter Follower Power Stage of an Amplifier with Switch-off capacitor

I know exactly how emitter follower (EF) arrangement of transistors works (when used as power current amplifying stage). But according to my book (G. Randy Slone: High Power Audio Amplifier ...
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1answer
802 views

Output impedance seen by the load in this emitter follower

I'm trying to understand what the concept of "output impedance" relates in a simple buffer such as an emitter follower conceptually without digging in formulas. Imagine the Rload is about to be ...
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5answers
346 views

(logic level) Gating the output of a 900hz (5v p2p) oscillator

Seems a simple enough problem this, and perhaps all that is needed is confirmation of approach (although a better solution always appreciated). So the problem: I have a 555 based square wave based ...
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2k views

What are the Advantage and uses of voltage follower circuit over emitter follower

Can I use voltage follower and emitter follower for same purpose
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563 views

Down-converting voltage

I'm trying to reduce the voltage of a power supply for a certain load without affecting the current the load draws. Since the op-amps I could find were not able to provide sufficient current, I added ...
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1answer
96 views

An emitter follower to isolate MCU from load?

I am trying to drive an LED strip (10 LEDs) from the output of an ESP8266 GPIO pin. I measured the short circuit current from the GPIO and got around 40 mA. My question: Is it recommended to include ...
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93 views

Emitter follower augmented input current

Hello, I have this emitter follower augmented ( I think that's his name in english) but I don't know from where is the beta+1 on the Iin ecuation?
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125 views

What would happen to the DC bias voltage of the emitter if this capacitor is omitted?

I'm not quite sure what the question means. I need to explain what would happen if I removed the \$1.0 \mu F\$ blocking capacitor from this circuit. Howver, I'm not sure what the "DC bias voltage of ...
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4answers
936 views

Linear regulator using emitter follower and operational amplifier

I have understood that you can create a linear regulator using a high-current BJT power transistor in the emitter follower configuration and one operational amplifier (and a voltage reference, which ...
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2answers
785 views

Emitter follower voltage regulator misbehaving

To make a crude voltage regulator, I've made a simple emitter follower using a BD139 transistor. When the 0.5A load is connected, the circuit behaves as expected: the voltage across the load sits at ...
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94 views

Using BJT emitter follower after microcontroller

I am trying to understand an already existing circuit shown below taken from http://boris0.blogspot.fr/2013/09/rotary-dial-for-digital-age.html. The aim of this circuit for the right part is to ...
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1answer
116 views

Emitter follower with extra load in emitter path

I was reading through Linear Technology's AN70 application note and on Figure 42 there are two parts of the circuitry that I can't understand. It looks like an emitter follower but there is a ...
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1k views

Single supply op-amp voltage follower - negative clipping with AC-coupled load

I am using a µC running DDS algorithm to synthesize certain waveforms (in fact I made 3 channel music generator with portamento&ampltude modulation effects, commands for changing waveforms etc. ...
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2k views

Emitter follower biasing with voltage divider

I have met a emitter follower design example in the Horowitz-Hill's book (scheme is below): And I don't understand why the resulting steps is correct: Step 1. Choose \$V_E\$. For the largest ...
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67 views

Are there methods to stabilizing \$V_{BE}\$ [closed]

For \$V_{IN}\$ >> \$V_{BE}\$ (\$V_{IN}\$ in reference to GND), the \$V_{BE}\$ is quite stable typically only varying in 8mV for silicon NPNs and gets smaller when the emitter is conducting less ...
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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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Horowitz lab 4.4

I have a problem doing lab 4.4 from Horowitz's student manual for the Art of Electronics. Here's the circuit and here's what I get from LTspice simulation, which corresponds to hardware circuit ...
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4answers
2k views

Why does the emitter follower clip?

The emitter follower bellow cannot follow the base voltage Vb after some point: Vin input is DC sweeping from +10V down to -10V. The output voltage Vout however stops following Vb at some particular ...
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2k views

Emitter-Follower Base Input Impedance

I am trying to solve this circuit and am getting confused by how the input impedance of the base of the transistor is calculated. I am confused how this is done? What are the general rules for ...
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3answers
462 views

Current source design

Please help me to calculate the value of resistor R1 so that the current through R2 was 100uA. The only thing I noticed is that the output current is pretty much sensitive to changes of saturation ...
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2k views

Emitter follower regulator with sziklai pair, transistor heating up!

I have a wireless chip esp8266 that requires input voltage of 3.3V and can draw current up to 500mA. Unfontunately at the moment I don't have any 3.3v regulator IC's or buck converters or any 3.3v ...
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3answers
1k views

Emitter Follower LED Circuit - LED in Collector, Resistor in Emitter

I have seen some examples of using an emitter follower circuit with an NPN transistor to light an LED. In those examples, it's mentioned the collector voltage must be equal-to or higher than the base ...
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1answer
646 views

Op amp voltage reference with emitter follower

The purpose of this circuit (taken from the Minimoog) is to provide a stable -5V across the 100R load resistor, as accurate as the -10V supply and the ratio of the 5K resistors in the potential ...
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487 views

Horowitz's exercise 2.2

Having done the exercise 2.2 from Horowitz's "The Art of Electronics," I feel uncertain and would like somebody familiar with the matter to check my solution. With this aim in head I've searched the ...
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484 views

Voltage gain of an Emitter Follower

Please see attached image. Can you please help me understand how they went from the first to the second? Not too sure how they got (B+1) in there. Thanks
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A question on emitter follower use

A DAQ board is outputting 0-10VDC analog voltage via its DAC. The DAC cannot supply more than 5mA so I'm planning to use the following emitter follower for more current(x-axis is the DAC outpout ...