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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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Constant current source with transistor

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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Transistor Driver - what is the purpose of Q2 on the included schematic?

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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Parasitic oscillation don't happen in an emitter follower

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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DC coupled common emitter amplifier

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 ...
creillyucla's user avatar
14 votes
4 answers
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What is the basic idea behind the so-called "diamond buffer"?

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 ...
Circuit fantasist's user avatar
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Transistor Re Model Input/Output Analysis

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 ...
Arcadius's user avatar
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3 answers
345 views

Maximum voltage range for input in emitter follower

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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How to set emitter resistors in transistor emitter follower

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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NPN emitter follower behavior when base voltage exceeds collector voltage

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. ...
Y Diranieh's user avatar
1 vote
1 answer
239 views

How is quiescent current related to maximum load current in an emitter follower?

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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Single-ended follower with zero quiescent current?

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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BiCMOS voltage follower analysis help

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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2 answers
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Emitter follower: \$V_\text{out}\$ smaller than \$V_\text{in}\$

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 ...
David's user avatar
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1 answer
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Emitter Follower, \$V_{out}\$ smaller than \$V_{in}\$ [duplicate]

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 ...
David's user avatar
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3 answers
397 views

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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1 answer
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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 =...
Dat's user avatar
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2 answers
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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 ...
user200783's user avatar
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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 ...
Ahn JIn Ho's user avatar
2 votes
3 answers
646 views

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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0 votes
2 answers
765 views

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}=\...
apadana's user avatar
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5 answers
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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 ...
Anna's user avatar
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1 answer
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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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4 answers
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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 ...
Paul's user avatar
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11 votes
1 answer
2k views

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 ...
Fuad Zadeh's user avatar
4 votes
3 answers
1k views

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 ...
Christianidis Vasilis's user avatar
0 votes
2 answers
120 views

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 ...
dirac16's user avatar
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2 votes
1 answer
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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 ...
Burt_Harris's user avatar
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0 answers
206 views

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 ...
osama afzal's user avatar
0 votes
2 answers
489 views

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 ...
Pərviz Piri's user avatar
1 vote
4 answers
522 views

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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2 votes
1 answer
1k views

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 ...
Rojj's user avatar
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1 answer
215 views

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 ...
Marco's user avatar
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1 answer
191 views

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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3 answers
287 views

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 ...
Fixer69's user avatar
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0 answers
184 views

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 ...
gurghet's user avatar
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18 votes
6 answers
5k views

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 ...
Xaser's user avatar
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-2 votes
2 answers
323 views

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.
Ahmed Redwan's user avatar
3 votes
1 answer
561 views

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 ...
johnny24's user avatar
0 votes
0 answers
134 views

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 ...
Jay 's user avatar
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1 answer
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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 ...
Mahmoud Salah's user avatar
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0 answers
136 views

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 ...
MadHatter's user avatar
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0 votes
2 answers
88 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 ...
Paumdrdo's user avatar
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2 answers
239 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 ...
Paumdrdo's user avatar
2 votes
1 answer
251 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 given ...
Paumdrdo's user avatar
0 votes
1 answer
517 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 ...
Abhishek's user avatar
0 votes
0 answers
54 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 9 V and a ...
S123l2000's user avatar
1 vote
2 answers
272 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 ...
Jay 's user avatar
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1 vote
2 answers
1k 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 ...
KMC's user avatar
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0 votes
2 answers
201 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'...
Jaime Miranda Ramirez's user avatar