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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5answers
8k views

Stiff Voltage Divider Bias for an Emitter Follower

Below is an ac-coupled emitter follower with base bias provided by a voltage divider. I'm having a slight issue with how the resistor values are chosen for the biasing in the design example provided ...
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3answers
837 views

BJT switch vs amplifier mode

I'm getting really confused about a specific BJT circuit. I want to control LCD brightness and contrast as suggested here. Apprently a capacitor is used to filter PWM output to the contrast pin, and ...
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1answer
612 views

Measuring input resistance to a MOSFET/BJT amplifier

How would one go about measuring the resistance of a Emitter follower in PSPICE?
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1answer
2k views

Lower corner frequency in an emitter follower (Common collector)

I have a doubt about the lower corner frequency of an emitter follower. I don't rember where, but I have read that it is given by: \$\omega_L=\frac{1}{R_BC_1}\$ where \$R_B\$ is given by the parallel ...
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4answers
4k views

Why emitter follower is so noisy and distorted in large signal?

I have a signal around 20 V peak-peak. I want to feed it into an emitter follower BJT and I have no experience in working with such large signals. The BJT is well in bias point ( I tested the ...
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1answer
156 views

Confusion about the Injection of electrons and electron holes in a BJT

On page 354 of the 6th edition of Microelectronic Circuits by Sedra & Smith under Current flow, the following statement is made; Current will consist of two components: electrons injected from ...
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1answer
375 views

Can Emitter Follower BJTs work with large signal?

Sorry for such elementary question. As anyone knows emitter follower design of BJT has some specifications . For example they are suitable for driving low impedance loads and so. But because the ...
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3answers
14k views

Emitter follower: Icq and Vceq calculation

I have problem with understanding how to calculate \$ I_{cq} \$ and \$ V_{ceq} \$ of this circuit. Q1 has these details: \$ h_{FC}=150 \$ and \$ h_{fc}=100 \$ As I understand it I should find \$ V_{...
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1answer
346 views

Why does a relay open gradually when driven by 555 through an emitter follower?

A follow-up to my earlier post Why is the output from this astable 555 the reverse of it's simulation? The 555 output drives a 2N2222. The 2222 emitter-follower with a 4.7 kΩ resistance to ...
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1answer
903 views

Emitter follower

I'm having a hard time understanding an emitter follower. What I don't understand is why there is no voltage gain but only current gain. From my understanding when the transistor is turned on, the CE ...
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2answers
1k views

A phototransistor with LED and resistance in emitter

Earlier I used a simple phototransistor arrangement to detect an on/off signal via a laser pulse. I connected the collector to Vcc(5V), and emitter was grounded through a resistance. The base was ...
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2answers
884 views

Voltage Follower Saturation

I'm trying to use a 0.5V signal as a source. I've wired a TL072CN as follow: VCC+ to 11V VCC- to GND OUT2 to IN2- IN2+ to 0.5V The thing is when I measure the voltage on OUT2 I get 10V where I am ...
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1answer
472 views

Getting 3.3 (V) from a 5(V) rail - Emitter Follower, or something else?

I am using a Bluetooth module (RN-41 SM) that is spec'd to run at 3.3(V). I can operate this module at 5(V) however, due to another part of the circuit, I need to run the micro controller at 5(V) ...
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5answers
2k views

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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2answers
481 views

BJT transistor junctions: base-collector

I've been playing with voltage swings in a basic emitter-follower circuit. If I swing the input too large in the negative cycle, the base-emitter junction is reverse-biased and the transister goes ...
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3answers
4k views

Emitter Follower Output

I cannot afford a function generator and oscope right now, so I'm trying to learn analog electronics with Spice (MacSpice, to be specific). Below is the Spice model for a simple emitter-follower ...

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