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Questions tagged [bjt]

BJT stands for Bipolar Junction Transistor. It is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications.

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BJT push-pull modification

I am playing with BJT push-pull circuit from a previous question (there are 3 push-pulls with various speedup tricks for comparison): I've recently realized, that's it's voltage follower, so it's not ...
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2answers
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Edge detector - transistor only

I wonder, how can I make edge detecting circuit without using any logic IC's, using only transistors & passive components? I have digital signal with ~15ns fronts on my digital input (5v TTL), ...
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limiting base current to BJT

I'm actually working with a darlington pair of BJTs. My question is if I need to put a 1kohm resistor between my MCU pin and the BASE to use it as a switch. Since the Hfe ratio for my transistor is ...
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Prevent high-side BJT saturation

I am building high-speed (10-20ns on BC847-class transistors) digital "buffer"/"inverter" out of BJTs. Scheme is attached. While I can prevent saturation of low-side BJT by adding Schottky diode, it'...
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1answer
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Common Base Amplifier - Hybrid-Pi vs. T Model

I have a common base amplifier with a source resistance and a load resistor. I am trying to solve for the system gain including the source resistor with both the hybrid-pi and T model but seem to be ...
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When is a MOSFET more appropriate as a switch than a BJT?

In my experimentation, I've used only BJTs as switches (for turning on and off things like LEDs and such) for my MCU outputs. I've been repeatedly told, however, that N-channel enhancement-mode ...
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How do I saturate an NPN transistor?

I understand that in "saturation mode", a BJT functions as a simple switch. I've used this before driving LEDs, but I'm not sure I understand clearly how I got the transistor into that state. Does a ...
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3answers
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What's the difference between NPN and PNP transistors?

Suppose that I know how an NPN transistor works. How different is a PNP transistor? What are the operational differences between a PNP and a NPN?
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How do BJT transistors work in a saturated state?

This is what I know about NPN BJTs (Bipolar Junction Transistors): The Base-Emitter current is amplified HFE times at Collector-Emitter, so that Ice = Ibe * HFE <...
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5answers
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Low-noise audio-frequency BJT? [closed]

I found myself looking for a low-noise PNP transistor the other day. I couldn't find any parametric searches that listed noise performance. Even from the transistor manufacturers. You can search by ...
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2answers
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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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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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4answers
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Connecting piezo buzzer with BJT

I have a 4 KHz piezo buzzer and a microcontroller (arduino) that outputs that 4 KHz from one of it's pins. All is fine if I connect the buzzer to the output with one pin and to the ground with another....
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1answer
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How should I understand the amount of base current in BJT transistors?

I'm having trouble understanding how much current flows through the base of a BJT. With a MOSFET the answer is easy: 0. How do I calculate the amount of base current in a BJT and am I doing it wrong ...
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I don't quite understand this FET-BJT preamp circuit

I see this circuit a lot on electret microphone preamps, but I don't quite understand it. The FET is operated as a common source amplifier, so it has gain, inverts, and has relatively high output ...