Linked Questions

10
votes
11answers
4k views

Why is a BJT considered “current-controlled”?

With BJTs, we can control base current using Vin (from diagram). Why do textbooks state that BJTs are current controlled when it's obvious that changing the voltage controls the current through the ...
6
votes
3answers
4k views

Can this transistor (2N2222) take 6 V on emitter-base? Am I reading the datasheet incorrectly?

I have created the following circuit to better understand how to use a transistor as a switch*. I've been struggling with understanding datasheets for transistors. simulate this circuit – ...
3
votes
3answers
2k views

Terminology for BJT “regions of operation”

How regions (modes) of operation are defined and correctly named? The most controversial thing is the so named “saturated region/mode”. It is defined differently, sometimes radically different, in ...
0
votes
2answers
4k views

A confusion about the formula for transistor Vbe Ic characterisitcs

Below is NPN BJT transistor Vbe Ic characteristics and the formula: Many texts approximate this equation as: Ic = Is*e^(Vbe/Ut) and following this they say when Vbe=0, Ic becomes equal to Is. ...
2
votes
4answers
6k views

How does the current travel in Bipolar Junction Transistor (BJT)?

I am completely unable to understand the current direction in npn transistor. in figure 1, the red arrow indicates the electron flow(which is from emitter terminal to collector terminal). thus ...
5
votes
3answers
895 views

Differential and Multistage Amplifiers(BJT)

I want to determine the currents in each of the branches. I could analyse the current mirror portion and the differential amplifier portion, but facing problem thereafter. I could find the ...
2
votes
2answers
762 views

Input stage of a current mirror circuit

I'm trying to understand current mirror circuits and I've been reading this article. I'm unable to understand the input part of the circuit where the author says "Producing the opposite where the ...
5
votes
2answers
570 views

How to derive the precise gain of an NPN common emitter amplifier without emitter degeneration?

As a self imposed exercise, I tried to derive the complete expression of gain in a common emitter amplifier without emitter degeneration. I mean by "complete" that it also takes into account ...
1
vote
2answers
3k views

BJT: Equation of Vce for Saturation Region

In Sedra and Smith: Microelectronics Circuits (6E), it is mentioned, on page 185: Recalling that the CBJ is much larger than the EBJ, the forward-voltage drop \$v_{BC}\$ will be smaller than \$v_{...
2
votes
2answers
2k views

Dependence of transistor current gain on operating conditions

According to "Gray & Meyer: Analysis and Design of Analog integrated circuits" transistor current gain Beta (in forward-active region) depend on operating conditions of the transistor. Region 1 ...
3
votes
1answer
4k views

Relationship between base-emitter voltage, base current and collector current

I'm reading Sedra's Microelectronics book and I can't understand the following: We can get a relationship between \$I_b\$ and \$V_{BE}\$ (DC): $$I_B=\frac{V_{BB}}{R_B}-\frac{1}{R_B}V_{BE}$$ This ...
0
votes
1answer
2k views

what is the input impedance of a transistor (bjt)

That is the Hybrid-Pi model of the voltage amplifier i have. In our lectures we haven't been taught about anything regarding the Hybrid-Pi or transistors input impedance up till today. I figured out ...
3
votes
4answers
204 views

What's the correct sequence to start thinking about a BJT circuit

A very basic circuit as shown below, the 1V step voltage is applied @ +1V @ t=0. Edit: Unfortunately the entire question was asked based on a wrong assumption, ...
2
votes
1answer
1k views

Why Ic increases with increase in Ib?

simulate this circuit – Schematic created using CircuitLab First up I don't know if the direction of Ib is right for the pnp transistor in the circuit ( I need to know the active region ...
0
votes
2answers
2k views

Thermal voltage of a BJT vs. diode voltage drop

I'm learning about the hydrid-pi model of the BJT transistor: In this model, the base and the emitter have a resistance \$r_{\pi}\$ in between. The voltage between the base and the emitter is ...

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