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I have the following circuit.

enter image description here

The transistor is working in saturation mode. It means both p-n-junctions are forward-biased. Thus, there are two diffusion currents in the transistor (electrons move from the emitter and from the collector into the base, the currents of holes from base into the emitter and collector are fewer because of the fewer concentration of impurity in the base). So I expected, that the emitter current and the collector current had been equal. But it is not that in the computer model. The collector current is much greater than the emitter current. Why?

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1 Answer 1

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Your circuit is:

schematic

simulate this circuit – Schematic created using CircuitLab

which means you bring Q2's emitter and collector to exactly the same potential, so this is identical to:

schematic

simulate this circuit

So, your Q2 isn't working as a transistor, but really just as a pair of diodes: The base-emitter junction and the base-collector junction.

There's no need for these two to be identical; in fact, it's pretty typical that the base-emitter junction is better-conducting.

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  • \$\begingroup\$ Oh, I got it. Thank you very much. \$\endgroup\$
    – Tyo Hoy
    Feb 15, 2020 at 14:45

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