(Forgive me if I make a few mistakes in the text. My knowledge of the English language is poor.) I started learning how transistors work and I've got a question. Does the supply voltage affect the collector current? Since we have a resistor in the collector circuit, we should have a current in a collector circuit. I know that books say that base current affects collector current, but I haven't seen any of them mention the effect of supply voltage on it.
Edit: I guess I should specify that I'm talking about common emitter amplifier

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    \$\begingroup\$ It depends on the circuit the transistor is part of. You need to ask about a specific example. \$\endgroup\$
    – Finbarr
    Apr 2, 2022 at 10:55
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    \$\begingroup\$ The base current does not "affect" the collector current Ic. It is the base-emitter voltage which affects the current Ic. As long as the collector voltage is large enough (some volts) not to open the base-collector pn junction, the supply voltage has only a minor influence on the current Ic (Early effect). \$\endgroup\$
    – LvW
    Apr 2, 2022 at 11:24
  • \$\begingroup\$ Magnum, @LvW writes well about the topic. Careful thought regarding what he writes will advance your understanding. Worth the time. The base current is a recombination current that is required in order to keep the BJT operating when in active mode. It happens that this ratio, collector to base current, remains somewhat constant over several orders of magnitude range of currents -- for a specific BJT device. But any two devices may have quite a variance in this ratio, between them. So its specific value cannot be relied upon (its constancy can often be, but that doesn't help much in design.) \$\endgroup\$
    – jonk
    Apr 2, 2022 at 18:54

1 Answer 1


Google pictures of curve tracer output for a transistor. Note that Vce tends to be on axis X, and the resulting Ic on axis Y. The diagram typically shows several traces, at specific levels of base current Ib.

There's a simple transistor-based circuit that strives specifically to have the collector current independent of collector voltage - it's called the constant current source, and it's a crucial building block of modern linear analog electronics and integrated circuits. As a further reading, even just to take a glimpse ahead if you're a novice, I'd suggest a free book called Designing analog chips by Hans Camenzind.

I agree with the others - supply voltage is a parameter of the whole circuit topology, not just the sole transistor. So I do not mean to put Vce equal to supply voltage - they may be two different things.

One tangential note: as a general rule, increasing the supply voltage of a circuit tends to make it work faster. Logic achieves faster switching, analog amps get a higher slew rate and broader bandwidth. An analog amp that's borderline unstable may be convergent below a certain level of power supply voltage, but may oscillate at higher power supply voltages.


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