Why is a transistor used to discharge a capacitor?

Question

Electronics

Good evening, gentlemen, why the transistor?
What other elements can replace a transistor in order to cause a discharge of a capacitor in a DC circuit after it is charged?
And tell me more, for what needs is a capacitor installed in DC circuits?
I saw them on the motherboard and not one, it is unlikely that they are there exclusively for launching fans or what?

Answer 1

Why is a transistor used to discharge a capacitor?

The title of your question is erroneous, not only a transistor, but also a thyristor, a relay (with its contacts), a push button (with its contacts) and similar devices that can break and close an electrical circuit can act as a key for controlling the passage of electric current.

in this circuit, the transistor opens exclusively by avalanche breakdown, there is no control here.

This comment of yours is also wrong. It would be true if only avalanche transistors existed in the world, and they are both the usual bipolar ones, opened by the base current, and field ones, opened by the gate voltage. If you refer to the fact that on a working device the base output is also broken, as in your circuit, then there will be an error here too - there are optical transistors that are opened by crystal illumination. True, it is still generally accepted to connect the base output with a resistor to the emitter, because with the base thrown in the air, the key operation parameters are unstable.