Question

Which of the following statements is true?

(a) Solid state switches are applications for an AC output

(b) LED’s can be driven by transistor logics

(c) Only NPN transistor can be used as a switch

(d) Transistor operates as a switch only in active region

The question was posed to me in a job interview.

I'm obligated to ask this question of Transistor as a Switch in section Transistor Characteristics of Electronic Devices & Circuits

Answer 1

The correct answer is (b) LED’s can be driven by transistor logics

To explain I would say: Output devices like LED’s only require a few milliamps at logic level DC voltages and can therefore be driven directly by the output of a logic gate. However, high power devices such as motors or lamps require more power than that supplied by an ordinary logic gate so transistor switches are used.