Which is better for controlling a relay on a circuit? An NPN or PNP transistor?
It all depends on the type of control to be performed. If a relay must be de-energized for a longer time than energized, the ideal is to use an NPN transistor, as the transistor will drive for less time and with this the power consumption of the device will be less. However, if it stays on longer, switching off for short intervals, the ideal is to use a PNP transistor and switch it with a low voltage level at the input (grounding), as it will drive for less time and consumption will be less.
