In the early days, PNP bipolar transistors were common, but the bulk of circuits you see today use NPN transistors. As [Aaron Danner] points out, many people think PNP transistors are “backward” but ...

Over the recent weeks here at Hackaday, we’ve been taking a look at the humble transistor. In a series whose impetus came from a friend musing upon his students arriving with highly developed ...

1. Bob Pease used an LM334 current source to servo the current from a PNP transistor through an LED diode. The LM334 will draw current into its V+ pin until the voltage on the R pin reaches 0.068 V.