How NPN and PNP transistors work when used as switches

The difference between 1.1NPN and PnP

NPN and PnP are mainly in the direction of current and the voltage difference between positive and negative.

NPN is the current (IC) controlled c-e with B-e current (IB), the lowest e-pole potential, and usually the highest C-pole potential at normal magnification, i.e. vc>vb>ve;

PnP is the current (IC) controlled e-c with E-b current (IB), the e-pole potential is the highest, and normal amplification is usually the lowest C-pole potential, namely vc<vb<ve.

Use of 2.2NPN and PNP as switches

Transistor switch, working in the up and saturation of two states;

In general, the transistor's conduction and disconnection are controlled by controlling the base voltage UB of the transistor.

For the NPN, so that ube<uon, transistor disconnection, ube>uon, transistor conduction, wherein the general UE grounding, you only need to control UB, so that the ub>uon can make it conduction;

For PnP, so that Ueb<uon, transistor disconnection, ueb>uon, transistor conduction, which is generally UC grounding, so to make the transistor to control both the UE and control UB so that the Ueb>uon line. Therefore, the UE is usually a fixed voltage value, only by controlling UB to control the transistor conduction and disconnection.

2.3 Contrast

Compared with the NPN and PnP know: NPN switch, suitable for use in the ground terminal of the circuit, as shown in Figure 2 Q6; When PnP is switched on, it is suitable for use on the power supply side of the circuit. (This contrast is very useful when the transistor drives the relay)