Pnp High Side Switch

Notice that the emitter is connected to the positive voltage.

Pnp high side switch.

So the vgs in this case is 0 volts. Just use an integrated high side switch something like auri3313 and a sot323 transistor and you have a high side switch with 10mohm 20a thermal protection short circuit protection for few. The arrow in the emitter of a pnp transistor points in the opposite direction than in an npn transistor. That means the vgs is 5v 5v 0v.

The opposite of the low side switch is the high side switch. Building a high side switch with 2 components. This requires both a robust low on resistance power switch and accurate analog circuitry for diagnostic protection and control functions. The source is also at 5 volts.

Because of how transistors work these can be a little more difficult to use in an arduino or raspberry pi circuit. The real switch is still the pnp transistor on the right. Now this is the same circuit but the gate is connected to ground instead of 5 volts. Using pnp transistors is essentially the same as npn transistors except the polarities are reversed.

Figure 8 2 shows a circuit using a pnp transistor as a high side switch. Typically these use a pnp bjt or p channel mosfet. A p channel mosfet and a resistor. The gate is now at 5 volts.

Look at the voltages in this high side switch configuration. High side switches can safely drive high currents into complex resistive inductive and capacitive grounded loads in compliance with the harsh automotive environment. Which means that pnp transistor shown in the first image will always be on regardless of the i o pin state.