As discussed earlier that the transistor can be used as a switch.
Pnp high side switch circuit.
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.
This time however the emitter is tied high.
Alternatively we can use a pnp transistor to create a high side switch.
Referring to plate 1 whenever the voltage difference between the gate g and source s exceeds around 5 volts this opens a conductive channel between source s and drain d allowing current flow from the source back to the power supply.
The opposite of the low side switch is the high side switch.
This voltage means the mosfet is turned off or an open.
The easiest way to switch a higher power load than a microcontroller can handle is to use an npn transistor as explained in part 7.
The arrow in the emitter of a pnp transistor points in the opposite direction than in an npn transistor.
This transistor connects between v and the load.
Similar to the npn circuit the base is our input and the emitter is tied to a constant voltage.
One limitation with the circuit described in.
The source is also at 5 volts.
The gate is now at 5 volts.
We ll need a more complex circuit to implement a practical high side power on switch.
The real switch is still the pnp transistor on the right.
So the vgs in this case is 0 volts.
Notice that the emitter is connected to the positive voltage.
Because of how transistors work these can be a little more difficult to use in an arduino or raspberry pi circuit.
The schematic below shows how a transistor is used to switch the light emitting diode led.
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.
Here we are using electron flow from negative to positive this is often known as a series pass configuration.
Part 8 showed how to use a pnp transistor allowing the load to be at ground potential as is sometimes necessary.
When the switch at the base terminal is open no current flows through the base so the transistor is in the cutoff state.
That means the vgs is 5v 5v 0v.
The circuit above is called a low side switch because the switch our transistor is on the low ground side of the circuit.
Using pnp transistors to switch higher voltage loads.
Look at the voltages in this high side switch configuration.
Typically these use a pnp bjt or p channel mosfet.
Now this is the same circuit but the gate is connected to ground instead of 5 volts.
