The circuit above is called a low side switch because the switch our transistor is on the low ground side of the circuit.
Pnp high side switch circuit.
Figure 8 2 shows a circuit using a pnp transistor as a high side switch.
Alternatively we can use a pnp transistor to create a high side switch.
Microcontroller interfacing part 12.
We ll need a more complex circuit to implement a practical high side power on switch.
The schematic below shows how a transistor is used to switch the light emitting diode led.
The real switch is still the pnp transistor on the right.
Notice that the emitter is connected to the positive voltage.
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.
This transistor connects between v and the load.
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.
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.
Using pnp transistors to switch higher voltage loads.
That means the vgs is 5v 5v 0v.
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.
Look at the voltages in this high side switch configuration.
One limitation with the circuit described in.
The source is also at 5 volts.
Therefore the circuit acts as open circuit and the led becomes off.
Similar to the npn circuit the base is our input and the emitter is tied to a constant voltage.
This voltage means the mosfet is turned off or an open.
The gate is now at 5 volts.
So the vgs in this case is 0 volts.
Here we are using electron flow from negative to positive this is often known as a series pass configuration.
Using pnp transistors is essentially the same as npn transistors except the polarities are reversed.
The opposite of the low side switch is the high side switch.
Because of how transistors work these can be a little more difficult to use in an arduino or raspberry pi circuit.
Which means that pnp transistor shown in the first image will always be on regardless of the i o pin state.
Typically these use a pnp bjt or p channel mosfet.
This time however the emitter is tied high.
