Notice that the emitter is connected to the positive voltage.
Pnp high side switch circuit.
One limitation with the circuit described in.
Using pnp transistors is essentially the same as npn transistors except the polarities are reversed.
Which means that pnp transistor shown in the first image will always be on regardless of the i o pin state.
This voltage means the mosfet is turned off or an open.
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.
Now this is the same circuit but the gate is connected to ground instead of 5 volts.
The circuit above is called a low side switch because the switch our transistor is on the low ground side of the circuit.
Microcontroller interfacing part 12.
So the vgs in this case is 0 volts.
Part 8 showed how to use a pnp transistor allowing the load to be at ground potential as is sometimes necessary.
The source is also at 5 volts.
The gate is now at 5 volts.
Figure 8 2 shows a circuit using a pnp transistor as a high side switch.
Similar to the npn circuit the base is our input and the emitter is tied to a constant voltage.
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.
Typically these use a pnp bjt or p channel mosfet.
This transistor connects between v and the load.
Alternatively we can use a pnp transistor to create a high side switch.
This time however the emitter is tied high.
Because of how transistors work these can be a little more difficult to use in an arduino or raspberry pi circuit.
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.
As discussed earlier that the transistor can be used as a switch.
That means the vgs is 5v 5v 0v.
Here we are using electron flow from negative to positive this is often known as a series pass configuration.
Using pnp transistors to switch higher voltage loads.
The arrow in the emitter of a pnp transistor points in the opposite direction than in an npn transistor.
Therefore the circuit acts as open circuit and the led becomes off.
Look at the voltages in this high side switch configuration.
When the switch at the base terminal is open no current flows through the base so the transistor is in the cutoff state.
