When a p channel enhancement type mosfet has no voltage at its gate it is off and no current conducts across from source to drain.
P channel mosfet load switch circuit.
Keep in mind that you may never find a depletion mode p channel.
In most of the cases n channel mosfets are preferred over p channel mosfets for several advantages.
When there is sufficient voltage at the gate about 3v the mosfet is on and current conducts across from the source to the drain to power on the load.
N channel mosfet circuit on the left p channel mosfet circuit on the right.
Resistor r gs is used as a pull down resistor to help pull the ttl output voltage down to 0v when the mosfet is switched off.
Like with the low side you probably want to use an enhancement mode mosfet.
For a p channel mosfet the source connects to the voltage source and the drain connects to the load s positive side.
Notice the similarities and differences between figs.
When using a p channel mosfet in a load switch circuit as in figure 1 the source is directly connected to the input voltage rail and the drain is connected to the load.
In a mosfets switching circuit the drain is connected directly to the input voltage and the source is connected to the load.
Thus the load connected to the mosfet will not turn on.
A simple load switch typically consists of a mosfet pass transistor that is controlled by a gate driver circuit that level shifts the input control signal to a value that will fully turn on the mosfet reducing the device s on resistance to its lowest possible level.
Although the p channel mosfet cannot.
We would need to dedicate a tutorial on when to use an n channel and p channel mosfet.
They only exist in textbooks and as data entry errors.
Thus far we have looked at the n channel mosfet as a switch were the mosfet is placed between the load and the ground.
For example if you re trying to turn on a 5 volt relay with an arduino.
Mosfet passes the voltage supply to a specific load when the transistor is on.
Yet despite its shortcomings the p channel mosfet performs a vital ªhigh sideº switch task that the n channel simply cannot equal.
In order for the p channel load switch to turn on the source to gate voltage must be greater than the threshold voltage.
An excellent use for p channel is in a circuit where your load s voltage is the same as your logic s voltage levels.
