Usually the source pin must be more positive than the drain however this isn t true when using a p mosfet to provide reverse polarity protection for instance.
P channel mosfet high side switch.
There are a variety of configurations for driving the two mosfets with many different applications.
Then the p channel mosfet is used to switch the positive supply to the motor for forward direction high side switching while the n channel mosfet is used to switch the negative supply to the motor for reverse direction low side switching.
If your load voltage is higher like 12 or 24v then you might want to use an n channel mosfet in a low side configuration.
Because of how transistors work these can be a little more difficult to use in an arduino or raspberry pi circuit.
This transistor connects between v and the load.
The opposite of the low side switch is the high side switch.
Typically these use a pnp bjt or p channel mosfet.
P channel mosfet high side switch here s my schematic and board design for a simple high side switch using a p channel mosfet.
It s a simple circuit that has a input for positive and negative and an output for positive and negative connections.
To switch v with a p channel mosfet use a p channel mosfet with source connected to v either directly or via a current limiting resistor and the load connected to drain.
No charge pump is required for driving the high side switch.
In this configuration when the high side switch is realized with a p channel mosfet the driver design will be simplified enormously.
However this cure can also have some side effects.
The p channel high side switch therefore solves the problem of using an n channel mosfet for high side switching.
It can easily be driven by the mcu via a level shifter.
In this case use a p channel mosfet to turn the relay on from the arduino s i o pin.