n. Saving power with p-MOSFET switches

Most IC based devices have modules that can be turned off to save power. Probably the simplest way to control power supply to certain modules from a power management module is through p-MOSFET switches. A simple MOSFET switch which is controlled by a digital output can be implemented with one transistor, capacitor and two resistors. To assure that the switch fully opens it is important that the gate threshold is low enough to be fully opened at +3.3 V or +5 V. The switch must also fully close at about +0.8 V. The next concern is the electric current load. The transistor must be able to withstand the maximum current required by the module. Low power p-MOSFET transistors allow up to 100 mA to 200 mA. This should be sufficient to supply power to an average microcontroller (at least when it is being programmed). This kind of switches is therefore commonly used in PIC programmers. If you need more power, just use a power p-MOSFET transistor. They go up to 20 A. The parasite current on a power p-MOSFET transistor gate input is still negligible.

Here is the circuit diagram: