Introduction
In battery powered applications, such as laptop computers,
power control has a major impact on battery life. For
example, laptop or notebook computers often have a “sleep”
mode, where the hard drive spins down and the display
backlighting turns off while the RAM—containing valuable
user data—is maintained. A microprocessor can easily make
such power management decisions, but implementing the hardware for the actual switching can be complicated. "Highside"
switching is required; i.e., the positive supply voltage
must be controlled. Common grounds for busses and shielding
limits the possibility of “low side” switching in a standard
negative ground system. This note discusses a logic controlled
power switch that simplifies microprocessor driven
high-side supply switching.