Circuit for clamping power output to ground while the computer is deactivated

摘要

A circuit for connecting the power supply output of a computer to ground when the system is shut down to counter adverse effects of backfeed voltage which includes a MOSFET between the power supply output and ground. In one embodiment the MOSFET is switched on by a signal that deactivates the system power supply. In an alternative embodiment, two MOSFETs are used. The first MOSFET is controlled directly by the power supply output and shorts the second MOSFET's gate to ground when the power supply output generates a significant voltage. If the second MOSFET's gate is grounded, the MOSFET deactivates and opens a circuit between the power supply output and ground. When the power supply is turned off, the second MOSFET activates and grounds the power supply output. A resistor between the power supply output and ground allows the power supply to generate five volts when the system is power cycled and deactivate the second MOSFET.