Low power fan drive circuit for personal computers

摘要

An efficient fan drive circuit to drive a variable fan used in a power supply of a personal computer system. The fan drive circuit uses a diode to establish the minimum fan speed during operation in the normal temperature range. The bleeder resistor normally coupled between the fan and a negative output voltage is removed and replaced with a current source. The current source also serves to shut down the power supply if the fan is not operating properly or is not installed. A shut down circuit remains to shut down the power supply when excessive temperature occurs, or when the current source detects that the fan is malfunctioning or not installed.