Pravel, Hewitt, Kimball & Krieger
Low power fan drive circuit for personal computers
 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. 
Compaq Computer Corp.
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inventional inventional inventional
Hai N. Richard E.
Nguyen Walker