Control circuit compensating for malfunction of pulse width modulation circuitry
Number of patents in Portfolio can not be more than 2000
United States of America Patent
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-
May 29, 2001
Grant Date -
N/A
app pub date -
Aug 21, 2000
filing date -
Aug 21, 2000
priority date (Note) -
Expired
status (Latency Note)
Importance
Abstract
A control circuit for a pulse width modulation (PWM) driven electric motor is provided for operating a fan or motor at a full duty cycle in the event that the PWM input signal should malfunction or fail. The control circuit includes a pulse width modulation (PWM) source having an output; a switch having a control and being coupled between a voltage source and the motor; a capacitor having an input coupled to the PWM output and an output coupled to the switch control, and a diode coupled between the PWM output and the switch control for maintaining the output of the capacitor at a predetermined minimum voltage level. In response to a substantially direct voltage level at the PWM output indicative of a failure of the PWM source, the capacitor maintains at its output a voltage level sufficient to cause the switch control to connect the voltage source to an input of the electric motor and drive the electric motor at a full duty-cycle. The diode provides d.c. restoration at the output of the capacitor to ensure that when the voltage level of the PWM output is time varying, an input voltage at the input of the motor substantially corresponds to the voltage level of the PWM output.
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