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Short-circuit-protection-for-power-factor-correction-circuit

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Short circuit protection for power factor correction circuit

Details

Inventors: Ho, Simon Mo Chan;
Assignee: Astec International Limited (Wanchai, HK)
Primary Examiner: Gaffin; Jeffrey A.
Assistant Examiner: Huynh; Thuy-Trang N.
Attorney, Agent or Firm: Coudert Brothers

In a power factor correction circuit using a control power MOSFET connected in series between the boost converter and the output, overcurrent damage to the power MOSFET upon occurrence of a short circuit in the output is prevented by sensing a drop in the output voltage below a predetermined level above the peak of the rectified AC boost converter input, and shutting the power MOSFET off when such a drop is sensed.

DETAILED DESCRIPTION The present invention accomplishes the desired result by monitoring not the power MOSFET current itself, but rather the relationship between the input voltage and the output voltage.
A function of the voltage at the input to the boost converter, increased a fixed amount by a zener diode or a resistive network, is applied to one input of a comparator, while a function of the output voltage is applied to the other input of the comparator.
The comparator output is applied to a gate drive which shuts off the power MOSFET if the comparison indicates a short circuit condition.
Normally, the output voltage is always higher than the zener-adjusted input voltage.
When a short circuit occurs, however, on the output side of the power MOSFET, the output voltage instantly drops below the zener-adjusted peak input voltage.
This condition triggers shutoff in the inventive circuit before the current through the power MOSFET has time to build up to a harmful level.

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