Wholly integrated protection from the effects of a short circuit

Details Wholly integrated protection from the effects of a short circuit Wholly integrated protection from the effects of a short circuit

1999-09-24

2000-05-09

Tso, Edward H.

Electric power conversion systems

Current conversion

Including automatic or integral protection means

363 21, 363 97, H02M 318

Patent

active

060612576

ABSTRACT:
A method and device of protection from the effects of a persistent short circuit of the output of a DC-DC flyback converter self-oscillating either at a variable frequency or functioning at a fixed frequency in a discontinuous manner is provided. The voltage induced from the current flowing in a secondary winding of a transformer on the auxiliary winding is rectified and filtered to power, during a steady state of operation, the control circuitry of the converter. The turning on of the power switch is driven during a start-up or recovery phase by a primary control loop, when the supply voltage of the control circuit reaches or is over a preestablished enabling threshold of the control circuit. A secondary control loop includes a photocoupler of the output error voltage to an input of the control circuitry to which a compensation capacitor is connected. An output short circuit condition is discriminated from a start-up or recovery condition by comparing the voltage present on the auxiliary winding with a preestablished threshold which is higher than the voltage that is induced on the auxiliary winding under a short circuit condition of the secondary winding. And, the voltage existing on the compensation capacitor is compared with a second threshold of value equal or close to the value of maximum charge of the compensation capacitor, within a time interval sufficiently delayed from the turn-off instant of the power switch.

REFERENCES:
patent: 4724363 (1988-02-01), Buer
patent: 4763238 (1988-08-01), Maige
patent: 5949154 (1999-09-01), Williams

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