Peter J Resca

US Patent:

56943059, Dec 2, 1997

Filed:

Aug 30, 1996

Appl. No.:

8/705775

Inventors:

William King - Attleboro MA
Peter Resca - Braintree MA

Assignee:

Astrodyne Corporation - Taunton MA

International Classification:

H02M 3335

US Classification:

363 21

Abstract:

Protection circuitry incorporates detection circuitry and first and second timer circuits to protect power supply apparatus and associated circuitry from damage due to excessive voltages and/or currents. The detection circuitry initiates the first timer upon detecting potentially damaging voltages and/or currents, caused by, for example, a source or load impedance far different from that for which the power supply apparatus is designed. If the abnormal voltages and/or currents persist for longer than a first period of time, the first timer initiates a second timer that reduces the power output of the power supply apparatus for a second period of time. After expiration of the second period of time, the power supply apparatus returns to normal operation. The cycle described above an repeat indefinitely if necessary to protect against, for example, a sustained short circuit. Incorporation of two timers allows the power supply apparatus to properly power variable loads, such as a motor, that initially draw large current but that do not represent an abnormal load impedance, and to adequately protect the apparatus and associated circuitry from damage.