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Surge Current Limiting for Power Supply

IP.com Disclosure Number: IPCOM000059617D
Original Publication Date: 1986-Jan-01
Included in the Prior Art Database: 2005-Mar-08

Publishing Venue

IBM

Related People

Authors:
Morrish, AJ [+details]

Abstract

In a power supply for a display or TV, a surge current limiting resistor is included in series with the neutral input which is short- circuited by a triac during normal operation. Gate current for the triac is provided via an additional resistor. To permit a wide range of input supply voltages, this additional resistor is replaced by a positive temperature coefficient (PTC) thermistor. An existing thermistor used for degaussing may be utilized to heat the PTC thermistor to provide a greater change of resistance. Some method is required to limit the large current pulse in the mains supply when power is connected to a power supply. This is due to the charging current in the primary smoothing capacitors.