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Surge Current Limiter for Switching Regulator

IP.com Disclosure Number: IPCOM000052964D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

Driscoll, CD: AUTHOR [+2]

Abstract

A surge-limiting resistor is connected in series with a bulk capacitor in a switching regulator. The surge-limiting resistor can be bypassed after an initial startup period to avoid unnecessary power dissipation.

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Surge Current Limiter for Switching Regulator

A surge-limiting resistor is connected in series with a bulk capacitor in a switching regulator. The surge-limiting resistor can be bypassed after an initial startup period to avoid unnecessary power dissipation.

Referring to the drawing, a full-wave bridge 10 is driven by an AC line source through contacts 12A and 12B. The contacts 12A and 12B are ganged with a contact 12C, which is closed when contacts 12A and 12B are open, and vice versa. The output side of the full-wave bridge 10 is connected to a bulk capacitor 14 in series with a surge-limiting resistor 16. A diode 18 and a bypass SCR 20 are connected in parallel with surge-limiting resistor 16.

The control circuit for the bypass SCR 20 includes a fixed interval timer 22 having a control output to a transistor 24 and a reset input which can be selectively connected to ground through the contact 12C.

Initially, contacts 12A and 12B are open, and capacitor 14 is fully discharged. Timer 22 is disabled by the ground potential at its reset input. When contacts 12A and 12B are closed, contact 12C opens to start the timer 22. Timer 22 holds transistor 24 off for a fixed interval of time. The gate of SCR 20 is held at ground, keeping SCR 20 in its non-conductive state. The rectified output of bridge 10 charges bulk capacitor 14. The surge current is limited by resistor 16 during this time.

When timer 22 times out, transistor 24 is triggered into conduction. The resulting voltage across resistor 26 triggers SCR 20 into conduction to bypass the surge-limiting resistor 16. With resistor 16 out...