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Low Power Start Circuit for Switching Regulator

IP.com Disclosure Number: IPCOM000052962D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Driscoll, CD: AUTHOR [+2]

Abstract

This article describes a switching regulator start circuit in which an initial bias voltage is developed through an RC charging circuit connected to the bulk voltage circuit. The charging circuit is disabled by a voltage-sensitive control circuit after startup to reduce power dissipation.

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Low Power Start Circuit for Switching Regulator

This article describes a switching regulator start circuit in which an initial bias voltage is developed through an RC charging circuit connected to the bulk voltage circuit. The charging circuit is disabled by a voltage-sensitive control circuit after startup to reduce power dissipation.

Line-operated switching regulators lacking a separate bias supply must generate an internal bias voltage to drive their control circuits. During the startup period, the bias voltage is developed directly from the bulk voltage through an RC charging circuit. After the startup period, the voltage is usually obtained from a winding on the output transformer. While the RC charging circuit serves no function following the startup period, it remains in the circuit and results in considerable power dissipation.

The drawing illustrates a start circuit for a switching regulator including a full- wave bridge rectifier 10 driven from an AC line. The bulk voltage power supply includes a bulk capacitor 12 and a diode 14. The start circuit includes an RC charging circuit connected between the positive output of bridge 10 and ground. The charging circuit includes, in series, a resistor 16, an SCR 18 and a capacitor 2O. The bias voltage is equal to the voltage across capacitor 20.

The control circuit for SCR 18 includes a first resistor 22, a second resistor 24 and a transistor 26, the base bias for which is controlled by a voltage-sensing circuit...