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Control Circuit for Switching Regulator

IP.com Disclosure Number: IPCOM000045801D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 50K

Publishing Venue

IBM

Related People

Radcliffe, JK: AUTHOR

Abstract

A known integrated circuit timer is used as a combination summing device, level detector and single-shot in the control circuit for a switching regulator transistor of a variable-frequency flyback switching regulator.

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Control Circuit for Switching Regulator

A known integrated circuit timer is used as a combination summing device, level detector and single-shot in the control circuit for a switching regulator transistor of a variable-frequency flyback switching regulator.

By way of example, the control circuit 10 (Fig. 1) controls the base current drive circuit of a common-emitter switching regulator transistor (not shown) located in the power stage (not shown) of a triangular-wave flyback converter. The transistor collector (not shown) is connected in series with the primary winding (not shown) of the converter's partially shown flyback transformer T1. The base drive control circuits and the base drive circuits controlled thereby for the switching regulator transistor of the flyback switching regulator are well known ( J. K. Radcliffe, "Driver Circuit for Switching Regulator," IBM Technical Disclosure Bulletin 24 (11A). 5501-5503 (April 1982).

Both the previous base drive control circuits and the present control circuit 10 require that an output pulse be generated when the emitter current in the switching transistor exceeds a threshold value. The threshold variation is arranged so that any drop in the output voltage allows the emitter current to obtain a larger value before the output pulse is generated.

In circuit 10, the voltage of feedback winding Nf, which is part of the converter flyback transformer T1, is rectified and filtered by diode D1 and capacitor C2, to produce a feedback voltage Vfb. Voltage Vfb has a dual function, i.e., it acts as a sense voltage source for the timer 20 and as the power source for circuit 10. A reference voltage Vr is derived from voltage Vfb through Zener diode D2 and resistor network R3, R4, and R5 with an approximate value of: Vr=Vfb/3. Voltage Vr is applied to the input TRIGGER of timer 20, which is configured in a monostable operational mode.

The timer comparator 21 compares voltages Vr and Vc. Voltage Vc has two superimposed components hereinafter discussed. If voltage Vr is more negative than voltage Vc, the timer flip-flop 22 is triggered resulting, via timer output stage 23, in a single pulse V...