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Transistor Switching Regulator Control Circuit

IP.com Disclosure Number: IPCOM000080337D
Original Publication Date: 1973-Dec-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Wenzel, EP: AUTHOR

Abstract

The control circuit of this regulator provides protection during turnon and protection from short circuits. The switching device is confined to a safe operating area by placing it in a current-limit mode during turnon and short duration overloads, and the device is shutdown entirely in the event of a longer duration overload.

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Transistor Switching Regulator Control Circuit

The control circuit of this regulator provides protection during turnon and protection from short circuits. The switching device is confined to a safe operating area by placing it in a current-limit mode during turnon and short duration overloads, and the device is shutdown entirely in the event of a longer duration overload.

The control circuit is shown with a flyback switching regulator. Switching transistor Q5 passes current in pulses from Ein through transformer T primary
10. Diode D3 is poled with respect to secondary 12, to pass energy stored in the core of T to load RL when Q5 shuts off. Feedback winding 14 provides voltage Es during the off time of Q5 through a filter, not shown. Es provides a feedback signal 16 which is compared to a reference 18 by differential amplifier 20 to provide a control level on 22, which, via Q2, controls multivibrator M. In turn, M controls Q4 via 24 to provide the on-off operation of Q5.

During start-up of the circuit, Es is small and D1 is back biased. Current is provided from Ein through R7 to power M and, through R3, to the emitter of Q1. Ein through R3 turns on Q1 which, through D2, turns on Q2. Conduction of Q2 causes M to have a short on time output, which causes Q4 to have a short off time and Q5 a short on time.

If there is no overload during start-up, Es rises and forward biases D1, thereby turning over control of Q2 to the output of 20 so that the feedback loop is opera...