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Self Generated Bias Supply

IP.com Disclosure Number: IPCOM000089283D
Original Publication Date: 1977-Oct-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Hoffman, HS: AUTHOR

Abstract

A saturating transformer can be inserted in the switched current circuit of a switching regulator to provide a start-up bias supply for the regulator.

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Self Generated Bias Supply

A saturating transformer can be inserted in the switched current circuit of a switching regulator to provide a start-up bias supply for the regulator.

In the circuit of Fig. 1, flyback transformer L1 is placed in series with the main load transformer L2 of a transistor switching regulator. The flyback energy of L1 is delivered via diode D1 to charge bias capacitor C1, which provides bias energy to a bias load represented in the diagram as R1.

Prior to start up, C1 has been charged through high impedance bleeder resistor R2. C1 stores sufficient energy to power one cycle of main switch S1. In starting up, this first cycle saturates L1, the secondary of which flies back into bias capacitor C1 through D1 during the off time of S1. This supplies enough bias power for the second cycle.

The parameters are such that the minimum peak value of the current through S1 on the first cycle will saturate the core of L1 and store sufficient energy in the worst case to power a cycle. The bias voltage across C1 is regulated by skipping flyback cycles of the bias transformer L1. This is accomplished by a shunt switch S2 which shorts the secondary of L1. S2 is controlled by operational amplifier OP AMP which has a triggered output whereby S2 is always either on or off. The relative inductance values of the main load transformer L2 and the bias transformer L1 are such as to adequately limit the voltage across the shorting transistor S2 when it is off.

Fig....