Multiple output flyback DC-to-DC converter with synchronous rect

Details Multiple output flyback DC-to-DC converter with synchronous rect Multiple output flyback DC-to-DC converter with synchronous rect

1995-09-19

1997-09-02

Wong, Peter S.

Electric power conversion systems

Current conversion

Including d.c.-a.c.-d.c. converter

363 97, 363131, H02M 3335

Patent

active

056638744

ABSTRACT:
A multiple output flyback DC-to-DC converter with synchronous rectification and constant on-time current-mode control. A controller includes a constant on-time, minimum off-time oscillator that is coupled to control a gate of a first transistor which controls a current through a primary winding of a transformer having three secondary coupled inductors. Each of the three secondaries is coupled to a capacitor which is charged by each secondary current to an output voltage level which depends, in part, upon a ratio of windings. A transistor is coupled between each secondary winding and a resistive network. The gates of these transistors are coupled to be controlled by the controller for synchronous rectification. The resistive network monitors the secondary currents by generating a voltage signal that is representative of a weighted sum of the inductor currents. A difference between an output voltage level and a reference voltage level is added to the voltage signal generated by the resistive network for controlling the oscillator. When the voltage signal generated by the resistive network reaches a first predetermined level, the off-time of the oscillator is terminated and a new on-time is started, causing additional current to flow through the primary winding. When the output voltage level decreases, the first predetermined level is decreased. If the output voltage exceeds a second predetermined level, the controller enters a discontinuous mode whereby the oscillator halts until the output voltage drops below the second predetermined level.

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