Importance

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Abstract

A regulating control circuit for a single-ended switching power supply includes means for controlling the switching duty cycle during start-up, normal operation and current limiting modes. Normal operation utilizes a duty cycle of less than about 50%, but low input voltage operation can occur for limited times at duty cycles up to 70%-80%. A time base generator defines the maximum permissible switch conduction time, as well as the switching rate. During start-up, input current is restricted to reduce dissipation within the control circuit, the start-up duty cycle also being maintained at a low value by extending the switch non-conduction time. In the current limiting mode, the duty cycle is reduced as a function of current demand to achieve constant current operation over a given range of output voltages, and to achieve current foldback below such range. In current foldback, the switch non-conduction period is extended to obtain unusually low duty cycles in near shorted output conditions.

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First Claim