Unitrode Corporation

John R Wiggenhorn

Philip R Cooke

A power supply controller implementing frequency foldback and volt-second duty cycle clamp features. An oscillator timing capacitor is charged with a fixed current and is discharged with a fixed current when the output voltage is above a predetermined level and with a decreasing current when the output voltage falls below the predetermined level, so as to decrease the power supply operating frequency during short circuit or overload fault conditions. A volt-second duty cycle clamp circuit limits the duty cycle to a maximum value which is independent of the tolerance of a capacitor which sets the maximum duty cycle as a function of the power supply input voltage.

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Cary, NC, United States of America

John R Wiggenhorn