Switching power supply
AssigneeMotorola, Inc.
InventorJade H. Alberkrack
Life of this patent
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Abstract
A switching power supply includes a two input NAND gate one input of which is coupled to a differentiated fixed frequency signal. The output of the NAND gate is coupled to an output switching device which drives a transformer. The output voltage appearing across the secondary winding of the transformer is compared with a reference voltage in a comparator which drives a light emitting diode. The light emitting diode is optically coupled to a pulse width modulator circuit for varying the width of pulses applied to the first input of the NAND gate. The circuit also includes soft start and over-current protection features.
Claims9
A switching type power supply for receiving a fixed frequency pulse train at its input and generating therefrom an output voltage, comprising:
- first means having a variable resistance for differentiating said fixed frequency pulse train to produce a differentiated pulse train;
- a Schmidt NAND gate having first and second inputs and an output, said first input coupled to said first means for receiving said differentiated pulse train;
- switching means coupled to the output of said NAND gate;
- a transformer having primary and secondary windings, said primary winding coupled to said switching means and inducing a voltage across said secondary winding;
- second means coupled to said secondary winding for generating said output voltage;
- a source of a reference voltage;
- third means for comparing said reference voltage with said output voltage and for generating a signal indicative of the difference therebetween;
- fourth means coupled to said first means and said third means and responsive to said signal for varying the resistance of said first means;
- and
- fifth means coupled to said switching means and to the second input of said NAND gate for controlling passage of said differentiated pulse train through said NAND gate.
Dependencies are inferred from the claim text.