Current limit circuit for power supply regulators

Abstract

Most power supply regulators either cause the output voltage to drop-off gradually, or caused output oscillation upon reaching or exceeding the limit current. Current limit feedback to an error amplifier within a switching regulator is used to control the output voltage, prevent oscillation, insure that current limiting does not occur until a well-defined threshold is achieved and then steeply limit the current. The circuit uses feedback to the switching regulator to maintain the output voltage within desired limits. The output current flows through the current limit resistor R c thus providing a voltage proportional to the current at the base-emitter junction of Q 1 via CR 1 and R 2 . During normal operation, the forward biased CR 1 voltage maintains a reverse bias on the B-E junction of Q 1 . When the voltage across R c exceeds the forward bias on CR 1 , Q 1 turns on, hence turning on Q 2 , thus providing its contribution to the current limit feedback circuitry for use by the switching regulator.

What is claimed is: 
     
       1. A circuit for regulating voltage in a power supply, comprising: a power control circuit means for controlling a voltage of a power source,   a current limiting means for generating a feedback signal to said power control circuit means while limiting current to an output, and   a feedback circuit means for scaling a signal from a signal generation means to be sent to said power control circuit means.