Patent ID: 6683765
Filing Date: 2004-01-27
Classification: G05F

Abstract:
A switching power unit comprising:a switching element for switching an input d.c. voltage in response to an oscillation signal from oscillating means so as to obtain a voltage output of a desired level; overcurrent protecting means for shortening a switching pulse width so as to restrict an output current when overcurrent detection means detects that the output current is larger than a predetermined value; latching means for latching an overcurrent detection output from the overcurrent detection means for a period longer than a delay time taken to realize a protecting operation by means of the overcurrent protecting means; first oscillation frequency dropping means for dropping an oscillation frequency of the oscillating means from a first oscillation frequency under a normal condition to (a) an oscillation frequency lower than the first oscillation frequency and (b) a second oscillation frequency of a cycle longer than the delay time, in response to an output from the latching means; and second oscillation frequency dropping means for detecting a drop of an output voltage of a predetermined level so as to drop the oscillation frequency of the oscillating means to a third oscillation frequency lower than the second oscillation frequency.