Patent ID: 8174802
Filing Date: 2012-05-08
Classification: H02M

Abstract:
1. A switching regulator which converts a power source voltage input to an input terminal into a predetermined constant voltage and outputs the predetermined constant voltage from an output terminal as an output voltage, comprising: a first switching element which switches between on and off statuses corresponding to an input control signal; an inductor which is electrically charged by the power source voltage when the first switching element is switched to the on status; a rectifying element which causes the inductor to discharge electric charges when charging of the inductor is stopped while the first switching element is switched to the off status; a control circuit section which controls switching the first switching element between the on and off statuses so that the output voltage to be output from the output terminal becomes equal to the predetermined constant voltage; an overcurrent detecting circuit section which detects an overcurrent output from the output terminal and causes the control circuit section to switch off the first switching element so that the first switching element enters a cut-off status when a predetermined delay period has passed after detection of the overcurrent; and an UVLO (under-voltage lockout) circuit which causes the control circuit section to switch off the first switching element, when the power source voltage is lowered to a value less than a first predetermined value, the UVLO circuit causing the overcurrent detecting circuit section to stop counting the delay period and to reset the delay period to an initial value, when the power source voltage is lowered to a value less than a second predetermined value which is lower than the first predetermined value, wherein the UVLO circuit includes a proportional voltage generating circuit which generates a first proportional voltage that is proportional to the power source voltage and a second proportional voltage that is proportional to the power source voltage and is greater than the first proportional voltage, the proportional voltage generating circuit including a first reference voltage generating circuit which generates a predetermined first reference voltage, a first voltage comparing circuit which compares the first proportional voltage with the first reference voltage and generates a first low voltage detection signal signifying a comparison result and outputs the first low voltage detection signal, and a second voltage comparing circuit which compares the second proportional voltage with the first reference voltage and generates a second low voltage detection signal signifying a comparison result and outputs the second low voltage detection signal, and wherein the control circuit section switches off the first switching element when the first low voltage detection signal output from the first voltage comparing circuit signifies that the first proportional voltage is a value less than the first reference voltage, and the overcurrent detecting circuit section is caused to stop counting the delay period and to reset the delay period to an initial value when the second low voltage detection signal output from the second voltage comparing circuit signifies that the second proportional voltage is a value less than the first reference voltage.