Patent ID: 8237415

Claim:
A control circuit for controlling ON and OFF states of a switching transistor arranged on a path of a primary coil of a transformer of a capacitor charging circuit, the control circuit comprising: an output voltage monitoring circuit which monitors output voltage of the capacitor charging circuit; wherein the output voltage monitoring circuit includes a first sample-and-hold circuit which samples and holds voltage of a connection point of the primary coil of the transformer and the switching transistor, in an OFF period of the switching transistor; and a first monitoring comparator which compares output of the first sample-and-hold circuit with a predetermined first reference voltage; and when the output of the first sample-and-hold circuit exceeds the first reference voltage, executes predetermined signal processing, wherein the first sample-and-hold circuit starts a sampling period after a predetermined first time-period has elapsed after the switching transistor is turned OFF, and wherein the output voltage monitoring circuit further includes a first delay circuit which delays by the first time-period a switching signal controlling ON and OFF states of the switching transistor; and the first sample-and-hold circuit uses output of the first delay circuit to start a sampling period.