Patent ID: 7212417

Claim:
A dual-mode switching DC-to-DC converter capable of operation in either normal load mode or light load mode depending upon the power requirement of a load, the DC-to-DC converter having an active switch connected to DC input means via a transformer, a switch control circuit for controllably driving the active switch, a first rectifying and smoothing circuit connected between the transformer and DC output means for providing a DC output voltage to be applied to a load, and a second rectifying and smoothing circuit connected between the transformer and the switch control circuit for providing a control voltage to be fed to the switch control circuit for powering the same, wherein the improvement resides in the switch control circuit comprising: (a) feedback circuit means for providing a feedback signal indicative of the DC output voltage; (b) a control voltage monitoring circuit connected to the second rectifying and smoothing circuit for providing an output signal indicative of whether the control voltage is less than a predefined limit or not; (c) a switch control pulse generator circuit connected between the feedback circuit means and the active switch for generating switch control pulses thereby to drive the active switch so as to keep the DC output voltage constant; (d) a multiple reference voltage generator circuit connected to the control voltage monitoring circuit for providing a multiple-value reference signal that has either of first two different predefined values when the control voltage is not less than the predefined limit and that has either of second two different predefined values when the control voltage is less than the predefined limit, the second two different predefined values being intermediate the first two different predefined values; and (e) a mode select comparator having a first input connected to the feedback circuit means, a second input connected to the multiple reference voltage generator circuit, and an output connected to the switch control pulse generator circuit.