Patent ID: 6972970

Claim:
A dc-to-dc converter operating in either normal load mode or light load mode depending upon the power requirement of a load, with a capability of automatically overriding the light load mode under extremely light load, comprising: (A) a dc-to-dc converter circuit comprising: (a) dc input means; (b) a transformer; (c) a switch connected to the dc input means via the transformer; (d) dc output means to be connected to a load to be powered; (e) a first rectifying and smoothing circuit connected between the transformer and the dc output means for supplying dc power to the load; and (f) a second rectifying and smoothing circuit connected to the transformer; and (B) a switch control circuit connected to the switch of the dc-to-dc converter circuit for controllably driving the switch, and to the second rectifying and smoothing circuit of the dc-to-dc converter circuit thereby to be powered, the switch control circuit comprising: (a) a switch control pulse generator circuit connected to the switch of the dc-to-dc converter circuit, the switch control pulse generator circuit generating switch control pulses thereby to controllably drive the switch according to the power requirement of the load; (b) a mode selector circuit connected to the switch control pulse generator circuit for causing the same to drive the switch in normal load mode, in which the switch control pulses are applied to the switch continuously, when the power requirement of the load is above a predefined value, and in light load mode, in which the switch control pulses are applied to the switch at intervals, when the power requirement of the load is below the predefined value; and (c) a light load mode override circuit connected between the second rectifying and smoothing circuit of the dc-to-dc converter circuit and the switch control pulse generator circuit for overriding the light load mode, and causing the switch control circuit to apply the switch control pulses to the switch continuously, when an output voltage of the second rectifying and smoothing circuit of the dc-to-dc converter circuit falls below a predefined value.