Patent ID: 8213194

Claim:
A circuit, comprising: a current supply circuit having a switch and a transformer that includes a primary winding and a secondary winding and configured to supply a load current; a control circuit coupled to the current supply circuit and configured to maintain a constant current level of the current, the control circuit including: an auxiliary primary winding in the transformer of the current supply circuit adapted to sense a direct output voltage from the secondary winding in the transformer and to output a representative signal of the direct output voltage; a first circuit structured to multiply a signal representative of current flowing through the primary winding and a signal representative of an input voltage to the primary winding in the transformer and to output a multiplied signal that is representative of the product of the multiplication; a second circuit coupled to the auxiliary primary winding and structured to compare the multiplied signal with the representative signal of the direct output voltage and to output a comparison signal; and a driving circuit structured to receive the comparison signal and to generate a driving signal to the switch in the current supply circuit to maintain the load current at a constant level.