Patent ID: 8742685

Claim:
A power circuit comprising: a magnetic amplifier having a power supply signal as an input, wherein the magnetic amplifier comprises a saturable magnetic core and two windings around at least a portion of the core; a light emitting diode string coupled to an output of the magnetic amplifier, wherein the light emitting diode string includes a plurality of light emitting diodes coupled in series; a control circuit coupled to the magnetic amplifier and the light emitting diode string, wherein the magnetic amplifier and the control circuit are configured to regulate a current through the LED string; a current sink coupled to an output of the LED string and to the control circuit, wherein the magnetic amplifier and the control circuit are configured to maintain a compliance voltage of the current sink; and a reset current source coupled to the control circuit configured to regulate the current through the LED string and to control a reset current supplied to the magnetic amplifier; wherein a first winding of the magnetic amplifier is configured to transmit power to the light emitting diode string and a second winding of the magnetic amplifier is configured to receive the reset current from the reset current source; wherein a B-H curve of the magnetic amplifier exhibits hysteresis where the magnetic amplifier maintains a flux density with zero current passing through substantially equal to a saturation flux density level; and wherein the magnetic amplifier is configured to pass a power current to the light emitting diode string while in a saturated state and during an on-time of the power supply signal input to the magnetic amplifier.