High Efficiency LED Power Supply

A new high efficiency light-emitting diode (LED) and an organic LED power supply are presented. An LED string is split into two sections. A first LED string is driven by a conventional dc-to-dc converter, while a second LED string is placed in series with the incoming dc supply current. Power is delivered to the second LED string without passing through the dc-dc converter, thus improving the system efficiency of the circuit. The equations presented show that the efficiency of the whole circuit will always be higher than the efficiency of the dc-dc converter alone. The performance of the new high efficiency circuit was tested and it was found that the new high efficiency circuit offered an improvement in efficiency of the LED driver of 3% at an automotive supply voltage of 14 V.