Current and voltage control circuit and method for a class II LED driver

摘要

A driver circuit includes a combined current and voltage control circuit for driving a light emitting diode (LED) load. The driver circuit includes an isolation transformer having primary, secondary, and auxiliary windings. A primary side circuit is coupled to the primary winding and includes a power factor controller and a switch. The power factor controller controls an output current to the LED load by controlling an operational state of the switch. A secondary side circuit is coupled to the secondary winding. The secondary side circuit includes a proportional and integration (PI) control portion which outputs a control signal. A combined voltage and current control circuit is coupled to the auxiliary winding and includes an optocoupler coupled to the power factor controller and to the PI control section. The combined voltage and current control circuit transmits a control signal from the PI control section to the power factor controller.