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

A driver circuit having a combined current and voltage control circuit for driving a light emitting diode (LED) load, the driver circuit comprising:

• an isolation transformer having a primary winding, a secondary winding, and an auxiliary winding;
• a primary side circuit coupled to the primary winding of the isolation transformer, the primary side circuit having a power factor controller and a switch, the power factor controller configured to control an output current to the LED load by controlling an operational state of the switch;
• a secondary side circuit coupled to the secondary winding, the secondary side circuit having a proportional and integration (PI) control portion configured to output a control signal, the secondary side circuit configured to drive the LED load;
• and
• the combined voltage and current control circuit coupled to the auxiliary winding, the combined voltage and current control circuit having an optocoupler coupled to the power factor controller and to the PI control section and a voltage feedback resistor group, the voltage feedback resistor group having a first divider formed by a first and a second dividing resistor, and having a second divider formed by the optocoupler and a third dividing resistor,
• wherein the combined voltage and current control circuit is configured to transmit a control signal from the PI control section to the power factor controller, the control signal obtained between the collector of the optocoupler and an intersection between the first and second dividing resistors.