AN3111

Circuit design

Doc ID 16815 Rev 2

5/23

1

Circuit design

The L6562A is a current mode PFC controller operating in transition mode (boundary mode

between CCM and DCM). Its linear multiplier enables the converter to shape the AC input

current waveform following the input voltage. The block diagram of the L6562A is shown in

Figure 2 below. For more detailed information regarding the L6562A, please refer to the

device datasheet and application notes.

Figure 2.

Block diagram for the L6562A

Figure 3 shows the schematic of the proposed single-stage LED driver. If the inductor

current is constant, the power of the converter is constant. As the LED string is

a constant voltage load, we can obtain a constant current in the LED string. This makes it

possible to leave out the LED current sensing, therefore simplifying the circuit design. If the

inductor current is constant, then the power factor of the circuit is very poor. The input

current waveform is greatly distorted during line voltage zero crossing. If there is a way to

reduce the current amplitude near the line voltage zero crossing, the power factor can be

improved. The L6562A PFC controller is used to achieve this objective. The idea is to

reduce the current amplitude near the line voltage zero crossing, which results in an

improved power factor.