DocID024821 Rev 2

21/31

AN4314

PFC waveforms

31

When the load is disconnected, first the current loop tries to compensate the low current

sensed on R6 and R7 and increases the output of U1 (pin 5). As a consequence, the COMP

pin increases too, but as the output voltage reaches about 85 V

dc

, the voltage loop

operates, and the output of U1 is forced to decrease. The overlap of these two effects can

be seen on the COMP pin (CH2). As this signal falls, it triggers the burst mode. During this

operation the output voltage of the converter decreases, V

CC

voltage reaches its turn-off

level and the L6564H shuts down. Only when V

CC

voltage reaches the V

CC

-restart

threshold does the HVS generator pump current into the V

CC

capacitor and the L6564H

restarts switching.

Figure 18. Load disconnection transition at

Figure 20. Load disconnection transition at