STEVAL-ILL013V1 Datasheet, PDF (33/43 Pages) STMicroelectronics – 80 W offline LED driver with PFC

Design features
Figure 40. Proper startup using diode D104 and capacitor C110
UM0670
Figure 41. Improper startup without using diode D104 and capacitor C110
10.2
33/43
Zero dimming design implementation
During zero dimming (duty cycle is 0%) the high PF boost converter is in burst mode
because there is zero load. During this mode, capacitors C107 and C110 are charged only
in short pulses (C107 is also slightly charged via resistor from the input voltage, but it is not
enough) and therefore do not have enough energy to also supply the PWM generator and
the second L6562A controller used for the modified buck converter. The circuit shown in
Figure 42 allows brightness changes down to 0% without any problem, because if the
Doc ID 15327 Rev 2