STMicroelectronics 250W TRANSITION-MODE PFC PRE-REGULATOR WITH L6563S EVL6563S-250W EVL6563S-250W Data Sheet

Doc ID 16849 Rev 2

19/32

 and 

 show the waveforms during the startup of the circuit at mains plug-in.

The R5 and R11 startup resistors charge the Vcc C9 capacitor, therefore Vcc voltage rises 
up to the turn-on threshold, and the L6563S starts operating. For a short time the energy is 
supplied by the Vcc capacitor, and then the auxiliary winding with the charge pump circuit 
takes over. 

Because the startup resistors are always connected to the mains, their power consumption 
during normal operation might affect the efficiency of the power supply once it operates at 
light load. Therefore the value of the startup resistors must be found as a compromise 
between the startup time at minimum input mains and the power dissipation at maximum 
input mains. 

In 

 and 

 the waveforms during startup of the circuit at mains plug-in are shown. 

Notice that because the Vcc voltage rise depends on the input voltage, the wake-up time is 
dependent on the input mains voltage. 

The same figures show that the output voltage rises from the peak value of the rectified 
mains to the nominal value of the PFC output voltage and the good phase margin of the 
compensation network allows a clean startup without overshoot. 

         

CH1: PFC output voltage

CH2: Vcc voltage (pin #14)

CH3: RUN (pin #10)

CH4: gate drive (pin #13)

         

CH1: PFC output voltage

CH2: Vcc voltage (pin #14)

CH3: RUN (pin #10) 

CH4: gate drive (pin #13)