STMicroelectronics 100 W transition-mode PFC pre-regulator with the L6563S EVL6563S-100W EVL6563S-100W Data Sheet

18/33

Doc ID 16279 Rev 2

Comparing 

 and 

 we can see that the input current of the latter has a better 

shape and the 3

rd

 harmonic current distortion is not noticeable. This demonstrates the 

benefits of the new voltage feed-forward circuit integrated in the L6563S.  Allowing a fast 
response to mains disturbances but using a quite long V

FF

 time constant provides also very 

low THD and high PF at same time as confirmed by the measurements below.

Another function integrated in the L6563S is the brownout protection, which is basically a 
non-latched shutdown function that must be activated when a mains undervoltage condition 
is detected. This abnormal condition may cause overheating of the primary power section 
due to an excess of RMS current. Brownout can also occur because the PFC pre-regulator  
works in open loop and this could be dangerous to the PFC stage itself and the downstream 
converter, should the input voltage return abruptly to its rated value. Another problem is the 
spurious restarts that may occur during converter power down and that cause the output 
voltage of the converter not to decay to zero monotonically. For these reasons it is usually 
preferable to shutdown the device in case of brownout. 

Brownout function is done through sensing of the input mains by an internal comparator 
connected to RUN (pin #10), connected via a divider to V

FF

 (pin #5) which delivers a voltage 

signal proportional to the input mains. The enable and disable thresholds at which the 
L6563S will start or stop the operation can be adjusted by modifying that divider ratio. For 
additional information please see [

].

Ω

Ω

         

THD = 5.15%, 3

RD

 harmonic = 43 mA

CH2: MULT (pin #3)

CH3: V

FF 

(pin #5)

CH4: I_AC 

         

THD = 2.30%, 3

RD

 harmonic = 25.8 mA

CH2: MULT (pin #3)

CH3: V

FF 

(pin #5)

CH4: I_AC