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

Doc ID 16849 Rev 2

17/32

It is also possible to see, comparing 

 and 

, 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 into the 
L6563S, allowing a fast response to mains disturbances but using a quite long V

FF

 time 

constant, also providing very low THD and high PF at the same time, as confirmed by the 
measurements below in 

 and 

:

Another function offered by the L6563S is brown-out protection, which is basically a not-
latched shutdown function which must be activated when a mains under voltage condition is 
detected. This abnormal condition may cause overheating of the primary power section due 
to an excess of RMS current. Brown-out can also cause the PFC pre-regulator to work 
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. A further problem is the 
spurious restarts which 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 shut down the device in the case of brown-out. 

Brown-out function is done by sensing the input mains through 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 starts or stops the operation can be adjusted modifying that divider ratio. For 
additional information please see [

].

Ω 

Ω    

         

THD= 4.36%, 3rd harmonic=94.6 mA

CH2: MULT (pin #3)

CH3: V

FF

 (pin #5)

CH4: I_AC

         

THD= 2.94%, 3rd harmonic=30.5 mA

CH2: MULT (pin #3)

CH3: V

FF

 (pin #5)   

CH4: I_AC