STMicroelectronics L6563H 100 W TM PFC demonstration board EVL6563H-100W EVL6563H-100W Data Sheet

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Doc ID 16261 Rev 3

ripple at twice the mains frequency that will cause distortion of the current reference 
(resulting in high THD and poor PF). If it is too large, there will be a considerable delay in 
setting the right amount of feed-forward, resulting in excessive overshoot and undershoot of 
the pre-regulator's output voltage in response to large line voltage changes. Clearly a trade-
off was required.

The L6563H implements an innovative voltage feed-forward which, with a technique that 
overcomes this time constant trade-off issue whichever voltage change (both surges and 
drops) occurs on the mains. A capacitor C

FF

 (C13) and a resistor R

FF

 (R27 + R32), both 

connected to the V

FF

 (pin #5), complete an internal peak-holding circuit that provides a DC 

voltage equal to the peak of the rectified sine wave applied on pin MULT (pin #3). In this way, 
in case of sudden line voltage rise, C

FF

 is rapidly charged through the low impedance of the 

internal diode. In case of line voltage drop, an internal "mains drop" detector enables a low 
impedance switch which suddenly discharges C

FF

 avoiding a long settling time before 

reaching the new voltage level. Consequently, an acceptably low steady-state ripple and low 
current distortion can be achieved without any considerable undershoot or overshoot on the 
preregulator's output like in systems with no feed-forward compensation. 

In

 we find the behavior of the EVL6563H-100W demonstration board in case of an 

input voltage surge from 90 to 140Vac. As shown, it is evident that the V

FF

 function provides 

for the stability of the output voltage which is not affected by the input voltage surge. In fact, 
thanks to the V

FF

 function, the compensation of the input voltage variation is very fast and 

the output voltage remains stable at its nominal value. The opposite is confirmed in 

 where the behavior of a PFC using the L6562A and delivering same output power 

is shown. The controller cannot compensate a mains surge and the output voltage stability 
is guaranteed by the feedback loop only. Unfortunately, as previously stated, its bandwidth is 
narrow and thus the output voltage has a significant deviation from the nominal value. The 
circuit has the same behavior in case of a mains surge at any input voltage, and it is also not 
affected if the input mains surge happens at any point along the input sine wave.

         

CH1: Vout

CH2: MULT (pin #3)

CH4: I_AC

         

CH1: Vout

CH2:  MULT (pin #3)

CH3: V

FF

 (pin #5)

CH4: I_AC