Help: FA5331P Buck boost PFC can't run at 100Vdc input?

[CafeNovember]

Hello dear forum

I am having 1 active PFC circuit as photo. Now I want it to work in the 95Vdc -> 130Vdc voltage range.
According to its original design it can work from 85 * 1.4142 = 120Vdc to 373Vdc.
Can anybody tell me how I need to make modifications to make it work and stable with such low input voltage.

Thank you and very interested
CafeNovember
 

[fzabkar]

From the datasheet ...

"Design the circuit to keep the peak voltage at pin 3 [Vdet] within a range from 0.65V to 2V for FA5331"

Vpeak(min) = 0.65V x (240K + 240K + 2.7K) / 2.7K = 116V

R6 = 480K / (Vp/0.65 - 1)

If Vp = 100V, then R6 = 3.14K.

I would make sure that your PWM duty cycle is not maxed out at max load.

[CafeNovember]

  Dear Mr. fzabkar
 Thank you for your help! 
 I will try tuning the R6 and reply soon.

Wish you a nice day.
CafeNovember.

[CafeNovember]

  I have measured voltage values on IC FA5531 at voltage values in operating range and below threshold. Including the situation I changed the resistor value of the bridge for the voltage divider for pin 3- VDET.
  The final measurement in the table, when R7-8 was changed, VDET = 0.76V> 0.65V but Vo = 96.3V showed that the Boost circuit was not running.
  I have suspected pin 12 (On / OFF) is overridden by the connection to IC M51957B. I attached datasheet M51957B, then I will go and re-draw the 12 pin circuit connected to it so you can help me find the problem.

[fzabkar]

The application circuit for the other IC also has a potential divider on the input (R1/R2).

Would it be safe to disconnect ON/OFF for testing purposes?

[CafeNovember]

I adjusted to Vpin2 = 1.9V. R7-8 = 430K. R6 = 3K. Then the circuit worked at Vin = 100Vdc. Vout = 366V but appears a little noise ~ 1.3V.
   I started to try loading 3A-12A and 21A to see what happens.

[CafeNovember]

 The PFC circuit in this context is a PFC boost circuit for a switching power supply circuit (SMPS) 24V / 21A output Bucket behind. They are designed by manufacturers to work together.
   Can any one tell me what will happen if I lower the Vout voltage of the PFC circuit lower? And if so, how low is SMPS circuit still working properly?
 
  In this case I reduce Vin three times, For 1 bridge to divide the voltage for the parts such as voltage feedback, overvoltage protection feedback ... should I reduce the high side resistance (R7-8 440kOhm) or Will increasing low side resistance (R6 2k7) be better?
 
   Someone passing by can help me with some clarification!

Thanks & Brgds