Boost PFC design using PLC810PG

2 posts / 0 new

I tried to Use PLC810PG(Boost PFC + LLC control IC)
to design Boost PFC ( without rear LLC stage )
400W 90~264AC Input 400V Output
because I tried test PFC first , then add LLC stage.

It's a combo IC , some LLC sense Pin could effect PFC stage control
so I need to set three LLC stage sense pin to specific value

I set "FMAX" and "FPL" to a specific value so I can get constant frequency in Boost PFC

and I set ISL to ground , make sure over current protection in LLC stage won't happen.

Then start of my PFC design
The IC is use the DC bus voltage feedback pin "FBP"
and boost current sense pin "ISP" to adjust duty cycle of Boost PFC

but i notice that, the duty limits are ... no limit .
so duty can operate at 0% ~ 100%

when I sent power to my PFC . Initially the DC bus Voltage is far less than balance point.(Vbus go through resistor divider compare with 2.2V ref on OTA)
so the duty "fully on" and shorted inductor.
although the ISP got over-current protection and turn off MOSFET when reach the Upper current limit.
but it's still a wrong operation .

because datasheet has rare information about control method and how to control the duty

so I want to ask

How to solve the initial 100% duty problem in PFC?

My OTA compensate is 2.2K resistor to ground with parallel 22nF noise avoid capacitor.

It is normal for PFC to hit "100% duty cycle" at startup because it is monitoring the choke current and it is very low at startup. As soon as the current reaches the target or max allowable current it will reduce the duty cycle as needed.