Active PFC with FAN9611 Problem

Thread Starter

Lolrapa

Joined Sep 19, 2018
18
Hello! I'm trying to design and implement an active pfc for a power supply.
Here is the circuit i've made based on the FAN9611's evaluation board.

pfc.png
I've been using the FAN9611 documentation to verify the signals of every pin and I can't figure out why won't it work.
The drive signal is a square wave with holes, in other words, the ic starts to create a pwm drive signal and the it stops and starts again all the time. I'ts not a constant pwm signal as it should be with 40W load (specally when considering the point below)
The circuit its calculated to have a 400V output, but it barely has 10 volts over the rectification voltage (170) (from 120v rectified).
The voltage on the feedback pin is correct, its a portion of the output voltage. In the datasheet says that the feedback voltage should be 3v, but its only 1.9V. I assume then that the feedback is correct but the IC is not being able to rise the output voltage until the FB voltage is 3v

The drive signal is something like this:
drv.png
Where each line is a burst of PWM (about 15-20 cycles)

I know I'm being very vague with this explanation, but I'll happily provide you with all the information you request
Thank you for your time!

Edits:

The IC is powered from a 12v switching power supply in the same board
 
Last edited:

ronsimpson

Joined Oct 7, 2019
908
Think of all the things that could go wrong.
Pins 1,2, the phasing on the transformer could be backwards.
Pin 10, can it see line voltage?
Pin 9, does the IC think there is an over voltage condition?
Pins 15,16, is there over current happening?
Pin 14, does it ever drop below 9 volts?
Pin 10, brown out condition?
Pin 7, should be 4.5 to 5V? Check if this pin or any other pin has a wave form that has the same frequency as your picture.
 

Thread Starter

Lolrapa

Joined Sep 19, 2018
18
Think of all the things that could go wrong.
Pins 1,2, the phasing on the transformer could be backwards.
Pin 10, can it see line voltage?
Pin 9, does the IC think there is an over voltage condition?
Pins 15,16, is there over current happening?
Pin 14, does it ever drop below 9 volts?
Pin 10, brown out condition?
Pin 7, should be 4.5 to 5V? Check if this pin or any other pin has a wave form that has the same frequency as your picture.
Thank you very much for your reply, I've been measuring all this things for the last few days and here's what I got:

Pins 1,2 is not backwards phased although I suspect the problem may be here, I've read that the FAN9611 is very susceptible to noise in this lines.

Pin 10 can see line voltage and it is within parameters, its a rectified sinusoidal (full) with a peak value of 1.12v so it isn't in brownout condition either (circuit does not work with an input voltage of AC220v either)

Pin 9 is 1.2v way below the over voltage threshold

Pins 15,16 are really hard to measure. I don't fully understand what's happening there. Measuring the voltage drop across the 0.022R current-sense-resistors displays some spaced peaks with max vale of even 3 to 4 volts. Datasheet says that the maximum voltage in this pin is 0.2v. I cannot understand how are there peaks so big, I've been thinking it may be readout error or maybe switching noise. I've tried to bypass this resistors with a 0R bride to disable the over current protection but the circuit didnt work either.

Pin 14 is a 12v steady supply line

Pin 7 is 5v
 

mlsirkis

Joined Aug 11, 2010
26
Hello! I'm trying to design and implement an active pfc for a power supply.
Here is the circuit i've made based on the FAN9611's evaluation board.

View attachment 217658
I've been using the FAN9611 documentation to verify the signals of every pin and I can't figure out why won't it work.
The drive signal is a square wave with holes, in other words, the ic starts to create a pwm drive signal and the it stops and starts again all the time. I'ts not a constant pwm signal as it should be with 40W load (specally when considering the point below)
The circuit its calculated to have a 400V output, but it barely has 10 volts over the rectification voltage (170) (from 120v rectified).
The voltage on the feedback pin is correct, its a portion of the output voltage. In the datasheet says that the feedback voltage should be 3v, but its only 1.9V. I assume then that the feedback is correct but the IC is not being able to rise the output voltage until the FB voltage is 3v

The drive signal is something like this:
View attachment 217660
Where each line is a burst of PWM (about 15-20 cycles)

I know I'm being very vague with this explanation, but I'll happily provide you with all the information you request
Thank you for your time!

Edits:

The IC is powered from a 12v switching power supply in the same board
Does pin 14 receive power before pin10?
 
Last edited by a moderator:

Thread Starter

Lolrapa

Joined Sep 19, 2018
18
Does pin 14 receive power before pin10?
Hello, sorry for the delay. I've found many ground problems in my layout and i'm doing a new pcb layout.

I'ts mandatory pin 14 to receive power before pin 10? Pin 10 is connected to the retified mains through a divider. So I think this pin recieves power beofre pin 14
 
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