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Original question:

UCC25660: UCC256601 FB questions

UCC25660: AFPC not starting / working ucc2818

Dietrich Rushing
Prodigy 81 points
Part Number: UCC25660
Other Parts Discussed in Thread: UCC28180

Tool/software:

Hi,

So my architecture is something like this:

Mains -> filter + inrush limiting -> rectifier-> UCC28180DR APFC  -->  UCC256601 LLC

I plunged in the design and i saw what I expected after the rectifier BUT when i did check the high voltage capacitors after the APFC stage they were well under the 390-400Vdc i was expecting so the UCC28180DR was not working properly for sure.

I did check that the Chip is powered, there were about 13V on the Vcc pin ( from a small aux power supply that i built in just in case) but still no sign that the UCC28180DR was doing anything.

The FB pin was at about 4-4.1V far lower then the 5V FB reference so i was sure my FB resistor math was still ok.

BTW there was no load connected to the SMPS the only power draw was the board itself . Nothing seemed to get hot ( except the NTC but that is supposed to get a bit hot at start up).

Any advice on what i should check? Should i post a schematic out here? ( i mostly did copy from a reference design + used the excel calculator provided by TI to validate my component choices)

Best regards

  • 0
    TI__Genius 12795 points

    Please share schematic here. Please share the waveform on the UCC28180 pins as well

  • 0 in reply to Ning Tan
    Prodigy 81 points

    Hi,

    Here are my schematics, i dont know how to attach PDF so ill post pictures

    As for signals:

    Vcc 13Vdc nothing interesting here

    Vsense 4.1V dc nothing changing here ( PCB was powered from 240Vac, and after the rectifier i had about 310Vdc)

    GATE from what i remember there was nothing there

    I`ll check them again and return here with more data, i hope there is a easy identifier small mistake.

    NOTE: R70 is mounted and it is 0ohm

    Q12 and D18 and DNP

    The rest is like in the schematic.

    Best regards

  • 0 in reply to Dietrich Rushing
    TI__Mastermind 40580 points

    Hello Dietrich, 

    The PFC schematic with UCC28180 shows no obvious mistakes, and I don't think there is any subtle bug in this design. 

    Therefore, I conclude the problem is on the actual pcb.  
    Please check all connections to verify connectivity between component pads, in case there may be an undetected open circuit.
    Also check for any unwanted short-circuits between separate nets, possibly from solder blobs or a stray wire clipping, etc. 

    Also check your polarized components to verify correct installation.  A diode or the IC may be installed backwards, for example. 
    A component may be missing, or the wrong value installed. 

    Since the PFC controller is apparently "doing nothing", check that the 13V can actually be measured on the IC pin itself, to verify that the IC leg is properly soldered to the pad.  Same with the other pins, GND, GATE, ISENSE, VSENSE, etc. in order of importance.   

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 81 points

    Hi,

    I`ll take it slow then and check them all, maybe also resolder here and there just in case.

    Ill return if i find something or it is working, wish me luck.

    Best regards.

  • 0 in reply to Dietrich Rushing
    TI__Mastermind 40580 points

    Good luck, Deitrich!

    Ulrich