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UCC28950 not running...

Paolo Reggio
Intellectual 930 points
Other Parts Discussed in Thread: UCC28950

Hello everybody!

I'm experiencing some troubles on UCC28950.
I designed a DC/DC converter able to step down a 370-410VDC PFC output voltage to a 250VDC battery pack with an insulated step down (no SR since current is low and voltage is very high, so no efficiency improvement can be achieved).
See schematic in attachment.
I'm sure to not have made mistakes (take care that the 825k resistor between SS/EN pin and GND has already been removed!), but it doesn't start!
I can observe the voltage on the SS/EN pin reach the 5V level when I pull down the DCDC_EN pin, but PWM on output are not present and also the SYNC pin doesn't run...
Any idea???

Thank you very much for your help!

Paolo0724.ZVT Control.pdf

  • 0
    Prodigy 10 points

    Hi Paolo,

    Most probably, if your board is OK versus your schematic, it seems you are not right on your feedback path.

    But first, please change one you schematic the arrow sign used for VREF and VDD with bares names VREF and VDD, or even better right +VREF and +VDD.

    As it is right now it's confusing, seems to be ground!

    I am an electronic power engineer and I am using UCC28950 controller in a SMPS AC-DC power supply.

    My controller board is tested putting some jumpers on X7 - on the feedback path and X10 on the ON/OFF command to start-up the driver (a little bit complicated schematic in this place, but it has some reason why it is like this).

    When the board is powered up with +15Vp supply and X7, X10 jumpers are on their place at the outputs A,B,C,D you have signals as mentioned into the datasheet.

    Hoping it's useful I am attaching my schematic.

    Just let me know if you solved your problem already or my file was useful for you.

    Best regards,

    Alex

    5700.Controller UCC28950_Paolo_FIAT.pdf