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UCC28C43: Replace UC3843/45 with UCC28C43/45

Omer Faruk
Prodigy 150 points
Part Number: UCC28C43
Other Parts Discussed in Thread: UC3843,

Hi,

Please check the schematic, I have uploaded as PDF. When I use this schematic with UC3843/45, I can get 55V, 1.2A Output without any problem. I have seen some posts in TI to change directly UC3843 with enhanced version IC UCCX8C4X

I have tried several times but can not find what is the problem. When AC energy arrives in the circuit, It works for 1sec and can read 55V on the multimeter, 1sec later, circuit not work. I check components on the circuit, IC and MOSFET broken. 

I use 18V Zener VDD-Ground, and normally I have measured 17V. 

I want to say again, I use this schematic with UC3843/45 without any problem, but not work with UCC28C43/45. As last, I have created a schematic on Webench Power Designer and changed components according to that, but the same result.

Please help me to resolve that problem. 

Last question, Should I change UC3843 with UCC28C43? What are the advantages for my power supply? 

Thank you very much

1805.schematic.pdf

  • 0
    TI__Mastermind 34465 points

    Hi,

    I had a quick loo at your schematic and I think I see what the issue may be.

    You need a 10k resistor from the gate to source of your FET labelled ??? Q1 in the schematic

    The UC3843 driver output  pin is bipolar.  This  tends to pull current from the gate of Q1 and keep it off when OUTPUT is low

    The UCC28C43 output pin is CMOS and has lower leakage currents.
    This means you need some other means of discharging any voltage on Q1 gate.

    Therefor I recommend you place 10k form the gate to source.

    Regards

    John

  • 0 in reply to John Griffin1
    Prodigy 150 points

    Dear John,

    Thank you for the valuable answer. I will try it asap and give you feedback.

  • 0 in reply to John Griffin1
    Prodigy 150 points

    Dear John,

    I have tried but not work. Mosfet was not broken, but IC dead. By the way, When I check the datasheet of UCx384x and UCCx8C4x, Typical application is %100 same. 

    After energy arriving in the circuit, IC works and can get voltage from output about 1-2secs. After that duration, IC not work.

    It is really interesting. 

    By the way, do you advise to use UCCx8C4x instead of UCx384x? What is the advantage?

  • 0 in reply to Omer Faruk
    TI__Mastermind 34465 points

    Hi,

    The UC part is bipolar and the UCC part is CMOS. That is the difference between these two parts.

    It is difficult to know what is happening without any scope waveforms showing the switching behaviour.

    I dont see any thing unusual about the schematic.

    Maybe try using a 16V zener and make sure that the decoupling capacitor on VDD is close to the pin.

    You should try replacing the MOSFET, IC and the current sense resistor R10.

    All of these parts are suspect if the power supply failed.

    Unfortunately I have no more ideas

    Hope this helps

    Regards

    John