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UCC3802: 280-700VDC Input, 15V output down-chopper

Bryan Boonekamp
Prodigy 40 points
Part Number: UCC3802


Hi experts,

I'm trying to design a down-chopper using the UCC3802. I'm quite familiar with the down-chopper basics, but I am having trouble understanding the UCC3802 itself. I've tried reading the datasheet for it but it's overwhelming for me. I know that you can "program" the frequency with a small RC network, and that the duty-cycle is unprogrammable because of the internal resistor. 

I'm wondering how I could "program" the UCC3802 for a wishful 15V DC on the output of my down-chopper, with an input between 280 and 700V DC. (note: the circuit does not need to be isolated)

I've been making a test circuit, where I'd like to see the pulses on the output of the UCC3802, with a frequency of 100kHz. ( see attachment ),

In the testcircuit I use 10V DC to supply the chip, and I attached a 5 V DC source to the FB pin. So I'd expect a signal of 100kHz and a duty cycle of 50% on the Output (6). Sadly I only measure noise with my oscilloscope.

Could anyone tell me what I'm doing wrong?

Kind regards,

Bryan Boonekamp

Bryan Boonekamp

  • 0
    TI__Mastermind 34465 points
    Hello Bryan,
    I'm afraid all of the details are in the datasheet.
    You should proceed very cautiously when designing with a 700V power source.
    For your own safety you should work under the supervision of an experienced colleague.

    The UC3802 is the wrong part to use in your application circuit.
    Use the UC3802 or UC3805.
    These parts will work at a 50% max duty cycle and start up a voltage below 10V.
    Also you need to connect FB to GND not to 5V.
    This should get your test circuit working.
    However you wont be able to see the LED blinking on/off at 100kHz

    Regards
    John
  • 0 in reply to John Griffin1
    Prodigy 40 points
    Dear John,

    Thank you for the quick reply,

    I will indeed test my 700V circuit under the supervision of an experienced colleague. I will also try and connect FB to GND and measure the output with my oscilloscope again.

    Kind regards,

    Bryan Boonekamp