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  1. #1
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    30w flyback not giving output.

    Hello everyone,

    I am making a 15V 2A (30W) CCM flyback converter with UC3843 and the feedback loop is with PC817 and TL431. I am not getting any output power at all. I am testing it with a 100W 8 ohm resistor.

    In my initial test, there was no output at the secondary. I made a few test and I found that the UC3843 was switching. In the process of doing this test, I mistakingly shorted some pin and there came the magi smoke. Oops!

    I did necessary clean up retested the components, replaced the some components and then I realised I had connected the MOSFET the wrong way. I replaced the the MOSFET entirely and retested. Love and behold my inverter disconnected it's output and reconnected as soon as I switched of the DUT. That would be a short circuit to me so I checked the transformer and it was gone, probably due to the incident of the magic smoke that occurred earlier. I then wound another tansformer and replaced the bad one.

    I put on the converter again but still I didn't get any outpt voltage but this time it didn't short out the inverter. I heard a sound like something sparked and I noticed the the bridge rectifier is gone. No physical damage though.

    I do not know what is causing this problem. I need your help. Thanks.

    ElZero.

    - - - Updated - - -

    Duty cycle was selected to be 0.4 so I did not add any extrnal vlotage ramp.

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  2. #2
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    Re: 30w flyback not giving output.

    Hi,

    if it is not working, then there will be an error.
    Something in your circuit is not according the informations given in the datasheet.

    Where may be the difference:
    * Schematic --> show us your schematic
    * PCB layout --> show us your PCB layout
    * wiring, soldering, wrong chosen parts --> show us detialed photos of your circuit.


    Klaus
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.


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  3. #3
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    Re: 30w flyback not giving output.

    With a flyback it's very easy to generate high voltage spikes. The reason is because you're abruptly shutting off current through an inductor (in the transformer).
    Volt levels can reach several hundred or even kiloVolts. It can destroy components. It can cause arcing between windings. Once the varnish is penetrated current can leak between wires at lesser volt levels. The problem may be unfixable.

    Some load must always be attached across the secondary.
    And some kind of snubbing network should be attached across the primary. The snubber needs to consist of components that can cope with supply voltage at 30W.


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  4. #4
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    Re: 30w flyback not giving output.

    You have toasted a lot of bits, if you cannot fault find, re-build the whole ckt anew.



  5. #5
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    Re: 30w flyback not giving output.

    I would with easy peasy. you need to rebuild it. also keep in mind that your transformer is done properly and the snubber is done properly. do you have oscilloscope ? Please share schematic.



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