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TO-220 heat sink electrical isolation

Discussion in 'General Electronics Discussion' started by ida, May 14, 2013.

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  1. ida

    ida

    4
    0
    May 13, 2013
    Greetings!
    I have a power supply that made a sound when I first plugged it in for a second then died and won't do anything now. When I cracked it open I saw that a 400v wire was touching the ungrounded heat sink that is attached to two TO-220 13005 transistors. I was curious if this could have possibly fried anything or if there is enough electrical isolation between the transistor internals and the heat sink to protect it from getting zapped like this.
     
  2. Rleo6965

    Rleo6965

    585
    9
    Jan 22, 2012
    Check the collector and emitter for short using multimeter to confirm.
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,271
    Nov 28, 2011
    Usually any fault with an SMPS like that will blow the fuse... after the main switching device(s) have blown.

    Are you sure there was a bare wire at 400V touching the heatsink tab of the transistor? Power supplies don't usually have free-hanging uninsulated wires like that.
     
  4. ida

    ida

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    May 13, 2013
    Thaniks! Had not thought of that. Tested clear.
     
  5. ida

    ida

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    May 13, 2013
    Yeah. Whoever put it together had an unshielded wire that touched the heat sink when assembled. They also unfortunately didn't put a fuse in it.
     

    Attached Files:

  6. duke37

    duke37

    5,364
    771
    Jan 9, 2011
    The red wire looks to me to be insulated with thick insulation. High voltage can punch through this but 400V would not be enough unless it is damaged.
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    Do you have electronics experience?
    How do you know that the wire is a "400V wire"?
    Is it possible that the wire is deliberately connected to the heatsink?
    Do the TO-220 packages have metal tabs?
    Are there insulating washers (e.g. soft grey, or brittle transparent, washers) between the TO-220 packages and the heatsink?
    Is there NO fuse at all in the power supply?
    Can you upload a few more photos? It's impossible to tell much from the one you've posted.
     
  8. ida

    ida

    4
    0
    May 13, 2013
    Thanks for your reply.

    I have a little electronics experience.

    The power transistors on it are e13005. Did some web searches, saw that their operating range is 400 - 700 volts, kind of assumed 400 from that but there is probability that I'm wrong.

    The wire was not shoved into the case so when the top/heatsink was put on it, an electrical connection was made. It was not intended to be connected.

    They have metal tabs. After looking better, they do have insulating washers, and appear to be well insulated. That helps rule them out, thank you.

    There is no fuse.

    Please consider my question answered, but I'll attach more pictures anyway.

    Thanks again, everyone.
     

    Attached Files:

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