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Power supply for ~170 VDC

Discussion in 'Electronic Design' started by lsiu, Jan 17, 2004.

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  1. lsiu

    lsiu Guest

    Hello,

    I am trying to build a DC power supply by simply using a bridge rectifier
    and a capacity. The circuit is shown here:

    http://lsiu.dyndns.org/static/circuits/supply01.png

    However, when I pluged it in, the rectifier blew up on me. Since then I have
    added a fuse :).

    Any idea while the circuit doesn't work? The recitifier I used is RS206
    (http://www.rectron.com/data_sheets/rs201l-rs207l.pdf), which should be able
    to withstand 800 VAC.

    I notice that when I tried out the bridge rectifier with a function
    generation giving 20 Vpp sine waves, the output is not full wave rectifier,
    rather, the supposing inverted bottom half of the sine wave is a "shaky
    almost 0 V" curve on my oscilloscope.

    Thanks for helping.

    Leonard
     
  2. Whoa,
    Never do that with line power without a transformer in between.
    The line impedance is just too low. The transformer limits the current
    amonst other stuff. Plus an additional resistor limiting the current
    into the cap would help.

    Rene
     
  3. Fred Bloggs

    Fred Bloggs Guest

    It is ***EXTREMELY*** important that you ***NOT*** place your scope GND
    probe at the negative terminal of the capacitor- this will create a
    short circuit in the rectifier, and you cannot GND any terminal of the
    output capacitor with your loading. If you want to probe it this way,
    then you will need to find an isolation transformer for the 120VAC line
    voltage, or use a handheld voltmeter.
     
  4. lsiu

    lsiu Guest

    please reply to lsiu0809[at][not_cold]mail.com
     
  5. Gary Lecomte

    Gary Lecomte Guest

    In a Circuit like this you need a Current Limiting Resistor. The
    In-Rush current to initally charge the capacitor is VERY HIGH.

    I don't know the load current you expect to get, but I would suggest a
    25 to 50 ohm resistor, Quite high wattage!

    Gary
     
  6. You have nothing to limit the inrush current into the uncharged
    capacitor. So your current is limited only by the resistance in the
    rectifier and the ESR of the capacitor - perhaps 1 ohm in total - giving
    a potential 170 A peak!
     
  7. I read in sci.electronics.design that John Woodgate <
    But the primary cause of your burn-up may well be that you connected the
    scope ground to the negative DC line, as given in another post.
     
  8. N. Thornton

    N. Thornton Guest

    Both output wires will be live. Its a circuit to be avoided.

    Regards, NT
     
  9. lsiu

    lsiu Guest

    Thank you very much for your help.

    Leonard
     
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