IGBT Test Jig

Discussion in 'General Electronics Chat' started by R!f@@, Apr 13, 2014.

  1. R!f@@

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    Apr 2, 2009
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    These things are becoming a nuisance to me.

    Any one got any idea on a test jig to test these darn things
     
  2. wmodavis

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    Oct 23, 2010
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  3. ian field

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    Oct 27, 2012
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    For simple go/no-go checks they should behave pretty much the same as MOSFETs.

    I have a Steinel continuity/voltage tester - it has a thin filp PTC thermistor as the current limiting for voltage testing (4 - 415V) and an A23 12V battery for continuity. If you use the test voltage of a continuity tester to charge the gate capacitance positive, that should switch the device on, reverse the continuity prods on gate/source to reverse charge the gate capacitance turns the device off - any leakage whatsoever is a fail (your continuity tester might not be sensitive - use a DMM for the leakage test).

    If the gate charge leaks away before you can complete the test - that is also a suspect device.

    Your IGBT is just a MOSFET with a PNP transistor stuck on the output Szicklai style.

    http://en.wikipedia.org/wiki/Sziklai_pair
     
  4. R!f@@

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    I did check two IGBT's with gate voltage and resistance check at CE.

    A mosfet shows very low resistance to when voltage is applied to gate.
    But the IGBT shows R is around 1K when I apply the gate voltage specified in the data.

    A transistor will show a voltage drop across CE.
    Will the IGBT show the same 0.6V or so V drop across CE?
     
  5. ian field

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    There's no "0.6V" associated with an IGBT - although there might still be a parasitic "body diode" if you reverse the D/S connections.

    The gate is exactly the same as in a MOSFET - its isolated from the channel by a layer of silicon dioxide, should be practically infinite resistance until you hit the breakdown voltage (somewhere around 20V).

    The IGBT was developed to combat the high RDSon of high voltage MOSFET, by strapping a PNP transistor on the output Szicklai style; it replaces RDSon with VCEsat of a BJT.

    The downside is that its basically an emitter follower on the output, which slows things down a bit - IGBTs are not suitable for high speed switching PSUs, they tend to be more popular in variable speed motor drives.
     
  6. R!f@@

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    These IGBT's are found in PLASMA TV Sustain power supply
     
  7. ian field

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    There is an ongoing trend towards increasing switching speed in PSUs to minimise MOSFET transition times and their associated switching losses, and also to use smaller cheaper components.

    If you go that route, you probably have to choose the MOSFET carefully for optimised switching times, going the other route of high switching currents, you have to minimise RDSon, that's where IGBTs come in - but you can't run them anywhere near as fast.

    If the designer of your equipment tried to have it both ways - that might be the source of your problems.
     
  8. R!f@@

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    That could be the Plasma Sustain assy issues.
    Freaking IGBT's
     
  9. ian field

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    You could try substituting generously rated MOSFETs, but if the conduction current is high the RDSon will produce excessive dissipation.
     
  10. R!f@@

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    I thought transistors have higher on resistance than Mosfet's

    So why IGBT is better than Mosfet regarding the on resistance
     
  11. ian field

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    Because (as I already pointed out) it has a PNP emitter follower strapped on the output.

    Its only better relative to high voltage MOSFETs - they have a long narrow channel.

    Low voltage MOSFETs have a short fat channel - the high current types can have an RDSon of only a few milliOhms.
     
  12. R!f@@

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    hmm !

    When replacing them, the only issue I get is that I cannot find any data on 'em.

    Like the 30F124, 30F125 and 30F131
     
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