Fast DC solid state relay

Discussion in 'The Projects Forum' started by nenadilic84, Jan 17, 2014.

  1. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    Hello all,
    for specific timing tests of output driver diagnostics, I'd need some kind of very fast switching (solid state) relay with low on-resistance (definitely below 0.1Ohm).
    In a nutshell, I'd like to apply e.g. a 100 to 10 µs short circuit to ground, open load or short circuit to power condition on low side driver outputs and also on high side driver outputs. Since the outputs have full diagnostic capabilities, they will switch off quickly in case of critical overcurrent (within a a few microseconds), but for this short time, the short circuit current will be pretty high (let's say like 30A or even more). Also I will place this on couple of points in the circuit as well.

    While I think I could probably use an N-channel logic level FET controlled by a signal generator with an according offset/amplitude, I'd like to use a more solid solution for a couple or reason. E.g. I'd like to control the switch with a 0V/5V signal without the need to adjust the offset for the specific test case. And honestly there is no time to design and test a circuit. I'd need a solid product that's just working and that's easily available. Price is not so much of a problem. This is neither for private stuff nor for mass production.

    So are there faster DC solid state relays available?

    Thanks,
    Nenad
     
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    Solid state relays are (or used to be) opto controlled Triacs so they won't give you that low on resistance. Only a power FET will.
     
  3. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    Yes as you said "used to be". Now days there are MOSFET based relays. That said, I was thinking on using one of this isolated gate drivers and FET which can be fast and have low resistance.
    Here is the datasheet:
    http://www.analog.com/static/imported-files/data_sheets/ADuM5230.pdf

    The only problem here is that gate current is two low for any serious power FET, and the isolated power supply is only 150mW.

    If I use 4A one (ADuM3220) then I will require an additional isolated power supply, and if I have couple of this in my testing circuit I will then need couple of isolated power supplies which is not practical at all.

    Any thoughts on that?

    Thanks
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,003
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    Most isolated SSRs are rather slow. The fastest I found after a quick search are these at 15μs, but they may still be too slow for your purposes.
     
  5. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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  6. crutschow

    Expert

    Mar 14, 2008
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  7. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    As I would need 5 or 6 of this it will cost me over 800$. That is expensive...
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Simple circuit: Reproduce the type in the link, order parts from Digikey, next day delivery, same day/next day assemble.
    Total Cost: probably under $150.00?
    Max.
     
  9. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    Yes it looks really simple, but finding the components, and designing the circuit will cost more time and money (especially with my small experience with circuit design). It seems that is a logical way to go, but as I said it will be best if I can find something out of the box that just works.

    Thanks
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    3,790

    I think a logic-level (5 volt gate) mosfet should work for you.

    http://www.digikey.com/product-detail/en/STP60NF06L/497-5895-5-ND/1039555


    60v, 60 amp
    0.015 ohms resistance at 30 amps


    We need to know more about your operation cycle to really recommend a part, this just shows a mosfet can get close to what you want.

    If continuous 1MHz operation vs intermittent single 1 uSec test pulses are supplied, then heating may or may not be an issue.
     
  11. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    Finding a MOSFET is not a problem, the problem is that I will need galvanic isolation from the test circuit. I will need to break, the circuit and short it to ground in couple of points.
    The picture below is good example what I need
     
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    Last edited: Jan 18, 2014
  12. crutschow

    Expert

    Mar 14, 2008
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    The one I referenced in post #4 was listed at $55.58US.
     
  13. nenadilic84

    Thread Starter Active Member

    Aug 7, 2009
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    Last edited: Feb 2, 2014
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