Use MOSFET as relay

Discussion in 'The Projects Forum' started by XOIIO, May 19, 2013.

  1. XOIIO

    Thread Starter Member

    Mar 1, 2013
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    Hello all, I need help using a MOSFET as a relay. I am going to be switching 250v DC, but I am unsure of the amperage. The MOSFET I will be using is an IRFP460A, it can handle 500v and 20 amps. I have other MOSFETs (even one going 800v), but this one has the highest amperage. I was wondering how I can add it to this circuit. Basically I just want to press a button and have it switch, just like a relay.

    Here is the circuit.

    [​IMG]
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    You need to apply a gate/source voltage like this circuit

    to make the Drain conduct to Source you will have to common the source supplies together, why don't you just use a Relay or solid state relay instead?
     
    Last edited: May 19, 2013
  3. XOIIO

    Thread Starter Member

    Mar 1, 2013
    39
    1
    Because a DC relay of this voltage, and possibly very high current would be very expensive, I have not looked into solid state relays, but I imagine they are not cheap either.

    Is there a simple way to calculate what value resistor I need for 250v, or would it just be a 200kohm (or maybe a bit higher) resistor?

    Also I would need to order said relay, and I do not feel like waiting for it in the mail :/
     
    Last edited: May 19, 2013
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    you have to join both the high voltage and low switching supplies together at the Source pin, this is very dangerous , i strongly recommend you use a Relay
     
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  5. XOIIO

    Thread Starter Member

    Mar 1, 2013
    39
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    Shoot. Do you know where I can get a solid state relay for a good price then? 300v would be fine but the amperage might be pretty high, so I'm not sure. Ebay only has AC ones, and the ones I've found through google are crazy expensive
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    I dont know your location but here is one type upto 100V

    relay
     
    Last edited: May 19, 2013
  7. XOIIO

    Thread Starter Member

    Mar 1, 2013
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    I am in Canada, I can't find any DC relays that go up to 250v except one or two that can barely handle any current. I'll look on ebay under contactor, at least they are cheaper, but from a quick glance people are charging quite a bit for shipping :/
     
  8. apprenticemart2

    Member

    May 7, 2013
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  9. crutschow

    Expert

    Mar 14, 2008
    13,000
    3,229
    You could use an opto coupler to isolate the MOSFET from your control signal. You would use a resistive divider or resistor and zener to limit the voltage to the opto and the MOSFET gate.
     
  10. XOIIO

    Thread Starter Member

    Mar 1, 2013
    39
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