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5308 Views 2 Replies Latest reply: Apr 28, 2014 1:05 PM by nsayer RSS
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Apr 25, 2014 11:27 AM

Solid State Relay (SSR) advice

Does anyone have any recommendations on SSRs?  They seem powerful, reliable, with minimal current to switch them, all around better than their mechanical counterparts.  Are there any drawbacks that I'm not aware of?


I'm also looking specifically for one with a low gate voltage, less than 1V.  Is there anything out there that will still be reliable at that point?

  • LanceLK Apprentice 164 posts since
    Apr 4, 2014
    Currently Being Moderated
    Apr 28, 2014 11:52 AM (in response to JohnDavis)
    Solid State Relay (SSR) advice

    As with anything in life, there are drawbacks to SSRs.  They have higher "closed" resistance and lower "open" resistance, as well as they're not purely resistive when closed, so you don't get linear responses to voltage changes.  There are other disadvantages as well as other advantages, but it's all about what you need in certain situations.  The fact that they don't spark can be helpful in, say, gas station applications. 


    I did a quick search on Digi-Key and came up with this:


    That's actually slightly greater than one volt.  I don't know what you're looking for specifically and if that's unacceptable but if you're working in such a low power / low voltage domain, perhaps you need something besides an SSR?

  • nsayer Novice 4 posts since
    Mar 22, 2014
    Currently Being Moderated
    Apr 28, 2014 1:05 PM (in response to JohnDavis)
    Solid State Relay (SSR) advice

    In my (admittedly limited) experience, I've not found much use for SSRs. If you're switching line powered AC, then triacs are a lot cheaper. If you're switching DC, then BJT or FETs, again, are a lot cheaper. The downside is that you need to do a little more work to design the circuit for your application.


    So far as I have heard, the big disadvantage to SSRs is that they tend to fail closed rather than mechanical relays that usually fail open. Also, they tend to have heat sink requirements far beyond what mechanical relays would switching the same power.

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