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I'm designing simple circuit for ssr control.

I reviewed some sort of related circuits and previous version of the product(our company's)

Many of them are including photocoupler before S.S.R. control pin not in the diagram of S.S.R.

I thought S.S.R already has photocoupler in own module, so adding photocoupler is over spec or superstition.

Anyone use it for specific reason?

P.S. Surely I wanted to ask why the previous version has it, but there's no records, no one related with that.

Aveugles
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    Could you post the links to the datasheets for your SSR and the opto-coupler? One possibility is that the opto-couplers have a higher isolation rating than the SSRs. That's just a guess, though. – Nick Alexeev Aug 19 '13 at 06:03

2 Answers2

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The answer to your question is, "Go find the data sheet for the SSR you are planning on using, and find out". I would expect that the majority of SSRs would have opto-isolators built in.

Note that some SSRs with optos have resistors in line with the LEDs, some of them don't. If they don't, you'll need to add an appropriate dropping resistor.

Eric Gunnerson
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  • This answer is pointing out that some have them, some dont, you have to check the config to know. – Kortuk Aug 19 '13 at 14:08
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Whether it be SSR( Solid State Relay) or Opto-Coupler, both of them are very useful when you are looking to provide the Galvanic Isolation between your circuit.

Here you are talking about rigging up an opto-coupler before SSR, which doesn't seem to be very practical but there is no boundation that you can't connect a opto-coupler, I suggest to cross check your requirement twice before connecting opto-coupler with SSR.

AKR
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