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Currently I'm designing Voltage Stabilizer and I'm using three DC relays at the output of my AVR Controller, at the output of relays I have connected ac sources which is in the range of 190V to 280V and current ranges from 0.9A to 2A, whether I can use opto-coupler (opto-isolator) instead of relays or not ?

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Devices sold as optocouplers generally have a an output that approximates a current source, with high output impedance, which is very different than a relay. Also they generally only pass current in one direction.

Depending on what you're actually trying to do, you might want to investigate solid state relays or SSRs.

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What you most likely need is an SSR. Do you really need 280 VAC rating? ..or do you just need to operate on 230-240 VAC? If you only need 230 VAC, then look for "Arduino SSR" on Amazon or Ebay. There are lots ranging from single through to 8 channel that will likely support what you need.
Be aware that some are not using zero-crossing SSR's. However if you need to you can detect the mains zero crossing in your microprocessor and switch them on at the right times.
Some variants seem to use the Omron G3MB-202P (http://www.mouser.com/ds/2/307/g3mb_0609-298620.pdf) which is zero-crossing, but some product images show the G3MB-202PL which is not zero-crossing.

enter image description here

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Devices we call "optical couplers" or "opto-isolators" are typically low-power, logic-level devices which are NOT SUITABLE for switching mains power.

Your description of the requirements are exactly what solid-state relays (SSR) are made for. They are available in a wide range of ratings from small units the size of a large capacitor (as shown in Jack Creasey's photograph) up to larger "hockey-puck" style which are quite popular for microcontroller switching of mains power up to 20-30A, and even larger ones capable of handling rather large loads. There are many SSRs for sale on Ebay at all times.

Your circuit description is sufficiently obscure and unusual to warrant additional caution to select appropriate SSR products as it doesn't sound like your typical mains AC control situation.

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