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This is a follow-up to a previous question, regarding the VO2223A opto-coupler/Phototriac. My understanding of the chip is that the IR LED triggers a phototriac, which in turn drives the gate of a power triac. In which case... what's pin 5 for? It's listed as a "triac gate", but there's no obvious reason that I can see for it (unless it's in a different configuration to the one that I'm assuming).

And if I don't need to use it, do I need to strap it to ground, to another input, or to leave it floating? Unfortunately the specimen circuit diagrams in the datasheet (which are usually my first point of reference for pin assignments) aren't particularly helpful -- they don't include pin numbers, and appear to omit 5 entirely -- and I've never been able to find online any circuit example that uses the chip.

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Please add a link to the previous question. – Camil Staps Jan 20 '13 at 18:08
@CamilStaps: If you just click on the OP's name, you'll see his previous question(s). However, I have added the link here for your convenience. – Dave Tweed Jan 20 '13 at 18:19
Yes I know, but for the convenience indeed. (And theoretically you might ask a follow-up question on another one's question, but you're right, that's not the case.) Thanks for adding it anyway! – Camil Staps Jan 20 '13 at 20:39
Another learning experience... I'll post cross-links in future (as well as to component or other external references). Many thanks for pointing it out (and also to the person who then edited the message). – Peter Reid Jan 20 '13 at 22:11
up vote 0 down vote accepted

Often, gate connections on photootriacs (and phototransistors) are used to:

  1. Turn on the device separately from the LED (a remote trigger function)
  2. Hold the device on once the stimulus goes away (a latch function)

I would leave the gate floating, with an option for a tie-down resistor in your layout. Most of the time, you need to supply current to the gate in order to activate the device - tying the gate high will most likely turn on the triac all the time, which is something you don't want.

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protected by Kortuk Mar 23 '13 at 13:52

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