Author Topic: Help me with some triac optoisolator questions (Vishay VO3023)  (Read 287 times)

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Offline dsegel

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Help me with some triac optoisolator questions (Vishay VO3023)
« on: February 08, 2018, 01:57:08 am »
I have some of these (VO3023) and am wondering if and how I can use them in a specific project where I will be driving them with an Arduino Pro Mini using digitalWrite. I've never used optoisolators before.

Here's the datasheet: http://www.vishay.com/docs/84132/vo3020.pdf

Here are my questions:

1. Do I have to use a resistor on the input to the chip to protect the internal LED? It looks like the trigger current is listed as 5mA, so that would mean a 1K resistor for a 5V signal, right?

2. Most circuits I see using this kind of optoisolator drive an external triac. Why would I need that since this has one internally?

3. If I do use an external triac, what purpose do the resistors (56R and 100R) in a circuit like this perform: https://www.electronics-tutorials.ws/articles/opto6.gif

4. How much current can I pass through the internal triac? Is that the "RMS On State Current"?

5. Finally, probably the biggest question - I need to use it to turn a DC line on and off that may have it's polarity reversed (i.e. positive and negative are reversed sometimes). Is this OK with a triac, and how do I calculate the current when specs are written for RMS?

Thanks in advance to everybody.
 

Offline Benta

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Re: Help me with some triac optoisolator questions (Vishay VO3023)
« Reply #1 on: February 08, 2018, 02:19:15 am »
1: yes.
2: to increase power capability.
3: limit the gate current.
4: yes.
5: a triac optocoupler is not suited for DC. Once it's turned on it will not turn off until power is removed (or AC reverses polarity).
 

Offline dsegel

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Re: Help me with some triac optoisolator questions (Vishay VO3023)
« Reply #2 on: February 08, 2018, 05:57:16 am »
I have a relay to cut power to the triacs after they do their thing (briefly energizing the coil of an electromagnet). The only reason I want to use a triac is because I need to switch on and off current flowing in either direction (the direction of the current flow is reversed to switch the pole of the electromagnet), and I will eventually have 56 of them so individual relays would make me unhappy.
 

Offline Benta

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Re: Help me with some triac optoisolator questions (Vishay VO3023)
« Reply #3 on: February 08, 2018, 06:20:59 am »
Quote
(briefly energizing the coil of an electromagnet)

Won't work. When the triac is on, it's on. Cut current to the LED and it still stays on.

Avoiding the polarity reversal is probably a better idea, either with a bridge rectifier or just a series diode before your circuit.
 

Offline dsegel

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Re: Help me with some triac optoisolator questions (Vishay VO3023)
« Reply #4 on: February 08, 2018, 07:48:31 am »
I meant that the power the triac is switching will be cut by the relay, not the gate signal.

And I need to reverse polarity to swap the ends of the magnets (north-south).
 


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