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opti-triac for low voltage AC


Apr 25, 2024
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Hello all, I've been reading an interesting thread re opto triac for AC switching.
I wonder if betwix or others can help me as this is not my subject.

I wish to switch a low-voltage AC signal to ground - just a volt or two pk-pk.
Very low current too, just a few mA max, so 'hold current' whatever that means may be significant too.
The opto triac idea looks good, but I am not sure they are suited to such low voltages (and currents).
Maybe someone can suggest a suitable device.
It needs to be fast, so relays are not suitable.

Thanks in advance.

So we know the "load" is AC, 2Vpp, a few mA
--> What AC frequency?

We know nothing about the "control" side.
--> So tell us V and I capabilities of the control side.

--> For "fast" switching we need to know numbers.

The "opto" in opto triac means "isolated".
--> What is the voltage of isolation you need?

Generally speaking a triac as well as an opto-triac is not very well suited for low voltage and low current.

A bit more information about the whole project would be helpful to give suitable advice.
And as always: a sketch says more then a lot of words.

Nice to be mentioned in dispatches!

The other point Klaus didn't mention but is relevant at low voltages is how 'closed' the switch has to be. A triac will still drop around 0.6V when fully conducting and that could be significant. There are other possibilities that might work but more information on your application and the voltage/current/speed are needed to give better guidance.

Hello all,
The frequency is low - 80Hz
For the control side, we have a 3v3 logic signal, but have +/-10v available at some power, so could drive e.g. 10mA if required.
Switching in a few 10s of uS would be in the order I am looking at.
I don't need any isolation, I just thought the opto controlled device would be easier to interface with.
A 0.6 offset would be reasonably significant, as the unswitched signal is only a few volts to start with.
I am also considering using an analogue switch to do this which might be more suitable - lower offset? and we have the power rails to allow it to switch the voltage range =/- a few volts.

The application is a system we use to measure the resistance of some fluid that passes through a pipe - one 'electrode' having the AC signal on it, the other being GND - and I want to connect and disconnect that ground to check if there is a resistance to a different fixed GND.

or a simple analog switch. Like good old DG201 ...
But there are many many more others.
Just use the selection guide of your electronics distributor.


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