I'm looking to switch (not dim) <30 VAC @ <250 mA using a DIO pin.
Most projects I see for controlling AC use a MOC3010, MOC3041 or similar driver/optocoupler to drive a triac, quadrac or the like. All of these designs are for controlling line voltages exceeding 110 V, is there a better solution, aside from an expensive SSR for controlling low voltage AC with a micro?
It "ain't pretty", or "clever"... and not suited if you need high frequency switching... but for SIMPLE a good old fashioned relay is hard to beat.
If you don't know about "the diode" (to snub reverse voltages) you need to... BEFORE you connect your first relay.
And you almost certainly need to have a transistor involved.
Apologies if you already knew these things, but not everyone does. If you didn't/ don't, you may find the following useful...
Not sure if even close to what you want .. but have you seen this? It switches AC for el wire.
tkbyd,
Thanks for the reply. I should have mentioned that I'm trying to stick with a solid state solution for multiple reason not the least of which is size. I should have mentioned that up front.
marklar,
That's not exactly what I'm looking for, I only need to control a single circuit, but that Z0103MN triac looks interesting. The data sheet mentions "Direct interfacing to logic level ICs". I assume that means I can avoid a triac driver/opto and drive it straight from the micro (SparkFun is doing it). I'm just not that clear on exactly how much power the triac can switch.
Are you saying that an MOC30XX can safely switch a <30 VAC @ <250 mA load without the aid of an external triac?
I'm new to AC loads. I'm sitting here paging through The Art of Electronics and a note from Phillips/NXP titled Power Control with Thyristors and Triacs trying to get a better understanding of limiting values and specifications.
Thanks for the help.
Sometimes the simple relay doesn't get the respect it deserves. Such a flexible and useful device. For your operating requirements the below would seem very appropriate.
Cheap, small, quite reed contacts. Only needs 25 ma of coil current so can be directly wired to an Arduino output pin, no switching transistor required, although you should wire a diode across the relay coil contacts for transient suppression. Tell me why this simple device would not be better then anything else you might come up with for 60 cents and fits in a DIP footprint?
Lefty
Sometimes the realy has its problems too... Mainly the footprint, it is quite common to use a relay and when we need to change it, its difficult to find a replacement for that footprint.
But, it is as far as I know the best solution for this problem and maybe even the safer as there is very little to be done on the AC side of things whilst with a MOC you still need some resistors.
About the MOC, you can use it with 30V. Check the manual and application notes and you may even get away with using just the MOC, although I do not advise it.
retrolefty,
You make a good point, I will think about using a relay. Maybe I do have a bad attitude about relays, I just can't get the picture of big clunky 12V relay cubes out of my mind.
Richard Crowley,
Thanks for the info on the MOC30XX drivers. Since I think I have a few laying around I'll probably go ahead and try one out on a breadboard.
for 30V @ 250mA load, the MOC + TRIAC will probably take up more space than a relay... and more tracks to design.
The way I read what Richard wrote is that in this low power situation a MOC should have no problem switching this load without the external triac. If this is true than the pin count would be the same as using a relay and probably take a tiny bit less board space.
If I'm mistaken, please, let me know.
There's nothing inherently wrong with relays, but they:
Note: This optoisolator should not be used to drive a load directly. It is intended to be a trigger device only.
Not sure why they say it, but every example circuit describes how to use it to drive a TRIAC, with the TRIAC driving the load.
-j