Transistor Optocoupler MCU Switch

I created a sort of 'MCU controlled power switch' for AC power source based on the deseigns here:

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It uses optocouplers and triacs to turn each load on or off. It seems to work to switch anything within reason (like light bulbs of different wattages).

Is it possible to do the same thing with a 12v DC power source, by using transistors and optocouplers with transistor output? Someone told me transistors are more complicated to work with than triacs. I wasn't sure what he was talking about.

Reply to
Dave
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not sure I'm reading you correctly . . .

You want to control a triac with a 12 dc signal voltage? using the same kinda optocoupler you used with the MPU output?

YES that's easy to do (assuming I got it right) just put the 12 VDC signal into the opto coupler, to light the LED inside of it, with a dropping resistor to limit the current to the LED . . . and you are done.

IF you're asking if you can just put 12 VDC into a triac gate to turn it on - well you can sort of - but you won't have isolation - the mains will eat the power source if it is referenced to ground - and it will be dangerous if not referenced to ground.

Your question needs clarification.

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I want to have two DC power sources, 1) 5 volt, and 2) 12 volt. The 5 volt source should turn on an optocoupler which should turn on a transistor which will turn on a 12 volt connection from the other source. Actually the 5 volt MCU will control 6 or more optocouplers with transistor outputs.

So I'm asking if transistors to control the #2 DC power source would work, the same way it is working now with triacs controlling the #2 AC power source.

Reply to
Dave

Based on this question NO. The triac requires that the current through it be reduced to zero (low value) before it will turn off !

In a DC circuit once you turn it on it will stay turned on !

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Baron

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Yes. 

The thing you need to watch out for is to make sure your MCU can
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Reply to
John Fields

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you may not need opto-isolators, if you can connect one of the MCUs powewr supply wires to one of the DC supply lines, (typically the negatives are connected, but all possible arrangements can be made to work)

they probably meant that because transistors dont turn all the way on automatically like triacs do you need to make sure that you make them turn fully on otherwise they heat up...

Bye. Jasen

Reply to
jasen

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