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Triggering a TRIAC - need help

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Shandinesh

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I am using an Opto-coupler to trigger a BT136-600 TRIAC. I need to supply some 15ma to trigger the gate.I have connected everything perfectly and I am giving the required current. But my TRIAC is not triggering. Pls help me. The project is Under/Over voltage protection using SSR. I am using LM339 and an Op-amp to input the base of the photo transistor of the optocoupler.
 
Shandinesh said:
I am using LM339 and an Op-amp to input the base of the photo transistor of the optocoupler.
Please attach your schematic and show part numbers.
An opto-coupler for a triac usually also has a triac, not a transistor.

An opto-coupler has an LED as its input, not the base of its transistor. The transistor is the output and is activated by light from the LED.
 
Here is how a triac is usually driven:
 

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I have attached the ckt. The optocoupler consists of an LED and also a phototransistor.The transistor base is connected to the output from the LM339 and Opamp.
 

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I don't see any control current being applied to the led in the optocoupler, what are you using to control the optocoupler ?
 
Have you checked for a pulse train at the output of the zero crossing detector ?
also, double check that the diodes all have correct orientation.
 
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I've had a glance at the schematic but I haven't thought about it, what exactly does it do? I'm sure there's an easier way of doing this.
 
Hero999 said:
I've had a glance at the schematic but I haven't thought about it, what exactly does it do? I'm sure there's an easier way of doing this.

Yes, you just buy an opto-coupler with zero-crossing built-in - that circuit must be a seriously old design, and was probably far too over complicated even then?.
 
There are IC's from the likes of Burr Brown and Sanken etc that do exactly this kind of job, i.e universal voltage input. I'm not sure of his reasoning for wanting to have a discreet design though, but madness comes to mind...:)
 
Nigel Goodwin said:
Yes, you just buy an opto-coupler with zero-crossing built-in - that circuit must be a seriously old design, and was probably far too over complicated even then?.
So that's all it does?

A single comparator can do that!
 
actually, if you look at the circuit, 2 of the comparators are for detecting under and over voltage situations. They pull the trigger low in those situations. I think the op amp is part of a start up delay.

It does seem complex but I don't see a way to get rid of the hi/low comparators. zero crossing is pretty easy these days. I think the start-up delay could some how be incorporated into the hi/low comparators.
 
Thank U all, dear Guys for ur valuable posts.At last I found that my optocoupler has been damaged due to excessive heat when soldering. Also I have changed the transistor base resistor value to a higher one than that I have been using already. Now the circuit is working fine.

I know that there are superior designs than this. But I used it to do as hobby project with very low price components. Also it produces a perfect delay of approx. 1 min.

Thank U all once again for ur replies.
 
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