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Need help in Opto-Triac Driver Circuit

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kushagra411

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Hi Friends,
Iam using the following circuit using MOC3021 Optocoupler and BT-136 Triac.

triac_circuit.png

When 5V is applied then the bulb glows but when 0V is applied it do not completely switch off.
The bulb just gets dim and do not completely turn off.

On State --
IMG_20151213_130052.jpg

Off State (Bulb gets very dim but not completely off)--
IMG_20151213_130027_1CS.jpg

Please help. Thanks in advance :-?
 

If the circuit is built according to the schematic, it should work. I see that you also have the missing LED series resistor in the real circuit. I'm however not sure if the small blue ceramic capacitors are rated for 230 V AC.
 

That also looks like it might be an LED light bulb. It depends on their internal circuitry but some will light up with very low current, there may be enough flowing through the snubber components to make it glow dimly. You do not need the snubber circuit unless you are switching a reactive load so try removing it.

Without the series resistor FvM mentioned you risk damaging the opto-triac.

Brian.
 

FvM said:
If the circuit is built according to the schematic, it should work. I see that you also have the missing LED series resistor in the real circuit. I'm however not sure if the small blue ceramic capacitors are rated for 230 V AC.
Click to expand...

thanks but yes Iam using a 150ohm resistor with opto-led and blue cap are 0.1u 400v.
I guess its problem due to snubber part.
Iam designing this for general purpose use and it might be possible sometimes that AC motor may be used as load. So i guess snubber is required. but its not working with led. can you suggest something? :(

betwixt said:
That also looks like it might be an LED light bulb. It depends on their internal circuitry but some will light up with very low current, there may be enough flowing through the snubber components to make it glow dimly. You do not need the snubber circuit unless you are switching a reactive load so try removing it.

Without the series resistor FvM mentioned you risk damaging the opto-triac.

Brian.
Click to expand...


Thanks brian but its for general purpose and i might use AC motor sometimes so i need snubber of some kind. I see that the problem is because of snubber part but can you suggest some other way around..
 

Perhaps putting a diode in series with pin 1 of the opto could ensure a level of 0v there, remaining no eakage current capable of biasing the LED.
 

I think your only option would be to use a 'snubberless' triac instead of the BT136. If you search for 'snubberless' or 'Alternistor' it will show alternatives with similar switching capability.

Brian.
 

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