moc3023 triac optocoupler

Thread Starter

denison

Joined Oct 13, 2018
137
Hi all, connected this first without a snubber for a 240vac light globe. the globe was on all the time without a signal to the infra red emitting diode. then I tried the recommended snubber. globe was then flickering on and off.
I looked up snubberless triac optocouplers on google. got the fod420 and fod4208. also from Fairchild same makers as the moc3023 I think.
Can any of you guys recommend them and a supplier? thanks.
 

Thread Starter

denison

Joined Oct 13, 2018
137
Eric, please find enclosed attachment of my snubber circuit which does not work. Any suggestions to make it work would be appreciated.
 

Alec_t

Joined Sep 17, 2013
11,728
It is a 240vac led.
If it's rated for 240VAC that 'led' includes circuitry to drive the LED itself. Not all mains-rated LED-based lights are dimmable, so your 'led' may present problems in a triac circuit (whether it's for dimming or just for switching on/off).
 

Thread Starter

denison

Joined Oct 13, 2018
137
to bordodynov, thanks for the circuit.The globe is a 240vac led globe. not a small led as your circuit shows. could you amend it? what is interesting and may work is the resistor you show between the triac gate and a terminal of the main triac. the resistor also connects to mt1 of the opto coupler. I have seen other suggested circuits like this for the snubber but they give no value for the resistor. but then they say its for high temperatures?
I have ordered a fod4208 opto which claims to have an active dv/dt clamp. this might fix the problem.
 

Thread Starter

denison

Joined Oct 13, 2018
137
If it's rated for 240VAC that 'led' includes circuitry to drive the LED itself. Not all mains-rated LED-based lights are dimmable, so your 'led' may present problems in a triac circuit (whether it's for dimming or just for switching on/off).
Thanks Alec. I think that must be it. It is probably not dimmable. I previously used filament globes but they are getting hard to find. I will try a different load.
 

Bordodynov

Joined May 20, 2015
2,693
to bordodynov, thanks for the circuit.The globe is a 240vac led globe. not a small led as your circuit shows. could you amend it? what is interesting and may work is the resistor you show between the triac gate and a terminal of the main triac. the resistor also connects to mt1 of the opto coupler. I have seen other suggested circuits like this for the snubber but they give no value for the resistor. but then they say its for high temperatures?
I have ordered a fod4208 opto which claims to have an active dv/dt clamp. this might fix the problem.
You are mistaken. There are no mistakes in my scheme. You just don't know all the features of LTspice. If you take a closer look at the schematic, you will see next to the LED name the inscription: n=24 m=3. This means that it is not a single LED but 24 LEDs in series connected by three parallel LEDs. Apart from the current I have also graphically shown the power dissipated by this LED assembly. I have applied this LTspice feature and it speeds up the counting!
 

Bordodynov

Joined May 20, 2015
2,693
what is interesting and may work is the resistor you show between the triac gate and a terminal of the main triac.
I put on a triac circuit with a Russian spice model. The scheme did not want to work. I found out that the circuit did not work because OPTO-TRIAC was not turned on. This was because there was no control current on the triac. I.e., the triac model was defective. I solved the problem by setting the resistor. Then, I put a 1 kOhm resistor into all Russian models. Actually, you need a slightly smaller resistor but that's a good start. The internal semiconductor resistors included in the triac have a positive temperature coefficient. And the base-emitter voltages of the internal transistors decrease as the temperature increases. The bipolar transistor coefficients also increase and make up a triac. As a result, the triac current decreases significantly, and this leads to the fact that interference may cause false switching on the triac. To solve this problem, an external resistor is added to the internal resistor, which has a much lower temperature coefficient. In general, the smaller the resulting resistor, the more reliable the circuit is.
Ps. I will update the spice models on my web page tonight.
 

Thread Starter

denison

Joined Oct 13, 2018
137
I put on a triac circuit with a Russian spice model. The scheme did not want to work. I found out that the circuit did not work because OPTO-TRIAC was not turned on. This was because there was no control current on the triac. I.e., the triac model was defective. I solved the problem by setting the resistor. Then, I put a 1 kOhm resistor into all Russian models. Actually, you need a slightly smaller resistor but that's a good start. The internal semiconductor resistors included in the triac have a positive temperature coefficient. And the base-emitter voltages of the internal transistors decrease as the temperature increases. The bipolar transistor coefficients also increase and make up a triac. As a result, the triac current decreases significantly, and this leads to the fact that interference may cause false switching on the triac. To solve this problem, an external resistor is added to the internal resistor, which has a much lower temperature coefficient. In general, the smaller the resulting resistor, the more reliable the circuit is.
Ps. I will update the spice models on my web page tonight.
I think what Alec T says is right. I have been using an 240vac led globe which is not dimmable. I now have a dimmable halogen 28w globe. I am about to try this. I am expecting it to work even without a snubber. Previously with the led globe the flickering could be explained by the opto being off in 1 half cycle and on in the other because the led globe is actually dc operated.
 
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