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[SOLVED] The Triac would not turn on. Any help?

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papaisou11

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The above circuit I made to switch on a CFL bulb of 14 Watt at 220VAC. My problem is, it is not turning on. As per the datasheet there is no snubber required for 2A of load.

Well, I have changed the R1 value upto 100 ohms, tried 33 ohms also.

However, whenever I am testing the Triac gate AC voltage using a multimeter, the CFL bulb blink once. It is only happening when I connect the positive lead of the multimeter in the gate, and the negative lead is connected in neutral.

My load is connected in series with the X1-1 with neutral, the X1-2 is connected with a HOT line.

Any help is highly appreciated. Where I have done wrong? Any suggestion?
 

KlausST

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Hi,

possible reasons:
* wrong triac wiring --> check wiring and / or post a photo of the wiring.
* the logic signal is too weak to drive LED and MOC. Either too low voltage or to low current --> try without the LED
* the CFL is too high impedance for the TRIAC to stay ON --> try an incandescent light bulb. If it works then try the CFL in parallel with the incandescent bulb.

Klaus
 

RCinFLA

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Fluorescent light don't work with triac switches without a more elaborate triac gate control circuitry.

The poor power factor reactive load of fluorescent light causes triac to immediately shut down after being triggered.

Triacs shut down conduction when current though it passes through zero. Trigger happen by voltage level rise.

CFL are highly capacitive load due to their simple rectifier to filter capacitor HV DC supply. There is just a small duration AC input current pulse at peak of AC input voltage sinewave to charge HV capacitor then current drops to zero for most of cycle. When current drops to zero the triac shuts off.

Triac will trigger as input sinewave voltage rises slightly pass zero crossing but there is no current flow to capacitor until AC input voltage hits near peak so triac seeing no current immediately after trigger just shuts back down.

If you can find a power factor corrected CFL it will work. They are rare and hard to find as EU regulations do not require PF correction on devices drawing less then 75 watts from mains. U.S. has no power factor requirement for residential use.
 
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FvM

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RCinFLA is basically right. Triacs have however quite different holding current, it may be possible to make a working triac switch for CFL lamp. But it will hardly work with a zero-crossing opto triac. Check with a standard opto triac.
 

papaisou11

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Thanks all of you for valuable information. I tested the circuit with only triac and Rg restistor. Disconnected the opto. No luck.

I have a led night lamp of philips. Rating 0.5 watt. Its led and no luck.


I will buy a incandescent bulb with 100 watt rating today. Will provide all of you the details. Lets see what happen.

Yeah...I have tested the footprint they are ok and it is in a small pcb.
 
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FvM

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Your latest observation indicates that there's something seriously wrong with the triac or your circuit wiring. Triac with 100 to 500 ohm between A2 and G would effectively act as short and light the lamp continuously.
 

papaisou11

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Hi... Nope the circuit did not worked with 100 watt incandescent bulb also.

I am again sharing just one finding if it really help... This time also the light bulb glows for around 500ms (Approximately) when I have connected the multimeter proble across the gate. Let me describe. I have first connected the negative, black probe in the variac neutral. My variac is set to 230VAC. I have used 100R resistor as a Rg. No opto-coupler is connected. At this situation my positive probe of the multimeter is touched with the gate pin. I have not disconnected the probe from the Triac gate pin. As soon as I touched the probe the Light just blinked one time and then no output. However it is not happening every time. I have tried repetitively for 10 times or so. This happens almost 3 or 4 times. This 3 and 4 times are random, not in any sequence.


I am sharing the PCB design now. If there is any mistakes I did please do notify me. Actually I am feeling helpless without any clue.

1600275995900.png

@danadakk No i was used CFL lamp (It is sold as just CFL in india, it is almost 3-4 years old, but fully working), I do not have knwoledge about the CFL and CCFL, I need to study a bit to reply you. Thanks for the schematic, I will try this also.


By the way, I had two pcs of triac, I have also changed and used both of them for the reason if there is any luck. But, if I made something terribly wrong, maybe both triacs are destroyed. In that case, farewell to me :( . It will take a long time to receive component again in India due to covid situation.
--- Updated ---

This is
Your latest observation indicates that there's something seriously wrong with the triac or your circuit wiring. Triac with 100 to 500 ohm between A2 and G would effectively act as short and light the lamp continuously.
This is what I am thinking during the testing and thats why I am very confused.
--- Updated ---

you can also try to revert the two triac anodes
Did it. No luck.
--- Updated ---

Hi,

possible reasons:
* wrong triac wiring --> check wiring and / or post a photo of the wiring.
* the logic signal is too weak to drive LED and MOC. Either too low voltage or to low current --> try without the LED
* the CFL is too high impedance for the TRIAC to stay ON --> try an incandescent light bulb. If it works then try the CFL in parallel with the incandescent bulb.

Klaus
I will share the wiring also. Unfortunately I forgot to click it today.
 
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FvM

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The triac has A1 and A2 (com and out in datasheet terms) flipped. Can't work.

By the way, PCB clearance between 230V and control circuit is rather small.
 

Easy peasy

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Try a 40W bulb for starters - as the > 100A inrush on the 100W bulb may kill a small triac every time - that is one reason why a series choke is needed ( to limit di/dt - there is a rating on the data sheet ).
For powering CCFL try 2 x 40A 500V mosfets in inverse parallel - ( or a single mosfet inside a diode bridge )

The ckt above seems like a good idea if you insist on using a triac for CCFL - you must supply gate current all the time to the triac if you want it to work properly .... remember most CCFL's have a diode brisge and 400V cap on the input and so only draw current near the mains peak ...
 

papaisou11

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The triac has A1 and A2 (com and out in datasheet terms) flipped. Can't work.

By the way, PCB clearance between 230V and control circuit is rather small.
So you are suggesting to flip the com and out pin?
 

papaisou11

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Hi....

Thanks FvM and all of you. Finally I made it. I have removed the MOC3031S and connected the mcu negative via a 100k resistor to the neutral line. The COM pin of the ACST is now connected to neutral as well as with the MCU with a series resistor. The load is connected in series with the Hot line and getting connected with the Neutral using the ACST.

Now, when I providing 3.3V to the gate, it is working perfectly.

I am also giving the link of ST document for those who are interested -


The Application note number is AN-4363.
 

KlausST

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Hi,

best if you show a schematic of your working circuit. Hand drawn is O.K.

Klaus
 

papaisou11

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Sure KlausT. Hope this will help all - Here is the updated working circuit.
 

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