Problem with triac circuit

triac circuit

Hello
I've constructed a triac circuit using the suggested circuit on the triac driver's data sheet. It doesn't work and since I don't know what to expect, it would be great to get some troubleshooting help.
I've attached the circuit snip.
There is a pulsing output from the uP that goes to the optocoupler (triac driver MOC3023) that I can see as there is an LED to reflect. I also verified pulsing output with scope.
On the other side of the triac driver, I think I'd expect to see more pulsing, but don't. And since there is no signal whatsoever outputting from the triac driver, there is nothing getting to the gate of the triac.
Datasheet here:
https://www.st.com/stonline/books/pdf/docs/7472.pdf

My load on the 115AC side is only 24ohms. I wonder if it is too small? Does the triac need more load?
Or is one of my parts busted?

Thanks in advance,
Nora

triac troubleshooting

try reversing your triac pins MT1 and MT2:
on the moc 30xx family the moc output MUST be between MT2 and G
and your's is between MT1 and G
this is written nowhere but some triacs dont connect if...

I had the same problem this week...

troubleshooting triacs

The 1k resistor limits the current in the LED of the opto to only 3mA. The minimum current on the datasheet is more so reduce the value of the 1k resistor. The max allowed current from a PIC is 25mA.

24 ohms on a 115V circuit is 551W. The peak current is 6.8A.

how does a triac work

BTW what is TB1 & TB2?

If it is a transformer nothing is going to work

Regards
Nandhu

troubleshoot triac

Thanks for replies.
Kripton- I am going to switch MT1 and 2 this week- what a strange thing to NOT print on your datasheet!

TB1 and TB2 stand for terminal block 1 & 2.

Yes, the watts are high. The load is a heater. The triac is rated for more that 6.8A so should be OK.
In the datasheet that I'm looking at- page 3 of 10
www.fairchildsemi.com/ds/MO/MOC3010M.pdf

It says that the LED trigger value (IFT) for a MOC3023 should be 5mA, so yes, more than 3mA. So 5V- 1.2V (LED) / 5mA = ~750ohm. OK, can reduce 1k- thanks for pointing that out!

Nora

triac circuit troubleshooting

is your stuff working NOW?

triacs moc

Nora said:

Kripton- I am going to switch MT1 and 2 this week- what a strange thing to NOT print on your datasheet!
Nora

Click to expand...

in fact if you look at schematics around the web with a moc30xx, and if the terminals are written, there is always MT2 (or A2) - the moc - and G
but it is not always written
and the triacs are supposed to be reversible between mt1 and mt2
I found once someone that pointed out that fact of mt2 and moc, and as I came on the same problem I remembered it...changed mt1 and mt2 and my triac was switching !!!!
some triacs need this, I dont know why, but it's a fact I experimented really.
my triac was a BTB16-600BW
regards,

triacs sample problem

the triacs are supposed to be reversible between mt1 and mt2

Click to expand...

They are reversible in respect to the load connection, but never reversible regarding gate drive. You can easily identify a low resistance between G and MT1 (A1).

problem with triacs

Hooray! It works. I switched MT1 and MT2 and all is well.
I'll switch out the the resister too in the final version so its not so marginal.
Will go and click on "helped me" now.
Cheers!
Nora

problems about triac

Some triacs are spec'd with how well or not they work in different quadrants.