Triac Circuit Not working right ?

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That's the way it's supposed to work.  When you remove the 5V you are
no longer supplying current to the LED in the opto, which disconnects
the TRIAC's gate from its trigger source, the mains.

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Thanks John, I'm glad it works sorta the way it is suppose to. I think I have read about 5 or 10 of similar circuits and some of them they call them latching. I must have had that confused.

Yes the "hump" is NOT connected. -thanks.

When you say

I do have the Cap between R3 and R4. From there the cap is connected to a common line that has the R5 / MT1 and load connected up to it. (bread board).

4-------Gate | ..01u R5 MT1 |______|_____|______(Load)__

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For your circuit, if the load is an incandescent lamp there's no need
for the 2.2k or the 10k resistors or the capacitor, since what you
have is what's called a "static switch" and you have no need for phase
control.
 
I think van Roon was confused and wanted to use the 2.2k and the 0.1µF
as a snubber.   Take a look at

http://www.littelfuse.com/data/en/Application_Notes/AN1007.pdf

for some circuits that work.

3031

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Thanks I will do some experimenting with them.

Ive done a little reading and found this ..

To prevent sensitive gate devices from false triggering due to high rates of rise of off state voltage, 1 kW resistor in parallel with a 10nF

capacitor may be fitted between gate and cathode (gate and terminal 1 for a triac). This approach is less effective for standard gate

devices. In this case, the preferred option is to fit an RC snubber between anode and cathode (T2 and T1 for a triac) to reduce the dVD/dt below

the critical value.

I did read some other documents about snubbers before and wondered if this was the problem.

So the questions I have is, When would the circuit that I started out with work exactly as drawn. Is the schematic wrong ? Is it for electric motors etc. That is, a non resistive load ?

I suppose the begging question which you can't answer is why would an intelligent electronics person put a schematic out there when it does not work ? Or at best is not really going to work on an ordinary Incandescent Light Bulb which it describes as the load?

Regards.

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Thanks for that. I did actually do some other circuits like the one you indicated. Although I used a 3031 (as I recall) The reading I did seemed to indicate that the 3031 does the Zero thing which minimized RF if there are TV's/ Radio etc around. At least that seem to be what I understood. I kinda wish that people would actually tell us the parts they used and then give us the theory as to how to arrive at the right part. This would help me anyway. If I can see exactly what they used. This way I can figure out their math and test mine and hopefully come to the same conclusions. When I finish a little project I write the my observations, and what chips I used that worked so Next time I dont have to expriment all over again.

Regards

Look at the datasheet for the MOC3010. There is a sample circuit which could be better for powering a lamp.

See Figure 6.

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Regards,
   Robert Monsen

"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

There are *lots* of circuits that don't work on various web pages. There are also lots of circuits that work, but only marginally, with parts that may have different specs than your part.

I'm guessing that Tony Van Roon tried the circuit out, and for the triac he was using (which is probably different than the one you are using) it worked fine. The amount of current required by his triac was possibly less that that required by yours.

Another flaw with the 'van roon' circuit is that the circuit is powered at line voltage when the lamp is disconnected. If you touch it after you've unscrewed the bulb, you'll get shocked. Many circuits put the load on the high side (the Line side, black wire or small hole on the plug) for that reason. The center tap of the socket (which is hardest to touch) should be at Line, and the screw part should be at Neutral. The fuse should also be on the Line side, preferably before the lamp itself.

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Regards,
   Robert Monsen

"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.

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They are???

In what respect?

Stacy,

You are seeing what happens when a circuit is built with trial and error or leaving out the most important parameter such as gate current sensitivity range for the triac. Also there are many thousands of folks that dabble in electronics that are successful in building one circuit that works. It is quite another answer for a circuit that is described in enough detail to be mass produced or copied with the expectation of working. The above issues are the difference between the digital designs and analog designs.

Ray

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John,

You are seeing that the circuit does not work as expected or suggested when the circuit was offered. There was not enough information to hint at the potential problem of gate sensitivity or special selection of components. Ray

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--- Most of us here reply to newsgroup posts by bottom-posting, so if you don't mind please follow that convention.

You misunderstood my post. What I was questioning was your statement that:

"The above issues are the difference between the digital designs and analog designs."

Which makes no sense to me. What were you trying to say?

-- John Fields