I'm looking for a cheap simple Triac driver circuit. I still don't understand the uses of a DIAC I mean not as a switch with only two pins. I've heard of opto-couplers being used to switch a triac. I've been using a relay which costs 1.7 dollars if bought singley. Still can't post a schematic even cutting from a bitmap.
Posted on 2003-09-25 07:06:54 by mrgone
it simply the same like what i saw those days. a driver bd, with opto-coupler and with mosfet/triac, plus some MOV and fuses, and some resistor.

today, i am pending replacement for triac AC16 for After Burner 2 @SEGA driver BD. maybe tomorrow we'll find out if there is. the opto-couplers used for those bd usually white in colour, i.e. moc???, til???, etc ( it have 6 pin all.).

about the schematic. ahh, i cant remember it, the main part on the bd is opto-coupler, so, i think i can find it on they datasheet/application notes.
Posted on 2003-09-25 07:31:01 by dion
I checked to see if you had instance messenger or ICQ
Posted on 2003-09-25 07:38:28 by mrgone
Posted on 2003-09-25 21:05:21 by Ratch
I usually use Overture search performance and have acheived excellent results as far as computer information. Things like Window IT Library which blew me away when I found that one. I will take a look as soon as I figure out how to implement Icz's Tut-20 into my program. I need that filter function but these dern WindowProc's are driving me waco.
Posted on 2003-09-26 17:11:25 by mrgone
Hi, mrgone,

The cheapest triac drive scheme is the one commenly employed in the light dimmers, or kitchen appliances.
I am attaching a crude schematic.

As for how the diac works, look at the links posted by Ratch first. A diac turns on (its resistance drops abruptly) when the voltage across it reaches the threshold. This happens in either direction.

To turn on a triac, you need to inject a current into the gate. The direction of the gate current must be reversed when the voltage across the triac is reversed. The diac will help do the job.

So, this is how the circuit works:
Initially the triac is off. Through R2 (and the load), a voltage across the two zeners is developed. It is clamped by the zeners, so it looks pretty much like a square-wave, in synch with the AC line. This is integrated by the R1-C1 group. The voltage across C1 thus increases exponentially. When it reaches the diac's threshold, the diac abruptly decreases its resistance, which causes C1 to discharge into the triac's gate, injecting a high current and turning is on. Note that it took some time for C1 to reach the diac's threshold. By adjusting R1 you adjust the time from the zero-cross to the triac's firing.

When the current through the triac decreases (we are using AC) below its hold-up current, the triac turns off. The next turn on will be initiated by the diac again, this time for the negative side of the AC sinewave. The diac works both ways, remember? And since the polarity of the voltage across C1 is now reversed, the current injected into the triac's gate is also reversed, as it should.

By adjusting R1, you effectively adjust the voltage applied to the load. Note this voltage is not a sinewave, but a portion of a sinewave, with an adjustable dead time.

Generally, some RC snubber across the triac and LC filter at the load are needed in a practical circuit. They are not shown on the schematic for clarity.

If you need more info, let me know.

Posted on 2003-09-30 22:22:04 by VVV
Thanks, NaN for resizing my picture.
How can I do that in the future? I don't know why this picture came out so large.
Posted on 2003-10-01 11:35:05 by VVV
The program you use makes a very large bitmap to display all the schamtic information. Im assuming anyways. When you exported it, i mearly exported it with no modifications.

I used paint shop pro to resize it by 20% of the origional, and resaved/uploaded it.

Posted on 2003-10-01 15:53:36 by NaN
I better get busy with my new home work assignments...lol. My computer has been down almost three days. Sheroc inadvertantly sent me a virus. My Win2k disk is all scratched up because I loaned it out so had rough time. But thanks loads. This final product should be for sale at Home Depot very soon.
Posted on 2003-10-02 19:31:46 by mrgone