Triacs and Optocouplers

[a31ford]

Greetings All ! (Almost Seasons, even !)

 

Many have had issues with stuck channels (full or partially lit).

 

For what it's worth, (And those that want to know....) I'm going to speak about these two components (Triacs and Optocouplers).

 

Triacs, are a 3 wire device, they are inserted "INLINE" with the load (one wire in, one wire out, and a "trigger" wire), the trigger wire needs to be connected to the "line" side of things, BUT, must be through some form of "ISOLATOR" (Hence the MOC-3023, optocoupler).

 

Triacs themselves are really only two gate controlled diodes side-by-side in the same package (you can do the same function with a PAIR of SCR's but that is "off topic".

 

The two diodes  are connected "opposite directions" this way you get the full 120v AC (Alternating Current) through the triac when it is triggered on (If you used an SCR in place (NOT two, only one)  you would only get 60 volts @ 30 hz.

 

The Triac is a very simple device, for 99% of the problems it will only have 6 states of.......

 

A) Off, no current flow (Normal Operation).

 

Triggered (at "X" trigger level), depending on what trigger level, the triac will conduct "X" amount of voltage (in BOTH directions of the AC cycle). (Normal Operation).

 

C) ONE of the internal diodes shorted (only one), In this case the channel will be on 50% brightness, ALL the time. (Partial Problem).

 

D) BOTH of the internal diodes shorted, In this case the channel will be on 100% brightness, ALL the time. (Full Problem).

 

E) ONE of the internal diodes OPEN (only one), In this case the channel will ONLY go to 50% brightness (Partial Problem).

 

F) BOTH of the internal diodes OPEN, In this case the channel will Simply NOT WORK (DEAD), (Full Problem).

 

 

The above is 99% of the problems that occur with triacs.

 

Optocouplers.

 

Optocouplers on the other hand, come in many types, the MOC-3023 Used on the LOR, DIY, CTB-16-PC Kits are dimmable (proportional input voltage) units, the 6 pins are as follows, 

 

 

If you understand even basic electronics, you will see that  pin 1 is the + side of a LED, pin 2 is the - of the same LED, 3 is no connection, pin 4 is connected to a triac ? YES, actually it's a light controlled triac (NOT a diac as some people call it) (A diac has only 2 inputs, the item in the MOC has 3 connections, pin 4, pin 6, AND the light input from the LED).

 

THE isolation from the 120VAC comes from the fact that there is NO electrical connection between the two sides of the MOC, in fact, the isolation (INTERNALLY) is rated at over 2500 volts !, HOWEVER, the outside case CAN be affected by dampness or moisture (this is where keeping them dry, and drying them (the controllers) out with a hairdryer comes in).

 

There are OTHER types of MOC's HOWEVER the MOC-3023 MUST be used in the LOR controllers to keep both the isolation AND dimmability. Other version of MOC's are 3031 (only a switch, NOT dimmable), MOC-3030, connected substrate (NO Isolation), etc, etc, etc. The list goes on, and on.

 

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Here's the thing, OF the 6 basic problems with triacs, the most common is "Stuck on" 100% (blown) from a shorted cord, is the usual cause (triac overheated from too much current).

 

HOWEVER, MANY problems can be attributed to OPTO's as well, the main one being dampness between pins 4 and 5, AND 6, ANY combination of wet in this area will cause "STRANGE THINGS" to happen, random "spastic issues" phantom on/offs, etc. etc, etc.

 

All in all, unless the channel(s) is/are ONLY doing one of the 6 issues listed in the triac section above, I would suspect the MOC instead......

 

IF you notice, I went out and bought the 6 pin sockets for the MOC's ONLY because of my electronic background AND my former knowledge of optocouplers, for the most part, keeping them (The MOC's) dry would be 99% of the battle.........

 

 

 

Greg

 

 

 

 

 

[Santas Helper]

WOW Greg,

That was a very impressive explanation of Triacs and Optos and possible problems related with them.

 

Thank you!!!

 

Tom

[Max-Paul]

Greg,

 

Kudos on your attempt to teach the masses some information that would be new to them. But I have issues with your information. First a SCR outputs only have of a wave form. When in circuit of 120 VAC 60 Hz. When fully turned on the output would still be 120VAC, but only halve of the wave. But still would be 60hz. Where as a Triac will give you a full wave still at 120VAC 60Hz. But how you have both the positive and negative half of the wave form.

 

A common mistake that new people to electric / electronics. Otherwise a good training post.

[a31ford]

Max, I disagree (Sorry) if that was the case (1/2 waveform giving 120) then why triacs ? just use SCR's  the electrical symbol for an SCR is a gated diode, a triac is a DUAL (side by side OPPOSED) gated diode.

 

I stand by what I said, SCR would be 60v 30 CPS (only conducts one way).

 

remember, 0 crossing...... of you only conduct 1/2 the waveform, then only 1/2 the voltage

 

The principal of using a gating diode in a string of lights consisting of bidirectional LED's (red forward bias, green reverse bias) is the exact same as a 1/2 wave rectifier.

 

 

 

Greg

Edited November 6, 2013 by a31ford

[plasmadrive]

Gotta go with Max on this one about the frequency.  The SCR may only conduct half of the cycle but it is still 60 Cycles per Second.  or 60hz. 

 

Think about this, if it were a square wave with the bottom being 0v and the the leading edge rise time is at 16.67 ms intervals what would you have?  60hz.  Same with the half wave AC waveform. The repeating cycle is still the same time constant. It is not about zero crossing, it is when the cycle repeats.  Many wave forms don't cross zero but they still have a frequency.

 

If however you put a full wave bridge in there you would get two repeating positive half cycles in the same 16.67ms, thereby having a 120hz rate. 

 

As for the voltage, that is a different story.  The voltage is expressed in RMS value

Edited November 6, 2013 by plasmadrive

[a31ford]

If you are conducting at only one side of the cycle, I will agree (now that I think about it) still 60 CPS, however, only 30 of the "humps" show within that 60, therefore you only have 1/2 the voltage (60) VPDC (Volts Pulsating DC) so it would be 60 volts in 60 cycles.

 

Math is not my strongpoint for the next few days, time change toasts me....

 

sine is still sine, 1/2 wave sine, is also still sine, just 1/2 the voltage.... 

 

 

So therefore, I was 1/2 right (the voltage 1/2) and Max was right about the frequency 1/2.

 

 

 

 

 

Greg

Edited November 6, 2013 by a31ford

[plasmadrive]

.637 or .707 x Vpk  half wave average, full wave RMS

[Ken Benedict]

Peak, average or RMS, it's still 60Hz with an SCR.

 

Without a full wave bridge preceeding it.

[plasmadrive]

Peak, average or RMS, it's still 60Hz with an SCR.

 

Without a full wave bridge preceeding it.

Unless of course you are in another country where the freq is only 50hz 

[a31ford]

Like I said in my post #6, YES, I agree, 60hz, BUT only 60 volts.......

 

I live in THE country (not A country... LMAO) it SHOULD be 60 hz, BUT my kill-a-watt says the line is 59.3 HZ (Oh, and BTW, it even reads 60 volts when an SCR is triggering the circuit).

 

Greg

 

P.S. Plasma you crack me up !!

Edited November 7, 2013 by a31ford

[Santas Helper]

[-klb-]

How about the idea that an opto triac can dim in proportion to voltage?

The key spec that allows dimming is that the opto triac can be fired at any phase angle, not just zero and 180. Most opto triacs only switch on at zero crossings, and are only suitable for on/off control. The input is still digital, LED on, or LED off for either version. But with non zero crossing versions, the micro controller can detect the zero crossings, and after a suitable delay trigger the opto, which will trigger the main triac. Then it turns off the signal, knowing that the triac can't turn off until current goes to zero again. So the less delay, the more on time, and the brighter it is, the longer the delay is, the less on time and brightness you get.

[Ken Benedict]

Like I said in my post #6, YES, I agree, 60hz, BUT only 60 volts.......

 

I live in THE country (not A country... LMAO) it SHOULD be 60 hz, BUT my kill-a-watt says the line is 59.3 HZ (Oh, and BTW, it even reads 60 volts when an SCR is triggering the circuit).

 

Greg

 

P.S. Plasma you crack me up !!

 

I've heard that even though there are fluctuations in the actual frequency, the total cycles for a 24 hour period should remain the same, to keep clocks accurate and other stuff.

 

Southern California was 50Hz until 1948: http://en.wikipedia.org/wiki/Utility_frequency

 

There's also enough leakage current through most lighting dimmers to randomly fire strobes and "flicker" type bulbs.

Hence the use of artificial loads to drain it down: http://forums.lightorama.com/index.php?/topic/28849-i-am-at-a-complete-loss-dimming-led-anomaly/page-1#entry269278

 

And "dimmer noise" is mostly caused by the high rate of voltage increase when the triac fires: http://upload.wikime...d_rectifier.gif

 

Better dimmers use a choke coil to keep the increase rate down: http://en.wikipedia.org/wiki/Inductor#Applications

 

 

 

Just more triac trivia.

Edited November 7, 2013 by Ken Benedict

[plasmadrive]

I did not know that about southern Cal being 50hz... wow!  that is wild..

[plasmadrive]

Like I said in my post #6, YES, I agree, 60hz, BUT only 60 volts.......

 

I live in THE country (not A country... LMAO) it SHOULD be 60 hz, BUT my kill-a-watt says the line is 59.3 HZ (Oh, and BTW, it even reads 60 volts when an SCR is triggering the circuit).

 

Greg

 

P.S. Plasma you crack me up !!

 

Here in THE country   (hee hee).. your Kill-a-Watt is most likely reading the AC component.  When you have only one SCR firing on that AC circuit you in reality have pulsating DC. Not sure if the KaW will read that accurately. 

Greg, glad I can make you smile!  

[a31ford]

I did not know that about southern Cal being 50hz... wow!  that is wild..

 

 

 So they DID fall of the continent ? WAY too HIGH-BROW in the humor department......

 

Greg

[a31ford]

KLB, you hit the nail on the head !

 

Greg

 

 

How about the idea that an opto triac can dim in proportion to voltage?

The key spec that allows dimming is that the opto triac can be fired at any phase angle, not just zero and 180. Most opto triacs only switch on at zero crossings, and are only suitable for on/off control. The input is still digital, LED on, or LED off for either version. But with non zero crossing versions, the micro controller can detect the zero crossings, and after a suitable delay trigger the opto, which will trigger the main triac. Then it turns off the signal, knowing that the triac can't turn off until current goes to zero again. So the less delay, the more on time, and the brighter it is, the longer the delay is, the less on time and brightness you get.

[Max-Paul]

What you might be confusing is that even if you only have half of the wave. The voltage is still 120 volts. You really need to use an oscilloscope to see this. Unlike D.C. your reference is always changing, not stable like a ground wire in a D.C. circuit. When and if you ever build your own LED string you will then might understand what is what. 

 

And to answer your question as to why we dont use SCRs is that it is only half wave and will only conduct for half of a wave. Where as a triac will conduct for a full wave. This is when both are driven on for 100%. One could cobble together two SCRs and get a triac out of it. Geez, look your own drawing and if you cant see that. Then you really need help. As you can see, others have already proven you wrong about your 30 Hz and back me on this same part of it. I think that a few have also tried to tell you that that one half of the wave is still going to be 120 VAC not some vodu magic that will drop down the voltage. Sure you might be seeing 60 volts with a meter. But that meter also does averages, not peaks. Only a scope will show peaks.  Again I ask, so where did you get that E.E. from? Some on-line school? I got my education the old fashion way, hands on at a VoTech.

[a31ford]

Max ... you have to get out more..... 

 

Line Cord, Terminal Block, and BECKMAN CIRCUITMATE  Digital (in my world, Beckman is a trusted name in test equipment)

 

Across the white and black (NOTE which side of the diode the red lead is on......

 

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NOW, on the "far end" of the Diode (Diode is NOW in circuit)

 

NOTE that the setting is AC 200 volts on the meter..... (zoom in on the photo if you have to).

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NOW... the same stuff on 200 DC volts (NOT ac, the meter is now set for DC).

 

NOTE; the meter reads 0 DC (as it should on an AC circuit)

 

 

 

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AND NOW.... on the FAR end of the diode.... 

 

 

Max....(and others, Sorry Max)

 

Do the SAME tests yourself

 

I also own the following DMM's (And notice that they ALL read within .2 of a DC volt of each other.

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and YES, even a SIMPSON 635 Analog, meter..... (the DE FACTO-Standard, of true RMS meters.........)

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Sorry Max (and others) but I built lighting systems for rock bands when I was younger.... I DO know what I'm talking about.

 

Greg

[a31ford]

the above Simpson meter reads correct, 54 pulsating DC volts, PULSATING, that meter cost me over 600 dollars when I bought it back in 1974. it is STILL accurate today....

 

PULSATING (half wave AC) is still an RMS voltage, the Simpson is actually reading the correct real value, where as the cheaper DMM's (Fluke being cheap ??? What !) are NOT RMS corrected line the Simpson is.

 

The DMM's are treating the voltage as DC (real DC), which is NOT really correct with a single diode ( or an SCR. ) in circuit................

 

Greg

[a31ford]

One Last thing.... (sorry everyone, but I need to get this 'Out of my system"........)

 

 

Max... do you mean one of these ???? (bought in 1988)

 

 

Greg

[a31ford]

Panoramic of the electronics dungeon.......

[plasmadrive]

a31ford..... Couple of things..

 

1st off.. The Simpson 260 was the defacto standard when buffalo roamed the plains   You have the newer version!  

2nd... a damp rag would make that Beckman look 50 years younger.. That thing looks like my field meter.  

3rd... Does that scope still have a trace?  I bet it is grey now instead of green.. just like me!  

4th... The OLD Fluke with the buttons.. Can you still move those sliding buttons?  They aren't frozen yet?  Wow! 

 

OK.. OK.. had to give you a hard time about the old stuff.. but that old gear is good stuff.  I still have a Fluke 71 (decades newer then that button one of course) that has never been calibrated since it left the factory and compared to a fluke reference standard, it is still right on the money. 

 

Oh, one more thing.. half wave AC is pulsating DC.  Unless the voltage actually goes above and below the zero line, (.6v doesn't count) it is not Alternating Current! 

 

At your input of 120.3VAC the calculated voltage is 60.13V if you were reading True RMS AC (even though it is not technically AC).  If you are reading DC, you should see 54.18v if I remember my math.  You are pretty much right there..

Gotta say, nicely put together demo.

[a31ford]

TY, sorry for all of this, and now that I think about it... (GAWD it's been a while) yes, I remember I could NOT afford the 260 at the time.

 

I might be off a bit on some things, (age does play a factor) but when proven wrong (like in post # 6) I will own up to it being "my mistake".

 

I did NOT want all of this to happen, so "Sorry all"  It has made me think, and yes, I love the banter and conversation. 

 

It's good to get one's mind "KICKSTARTED" every now and then, and MINE got a GOOD kickstarting, in the replies in this post....

 

Thanks all !

 

 

a31ford..... Couple of things..

 

1st off.. The Simpson 260 was the defacto standard when buffalo roamed the plains   You have the newer version!  

2nd... a damp rag would make that Beckman look 50 years younger.. That thing looks like my field meter.  

3rd... Does that scope still have a trace?  I bet it is grey now instead of green.. just like me!  

4th... The OLD Fluke with the buttons.. Can you still move those sliding buttons?  They aren't frozen yet?  Wow! 

 

OK.. OK.. had to give you a hard time about the old stuff.. but that old gear is good stuff.  I still have a Fluke 71 (decades newer then that button one of course) that has never been calibrated since it left the factory and compared to a fluke reference standard, it is still right on the money. 

 

Oh, one more thing.. half wave AC is pulsating DC.  Unless the voltage actually goes above and below the zero line, (.6v doesn't count) it is not Alternating Current! 

 

At your input of 120.3VAC the calculated voltage is 60.13V if you were reading True RMS AC (even though it is not technically AC).  If you are reading DC, you should see 54.18v if I remember my math.  You are pretty much right there..

Gotta say, nicely put together demo.

 

 

1st,  you are correct the 260 was the de-facto

2nd that IS my field meter ! LMAO! !!

3rd, the trace is STILL green (but the illumination bulbs are burnt out.

4th, they are harder than when it was new, but still work.

 

 

Greg

[plasmadrive]

This topic of triacs has been on several sites including this one.  I started several of them myself,  and boy, have these people made me think ..  Scared the spider right out of the cob webs at times...

Great topic, and banter is good so long as everyone does what you did and keeps there cool and just proves their point or says "oops.... now I remember."  LOL  Can't tell you how many times that has happened to me..   That is what makes us old guys (assumption by the equipment)... worth having around.. Been there, Done that... over and over again!   LOL

 

Craig