This is the first time I really understand what a triac is about. Try more basic electronics tutorials from time to time. Please.

I’ve seen triacs and diacs used in buIdling systems, like light bank control (couple dozen lights controlled by one switch or control signal) or motor control in a pump or an AC system. I’ve never been the one to make them work....I simply often oversee those kinds of systems. Good stuff! I just found your channel and I love it! I’m well along in the very process of setting up my own test bench (so far, spec an, oscope, various power supplies and all kinds of other goodies. I’ve spent years doing this for my job...now it is time to do it for me! Especially when a very patient and loving XYL thru the years is “demanding” that It is high time that I do this for me!! Who am I to argue! Thanks for GREAT content!

Zero crossing they reset - I knew it was DC in the beginning that way.. They're clever

TRIACS are usually "turned on" or triggered by PULSES and not DC. Controlling it this way makes it turn on quickly and not exceeding the maximum average gate power rating.

Another odd thing about Triacs is that there are different characteristics in each of the four 'quadrants' where each quadrant applies to one of the four possible combinations of polarity for the Gate and the Anode/Cathode voltage. This can be hard to understand and 'get one's head fully around' and when not handled correctly, can result in good operation on one half of the AC waveform but less than desirable operation on the other half. As for triggering the Triac when a DC control is being used but the Anode/Cathode signal being controlled is AC, there is an older solution than the AC optocoupler, and that is the 'pulse transformer', which is usually just a tiny transformer with a single primary winding and single secondary winding. The secondary is connected between either Anode or Cathode and the Gate, and the primary coil has brief pulses applied at the appropriate time to trigger the Triac to conduct. I used to make a series of simple DC motor statically powered field winding, dynamically powered armature) controllers where the motor mostly just hummed quietly without turning (almost no energy being put into the armature (but it was AC at that time and this had the effect of locking the motor until needed) but when required could quickly jump into action and turn one direction or the other, either slow or variable faster speeds, in order to drive a steering mechanism to correct a process that sometimes deviated from a central path. 'Electric eye' sensors monitored the mechanism and would result in a control signal that would determine when, and how fast, a correction needed to be made in one direction or the other. The motor armature was the 'load', although it was connected to 120VAC through the Triac. The control signal was applied to a comparator whose other input was a low voltage signal derived from the 120VAC and thus synchronized with that. The comparator output drove one side of the pulse transformer primary, while the other side of the primary was held at a DC voltage that was half of the control circuit power supply voltage; this allowed applying pulses of either polarity to the pulse transformer. (This controller and its motor would have done a nice job of controlling the steering wheel of an automobile, with the "electric eye" monitoring the car's distance from the road centerline, and this would steer the car to remain centered in its lane......but the application was actually for a process unrelated to cars and roads). I recall getting into an embarrassing situation when I redesigned one of the motor controller PCBs and substituted the comparator (that drove the pulse transformer primary) with an op-amp configured as a comparator. The controller still basically worked, but the op-amp's output turned out to have a better drive when sourcing current than it did when sinking current, and this meant that the pulse transformer primary had less energy applied when one direction of correction was required than it did for the other direction. The Triac being used reacted to the weaker Gate signal in one quadrant with a lower power being applied to the motor armature, so steering corrections on one direction were more sluggish than desired. Luckily, I was able to whip up a small pinout adapter PCB that allowed the original comparator IC to be used with the product.

What about the power down reset function that occurs during the AC waveform that allows for things like fan speed control?

Funny, I was looking for triac videos as I just salvaged a couple of opto-triacs 😄. Most basic use of a normal triac known to me is a triac-diac dimmer circuit. Where an adjustable voltage divider wil determine at what point in the sine wave the diac will trigger the triac.

I took an electronics class in high school, and I remember designing a darkroom timer which used a 555 timer, and triac/optocoupler pair to control the lamp of a photographic enlarger. It wasn’t an immensely complicated circuit, but I was very proud of it.

Even I don't understand it well but the video is a very good and useful guide. Thanks!

Show us a video about Triac AC dimming digitally controlled by a micro controller. I want to use it to control a food blender/grinder speed for AC or universal motors.

Way back in the mid 60's I made a controller for my soldering iron to control temperature and allow a switched idle current. It seems to me I used a DIAC and used the phase angle of the input line to pulse {trigger} the variable

I still know the opto-coupler....the MOC3040 with zero-crossing detection.

Hello -great video- How do you choose what triac to buy- what maters (dc low voltage)

But, This is only part of the story ! The pins on a Triac are : Gate, MT1 and MT2... it has quadrants of sensitivity and the gate is more sensitive relative to each MT (Main Terminal)... Another video perhaps ? Your description may confuse folks between an SCR and a Triac ?

Yes, they stay on once your draw more current than the hold-on current.

Good explaination, taking the long way around the barn. One question though. Is the lamp you used in the demo commercially available with part # you could supply? Thanks.

Nicely explained! Are you using bt136 ?

what a great video I've always wanted to know how to use on of these the only Triac i have is called: BT137 mine is pretty similar

yo the device you used to identify the component... what is THAT?!?! link?!? great video btw

@13:10 it has to cross "0" to reverse the AC...

nice

WHAT KIND OF TESTER IS THAT? (the one used to determine what kind of component it was/is)

what is the name of your component tester ?

Ac have 3 stages positive Volt; 0 volt; negative volt. By 0 volt the triac get the Reset so simply!😅

You could use a transformer to drive the gate if you don't want to use a special optocoupler.

try putting a TL431 on your tester

You showed the visual representation of the DC circuit being turned off by removing the power to the load. For your explanation of why an AC arrangement does not stay turned on, the AC arrangement turns off as it crosses the zero volt threshold (at which point the voltage is, effectively, turned off, for a brief moment,) as the AC voltage swings between positive and negative cycles. If a triac is a current driven device, the explanations still holds true. All correct?

Back to back SCR'S .....

i was thinking about trias almost 40minutes ago

Name of that device?

Link that tester, please!

I opened up my stove to figure out why it wasn't heating well, and I discovered the electric elements were pulse width modulated with triacs.

Was researching the latest and greatest in homebrew tombstone welder circuit design thats cost effective and randomly came across "clipper" and "clamping" types circuit when I wasn't certain about the term clipper being correct for the ac welder balancing circuit where a TRIAC is used to "clip" the waveform in a way that is terms "zero crossing" versus the typical series negative clipping with negative bias. Then I was like... hhhmmm.... what's this series negative clipping with negative bias design? Seems better in regards to less time at zero volts in that 60Hz cycle (using old transformer 120/240 mains based welder designs where prior to the step down transformer to the typical higher current and lower voltage welding range the AC is "balanced" so like say 70% in the electrode positive waveform and 30% in the electrode negative waveform. This is so one cycle has 70% welding and 30% cleaning (blasts away oxidation) effect. The issue with the clipper circuit design isn't in theory, the issue is the practical way to get like 4000W at least in variable resistor capabilities. I'm guessing if that design was used ever cost way more and was way more lossy (inefficient) due to heat loss, since seems better in theory due to less zero voltage time and no requirement for continuous HF arc maintenance to prevent the arc from going out. I see now why the H-bridge designs are used where looks like at least the Miller Syncrowave 250 uses SCR's in that design and the later more nowadays common method like in the Syncrowave 210 are the IGBT based H-bridge design. Still, interesting seeing the TRIAC DIY welder and DIY welder mods for fine tuning control using the TRIACS where seems using a DIAC versus a series of zener diodes is the way to go to only clip the negative part/phase of the cycle. I've only seen this done once... since most of the circuit clip equally the positive and negative part of the waveform cycle where isn't a concern since most want to Stick, TIG or MIG weld using DCEP or DCEN only. The best way to weld aluminum appears to be TIG welding with AC that's a balanced DCEP and DCEN waveform with less time at zero like in a pulsed DC square wave appears. Bonus with the H-Bridge is one can tune the frequency as well from like 20-250Hz which also helps fine tune the weld and de-oxidation process. OK... have a good one!