TRIACs - The Dirty Details (3/3): Practical Considerations

[@MarcelHuguenin]

Thank you, it makes much more sense how triacs work now!

[@robertssmorgasbord]

Again, you're welcome ;-)

[@mumbaiverve2307]

Hi Mr.Robert , please consider doing an exhaustive tutorial like this for MOSFETs , BJTs ... Would be really useful.Your blend of theory and practicals is really very good !

[@robertssmorgasbord]

First, thank you for the praise! Your request is now on my wall of video ideas ;-) No promises though - I usually do these kinds of tutorials before I use a specific part in a project.

[@pasha_g.]

Thank you so much! Very helpful and easy to understand. Wish you all good.

[@robertssmorgasbord]

You're welcome!

[@vishweshgm]

Thank you so much!!!!! You have helped us young engineers save hundreds of hours probably in experiments and saved us from blowing up stuffs from rookie mistakes.

[@robertssmorgasbord]

You're very welcome and thank you for the praise (I'm blushing here)!

[@analoghardwaretops3976]

40:08 minutes...YOU MADE MY DAY..👍👍🙏🙏🙏 always knew abt. different requirements for control in different quads...BUT THIS ONE ON 3rd quad. and your practical demo..made it really sink in...🙏🙏

[@robertssmorgasbord]

You're welcome :-) I called this video series "The Dirty Details" for a reason ;-)

[@markdiener1425]

You are highly under-appreciated.

[@robertssmorgasbord]

Thank you very much!

[@kacperzielinski9870]

Very informative - indeed. Thank you.

[@robertssmorgasbord]

You're welocme!

[@DonatoGreco]

informative and torough series on the TRIACs, very well done

[@robertssmorgasbord]

Many thanks for the praise!

[@mihalym.6876]

Thank you your detailed explanaion about the subject. I am going to prototype two type of switching circuits controlled by uC to control inductive loads (AC solenoids on valves, AC circulating pumps). I hope your lessons gave all the information I need to design - prototype - check - correct - and finalise the project. I would like to emphasize how important is to check the prototype by scope to fully understand the actual operation of the circuit and modify it if it is necessary. Measurement of the key parameters of the triac and the opto coupler (in my case) is crutial in order to have a long lasting stable solution which is elementary on automation projects. It is especially true for selecting - fine tuning the right snubber circuits for a given inductive load.

[@robertssmorgasbord]

You're welcome! I don't if my three videos were really able to give you ALL the information you'll need to design your circuit ;-) But I guess they were pretty exhaustive in regards to TRIACS. Anyway, reading your comment I got the impression that you've got all bases covered ("design - prototype - check - correct - and finalise", "fine tuning the right snubber circuits for a given inductive load"). So good luck with your project! BTW I've got a video "Switching AC with Triacs and Zero Crossing Triac Output Optocouplers" kzbin.info/www/bejne/qH3Td6eJlt6NabM , but it might be a bit to basic for your purposes (switching resistive loads only).

[@ankara9594]

@@robertssmorgasbord i am confused about usinf snubber with the tiracs. i would like to drive selenoid valves 24 volt ac approximately 600 mA current. Snubber circuit is necessary for driving selenoids?

[@robertssmorgasbord]

@@ankara9594 A solenoid is basically a coil with an iron core, thus an (in most cases rather large) inductivity. If you drive an inductivity with an TRIAC you generally need a snubber network. So yes, in most cases a snubber network is necessary for driving a solenoid. For details see this application note from On Semiconductors www.onsemi.com/pub/Collateral/AN-3008.pdf.pdf or this one from ST Microelectronics www.st.com/resource/en/application_note/cd00004096-rc-snubber-circuit-design-for-triacs-stmicroelectronics.pdf However, nowadays you can also get "snubberless" TRIACs that endure much higher voltage transients. So in some cases and with the right TRIAC you can get away without a snubber network.

[@giannimariani9744]

Excellent description on Triacs. Thanks for making the video.

[@robertssmorgasbord]

I thank you for the praise! And of course you're welcome.

[@jasonbell3868]

Thanks for this series on triac's its the most in depth I've seen, could you please state how you arrived at a capacitor value for the rc network.

[@robertssmorgasbord]

You're welcome! And thanks for the praise! Regarding the capacitor value: I didn't really calculate the value of the capacitor used in that video (28:46 Phase shifting). I just wanted to demonstrate the principle. Anyway, if you want to calculate the capacitor ... The phase shift of the RC network is: arctan( R / Xc ) Xc is the impedance of the capacitor at the AC frequency: 1 / (2 * Pi * f * C) So the phase shift is: arctan( R * 2 * Pi * f * C ) Note that you get a 45° phase shift for: 1 = R * 2 * Pi * f * C, arctan( 1 ) = 45° You see why I didn't got into that in the video ;-) Anyway, I hope it helps. Cheers!

[@kafedral1]

Good work. Thanks

[@robertssmorgasbord]

You're welcome :-)

[@Yishushu]

Thank you!

[@robertssmorgasbord]

You're welcome :-)

[@tinkerman4774]

Great videos! ALL 3! Can a triac driven heat gun(2000W rated) be used as a "dummy load" for testing current output of a modified 12~14VDC PSU?(with an inverter between them) I know hairdryers don't use triacs(are more like a regular "resistor" and not "switched") like a heat gun. What are potential issues(problems) for using such heat gun(or small space heater) as a "dummy load"? Note: the testing would focus on high current output(70~100A @ up to 14V) over some time (e.g. 1 hour), and not intended for testing noise response in the PSU. Thank you! P.S. It would be a cool topic for another video!

[@robertssmorgasbord]

Well, if you have an 1.5kW inverter (100A * 14V = 1.4kW) I don't see why you couldn't use TRIAC driven heat gun as a test load - in principle. Just keep in mind that your inverter might not pull a smooth DC current out of your DC PSU. The current it draws might have quite the ripple.

[@tinkerman4774]

The reason I asked is because according to some folks at EEVBlog forum, a 2kW heat gun dialed back to say 700W level output is still a 2kW heater working 33% of time, and would still produce current spikes larger than the capacity of a 1200W~1500W server PSU.(?!) Is this really possible? I'm having a hard time understanding this and even harder time finding info that would explain such claims. My understanding was that as the duty cycle of the TRIAC is lowered(say from phase 90 degrees toward 180 degrees) , the current amplitude also decreases (not constant). So far in my search, your videos have been the most clear and detailed on the subject of TRIACs, but this matter is of course not discussed in any of them. Any pointers would be so appreciated. Thank you...@@robertssmorgasbord

[@robertssmorgasbord]

@@tinkerman4774 Well, the folks at the EEVBlog forum are not wrong. A 2kW heatgun running on AC 240Veff draws an RMS/effective current of 2000W/240V = 8.33Aeff. That's the current it would constantly draw if you run it with 240V DC instead of AC. So the resistance of the heatgun is 240V/8.33A = 28.8Ohm (I'm ignoring here, that the heating element might change its resistance with temperature). The peak voltage of 240V AC (sine) is 240Veff*√2 = 339Vpeak. So if the TRIAC switched on at peak voltage (90° or 270°) the heating element would draw at that moment 339Vpeak/28.8Ohm = 11.8Apeak or 11.8Apeak*339Vpeak = 4000Wpeak. So to avoid that your TRIAC has to be switched on after 90°, respectively, 270°. Limiting the heatgun's power to less than 1kW. However, the inverter making the AC will definitely "smooth out" that peak power on the AC side, so you won't see those high current spikes on its DC input side. How much will it "smooth out" those current spikes? It depends on the construction of the inverter (how much capacitance on the input, how the actual transformer is constructed, and how that transformer is driven).

[@tinkerman4774]

THANG-Q! You ROCK! 🤘🤘🤘 I'm now considering other options without a TRIAC (e.g. power resistors, nichrome wire in mineral oil etc.) to simplify the setup and make the DC load voltage more steady, as it would be in actual use. Cheers~!

[@robertssmorgasbord]

@@tinkerman4774 You're welcome 🙂 BTW, nichrome wire in mineral oil (or distilled / de-ionized water for lower voltages) is a common and cheap way to create loads for such applications. Dumping 2kW of power into power resistors will definitely break the bank. Those power resistors are quite expensive.

[@pranaypal7829]

Can we take KVL to calculate the gate resistor ?

[@robertssmorgasbord]

I'm not quite sure where you want/need to apply Kirchhoff's laws here. The calculation of the gate resistor is trivial after all.

[@arpitjain4025]

Great extreme detailed stuff sir, Much appreciated to enlighten us with ur knowledge,. Sir i have a very simple circuit of triac BT 136 in which i wanted to connect it with one LDR one 100k register and LED bulb in 240v AC mains, but LED bulb flickers and it generates sound also. Then i removed resistor and LDR both and connect it very simply like M1 with 240 V AC live, M2 goes to LED bulb, Gate i directly connected it to M1 and another terminal of LED bulb into neutral. but LED bulb still flickers with sound however flicker and sound gets reduce but LED bulb in direct 240V AC running without flicker without noise. What could be the problem sir?

[@robertssmorgasbord]

Most LED bulbs don't like phase control on their AC input. And that's what a TRIAC circuit does. Even if you connect the gate directly to M2 (not M1! and via a resistor! www.electronics-notes.com/images/triac-switch-circuit-basic-01.svg ) a little portion of each AC half wave is cut off. Maybe you have more luck with an LED bulb that is explicitly sold as "dimmable".

[@arpitjain4025]

@@robertssmorgasbord Sir means by no way we can pass the full AC signal (without ay cut) from TRIAC? even if we open the gate fully?

[@robertssmorgasbord]

@@arpitjain4025 No, there isn't (at least none I know of). You will have always a short time after a zero crossing of the AC where the TRIAC is off.

[@arpitjain4025]

@@robertssmorgasbord ok sir, means triac cant be use as a pure switch. thus we cant use them as relay......all these videos on TRAIC as relay is misleading :(

[@arpitjain4025]

@@robertssmorgasbord Also sir why LED bulbs circuit cant handle such short elimination of AC wave?

[@lyudmilvarbanov7294]

Hi, I have an electronic board to control an AC motor -2500 watts/220v. On the board are mounted two TRIAC - BTB24-600BW . The motor has a problem-runing on reverse only-no matter which button is pressed-FW or RW. I found that the resistor who is connected to the Gate terminal on TRIAC 1 is burned and I replaced with a new one 47 Ohm/1 w . Also I found a short cut between the Gate and Terminal 2 (the midle terminal) on the same TRIAC and replace it with new TRIAC--BTB24-600BW.After that I did a check by multimeter between all soldering points. Then the board was connected to the motor.Unfortunatly the motor not run-in any directions- clock wise or reverse ! Do You can to gave me any advice?

[@robertssmorgasbord]

Hi, I've already answered your comment on the other video, but here it is again: Well, without knowing the whole circuit and the type of the AC motor (I'm assuming it's a single phase universal AC motor) it's quite hard to give some advice. For example: Are your sure the burned out gate resistor was 47 Ohm? Because that would give you a peak gate current of 220V*1.41/47Ohm = 6.6A, while the BTB24 is only rated for 4A peak gate current. Also, how does the FW/RW button/circuit work? Anyway, if you desolder the BTB24 again and just solder in a (reasonable thick) wire between terminal 1 and terminal 2, then the motor should run at full speed as soon as you connect the circuit to AC mains. If that's not the case, than something else beyond the TRIAC has been damaged.

[@lyudmilvarbanov7294]

drive.google.com/drive/folders/1G7bJHQIAiZXTSImx89NcJthaKAHLQl6x?usp=sharing@@robertssmorgasbord

[@lyudmilvarbanov7294]

@@robertssmorgasbord www.farnell.com/datasheets/1729048.pdf

[@lyudmilvarbanov7294]

@@robertssmorgasbord This is the resistor who I use: docs.rs-online.com/6cc6/0900766b81553f99.pdf

[@lyudmilvarbanov7294]

@@robertssmorgasbord eandc.ru/catalog/detail.php?ID=2938 - There are all details about BTB24-600BW TRIAC

[@allinthefamiliy3122]

Thanks for your very clear explanation. Triac's look bulky power switch components easy to use, but I see that it way more complicated then I thought. I understand it better now, at least the basics that I need to make it operate in a controlled way. From the schematics that I see using Opto-coupler devices to control the gate current, I do understand now that these work in Q1 and Q3 assuming they have connected the Opto-coupler between MT2 and the gate. I saw you trying to calculate the power dissipation of a triac in function of a sine wave current. You said it was complicated to do that. A while ago I spend some time to crack that problem which is about mathematics. Here is the link to the math and the final formula you were looking for. www.holamex.nl/files/img/Triac%20Power%20Dissipation%20Math.jpg I hope by this to have contributed to this explination about triacs and to have contributed to more reality in this world. I need that because there are to many excel sheet dreamers around.

[@robertssmorgasbord]

I thank you for actually doing the integral math for the power dissipation! I try to keep the math in my videos as simple as possible. And to be honest, I was never really good with integrals. Maybe I should reeducate myself and make a video about the most important differentials/integrals for electrical engineers (sine/cosine and e).

[@allinthefamiliy3122]

@@robertssmorgasbord Don't worry, I like people who make videos like you do. You do your part I do mine, together we have more. Greetings from your neighbor Dutch

[@robertssmorgasbord]

@@allinthefamiliy3122 Again, thanks! I always wanted to visit the Netherlands. You know, rent a little boat and tour all the channels. Anyway, greetings back from Germany!