Understanding DIACs

[@captainboing]

When I was a telephone engineer, I used diacs as a privacy device where multiple telephones were on the same pstn circuit. Put one in the line path on each telephone. The line voltage across the diac wil be around 50v so you get dial tone when you pick up, the line voltage falls to around 12v but the diac continues to conduct. Anyone else picking up a phone on that circuit gets a dead line because the 12v is below the break over voltage. Simple single component privacy.

[@ElectronicsNotes]

Yes they had a good number of different uses in s variety of circuits.

[@clownhands]

Genius use of a diac!

[@jamescollier3]

That's like the most intelligent comment in socal media lol

[@rex-up9ln]

​@@jamescollier3cool

[@gustavotasquer7389]

Brillant

[@headpox5817]

Thank you for this no-nonsense description of a DIAC.

[@ElectronicsNotes]

Glad it was helpful!

[@deantiquisetnovis]

Short, crisp, clear. In other words: brilliant!

[@ElectronicsNotes]

I’m really glad you found it useful.

[@dl5244]

Despite the symbol appearing as two diodes with opposite orientation in parallel, it seems that a DIAC behaves very similar to two Zener diodes in series with opposite orientations. This arrangement of two zeners in series would block current flow in both directions until Vbr+Vf is exceeded, just like a DIAC

[@Vincent_Sullivan]

Not so much... Notice in the DIAC V/I curve shown that when the DIAC breakover voltage is reached the voltage across the DIAC falls to a very low voltage (Vf is much less than Vbo) whereas the arrangement of 2 opposite polarity Zeners in series will clamp the voltage across them to the Zener voltage plus the forward voltage of the conducting diode as you state - so the overall effect in a circuit may be quite different.

[@SimEon-jt3sr]

Was just wondering lol like why block it both ways, the zener make a lot more sense but now the symbol still makes sense

[@SimEon-jt3sr]

​@@Vincent_Sullivan Oh..... Well luckily I probably won't ever need to design my own circuit with one...

[@peterbulanyi1708]

Very nice description of the Diac. I remember seeing these devices on the control terminal of Triacs in simple electric fence energisers when I used to repair them in the early 90s.

[@ElectronicsNotes]

Thank you very much for your comment. Yes, they were very common. I remember them from their use in light dimmers. But the application you found them used in shows how widely they were used.

[@louco2]

Learned something new today! Thank you so much for taking the time to do these videos.

[@ElectronicsNotes]

Glad it was helpful! It is so good to hear when someone finds these videos useful.

[@stupossibleify]

Hackaday brought me here, and I'm so glad it did. Thank you.

[@ElectronicsNotes]

I'm really glad you arrived on the channel - please check out some more videos. Thanks for your comment.

[@Doom2pro]

I always thought of them as a solid state spark gap of sorts.

[@xanataph]

Yeah definitely, or I would also say, like a solid state replacement for a neon bulb in such triggering circuits.

[@borisj4054]

Very basic but good for beginners

[@ElectronicsNotes]

It is aimed at providing the basics for those who are not familiar with DIACs. I hope you managed to take something away froth e video. Thanks for the comment.

[@SlyerFox666]

Such a good video, could have mentioned the 5 layer as a SIDACs as that's a component that hardly anyone's heard of. 👍

[@ElectronicsNotes]

Glad you liked the video. Yes, I suppose I could have mentioned the SIDAC but I wanted to focus on the DIAC. Thanks for the idea though - maybe another video sometime.

[@arthurmoore9488]

@@ElectronicsNotes Please. I've used DIACs before, but never even heard of a SIDAC.

[@ElectronicsNotes]

@@arthurmoore9488 I thought I had a description of them on my website, but could not find it. However, you can take a look here: en.wikipedia.org/wiki/DIAC#:~:text=A%20silicon%20diode%20for%20alternating,member%20of%20the%20thyristor%20family.

[@bretfuzz925]

I used a SIDACtor to protect the TX side of a DS1 (T1) line interface module from CMOS latch up from transient voltages. Very handy device indeed as it would reset on the zero voltage crossing after a transient event. Much better solution than PTC thermistors.

[@SlyerFox666]

@@bretfuzz925 Well you just taught me a few things there, nice example 👍

[@rohnkd4hct260]

Thanks for the refresher lesson! Electronics School was llllllloooonnnnggg time ago 😆

[@ElectronicsNotes]

You're welcome! Glad you found it useful.

[@Necrocidal]

Really nice and to-the-point, thanks!

[@ElectronicsNotes]

Glad you found the video useful. Thanks for your comment.

[@arthurmoore9488]

Randomly was suggested this video. I have designed a voltage to frequency converter for an isolated high voltage power supply before. They're extremely useful wherever a trigger threshold voltage is needed. Now I'm wondering if I can make a DC mains voltage 555 timer.... On the other hand, Mains AC has such a consistent frequency I could just make a clock.

[@AdrianHiggins83]

Very good explanation

[@ElectronicsNotes]

Thanks for your comment. I really appreciate it.

[@tenlittleindians]

So how do you test these components when found in a circuit?

[@ElectronicsNotes]

Not easy to test, and especially when in circuit.

[@xDR1TeK]

I see the KZbin algorithm is working well at last. I liked its suggestion quite well. One question though, seeing how the diac is a diode for ac, but works as two zeners back to back, shouldn't it be called a zener for ac instead? Ziac or something like that? Just wondering. Thank you for the wonderful presentation.

[@ElectronicsNotes]

I love your idea. A DiAC actually works in a different way to two Zeners back to back, in terms of the underlying physics, but it does appear to give a similar effect in the surface. Great idea!!

[@wisteela]

I didn't know these existed.

[@MrAvant123]

Also, I would say using a DIAC to switch a Triac cuts right down on the nasty crossing RF interference you get from a raw switched Triac.......

[@ElectronicsNotes]

Indeed it does.

[@jonathanwilhelm8891]

Very nice video ❤ great work

[@ElectronicsNotes]

Glad you appreciated it. Thanks for the comment.

[@maxwang2537]

2:32 a question here. I suppose what’s shown here is the behaviour of an ideal triac we would expect. How far off are the actual characteristics of a real triac from this?

[@s.hutton2100]

Excellent video thank you. Have subscribed. Regards Stephen.

[@ElectronicsNotes]

Glad you liked the video and thanks for subscribing.

[@maxwang2537]

2:43 I have difficulty understanding triac. Some questions please. Are the two main terminals of a triac symmetric with reference to the gate. In other words, can we apply a trigger voltage between the gate and either terminal 1 or 2 to switch it on? In the schematic here, which voltage is working as the trigger, the voltage across the pot or the cap, or both? Any help is appreciated!

[@xanataph]

You see in a lot of older schematics for light dimmers, drill speed controllers etc they used neon bulbs to do a similar job to the DIAC due to their breakdown characteristics. But I would presume the DIAC's characteristics are sharper than that of a neon? (And of course exhibit the breakdown at a lower voltage)

[@ElectronicsNotes]

I confess I've never thought of using a neon, but good point.

[@MrMulleteer]

Triac/diac dimmers are getting pretty rare because they cant reliably work with the light loads like leds. IC controlled triacs are becoming the norm.

[@ElectronicsNotes]

Indeed, but the DIACs are still used wit them in some instances and also they can be used for other applications such as transient limiting. But yes, with modern LED lamps which require the cycle to be cut on the trailing edge, the traditional circuits are not as widely used.

[@Accumulator1]

On those light dimmers, what component is likely to fail on them? Would it perhaps be the triac or diac? I have several that stopped working, I like to repair.

[@ElectronicsNotes]

My guess is that kit is most likely the Triac, but I've no great experience on fixing light dimmers.

[@StephanBuchin]

2:33 Is the conduction waveform presented here corrected by the diac? Because it looks pretty symetrical to me.

[@ElectronicsNotes]

I used the perfectly switched waveform and not one that you might find from a triac on its own. I was trying to illustrate the way the triac controlled the waveform.

[@StephanBuchin]

@@ElectronicsNotes Thank you for answering my stupid question, you relieved my anxiety of not understanding. I remember i was already this tiring when I was a student 🤓

[@ElectronicsNotes]

@@StephanBuchin You question was perfectly valid and not stupid in anyway. We all learn by asking questions, and often the 'stupid' questions are the ones that everyone else wants to ask, but nobody dares. Thank you.

[@enggdiplomabook7076]

Very nice video❤

[@ElectronicsNotes]

Thank you!

[@maxwang2537]

Short and sweet!

[@ElectronicsNotes]

Hope you found it useful.

[@maxwang2537]

@@ElectronicsNotes yes very helpful. Recently I cam across one on a modern sewing machine foot pedal (motor speed controller), which I mistook as a diode.

[@peetduplessis7796]

Like your AVO Model 8/9. Still have a 9 Mk II.

[@ElectronicsNotes]

Yes, it’s an AVO 8 and it still works well.

[@peetduplessis7796]

Proper equipment that is well cared for will work for many years! @@ElectronicsNotes

[@user-lp3cf5yn5b]

So basically it acts like a wall until the breakdown voltage is exceeded then it conducts like a diode until the voltage drops below breakdown voltage again?

[@ElectronicsNotes]

That is a sort of descriptor it. The characteristic is a little more complicated, but it acts like a “wall” until a break over voltage is reached. Then the voltage falls and slightly rises with increasing current.

[@cyber5515]

Here's a better description. The wall has a hinge, a spring and a latch. When the current stops flowing (almost) the wall springs back up and latches until the pressure builds back up and overcomes the latch. - (Practical descriptions are are always better than mathematical ones. Besides that, in maths you are not allowed to have 2 Y values for each X value on a cartesian plane, as shown here: 1:46 .)

[@kamalhamdi6739]

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[@ElectronicsNotes]

I’m glad you found the video useful.

[@bob_mosavo]

Thanks 👍

[@ElectronicsNotes]

Thank you too!

[@Tref-k6j]

I do not understand how you read that plot at 1:45

[@ElectronicsNotes]

Looking at the top right quarter, imagine the voltage rising and little current is passed, when it reaches its breaker point, the current increases and the voltage across it falls, and then this voltage is increases slightly as the current increases much more.

[@johnaweiss]

I wonder if it could be used as a dead-time generator.

[@ElectronicsNotes]

I had never thought of that - may be it could.

[@johnaweiss]

@@ElectronicsNotes i guess maybe you'd have to feed it a sine wave... mains is a sine wave.

[@petersketch1990]

Can it convert to dc ?

[@ElectronicsNotes]

It’s a bi-directional device so not a rectifier.

[@qzorn4440]

very nice. Thanks.

[@ElectronicsNotes]

Most welcome - glad you appreciated it. Thanks for the comment.

[@ECHQ23]

you could expand on this and compare to a "modern" bidirectional TVS diode.

[@ElectronicsNotes]

That is certainly a possibility.

[@stanleybest8833]

Don't advocate dimmer switches. They generate a heap of radio noise.

[@billfargo9616]

LEDs are dimmed using pulse width modulation, not voltage control. .

[@ElectronicsNotes]

I wanted to say that the light dimmer I was showing was for incandescent lamps as LEDs use a different approach.

[@rickhunt3183]

A diac never met a triac it didn't like.

[@alunroberts1439]

Get that AVO on it;s back no one knowing about them stands them up like that

[@ElectronicsNotes]

Indeed you are right - when it is used, it is most certainly on its back, but it lives there when not in use.

[@alunroberts1439]

@ElectronicsNotes still never store it like that it not a show pice