Understanding DIACs

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Күн бұрын

In this video I explain the basics of the DIAC - what it does, how it works, how it can be used, and I show how it is used in a circuit with a TRIAC.
The actual word DIAC stands for DIode for Alternating Current and this gives a clue about what these electronic components do in an electronic circuit, often assisting in a switch circuit
A DIAC is a two terminal device with its circuit symbol looking a bit like two parallel diodes in opposite orientations closely placed and merged together The electrodes are designated MT, standing for main terminal that's MT1 and MT2 - they may also be called Anode 1 and Anode 2 on some occasions.
There are two types of structure used for DIACs, the three layer structure and a five layer version. There are some differences between the two, but essentially they perform the same function in a circuit.
In terms of its operation the DIAC is not like an ordinary semiconductor diode that allows current through in only one direction, but instead the DIAC allows current through after a certain breakdown voltage is reached - often it is called a DIAC switch for this reason. This is known as the breakover voltage - typically this is between about 25 and 48 volts. The DB3 is a popular DIAC - the DB3 DIAC has a breakover voltage of around 32 volts.
The most common use for DIACs is with TRIACs. TRIACS are widely used for AC mains control - one of the very popular applications is within light dimmers. However TRIACS are notorious because their switching characteristics are different in different halves of the cycle and that's not good.
To overcome this, a DIAC can be placed in the TRIAC circuit in the gate circuit. As DIACs have a nice defined breakover voltage in both directions, it means that when the DIAC reaches its breakover voltage, the TRIAC will be fired and it will switch.
To find out more about DIACs check the following link: www.electronics-notes.com/art...
Website homepage: www.electronics-notes.com
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Пікірлер: 95

@captainboing 6 ай бұрын

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 6 ай бұрын

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

@clownhands 6 ай бұрын

Genius use of a diac!

@jamescollier3 6 ай бұрын

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

@rex-up9ln 6 ай бұрын

@@jamescollier3cool

@gustavotasquer7389 5 ай бұрын

Brillant

@headpox5817 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

Glad it was helpful!

@dl5244 6 ай бұрын

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 6 ай бұрын

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 6 ай бұрын

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 6 ай бұрын

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

@deantiquisetnovis 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

I’m really glad you found it useful.

@peterbulanyi1708 6 ай бұрын

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 6 ай бұрын

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 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

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

@stupossibleify 5 ай бұрын

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

@ElectronicsNotes 5 ай бұрын

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

@Doom2pro 6 ай бұрын

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

@xanataph 6 ай бұрын

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

@arthurmoore9488 6 ай бұрын

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.

@Necrocidal 5 ай бұрын

Really nice and to-the-point, thanks!

@ElectronicsNotes 5 ай бұрын

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

@rohnkd4hct260 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

You're welcome! Glad you found it useful.

@wisteela 6 ай бұрын

I didn't know these existed.

@MrAvant123 6 ай бұрын

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 6 ай бұрын

Indeed it does.

@borisj4054 6 ай бұрын

Very basic but good for beginners

@ElectronicsNotes 6 ай бұрын

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 6 ай бұрын

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 6 ай бұрын

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 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

@@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 6 ай бұрын

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 6 ай бұрын

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

@xDR1TeK 5 ай бұрын

I see the KZfaq 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 5 ай бұрын

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!!

@AdrianHiggins83 6 ай бұрын

Very good explanation

@ElectronicsNotes 6 ай бұрын

Thanks for your comment. I really appreciate it.

@xanataph 6 ай бұрын

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 6 ай бұрын

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

@jonathanwilhelm8891 6 ай бұрын

Very nice video ❤ great work

@ElectronicsNotes 6 ай бұрын

Glad you appreciated it. Thanks for the comment.

@maxwang2537 5 ай бұрын

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!

@s.hutton2100 6 ай бұрын

Excellent video thank you. Have subscribed. Regards Stephen.

@ElectronicsNotes 6 ай бұрын

Glad you liked the video and thanks for subscribing.

@maxwang2537 5 ай бұрын

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?

@maxwang2537 6 ай бұрын

Short and sweet!

@ElectronicsNotes 6 ай бұрын

Hope you found it useful.

@maxwang2537 5 ай бұрын

@@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.

@tenlittleindians 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

Not easy to test, and especially when in circuit.

@qzorn4440 6 ай бұрын

very nice. Thanks.

@ElectronicsNotes 6 ай бұрын

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

@henryj.8528 6 ай бұрын

What was that four-layer device Shockley was always working on?

@ElectronicsNotes 6 ай бұрын

He was working on a four layer device, and it probably developed into what we know today as a Thyristor.

@enggdiplomabook7076 5 ай бұрын

Very nice video❤

@ElectronicsNotes 5 ай бұрын

Thank you!

@Accumulator1 5 ай бұрын

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 5 ай бұрын

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

@StephanBuchin 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

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 6 ай бұрын

@@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 6 ай бұрын

@@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.

@peetduplessis7796 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

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

@peetduplessis7796 6 ай бұрын

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

@MrMulleteer 6 ай бұрын

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 6 ай бұрын

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.

@bob_mosavo 6 ай бұрын

Thanks 👍

@ElectronicsNotes 6 ай бұрын

Thank you too!

@user-lp3cf5yn5b 4 ай бұрын

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 4 ай бұрын

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.

@kamalhamdi6739 5 ай бұрын

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@ElectronicsNotes 5 ай бұрын

I’m glad you found the video useful.

@johnaweiss 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

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

@johnaweiss 6 ай бұрын

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

@ECHQ23 5 ай бұрын

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

@ElectronicsNotes 5 ай бұрын

That is certainly a possibility.

@billfargo9616 5 ай бұрын

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

@ElectronicsNotes 5 ай бұрын

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

@user-xi5oh9yc4c 6 ай бұрын

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

@ElectronicsNotes 6 ай бұрын

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.