Basic Electronic Components - The Triac

what the heck is up guys it's Jacob here and this video we're going to be taking a look at the triac now in my last video I did a video on STRs and I mentioned that they were very similar to Triax and we'll take a look at that in this video they're very very similar in fact you can actually build a triac out of scr the track is really just two silicon controlled rectifier so we're not going to go into too much steps as to how the actual current flows through the PN junctions or anything in this because really it is the same as the SCR so if you guys are really interested in how these junctions how current really close to the junctions at different parts of the cycle look at the scr video you'll see how that works but yeah so for this video we're just really going to focus on a little bit higher level words can look at the track itself as composed of two SCRs alright guys so start here is the actual symbol for a triac so it is a three terminal device and it has a lot of the same properties as a Dayak or another die I'm sorry a SCR so the triac is really just like an SCR if you watch my other video you'll see all the properties as far as how it behaves with a CDS these guys perform just as well as AC so they're very similar to that SCR really the only differences is it will work with full wave if you watch my video on SCR is you'll know that SCRs can pretty much control AC power you can use them as an AC switch assaulted a AC switch or you can use them as actual base controller so you can cut you can kind of actually it can act as a switch which will cut in at a very specific point of your actual AC sine wave and that's what we call on phase control so this guy will here will do full wave based control so do your positive and negative half the cycle and we'll look at that in a little bit more detail here in a minute but so here's the terminal so there's a 1 and a 2 is sometimes what they're called this is just a node 1 and node 2 so you can see here there's two SC RS we'll look at that in a second but so there's there's it's not really polarized like the SCR the SCR has has an anode and a cathode a terminal on it and then it has a gate terminal so it does matter what way you hook up an SCR in this case since there's two SCRs back to back it doesn't really matter you'll have a handled pin here and open here and there also commonly called main terminal one or main terminal two again it's the same thing it doesn't really matter what way current flows it's going to flow both ways anyways if it's using an AC application which is typically what these guys are used for and then there's your gate pin right here so if we look at it over here this is how how an actual track is typically composed of it's basically two STRs we can actually build a track out of two SCRs on a few disclaimers I just want to say Triax have are a little bit more complicated as far as their gate firing circuitry they operate in what we can think of as quadrants we'll look at that in a few minutes it's a little bit more advanced but they operate you can you fire these things in in the quadrants of your AC sine wave we'll look at that but the the actual gate current to drive a triac is a little bit more than an FC R as to a comparative SCR so if you had a a track an SCR with comparative current and voltage ratings you would still have to drive the gate of that track with a little bit more current and also it has different sensitivities depending on what part of the actual sine wave you're on but um anyway so here we have an SCR so if we just ignore this over here really all we have is an FDR right so it's the anode here's your cathode and here's your gate and so when you have you could imagine if you're feeding AC into here right on the positive half of your sine wave this track is going to be forward biased so it's going to be forward biased all the way up to to this point right here right and so if you're feeding your wave in here and your load is going through here to this side on this terminal on this half of your ways this track is going to be forward biased and if you have a positive voltage on your gate relative to your cathode current will flow through and you'll have your positive half of your way will make it out here right just like that not not too complex so we looked at that in the SDR video but the difference is now we have this other SCR here and it is flipped the exact opposite way so it'll be forward biased I guess you can think of it it is forward bias a little bit harder to think about kind of backwards on this negative half of the way because you're feeding a negative voltage in right and this side will actually be more positive relative to this side your Anna will be more positive relative to your cathode and this guy will be forward biased so now we'll let your other happier side way through and so as long as you have a negative voltage on your gate in this half of the cycle it will fire this scr and you can get full ways switching and you can so you can use this as a solid-state switch to actually turn on you can use it just like a relay if you want to get the full AC way through or you can look at how we how we did it in the other video where you can really control this deep this gate in a very precise manner with some resistors and diodes and things like that or you could actually hook this gate up through a triac driver and hope goes to something like a micro controller where you can monitor the wave and fire it at very specific points and so basically you can do the same thing that we looked at in our previous video we actually did that on the oscilloscope where you can do phase control and I showed you guys that if we use I showed you exactly a circuit and how was hooked up and kind of how that worked if you put a resistor on here your your your triac or your SDR will fire a very specific part of this wave and you can use that to do what's called phase control that's a very simple analog way of doing it you can also have like a microcontroller or something that's analyzing this waveform and looking for where the zeroes cross or it actually crosses through zero and you can have that microcontroller or something go to a triac driver and fire this triac at very specific points in this waveform and basically it'll you'll get something that looks like this where you can you can instead of getting a full sine wave out you can use it like a switch like that and get the full sine wave out but you can also hold off and not fire this not actually activate the triac or trigger it until this part of the wave or any part of the wave really and you're cutting off a fraction of your top and your negative half of your sine wave and that's basically limiting the amount of power current the amount of time that you know current is flowing through your load and that allows you to do things like you can you can control light like a incandescent lights or motors it's used often and motor controllers or and like resistive heating elements if you wanted to do a resistive heating control so you want to limit the amount of power that goes through your heater things like that all right guys so now we're going to look at just a IV curve for a triac it's very similar to a diet and in fact I just left the same graph up here from the diet and just fixed a few things over here but it would match with triac looks like so if you guys watch my diet video you'll know or not I just want to say diet because it sounds like half of a triac kind of but a diet is different will do a diet is not as acts I mean an SDR so it's very similar to an SDR curve in fact it's identical on this side and then this side was a little bit different it just didn't have that you weren't able to actually activate it in the negative half of the cycle the only time it would actually conduct and negative half of the cycles if you reach the break over voltage but so this is a triac it's really the same as the scr curve so let's go through it real quick so in the forward blocking region I explain this a lot more in my SDR video too so watch that definitely watch these two because they're very similar and I explain a lot more things in that video in greater detail but anyways so this is your forward blocking region right here so basically on the positive half of your sine wave if this will block the actual current flow it will not conduct unless you go over the forward blocking or the fourth for blocking voltage or the break over voltage which is not really recommended I said that amassed the r vo as well typically they don't want you even go anywhere near this and this can range anywhere from you know 25 volts up to I think there's like six or eight hundred volt tracks there they go way up there so they're very big I think it's probably even higher you know power tracks that go up like 12 or maybe even a couple killable that's kind of high but they go up they go way up there you know these are high power devices physically they're used in more industrial applications so it will not conduct it has a forward blocking region right kind of like a kind of like a diode in it and it won't activate unless you reach this forward break over voltage that's one condition that will push into the conducting region not ideal you don't want to use that too you don't rely on that in your design or if if you activate it from the gate so if you trigger the device from the gate and you have that gate current that's needed to actually put it into the conducting region it will then shoot over to the conducting region and you can see that your current goes way up in that region so this happens almost instantaneously takes you know just a couple of microseconds to switch from the forward blocking region to the conducting region and it works just like an SCR in a fact that it latches so once you're in the conducting region it will stay in that conducting region and it will it'll keep conducting until your current falls below the actual holding current so it'll hit the latching current and it will latch and then once it goes there it will stay latched and it will keep conducting you'll stay in this conducting region until you fall below your holding current and your gate is no longer triggered so those two conditions have to be true as well and same as the SCR these two the latching current holding current are typically the same not always but they're usually very close so they're about the same and this same exact thing happens in the negative half of the cycle it's just basically a mirror image but for the negative half of the cycle so you have a reverse blocking region as well and it will not actually conduct until you hit me I didn't actually label this I should have label that with the reverse break over voltage so this is if you're in the the negative half of your cycle right and if you reach that that extreme negative voltage that reverse blocking voltage maximum reverse blocking voltage it'll shoot into the conducting region here and become conductive but typically again that's not used you'll just have your gate trigger and you'll have a it actually triggers with a negative voltage on this half of the cycle so you'll push a negative voltage into your gate it'll trigger it and it'll shoot boom into the conducting region it'll act with your latching current and it will hold there until the current falls below the holding current for a significant amount of time it still takes that it takes a certain amount of time to actually unlatch so you have to fall below your holding current for like I said it's on the order of tens of microseconds so you know 20 30 microseconds somewhere around there so it does have to fall below that holding for a certain amount of time before the actual track will unlatch and they'll fall down - back into these blocking regions here so again these aren't used a lot in an AC control that's what they're mainly used for you don't see them use there's really no purpose of using this an NBC controller STRs maybe they're kind of useful on DC circuits but this is really just strictly an AC device I mean you could use it on AC or on I mean on DC but it's there's no there's really no purpose in it if you want a latching device in direct current you're probably going to use an SCR this is really just an AC specific device so typically you're holding current because you're you're constantly you know your currents constantly changing in an AC waveform you know it's going up and then it goes hits zero at some point right and let's say you're holding current is right here and right here so here's your positive holding current here's your negative holding current and as long as the time from from this to this point is is enough time for the sync unlatch it'll always on much so you have to look at that here in your datasheet if you're running out really high frequencies if this AC is a high frequency it's not like just your typical 60 Hertz sine wave it might not fall below the holding current long enough to actually unlatch the transferrin off the transistor the triac so you got to be careful with that these don't work at you have to make sure that your your actual current flowing through your device will fall below the holding current for the specified amount of time if you want this device to unlatch otherwise it's just going to say last once you activate it alright guys so real quick I just want to run down through the quadrants of operation of a track now this is a little bit more advanced and a few other things I should mention when we looked at that IV curve you remember that there was that forward breakdown voltage interval for the reverse breakdown voltage and it's kind of like the blocking voltages right if you go beyond that that triac can switch into the conducting state as we saw so it's really important when you're designing a circuit with these guys first off your loads if they're either inductive or capacitive loads if not resistive loads you got to be very careful because your current may not match your voltage right they can be phase-shifted a little bit with as much as 90 degrees and your voltages can get rather high in that case and you can actually exceed the forward or reverse break over voltage in your track and switch into the activated state when you don't want it to so those are just some design considerations to take into account also I don't really want to get into the great depths as to why this is but the triggering is also the level of triggering required at this gate is different depending on what quadrant you're in so it's easy easiest here and it gets a little bit harder as you go along through the cycle and that just has to do with how these currents are actually flowing through the actual semiconductor layers sometimes it's required you have to push a little bit more current through your date to actually open up those depletion layers layers in the in the actual junctions of the semiconductors and it requires a little bit more gate current in different quadrants to actually trigger your triac so here's let's look at it so here's quadrant one so this is the first ninety degrees of your of your cycle right so here is the first half of positive half of your sine wave if we're starting here at zero so this is zero degrees and 90 degrees would end right there right so this is your first quadrant or your first 90 degrees and in this case in the on state of your track your gate will have a positive current and positive voltage and this is all relative to mt1 so if Mt one was at ground mt two would be our positive half of our sine wave relative to ground rice and our gate would be have a positive voltage and a positive current going through mt one and so in this state a current would actually flow through this first half of this tractor this we can think of it as an SCR right so they would flow through here and so in this second quadrant your gate of voltage and your gate current is actually going to be negative this is the so this is going from that from ninety degrees up to one 80 degrees right there where it crosses that zero again right and so still your your current is going to be flowing this way through this through this SCR right here and so yeah and again safe relative to here so your your wave coming in on Mt 2 is positive relative to mt1 its ground and your gate voltage and current is going through to mt1 and it's negative relative to the ground and also here in patan so this is Quadra 3 this is going to be from 180 to 270 degrees so this is the first negative portion of your of your wave and it's going to have a negative voltage on the gate to fire it and so when you have a negative voltage and a negative current going through that gate relative to mt1 it will fire that that triac and then the last quadrant is going to be from 270 to 360 degrees of your wave and it is a positive gate voltage and current relative to the terminal mt 1 on your Shryock and what's interesting and we'll take a look at this is I will actually demonstrate this for you guys so I'll hook up a triac and I'll show you guys how we can kind of like in the SDR video will actually activate one and we'll do a full wave activation where we just basically use the track of the switch and your output will be all positive but what I'll also do is I will hook up I'll show you guys just kind of real quick how this is going to happen so if I put a diode right here our gate is only going to receive positive voltages that can only receive positive voltages so that means really it's only going to fire this half of this cycle and you'll see that basically the only fires would 1 FDR and our will only get it'll basically just be like an equivalent of an SCR will only get our positive half of our cycle and then if I flip this diode we'd only get negative voltages on either side and you'll see that we only will get our negative half of our cycle or FDR one of only one of our SCRs will be basically working because we in this case without doing any phase shifting or anything like that we have to fire on the first half of our waveform alright so I just want to show you guys real quick a circuit that we're going to build up here very basic and so here we have an AC source so you'll see this is just a transformer here RL this is just our resistive load and in my case is just a little hundred ohm wire around resistor and our track is in series with that so the load passes through a terminal a 1 and our actual power comes in here through a 2 or the other half of our AC source and so our gate we're just going to go ahead and drive this through a hundred ohm resistor and it's going to be tied up to our a 2 pin so current will flow through a tube back down or not through a two of current will flow through the gate into a 1 and so that's typically how it's done and this is also known sometimes as MT 1 or into main terminal 1 and mt 2 main terminal 2 so let's hook that up and let's see how it works also real quick I just want to explain something this arm this is just a simple wave turn it on if we break this it'll turn it off so this is just basically a very simple solid-state relay if you will and so we're just controlling it by either connecting or disconnecting the gate pin so it's not very advanced on there are other drivers that you can use to actually drive this with something like a microcontroller or some digital interface where you can use just like 5 volts or 3.3 volts or whatever to actually activate this track and turn it on and you can get very creative with that you can do phase control and stuff like that but in this case we're just going to do a very simple circuit where we use this thing as a solid state relay and we'll actually look at this waveform on the output and I'll show you guys that it does put out a full wave as opposed to the SDR which only gave us out a half wave interestingly enough I'll show you guys this real quick I just want to show you this if we if we put a diode in here right this is only going to allow positive voltages to flow positive voltages and currents to flow into our gate and consequently it will act exam like an SCR in this case so only one of these STRs in our track will latch and it'll only give us out our output will actually only contain the positive half of our sine waves so it'll look something like that right just like an SCR and if we flip this diode around so if it was something like this right you would only get negative voltages and currents to your gate and that would only activate the other triac right which would look something well of course it would be a different part of the wave it looks something like this right and you wouldn't get your positive cycles so that's some really poorly drawn sine waves but you get the picture right so if we throw this diode in there it's really only using half the triac and it's basically acting sort of like a just an SCR alright so I just like to show you guys this real quick we'll take a look at this in another video this is a sort of opto isolator it's actually a track driver so this is a part number MOC 30:41 and this is a really good way to actually trigger one of these tracks very precisely with a digital electronics or something like that so if you want to interface a triac to say in arduino you can do like web controlled AC things and stuff like that so you can actually turn on like lights or high powered appliances through an Arduino and not only that because you could do that with like a salt and not as you could do that with a relay or relay as well so it's not really unique in that aspect but you can actually do phase control with this too so you can do light dimming you can do motor controls you can do all types of AC waveform controls by you know doing that chopping that AC wave up and getting out what you want and you can do that all with an Arduino so this is a really good chip to interface one of these tracks with an Arduino will do a whole nother video on that because that's that's another project on its own but it is a really cool way to interface low-power with directly on the AC side alright guys so very basic set up here I just want to show you real quick how it stuff it tucked up exactly like that schematic but I just want to show you a real quick so we have one side of our transformer leg coming out and it's feeding into you straight into our load so it's going directly into our load and it's also being referenced to ground on our oscilloscopes this is our sillas cope alligator clip here and then the other half is just running through this current meter so we can actually monitor the current here on this meter and it's in series of course coming out and running into a terminal a2 or mt 2 on our triac right and then so mt 1 is going straight to our actual load and then the gate and actually also mt 1 so the output of the triac is going straight to our solar scope as well so that's what we're actually monitoring the waveform coming out of the triac on the oscilloscope and then the gate let me just zoom in a little bit so you guys can see this a little bit closer the gates of our track is being driven through this little hundred ohm resistor and you can see here that when I if I give it a little touch over here you can see the current starts to flow through so there's the current so there's a leakage current right there you know maybe close to 20 milliamp so it's got quite a large leakage current but like I said these things are typically used in high-power applications so it's not really that large a leakage current if you want to think of it on that scale but it is quite large and then when we touch it there it goes it actually activates and goes into that conducting state and it's acting really just like a solid state switch so let's look at the output of this triac on our oscilloscope and see what it looks like alright guys so here it is I'm about to actually connect the gate so I'll just go ahead and clip it in there and so there's the output waveform from our track so trying to find my marker here alright so I just want to explain something so if we look at it it's almost like a perfect AC sine wave all go ahead and put it into storage mode and it looks pretty much perfect right it almost looks like a perfect sine wave and it's really close but there's this little there's this little blip going on here where it transitions from negative to positive and we're basically where it crosses zero you can see a little bit of something going on there so let's go ahead and get a real close to look at that and actually if you look at it you can see that if I just shifted up a little bit to correct it let's see so basically as soon as it crosses zero it takes some time really before it actually activates and so that's because it takes time for our waveform to actually be able to push enough current through that resistor we have to wait I explained this really good in my in my SDR but I gave you guys an actual schematic but essentially our gate of our track is being driven by the AC waveform and it's being driven through that hundred ohm resistor so we have to wait for this AC waveform to progress so much in this case this amount of time before the voltage is high enough to where it can push enough current through that resistor to actually activate our triac so this is due to the resistance and this is a tiny tiny bit of actual phase control here and I want to show you guys if I actually bypass that resistor so if i bypass the if i bypass the hundred ohm resistor you'll see that this actually almost nearly goes away because we're basically feeding our AC signal straight into our gate which allows us to drive that gate current a lot faster and it allows it to switch into the on state a lot quicker so if i bypass the hundred ohm resistor you'll see here that it fixes itself a little bit it looks a little bit cleaner so this is without the resistor and this is with the hundred ohm resistor in series so you can see quite a bit of a difference it transitions a lot quicker still not perfect but it's better and it's actually more noticeable if I woke up 330 ohm in here so if I put a 330 on here let's see what that looks like alright guys so it's much more significant on the 330 ohm you can see that that delay is quite long and this really is how the actual phase control works and I showed you guys this in my SDR video and talked about it a little bit more detail but we can change the resistance value in here and add delays in these ways and this actually cuts off part of our sine wave and if I put like a potentiometer in here you would see so let me actually rack up 10 geometry and I'll show you guys alright so if you want a better explanation as to what's going on here again go back watch my SPR video but here we go I'm going to show it to you guys so I have a potentiometer and series instead of a resistor so this is basically just a variable resistor and so it's a trimmer pot pot turned a bunch of times but here the resistance is pretty much zero so it's just going straight through the pot and basically as if we just hooked it straight up before and as I start to turn the pot that resistance increases and you'll see that delay before the SCR kicks in starts to get longer and longer and so it is actually cutting out part of our waveform if I keep going and so basically you can use this as an actual phase control I drew this on the board earlier and it actually this is how light dimmers and things like that work and we can't go too far into it you can see it starts to cut out and it gets all wacky we can't go too far into it I explained that in my SDR video kind of why but I'll do a whole nother video on this later on but essentially we need to actually have our triggering a little bit out of phase with our actual line voltage so we have to add some capacitance and stuff in there but really these things are not typically controlled like that except for maybe in light dimmers typically they're actually monitored by a microcontroller and you'll fire it with a pin of a microcontroller and it has some intelligence to it but so you can see that they're quite useful not only as switches but they can actually do phase control as well alright guys so just like I explained earlier if we pop that diode in series with that gate I have a diode in there right now forward bias so we'll only get forward or positive voltages and currents at our gates so I'll show you guys that right now and you can see that it really just acts like an SCR we're only getting the positive half of our waveform let me go ahead and put that in storage mode so yeah we're only getting the positive half of our waveform and I'll show you guys by foot diode around it will act like an SCR reverse bias so let's look at that and so there's the negative half of our sine wave so it just really chopped off the positive half and again just really functioning like an SCR this is really just two STR so this is one of the SCR is working and the positive half of the wave is taking care of the other SCR but you would have to have the other voltage or current flowing through the gate the opposite way to actually trigger that that ser so really this is just functioning as an ser alright guys that pretty much wraps up for this one if you like this video definitely give it a like and subscribe because there's going to be a lot more material like this coming later on I hope you guys enjoyed this one and as always guys have a good one

Channel: Jacob Dykstra

Views: 13,566

Rating: 4.7699113 out of 5

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Id: vmx_owMVBos

Length: 29min 0sec (1740 seconds)

Published: Sun Feb 05 2017