Zener Diode vs Tube Regulation and More

hi there and welcome to tech tips Tuesday in this episode we're going to take a look at the Zener diode and some circuits that the Zener diode can be used in so let's get started this entered out is a very important device to anything that's modern day electronics since everything nowadays is so accurate and needs precise voltage references pretty much almost everything has a Zener diode in it in some way shape or form or hiding in some package or other so what we're going to do is we're going to take a look at the Zener diode and we're going to then take a look at it electrically over on the bench so I'll just cover a few things about the diode here first before we head on over to the bench in and I show you exactly how they work electrically okay so a Zener diode the symbol for Zener looks just like this and the cathode looks like a Z or Z depending on which part of the world you live in okay not to be confused with a Schottky diode the Schottky diode the cathode looks like an S so that's how you can pretty much tell the differences between a Zener and a Schottky alright now in order to understand the Zener we're first just going to take a look at a regular diode okay and that's the symbol for a regular diode right there now a diode is like a one-way check valve for voltage okay so if you if you can picture a one-way check valve in say hydraulics or anything like that you have a ball a spring in a tapered seat usually inside of a check valve so what it'll do is it'll let the the fluid flow in one direction but when it tries to come back of course the balls wedged in the seat and there can be no fluid passing the other way and that's pretty much what a regular diode is it only lets the voltage through one way and stops it from coming back alright so a diode let's the voltage go this way so if you have positive voltage here it will go through the diode here if you put positive voltage on this side of the doubt it will not go back this way all right very important diodes are used in absolutely everything and extremely important in electronics a Zener diode how it differs from this diode is that it will let voltage the other way but at a predetermined amount so say this is a 6.2 volt Zener diode the voltage on this side would have to reach six point two volts before it allows it through okay so now like a normal check valve they usually have a spring you know and a ball and a seat and it takes a little bit of pressure to push that spring out of the seat in order for fluid to travel in one direction a standard diode takes point six of a volt okay so that's a standard silicon diode takes point six of a volt before anything will travel in its regular direction in its forward direction okay you can always remember which way the positive voltage will travel in a diode just follow the arrow alright and if you want to feed voltage back this way it hits a wall that's one way of remembering it okay so this here takes point six of a volt before this thing will actually turn on okay so being at point six of a volt voltage will travel this way but it will also be minus that in the end so if you have 10 volts here you will have about nine point four here or something around there if you put DC voltage on this side of a regular diode you have 0.6 of a volt drop through the diode that point six of a volt drop is what creates heat in the diode in large power supplies and that's why you see diodes with studs and welding machines and things like that because they have to get rid of the heat that point six of a volt drop if that kind of current creates a lot of heat in the device okay this is why for larger power supplies Schottky diodes are preferred now because they have a forward of usually between point one and point four of a volt somewhere so you know there's less of a drop across the diode and that less of a drop creates less heat okay and that's how a standard diode works alright so if we want to make this into a Zener diode schematic wise that's very simple just do this and this here so now we have a Zener diode so see the Zener diode is rated at six point two volts so what's going to happen this diode still here has the same forward voltage okay it still takes in order to use this a regular doubt if you were going to use it below six point two volts oh right it would function as somewhat of a normal diet it still takes point six of a volt to go this way okay exactly six point two volts it will let voltage travel in the opposite direction on that diode and because of that we can use these things now as voltage regulators or a reference for a voltage regulator and when I call it a reference I mean that this is controlling another device telling it to do the voltage regulation okay so the simplest style of voltage regulator is really a shunt regulator and a shunt regulator really is just a resistor and then we have our Zener diode to ground and this is our voltage out okay so this is the load here really to the Zener and then this is our in okay so we can't tie the Zener diode directly to the power supply because if we did that then the Zener diode is going to try and pull a really rigid power supply down and what's that going to do exceed the ratings of the Zener burn it up and turn the Zener into a jumper and we don't want to turn our dive into a jumper because then it's going to be doing some pretty heavy voltage regulating all right so what we want to do is we want to have a resistor in line with the center so that this here is a load to the Zener so this here really is using this as a softener between this point here and this point here okay so just for an example sake okay we'll say there's 12 volts here and we want to bring it down to six point two volts here 220 ohm resistor here would be absolutely fine and what would happen is this would now act as a regulator and that wouldn't heat this say this is a 1 watt diode or something like that that would not heat the diode hot enough and we would get regulated 6.2 volts or very close to now here's another thing that if you play with simulators and stuff like that if you get a Zener diode and it's a 6.2 volt Zener diode they're not always at six point two volts some will be six point one five six will be some will be six point two five some will be you know in that area it all depends on how you load that diode in the we'll need on the curve and we'll talk about that knee here quite shortly okay so really if you if you buy in in the real world not on a simulator on a computer when you're putting this thing together in the real world if you buy a handful of diodes chances are you're going to find one or two that will be exactly at six point two after the diode has warmed up a little bit again we'll talk about that here on the bench again just quite shortly okay so this is just a regular shunt style regulator if you want to control more current with this particular style of circuit you can use the Zener diode to control the transistor okay so this would be classified as a linear regulator okay because the transistor itself is running in the linear region all right and of course that creates heat as well so here we have a transistor an NPN transistor of some sort here we have a diode Zener diode of some sort going to ground and we have a resistor here providing some current to this point for the base and the Zener diode here okay so just say we're going to put 12 volts here again and say this is a six point two volt Zener what are we going to get out of this point here five point six volts or around okay reason being is because across the transistor we also get point six of a volt drop okay so that has to be taken into consideration when you're designing a circuit like this there's a lot of things that have to be taken into consideration and I could sit here and talk about this for an hour choosing transistors and the gain of the transistor and how that affects the current and everything but for now we'll just touch on this we're trying to stick to the Zener diode here so really what we want to do we'll call this 220 ohms again just for argument's sake okay and this is a six point two volt Zener diode again we just have our standard to-220 a power transistor sitting here okay and we're getting five point six volts out all right and of course there would be a little bit of load on this as well we'll call this one kale or something like that okay so we're going to have a five point six volts out here so if you're ever designing anything if you wanted to have a 5 volt regulated supply and you're going to be using a transistor like this all right you're going to need to say if you wanted five point six volts or 5 volts out here you'd need a five point six volt Zener diode right here or around that okay and again if you go and buy a handful a Zener diodes you're going to find one that'll be exactly five point six or maybe a little bit higher or a little bit lower all right that's that's real world unless you're buying some very accurate components and that's really a linear regulator and that's how they function now when you buy a regulator like a 7805 or 79o five negative voltage regulator or anything like that it's like this but much more difficult inside they've got a lot of different transistors inside and you know it's really an IC inside of a to-220 package there's a much more than just this in a in a 78 or 79 series regulator all right in fact if you look up a 78 or 79 series regulator a lot of the times they show exactly what's inside it and you'll see that there's quite a few transistors and and stuff inside of an actual 78 or 79 series regulator so that really is how Zener diodes work in regulation service they can be used as all sorts of things they can be used as switches so basically um the voltage will have to get to a certain level before to let it go to a certain you know before to let it pass in a certain direction or things like that I've seen people use n or dollars to to turn on relays at different voltages and things like that so they do have lots of different purposes but we'll stick to voltage regulation here now if I compare this to older older stuff an older gas diode alright which could be either that's how they're drawn alright so this could be a an OE - Oh B - we'll say 56:51 what else is there od Oh c3 I think something like that okay these are all gas dials and they all have different voltages that they will regulate at depending on the gas that's put inside of this regulator gaseous regulator dot and they're really what it is is it's a tube okay and you'll see them in all sorts of different regulated power supply some glow orange some glow a powdery kind of purpley blue color just depending on the gas that's inside them and these things operate very very much like a Zener diode except that they're voltages are much higher some of these can be used directly as regulators like these can be used directly as regulators where 56:51 is usually used as a reference in a regulator so it's tied to the grid of a vacuum tube all right again a vacuum tube being much like a fat okay all right this would be controlling that much like that Zener diode I just showed you was controlling the base of a transistor all right the base of a transistor does take some current all right whereas the grid of a vacuum tube is much like a fad it's a voltage driven device so what we're going to do now is we're going to go over to the bench and what I'm going to do is I'm going to show you electrically how is N or looks inside and then we'll do some experimentation and I'll show you exactly how they work in in real life controlling in bringing voltages down and look at voltages at different points and things like that in order to look electrically inside of his N or diode we need to use a thing called a curve tracer and that's what this thing is right here now this is just something I put together Oh a number of years ago back in 2011 I bought this old ICO 430 oscilloscope and get them really cheap ten twenty dollars at your local flea market and I built a little curve tracer circuit board and put it in the bottom here so it's a bunch of ICS and even a vacuum tube on that so what I'll do is I'll edit in a picture of what's in the bottom of this little oscilloscope right here you can see I've added a transformer that goldish looking transformer and there's even that small circuit board with the small vacuum tube on it there the small vacuum tube all that really does is act as a screen saver so after about two minutes or so it'll pull this trace off the screen in order to stop any kind of burn-in so right now I've got the the actual trace on the CRT very low the camera itself seems very sensitive to that color so it's uh you know it's not very bright it's kind of dim on this side if I was going to be using this I'd actually have it much brighter than that but for the camera it seems to work okay on the top of the device here is just a voltmeter it's a basically it's nothing really super precise about it is one volt per led is really all it is so if I want to go between a volt I have an external voltmeter on the top on that circuit board is a peak detection circuit and then the voltmeter just ties into some of the the jacks on the bottom here and then again if I need a more precise reading that's what this is up here for now you'll notice that there's two green LEDs a yellow and a bunch of red LED LEDs there the green LEDs just tell me that it's safe to use in circuit there's a screen saver there the yellow means that I should probably turn the voltage down it's kind of pushing my luck in circuit and then of course the red LEDs is you know dangerous to be doing any kind of in circuit testing so this adjusts the voltage or the amplitude of the sine wave inside and when I do an actual video on this I'll explain exactly how this little curve tracer works eventually one day I'll I'll put another one together I would like to make one that's maybe just a little bit more intricate than this if you want to see the rough idea of how one of these littles curve tracers work you can look online for I think it's called the oscilloscope octopus that's kind of a really simplistic curve tracer right there I believe it's using a transformer if I remember correctly this is a little bit more intricate it uses a bunch of op amps and again there's a peak detection circuit on there and that tube and a whole bunch of other things to make this thing work properly and of course it also has a screen saving thing so touching the probes together brings the trace back so next what we're going to do is I will use this to look at an actual diode and I'll explain that here quite shortly I picked up some 6.2 volt Zener diodes just to keep this as close to the whiteboard as possible and here's a 6.2 volt our diode right here what I'll do is I'll just clip it onto the curve tracer here and I'll show you how to read this so I've got it hooked up like this alright so if you want to hook the diode up the other way around you would just have this on the opposite side here and I'll explain that again here quite shortly so what we're doing is we're looking at the knee of the forward voltage here and the reverse will go up so the forward voltage of the diode is that point six of a volt turn on that I was talking about on the board and how to find that out will turn out the horizontal gain and I'm going to turn the voltage down here just until this goes beyond that line so it's basically just a straight line and then the diode isn't turned on yet so right now the diode is not turned on and as you can see we're at about 0.38 something like that of a volt so I will advance this just until we come to that curve you can see we have the curve right here just until this thing starts to come into that curve it will be the the forward voltage of this thing so there's the curve there and that's just before the curve right there and as you can see we're exactly at 0.65 of a volt so we're falling within the region here the standard turn-on for these diodes is around point six of a volt so we know that we have a silicon diode here if we had a germanium diode this would happen down at about point three of a volt and if we had a Schottky diode it would happen between point one and point four all right so now what we want to do is we want to see the actual the six point two point of this Zener diode so that's the reverse portion of this diode that's when this diode will start conducting in the opposite direction so I'm going to turn this up alright and I'll turn the game down here and move this down the screen just a little bit as you can see we're getting up to about five point two volts now just as this starts to take the corner and go up that's the voltage for this Zener diode you see we're beyond it now so what I'm going to do is back this down hope that's bright enough for the camera the camera is so sensitive to this a little bit to brighten it looks fuzzy on the screen so I got to be careful with this so I'll turn this down this comes around the corner is where we're at the voltage of that diode so you can see we're at that straight line now this is a very sensitive adjustment that's why there's a fine and a coarse adjustment within this one knob here so you can see we're coming just around the corner so as I back it up right there in the corner right about there is the turn-on voltage and you can see that we're extremely close to six point two volts six point one five is very very good if I load this with just a little bit more current would probably bring it right to six point two volts this very very lightly loads the device under test and that's really what this is so when this line goes up we'll just give it a bunch of voltage here it's current limited so hurt anything so you can see here when it's going up like this this is the six point two portion of the diode so this is the reverse voltage and this here is the forward voltage and by just turning this one knob down right here alright we can test both sides of the diode just like that now when I actually design one of these things with a circuit board I would again like to put some attenuation in here so it would automatically keep this in the center of the screen so there would be an adjustable attenuation so as I turn the dials it's always correcting and keeping this directly in the center of the screen and that will be an updated version of this and one day when I get the time to do all this all I'll go through one of these things and put one of those together and I'll show you guys how to build one of these things I have another Zener diode here with a very gradual turn on and I'll just give you an example of that let's clip that into the clip here as you can see we're already starting to turn on here and as I turn this up you can see how gradual the turn-on is here so you can almost program this Zener diode with the amount of current that you apply to it now I'm a fan of you know a very tight forward in a very tight reverse I really I am not too keen on this gradual area here if I wanted to use something as a programmable Zener and maybe have a pre regulator in front of it which almost kind of defeats the purpose as in ER like this maybe okay but again you know the amount of current that we apply to it this is going to start you know regulating somewhere in this curve here and I'll demonstrate this on the board and this again is something that you would never know that you're dealing with if you had a whole batch of Zener diodes like this you would absolutely never know this unless you had a curve tracer and this is why it's so important to have one of these so whenever I replace the Zener diode in any device I always look at it on the curve tracer first just to make sure that it has a really you know a very tight forward and a very really tight reverse on there so a lot of people call that the Zener knee if you want it to reverse this diode in here like this you could call that the Zener knee all right it just depends on how you put it in your test fixture and which way you want to look at it we just looked at that diode with a really gradual reverse turn on which is this Zener diode right here right beside it I've got a 6.2 volt Zener diode that one with a really tight reverse turn on and what I'm going to do is I'm going to put a little bit of current across these diodes and we're going to see how far they move so right now I've got just very very little current going across these diodes I have a twelve volt supply here you can see that twelve volt supply and it's going through a 1k ohm resistor to the cathode side of this Zener diode so really it's just doing really light regulation service at this point and it's the same thing with this 6.2 volt Zener diode so what we're going to do is we're going to see how far these move when I increase the current so we have roughly six point one volts across this six point two volt Zener diode now what I'm going to do is I'm going to parallel a 220 ohm resistor across this 1k resistor upping the current to this diode here quite substantially and we'll see how far this moves so here we go now you can see this is moving up and that's because the diode itself is heating a little bit Zener diodes will do this all right now when I say T ting it's not getting hot like I can put my finger on it it's like room temperature but it's just very very slightly heating all right if I was to really heat this thing up we'd have a lot more movement in this diode itself right but right now it's you know just ever so gently warm maybe a little above room temperature no okay so you know we're roughly at let's say six point six point two three volts something like that okay so what did we move we move just a little bit over point one of a volt it was at six point one we're now at six point two three all right very very little movement and also demonstrate a grabbed a pair of pliers here I'll demonstrate that cooling the actual Zener diode off will cause a voltage to go back down this is a pair of well room temperature pliers are cooler pliers and I'll just pinch the legs here and sink some of the heat off of the diode and you can see it moving downwards that's just from a pair of pliers pinching the lead on that diode so you can imagine in circuit how far most of these Zener diodes will go when they get very very hot I've worked on some switch mode power supplies and even linear power supplies where these Zener diodes are absolutely cooking they've actually discolored the board so while you can imagine how much that Zener diode is moving from you know cold to that temperature this gives you an idea here all right so now let's move over to this Zener diode here with a real gradual reverse on it okay so we're at four point six volts so what did we move here roughly you know point one and a bit volts on this diode right here so let's see what happens when I up the current on this one here so we went from 4.6 to almost 5 volts four point nine seven volts so that's almost point four of a volt difference and if I change that load I'm sure I could get it to be at five volts right on again there's a little bit of movement in there from heat not too much all right pinching the leg of this would do exactly the same thing that it did on this here and the diode is just you know just gently warm so there you have it real gradual reverse almost point four of a volt movement really really tight reverse point one and a bit movement now you wouldn't know this unless you had an actual small curve tracer and you looked at these diodes on that curve tracer before you install them unless of course you created a jig like this and did this with all your diodes you could also determine you know the diodes this but if you're sorting mass amounts of diodes the curve tracer is you know a much more efficient way and a much nicer way of actually looking at the differences between the two I've copied the regulation circuit on the white board so really what this is is a Zener diode a 220 ohm resistor running a pass transistor so using this as the regulator all right so this pass transistor is just a random pass transistor I had in my junk box so I figured that it would work just fine a little heatsink on it and this is powering up a number 44 light bulb it's very bright and I'm covering it up because it makes the meter look like it's flickering in the camera so I'll just cover that up there so that again is this little circuit right here all right so the light bulb is coming off of the emitter here so what we're going to do is test the voltage at this point right here and we should have around six point two volts at the Zener diode here as you can see we have six point two one whatever five volts or something like that at the Zener diode and the reason that you see it going down there as I've got my probe on it just as I showed you earlier the probe of my voltmeter is sinking the heat off the diode all right so how much voltage should we have at the output of our regulator remember we have 0.6 of a volt roughly drop across the device so we should have somewhere around 5.6 volts at the output so let's measure it and find out like that five point six oh five so you need to keep that in mind whenever you're designing a small regulation circuit like that if you say wanted to make a five volt regulator like this you would use a five point six volt Zener diode and you would come up very close to five volts we're nearing the end of another tech tips Tuesday I believe this is one of the longest tech tips Tuesday's I've put together I have a very interesting bonus for you today vacuum tube versus solid-state so let's talk about the vacuum tube first the vacuum tube is a 56:51 cold cathode glow discharge tube or gas diode whoever you want to call the thing it's an 85 volt regulator and they can be found in those big old Tektronix oscilloscopes you see me using or you know some of the older spectrum analyzers a lot of HP gear uses them as well so a pretty common tube this tube here is a pole it's not a brand new tube and right now it's running within parameters so I've got about 150 volts on the rail here alright and it's going through a 36 km resistor into the plate of this regulator tube and then of course I've got a ceramic bypass capacitor to ground and the cathode is just tied to ground now this is exactly the same thing except with a Zener diode on this side this is an 82 volt 5 watt Zener diode so I'm being very kind to this circuit over here same resistor 36km 2 watt resistor and a point zero 2 micro farad ceramic bypass capacitor so let's do some comparisons between the two all right so this is an 82 volt Zener diode I'm using an 82 volt Zener because that's as close as I could get to an 85 and that's absolutely fine so I'll touch the Zener diode here so it's supposed to be 82 volts but it's you know seventy nine point three and it's moving a little bit there's a you know it takes a few seconds for the meter to settle down and then of course what we're left with is the residual cooling of the actual probe touching the Zener diode lead now the Zener diode itself is a 5 watt Zener diode and it's you know maybe just above room temperature no I can put my finger on the thing and it's you know doesn't feel warm at all so I'm being very kind to this circuit over here so seventy nine point three volts over here so let's check the accuracy of this 85 volt regulator tube here I would say that's very accurate so let's make this test a little bit more interesting let's turn on this fan here and cool everything down so let's watch the Zener diode here now keep in mind that this Zener diode is barely even warm so just think if it was running close to its parameters how much movement there would actually be ok let's check out the tube so there you have it the winner is the vacuum tube so if you ever feel like switching out a vacuum tube for a Zener diode you might want to think twice about that I hope you found this episode of tech tips Tuesday interesting if you did you can let me know by giving me a big thumbs up and hang around there'll be many more episodes just like this in the very near future touching on all sorts of different aspects of electronics so until next time take care bye for now you

Channel: Mr Carlson's Lab

Views: 107,267

Rating: 4.9684801 out of 5

Keywords: creativedesigncomponents.com, Creative Design Components, Power supply regulator, Zener regulator, 5651 tube, Zener Knee, Zener forward Voltage, diode Knee, Zener Explanation, Diode Explanation, Diode knee, curve tracer, pass transistor

Id: xXG3VmUBF_o

Length: 31min 34sec (1894 seconds)

Published: Wed Mar 02 2016