Hi welcome to Fundamentals Friday Hopefully a regular segment, although don't hold me to it. Where I explain just a little snippet of something to do with electronics, some little, you know, uh, little building block circuit or something like that. Today we're going to do high Voltage DC Generation like uh, this is a follow-up from the Uh Unit video I just did. If you haven't seen it, it'll be linked down below where it generated 5 Kilts uh DC inside and we had a quick look at the circuit and I said I'd explain it further So that's what we're going to do here.

Now my aim with this Uh segment is to keep it relatively short I Know I Always say that this is just a quick video I'll try and keep it to like 10 15 minutes something like that. eh. We'll give it a go if I'm doing half hour uh tutorials I think I'm doing it wrong. So anyway, let's take a look at high Voltage DC generation Now let's have a look here.

You've seen, uh, your traditional uh trans for here. Let's say it has the 1:1 uh winding ratio. so we're feeding in 1 VT AC and we're getting out 1 VT Now you've seen your regular halfwave rectifier like this, with your diode there and your capacitor, right? Everyone's familiar with that circuit. Okay, it rectifies the AC But some magic happens if you swap the diode and the capacitor there.

There's our capacitor and there's our diode. Like that, it has to be in that direction. Like that, This becomes what's called a Villard voltage doubler and this is how it works now. Um, as the blue waveform here.

Okay, we've got ground here. This is. it's not ground. it's just a circuit reference.

Uh, point. So G and that's at Z Volts. It's an AC signal. We're getting out the Transformer So the voltage.

uh, at Point A there is this AC Square wave. No, doesn't have to be a S Wave. In fact, in most cases it is actually a square wave. Okay, and B in the Green Wave form here will be our output waveform.

And as you can see it, you end up with a voltage doubled signal. So how does it do it? Well, it's actually very easy. Let me take you through step by step. Now, let's assume that our reference point here is Z Volts and we're on the positive cycle here.

So this point here is 1 Vols Now we have to assume that the capacitor is already charged up and the circuit's reached steady state. Let's not go into capacitor charging and all that sort of stuff. We've got no load, so the capacitor is going to charge pretty darn quick now. Uh, what we've got here: Zer volts 1 volt at this point here, but the capacitor is already charged up.

Just assume, follow me here, it's already charged up to 1 volt. Okay, so we have 1 Volt across our capacitor there like that. 1 VT Positive negative. But we've also also got 1 V here as well.

You add them up. 1 V + 1 V Relative to this point here gives us 2 Vols on our output. That's all there is to it. and that's why the green B Here, the green signal is at 2 Vols when the input signal here is on, its positive.

Peak At 1 volt, we've just doubled our voltage. Brilliant. But now what happens when our input signal? The blue waveform here goes negative. Well, the voltage on this capacitor is always going to stay the same.

Remember, there is no load here. Okay, so the charge is not going to drain off that capacitor. it's going to stay charged up to 1 volt all the time. So now we have minus 1 volt on the input here cuz our blue waveform has now gone negative like this.

and once again, we add up those two voltages. Minus 1 Vol + 1 Vol is 0 Vol. So instead of 2 volts we had before, it now drops down to 0 volts on the output. and that's exactly what the green waveform here shows.

It now drops down when this blue waveform transitions down. The green output waveform also transitions down to 0 volts. So it's converted. You'll see that the same amplitude the blue waveform has just been effectively shifted up like that.

and that gives us our voltage doubled signal. It's all there is to it. It's real easy. Yes, it changes once you put a load on and the capacity discharges and all that.

but we're not going to cover that today. That's our voltage doubler. But I Know what you're thinking. This is not DC it's AC Look at it.

this green waveform. It's yeah, it's It's not going negative, but well, it's a pulse. You know it's a pulsating DC signal. Okay, yes, it does not go negative.

so technically it's not AC But that's not really. you know, proper flat. DC We want 2vs. DC So how do you do it? Very easy.

You just add in another diode like this and another capacitor going down like that. and of course, that work. You can think of it as a rectifier same as what we uh showed right at the beginning, but it's actually like a peak detector. So now the output waveform here I'll show it in Black down here will now be like that.

and we get our steady 2 volts ignoring the diode voltage drop cuz these things usually work at quite high voltages and you can ignore the 0.6 volts or whatever in your diode. In this case, we're just going to assume an ideal diode, so that's all there is to it. We now get out 2 Vols DC and this circuit configuration here is no longer a Villard doubler. It becomes a Grena doubler now.

I Actually didn't mention the operation of the diod here I Sort of left that out of my previous explanation. and of course, yes, it is needed. doesn't work without it. So let's have a look in the case.

When you've got one volt here and you got your positive waveform, then you've got one volt and the two voltages add up. And the Di's reverse biased because it's zero here and 2 volts here so the diet doesn't conduct. may as well not even be there, but on the negative cycle of course it is required. So when you go to minus 1 V down here, then this diode then allows this point to go to Z volts because then it's forward biased.

So that's why that uh Junction there can now drop down to Z volts. If you didn't have the diode there wouldn't work all right. So now we have our voltage doubler. but that's hardly high voltage.

DC generation. Where's our high voltage? We want to multiply this voltage up to high voltages. How do we do it? Well, We can take our standard uh, Greenacre, double or more commonly known as the Cck, Walton doubler or Cockroft Walton multiplier as we'll see why it's called a multiplier in a minute and we can take this basic building block circuit and we can actually Cascade this along to generate higher voltages. And that's why it's often referred to as a cockroft Walton uh, Cascade or sometimes a grand Acre Cascade or even sometimes incorrectly, a Villard Cascade or something like that.

Lots of interchangeable ter terms here. Let's not argue over it, but what we're going to do is take this double a circuit which we've got here and I've just redrawn it. Nothing tricky going on here at all. There's the cap.

There's the Diode I've just put it on an angle like that. there's the other diode I've just put it going on another angle down like that, and there's the cap being returned to there Exactly the same circuit. So let's take a look at it if we've got our one Volt Peak here. I Forgot to mention it's Peak voltage I Was dealing with here before.

so we've got our 1vt Peak here. We've got our ground reference point down here, and as you saw before, we got our filtered, 2 Vols DC at this point, so this point here is 2 Vols DC Now what happens if we put an identical circuit in here like this? a duplicate and then actually have that diode coming back like that and then another diode going down here? You'll see that I've completely duplicated that circuit. I've added what's called another stage. so that is a two-stage Walton multiplier And let's have a look what happens.

We've got our 1vt Peak signal here and we've got out. But now, instead of having our ground reference over here Zer volts, we now have shifted that reference point up to 2 Vols So now we're working on that same. we've still got that same AC waveform here. We're still still got that switching waveform there.

and we've got a ground reference point here. So it's like we've just shifted this across. We've got the exact same amplitude waveform here as what we had before, but now we've shifted that reference point. So what do we end up here? We end up with a if I dot that along.

We end up with another shifted waveform there, but it's shifted up by 2 Vols relative to this point back here. and that's important. It's going to be relative to the ground Point That'll come important later. and then this point here will now be 4 Vols DC Filtered out.

that's a two stage cockroft. Walton multiplier. All right. So we have two stages there and we went from 1 Vols to 2 volts and 2 volts to 4 volts.

So we doubled and then we doubled again. What happens if we add another stage? Are we going to go from 4 Vols to 8 Vols? Well, let's see. H Let's add our our cap in and let's add our diode back here of course. and then we'll put in our Diod over here.

Boom and we're in like that now. What do we get at this point? Remember, the AC level is still exactly the same as before. It was one volt here. Uh Peak Oh sorry uh.

Two Volts Peak to Peak 1vt Peak It's also the same level here. Well, it's going to be exactly the same level again at this point. Except it's going to. You guessed it, it's going to be shifted up by another 2 Vols So this point doesn't become 8 volts.

Unfortunately, it's not a doubl doubl doubl doubl doubl as you go on. Eh, no free lunch there I'm afraid folks. But it does go up by two. so it goes up by 2, 4, 6.

And you guessed it, if we keep adding stages 8, 10, 12, 14, etc. etc. So that is why it's called a Crck Coft Walton multiplier and it's no longer a just a double. A double doubl doubler multiplier.

remember that one? But you can still generate really high voltages. Because let's say, out of the Transformer here, our Transformer was giving out 1,000 Volts for example. Then well, we get 2,000 4,000, 6,000, 8,000 10 kts and so on. You can get quite High voltages based on your trans for tap.

So I've gone in and I've added an extra stage here. So we now have a four stage cockroft Walton multiplier and we're getting 8 volts DC out. but 8 volts DC relative to where? Well, it's not. It's not just across this cap here because that would be a differential voltage.

You could use that if you really wanted to. Um, you could use that as a reference point there. But really, then you're only getting the 2 volts out or your 200 volts or your 2 Kilts or whatever your input voltage happens to be. So the ref reference point you remember.

We said the reference point was always back at this point. So that is where your reference point is. So that now becomes your positive negative output voltage. That is your final DC output voltage from this multiplier and you can see these points.

So basically the top of this network. Here these are all AC points like this and these ones down the bottom. Here are all DC points. That's why you can get your 8 volts or 8 Kilts or 800 Kilts out of this circuit.

So what do our components need to be rated at for this circuit? Well, if you look at these waveforms here, they're the exact same amplitude. It's the same amplitude AC signal is our input 1vt Peak 2 volts, Peak to Peak or whatever or RMS or whatever your input signal happens to be. So these points along here are still the same voltage. So the relative voltage across each capacitor and diode stage is still the same as your input voltage here.

So even though we're up to, let's say it's 8 kilovolts, let's say we're feeding in Uh, one kilovolts out of the Transformer and getting 8 kilovolts out. You don't need 8 kilovolt rated diodes and capacitors across here. You only need ones that are rated to the input voltage or two times. The input voltage depends on how you look at it.

So these components in here have don't have to be rated at the full output Vol. and that's a neat part of this cockroft. Walton multiplier. And if you look inside one that's actually built in a commercial product, that's why you'll find standard you know, th000 volt diodes or something inside something that can give out 5 or 10 kilovolts because they don't need to be rated that high.

Brilliant! So let's take a look at the waveform view of this and what we're getting. I've got Point 1, 2, 3, and four here and that corresponds to the waveforms over here 1, 2, 3, 4 And as as you saw here, we're getting oh I By the way, I've changed it to 2 volts Peak to Peak input not Peak anymore just to avoid confusion. So 2 volts Peak to Peak is going to give us 2 volts DC out here. So on the vertical axis here is just volts 2, 4, 6, 8 volts and that represents the voltage Peak You can see that there 2 volts Peak to Peak and the next waveform is shifted up by that 2 volts Because you remember our reference point down here is 2 volts so it shifted up and the next one is then shifted 2 volts above that 4 68 until the final waveform here.

this red one this one here is raised up at the reference level of 6 Vols but you can see that the amplitude in there of each of these waveforms is still the same as your original 2vs peak-to Peak input, but it's multiplied up like that. Four stages multiplied four times, And of course, this is assuming ideal diodes. Of course, if you have, especially when you're operating down to 8 volts, your diodes will have a huge effect. But as I mentioned before, this is assuming that there's no load on here at all.

So these capacitors aren't really getting a chance to discharge at all. But there is a practical limit where to how long you can make this thing. You can't just make it arbitrarily long because there is going to be some Um AC resistance, some impedance in here due to the components, and then of course it depends on the switching frequency as well. So when you dve driving a load uh, for example, or you know, even a tiny little load, the frequency is going to matter, the value of the cap capacitors is going to matter, and effectively, you can get the output voltages.

um, sagging because let's say we had the waveform at at this point. Here it's going to drop. It's not going to be a square wave like that. It's going to drop off like that.

So it's going to drop off and then the reference and then the Uh Peak value that's fed through to the next stage. AG is going to be lower than in this case with the peak value with no load. So and then this one is going to roll off like that and then this one's going to roll off like that and you won't have as high a multiplication at each stage. So when you start loading this thing down, then you're effectively going to lower your output voltage due to the nature of the discharger, the caps, and the AC impedance and it gets all complicated and the response curve can actually end up looking something like that.

if you, uh, end up going too far, it can actually be you know, higher back at this point than it was on your output. And all sorts of weird things can happen because you got this huge, uh, cascaded network, but we won't go into that. but that's what can happen when you load these things down. So these are primarily designed for essentially no load applications electrostatic driving and you know stuff like that.

So when you put a load on can get a bit complicated, whack this into the simulator or even better, build it up for yourself and see for yourself. Now it would be remiss of me if I didn't mention A variation on this and how you can overcome some of the limitations due to the halfwave rectified nature of this standard cockro Walter multiplier that we've looked at and you should be familiar with your full Wve and halfwave rectifiers in your linear power supplies. as we showed back at the very start, this was only a halfwave rectified and this one is a halfwave rectified Cockro Walton multiplier. But just like your linear A supply, you can do a fullwave rectified version.

You just mirror that circuit down and duplicate it. like that You have your extra tap on the Transformer exactly like your linear Supply and just like that, it doubles the frequency so you get less sag on your capacitors and greater output. Uh, you know, capability to drive a load just like a linear Supply So what we're going to do today is we're not going to build up that full one. We're just going to build up the halfwave rectified one and have a very quick play with it to the breadboard.

Very, very quick build up of this just to show you some waveforms on the scope. My Dave CAD drawing here we've got a four stage uh, Cockro Walton multiplier I'm only feeding in uh 2 volts Peak to Peak And the good thing is at this low voltage, we can see the effect of the diodes as well. So that I've got that exact Arrangement there build up here and I've got four channels probed at these points: Channel 1 Channel 2 Channel CH three Channel 4 Let's go to the oscilloscope all right now. As you can see, we've got a 1 khz signal going in here as I said 2 volts Peak to Peak as you can see there if I actually it's one all all four channels of 1 VT per Division If I move that up, you can actually see that it's there.

but we'll move it right down there. So that's our Zer volt reference that first graticule line. There is our Zer volt reference. so all of our channels will be uh, ground reference around around that point or DCR coupled of course.

So as you can see, we're not quite getting our 2 Vols out of there. In fact, we're getting 1.67 volts. We've got some diode losses there. You see how it actually pulls it negative like that.

That's that reverse bias diode in action which we saw on the circuit there so well. that's this one here when it comes into play. That's that one there when it comes into play, so it pulls it a little bit low like that. Now let's switch on Channel 2 and see what we get.

Now, the top voltage up there, which is effectively our DC uh output voltage is uh, two Vol is sorry, uh, 3 volts. So you know we're expected to get four volts out of this thing. So you can see how the diode uh voltages are already accumulating those diode losses. So let's switch on Channel 3.

and that's that third point there. and we're now getting 4.43 and we'll turn on the fourth Channel and we're getting 5.83 So you can see that our diod losses have accumulated very quickly here. We expected 2 volts top voltage there, and then four, and then six and then eight. But we're only getting 5.83 volts out because each time you Cascade through that stage, you're getting those diode losses accumulating until your top voltage there is.

You know, 5.83 instead of the eight you expect ah, death, taxes, and diode losses. Now, if we actually drop out input voltage down here instead of 2 volts Peak to Peak, let's drop it down to 1 VTS Peak to Peak and we'll be able to see that, uh, our input, we'll be able to see the discharge on our caps. Watch this. It takes actually some time for those to drop down like that.

And once again, if you look at the Uh losses in there, it's absolutely huge. You know, we're um, expecting uh 1 Vol 2 Vols 3 volts and 4 volts and we're only 2.19 Vols So that discharge there was was due to our scope input uh, resistance. So let's um, this is at 1 khz by the way. So let's uh, jump that back up and you'll see It'll almost jump back up instantly.

So we'll go back to 2 volts Peak to Peak and bang it jumps straight back up. Now if we up that to 20 volts Peak to- Peak input, then what do we get? Look there, it is 9.7 volts the top voltage of the first waveform 38.7 We expected 40 there. So we're getting a couple of Diod losses in there, and then 58 volts and then 76.5 So you know, Um, even at you know, those sort of high voltages, the diod losses still add up. We're getting at 3 1/2 volts less than our expected 80 volts.

So that's our AC waveforms 1, 2, 3, and four there. What about our DC voltages down here? Well, of course we are still on 20 volts Peak to Peak input. so expect zero here that's our reference point and then 20 40, 60, and then 80 volts. And what do we get? Well, we'll get a couple of Diod losses there.

zero And then down here, there's our 19 volts because we're getting that extra diod loss in there. whereas you saw before, it was 19.7 volts Peak because we've got that now that extra diode loss in there. So that was 19.7 So we're getting our diode loss across here and that one now becomes 19 volts of course, and this one over here is 37.8 whereas we were getting 38.7 before, and then once again, one diode volt less, we were 58 before. Now, we're 56.7 and it all adds up and accumulates and our final output voltage is 75.4 Vols there.

But as we said before, the voltage rating in these components doesn't need to be that full. 80 volts I've only got 63 volt uh caps in here and these are only 75 volt uh rated diodes. But let's look at the voltage across that final cap there and it'll be that differential voltage. It should be 20 Vols But because the loss is there, we're getting 19.1 Vols difference there.

Now let's have a look. look what happens when we whack a load on this thing. You can see the maximum top output voltage there 76.5 volts. I've got a 20 megga ohm load on this thing? Well let's drop it down to even 10.

Meg Look at that, it's dropped down to 75.6 Let's go down to you know one: Meg You would think that's a pretty low load on the thing. And it is. It's dropped down to 70 volts. Um Peak output voltage.

Of course that'll be like 69.5 or something. DC output volts and you know it's just crazy. So you can and that's a shorted output. By the way, there's a 100K it's just, you know.

Absolutely incredible. So there's a zero ohm output so that has completely shed the thing. If we go down there, we go that's completely shorted. That's at 2 volts per Division And what happens if we adjust our input offset voltage of our uh AC waveform here at the moment? For for all the stuff I've just been doing, it's been at Z Vols offset so it hasn't actually gone negative.

So let's actually change that offset there and we'll see our waveforms. There's our negative point and you'll notice that it doesn't change at all. You can see our offset changing over there. Well, waveform jumps around a bit of course, but once it settles, not a problem.

That's because our, uh, cockro water multiplier is all AC coupled. So there you have it. took a bit longer than uh, normal. that a definitely over a 20 minute video I Think oops.

Try and keep it a bit shorter next time. And speaking of next time, uh, next fundamental Friday I think I'll do a similar thing. but W for DC Like when you want to, uh, multiply your voltage or double your voltage so we'll look at a DC doubler next time. Hope you enjoyed it! If you like fundamentals, Friday Please give it a big thumbs up and as always, discuss it on the EV blog.

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