EEVblog #469 - Cockcroft-Walton Multiplier

[EEVblog]

A new EEVblog segment, Fundamentals Friday!
How to generate high voltage DC with a Cockcroft-Walton Multiplier circuit.
a.k.a Cockcroft-Walton / Villard / Greinacher Cascade

[c4757p]

A new EEVblog segment, Fundamentals Friday!

Haven't even watched the video yet and it's already my favorite segment! FF sounds great.

[Chipguy]

I like that idea, but i have to say i like teardown tuesday the most.
More important, once there is a whole lot of fundametal fridays they will make a really really useful educational collection.
Thanks for the good work.

[JoannaK]

Like the explanation of the doubler circuit.

One thing you forgot to mention, is that those voltage doublers (with high volt input) can be quite nasty things. So testing them on low volts is really good idea for first timers.

Or, perhaps you could add second part, with real Hi-pot design and some nice sparks 

[firewalker]

 

Alexander.

[hammy]

Fundamentals Friday is a very good idea! 

[c4757p]

One thing you forgot to mention, is that those voltage doublers (with high volt input) can be quite nasty things. So testing them on low volts is really good idea for first timers.

If you can't figure out that a voltage "multiplier" will produce a higher voltage than what you put into it, you will not be able to figure out which of the little bits in front of you are the capacitors and which are the diodes...

[Skimask]

If you can't figure out that a voltage "multiplier" will produce a higher voltage than what you put into it, you will not be able to figure out which of the little bits in front of you are the capacitors and which are the diodes...

And possibly if the place you are in is yours or your neighbors...

[c4757p]

If you can't figure out that a voltage "multiplier" will produce a higher voltage than what you put into it, you will not be able to figure out which of the little bits in front of you are the capacitors and which are the diodes...

And possibly if the place you are in is yours or your neighbors...

Well, that could explain how you came to have the caps and diodes in the first place!

[pickle9000]

15 minutes long eh? (we always say eh? in Canada)

Well I suppose you couldn't help being jinxed by the doubler subject matter and the oversized whiteboard.

[TacticalCode]

Actually, I was hoping to see a section like this on your blog. Considering that this is a form of education, don't worry about the time. I wouldn't have wanted to watch this information squeezed into 10 minutes... You often said in previous blogs that something's function was a whole separate video, and I really hope you'll catch that up and explain some "fundamentals" in detail. This is really important (to me), as beginners will learn from that, it helps them to find a way into electronics and how things work.
On my personal blog, I published an article about how we educate people and why it is important to make it easy for everybody to learn something, and I got many mails with feedback - there is a huge need for this way of education. Free knowledge for the masses. So I'd actually appreciate if this section wasn't too off-the-cuff.

Thanks Dave, please keep up the good work.

[EEVblog]

15 minutes long eh? (we always say eh? in Canada)

Well, I did decide to chuck on the practical demo at the end.

[EEVblog]

Actually, I was hoping to see a section like this on your blog. Considering that this is a form of education, don't worry about the time. I wouldn't have wanted to watch this information squeezed into 10 minutes...

The time limit problem is at my end, not necessarily the viewer.
If I go into a video with the mindset that I will keep it deliberately (fairly) short, then it motivates me to actually do it. There is nothing worse than realising from the get-go that a video will end up being an hour long. That means several hours of actual footage, plus usually some practical aspect as well which takes time to setup etc.
For regular weekly videos I do not want to pressure of knowing that it will take me all day to shoot something.

[EEVblog]

So I'd actually appreciate if this section wasn't too off-the-cuff.

Sorry, I only do off-the-cuff!
T-Shirt slogan? 

[c4757p]

Sorry, I only do off-the-cuff!
T-Shirt slogan? 

I've always liked that about EEVblog, but if you're going to do instructional segments like that, you need to be very careful about precision of terminology, etc. Things like suddenly realizing "oh, I should use peak-to-peak voltage instead of just peak" halfway through an explanation will confuse people.

[Skimask]

Finished watching this video less than an hour ago.
Had (notice the usage of the word HAD) a need for a quick/dirty method to trickle charge a 4 cell AAA NiMH pack off the USB port.

20 minutes, 1 BAV99S diode array, 1 4x .1uf SMT cap array, 2 resistors (current limit at the USB port and current limit at the battery pack), a microUSB connector, and a dead-bug layout later, I got a decent ~6v output for the NiMH pack that doesn't piss off the USB port when I plug it in.

Is it a fast charge?  No, doesn't need to be.
Is it clean?  Nope, doesn't need to be.
Is it quick, dirty, cheap, small?  Yep...meets every one of those requirements.

[c4757p]

Huh? Unless you left something out of that list, where's the AC coming from?

[EEVblog]

I've always liked that about EEVblog, but if you're going to do instructional segments like that, you need to be very careful about precision of terminology, etc. Things like suddenly realizing "oh, I should use peak-to-peak voltage instead of just peak" halfway through an explanation will confuse people.

Yeah, but that's the way I work.
I a) don't really know exactly what I will say until I hit record, and b) I don't review every segment after I shoot it.
So often I don't realise I've said something wrong or not clear until I go to edit it. And even then, I often miss it because I either don't watch the entire segment, or I simply don't notice because it's my work. (Which is why proofreading your own work doesn't work). I also do not watch the final video in it's entirety before I upload.
So yes, I can try to be a bit more careful, but ultimately, there will always be a good chance of things I miss, get wrong, or don't explain.
In this case I realised peak may have been confusing, but it wasn't really worth going back and reshooting that. And I also added a test annotation overlay in editing to clarify a point.

[nathanpc]

Loved the new segment. Looking forward to the next episode!

[Skimask]

Huh? Unless you left something out of that list, where's the AC coming from?

DOH!  Sure did.
Circuit has a PIC with a spare pin for some easy PWM, a 2N7000 MOSFET, and just added a 10uf bulk cap across the V+ from the USB which really smoothed out the output a bunch.
I'm happy.  Sure, it'll take literally days (4+ according to my calc's) to charge a dead 4 cell AAA NiMH batt pack, but that wasn't the point.

[Orpheus]

Love the idea of Fundamental Fridays. It doesn't matter how you do them, JUST DO THEM!

The details? that's what comments and the Web are for.\, once you're clued in and fired up.

I've been meaning to fiddle with diode ladders for, oh, 35 years now, at least. Never got around to it. So this example had special meaning for me. Maybe I'll even be motivated to try it myself now!

[Shale]

Actually, I was hoping to see a section like this on your blog. Considering that this is a form of education, don't worry about the time. I wouldn't have wanted to watch this information squeezed into 10 minutes... You often said in previous blogs that something's function was a whole separate video, and I really hope you'll catch that up and explain some "fundamentals" in detail. This is really important (to me), as beginners will learn from that, it helps them to find a way into electronics and how things work.

Thanks Dave, please keep up the good work.

I really like the new addition to the blog. This is already going to be my favorite part.

[owlhawk]

Great new segment! As interesting as test equipment reviews may be, the videos on actual electronic design are my favorite part of the show. I look forward to seeing more of that each week now.

[Flsgd]

As an ECE student struggling on electronics seeing it put so matter-of-fact gives me hopes!

Keep this a thing, Dave!

Thanks!

[Strada916]

Love the FF Segment. Keep it up. 

[Salas]

Dave's managed to become the first nice "fundamentalist" of our times. 

[mrkva]

Thanks a lot for this segment! How are voltage multipliers from the current standpoint? I am newbie, so I am not very sure about that, I always thought that if you *somehow* double the voltage it comes with consequence of loosing the current (as with 1:2 transformer). So, how does it work? Thanks

[Skimask]

Yep, Power In = Power Out + Losses...
Same thing here.
In the circuit I halfass described earlier, I'm grabbing the 5v off the USB, bumping it up a bit to trickle charge a 4 cell battery pack.
USB will give you around ~100mA @ ~5v, but I don't count on either being remote solid...doesn't need to be in my case.
So with my selection of components, I'm drawing about 60mA off the USB port at about 4.9v, about .3watts.
After a few diode losses and the stepping up, I'm getting about 5.6v at about 35mA (old meter, I don't trust the accuracy at all, could be higher, could be lower).
294 mWatts in, 196 mWatts out to the battery.  Losing ~.9v across the diodes, about 54mWatts there.
Only missing about 44mW in the calculations...likely due to crappy meters, sloppy math, and so on.
Point being, you are correct in the assumption that you can't magically gain power somewhere.

[staxquad]

I always wondered why the electronics in my speakers had so many diodes in such a pretty pattern

[jmole]

I've always liked that about EEVblog, but if you're going to do instructional segments like that, you need to be very careful about precision of terminology, etc. Things like suddenly realizing "oh, I should use peak-to-peak voltage instead of just peak" halfway through an explanation will confuse people.

Yeah, but that's the way I work.
I a) don't really know exactly what I will say until I hit record, and b) I don't review every segment after I shoot it.
So often I don't realise I've said something wrong or not clear until I go to edit it. And even then, I often miss it because I either don't watch the entire segment, or I simply don't notice because it's my work. (Which is why proofreading your own work doesn't work). I also do not watch the final video in it's entirety before I upload.
So yes, I can try to be a bit more careful, but ultimately, there will always be a good chance of things I miss, get wrong, or don't explain.
In this case I realised peak may have been confusing, but it wasn't really worth going back and reshooting that. And I also added a test annotation overlay in editing to clarify a point.

I can sympathize here. I've made several videos where I've said "rise-time", when I really mean "rising-edge", and other crap like that. Getting it perfect is very hard to do when you just want to show how something's done. Perfect is the enemy of good, as they say.

That said, I have great respect for lectures, even if they can't pull off "perfect". Case in point: Walter Lewin from MIT:

[sagdahl]

Dave,
Brilliant! This is what we want to see.
You are on the right track!
/Roger

[andete]

Thanks Dave, this is a great new segment!

[Barny]

Thanks Dave
That was an very invormative Video.

Don't bother to cut down the time to 15 Minutes.
I think, 30 Minutes Videos fits you best.

[Kremmen]

 
More of this, please.

I'm sure fundamentals are (mostly) familiar stuff for the old hands - nevertheless fun to watch and one always has the chance to learn new things.
On the forum there are lots of noobs with questions regarding the fundamentals and i think a quick scan of those posts could suggest a long list of topics for the F Friday.

[Vince]

Wow... after 4 years of blogging, we finally have a formal, official segment showing off what Dave's is really about : a marvelous teacher ! :-D
It has taken a long time, so I hope the segment will not get dropped.

Honestly Dave, you are just amazing. None of the many lecturers I came across while studying EE, ever came close to your talent. For something off-the-cuff, it feels incredibly smooth and thought out, the flow of speech is steady, no blanks, no long "huuuuuuuuuuuu", it just feels like you know exactly what you are going to say (and draw ! Board space management is excellent !).

I am just so glad you prefer (for now at least) exercising your talent for sharing knowledge, on a blog that millions of varied people of all ages and backgrounds,  can view anytime from anywhere in the world, rather than to just a handful of students in a closed room, especially since as you often say... most of them don't give a shit ! ;-P

I agree with the above comment about video length : don't try too hard to cram it into 10/15 minutes (unless the subject allows for it). This first video is 25 minutes but it felt like 5 minutes to me, because you are everything but boring, you are pleasing to listen to, and every word you say is worth hearing, there is no crap needing cutting out.   

Another reason not to be too strict/dogmatic about your 15 minute envelope, is that in order for your videos to be as interesting and efficient as a learning tool as possible, I think it's vital that we always get TWO parts in your videos: first the white board theory of operation, THEN the practical experiments on your bench, to fully assimilate the knowledge... engineering is a practical thing and as you keep saying... none of this simulator BS, just BUILD the thing and see for yourself ! ;-)  Having only the white board without the bench session, or vice versa, would leave a feeling of incompleteness.

So I say, maybe shoot for 15 minutes for the white-board part, then allow yourself to overflow 5/10 minutes as required in order to show at least some kind of experiment on your bench.  Your first video felt perfect, great balance between between the two : about 2 thirds for the white board, and one third at the end for the experimental stuff.

So in one word: excellent "first" video, no need to change a thing in my view !

FWIW of course...

[EEVblog]

For something off-the-cuff, it feels incredibly smooth and thought out, the flow of speech is steady, no blanks, no long "huuuuuuuuuuuu", it just feels like you know exactly what you are going to say

That's because I cut out the extra clips that I goof up 
Usually a couple of those per video, maybe 5%.
Sometimes I press record and its just gibberish.

[robrenz]

Most excellent video Dave!  This type of video is my favorite and don't worry about the length. I would watch if it was an hour long.  Why the concern about being 15 mins or so?  Many of your teardowns are way longer and IMO are not nearly as interesting as these informative teaching style.  I bet your statistics on minutes watched as a percent of the video length on this style will be the highest of all your video types.

Please more of these

[jebcom]

Hey Dave,

Thanks, it was great to see the Cockroft-Walton multiplier explained. That brought back memories of my first job many years ago, at Fermilab (Fermi National Accelerator Laboratory.)  Cockroft and Walton developed the voltage multiplier as part of their proton accelerator in the early 1930s.
http://www.fnal.gov/pub/news04/update_archive/update_9-10.html

Fermilab's Cockroft-Walton was in use as the early-stage proton accelerator from the early 1970s until just last year. You can also see a picture of it at the following link.
http://www.fnal.gov/pub/today/archive/archive_2012/today12-08-21.html

I could only see it through a window if I happened to be in that area, but Fermilab is full of electronics geeks, so I'm guessing there's someone on the forum here who knows a lot more about it than I do.

[PA0PBZ]

I always wondered why the electronics in my speakers had so many diodes in such a pretty pattern

OMG, not only did they put diodes where the electrolytic capacitors should be, but they built the rectifier bridge with resistors!

[SeanB]

The first circuit is very common in equipment, it is in almost every microwave oven, or at least those that are not inverter driven. It does need a second diode to feed the load with DC if you have output capacitors, in the microwave this is done with a dual function device, as the magnetron is a diode, albeit one with a very high ( 4 kV plus) forward voltage drop.

In microwaves though the anode is grounded, so the diode is connected the other way round. The reason the anode is grounded is just to make insulating the output easier, having to have 4kV of insulation for the output makes it more expensive, while the cathode and heater are a lot easier to insulate to the required voltage, as they do not have a large cooling area on them. The output antenna is a short circuit at any frequency below 2.4GHz, as it is just a copper strap loop connected to the one cavity to pick up a portion of the circulating energy.

[nitro2k01]

I always wondered why the electronics in my speakers had so many diodes in such a pretty pattern

Holy cow. That's not your grandma's speakers!

[Salas]

I always wondered why the electronics in my speakers had so many diodes in such a pretty pattern

The neatest trick there is the delay line on top of the schematic  for the concentric electrostatic elements so to wave launch as a coherent point source. Shifts time instead of voltage.

[BloodySword]

I just love this new segment.
Fundamental Friday is just awsome!
I learned MUCH with this video.
And I don't think that they're too long...

[olsenn]

You didn't make a voltage doubler, you made a voltage clamp. You offset the trough from -1V to 0V but the p2p voltage is 2v in both cases?

[EEVblog]

Why the concern about being 15 mins or so?

Answered earlier in the thread:
https://www.eevblog.com/forum/blog/eevblog-469-cockcroft-walton-multiplier/msg229962/#msg229962

[TheEPROM9]

A new EEVblog segment, Fundamentals Friday!
How to generate high voltage DC with a Cockcroft-Walton Multiplier circuit.
a.k.a Cockcroft-Walton / Villard / Greinacher Cascade

Thanks Dave for doing this, I enjoyed it. Perhaps the circuit can be modified to blow stuff up as well as make easy to build DC to DC converters as circuits I have found on line were useless to me. I look forward to more from this series. In the summer holidays amoungst work I will get the Weird Things Productions test lab in full operation. Need to Finnish my VFD clock that I have been working on for years, you might be interested so here is a link. http://www.eprom9.comeze.com/VFD%20clock.html 

It is built with descret logic and has been one fun learning curve, with the DC to DC converter I can reinitialize my portable TV project as well. 

[EEVblog]

You didn't make a voltage doubler, you made a voltage clamp. You offset the trough from -1V to 0V but the p2p voltage is 2v in both cases?

Yes, I explained that in a text overlay in the video.
2Vpp input gives you 2V DC output, so you haven't "doubled" anything, it acts more like a cascaded level shifter with peak detector. So the name is a bit of a misnomer, but that's what it's called. It does make sense if you think in terms of the rectifier configuration which would only give you 1VDC out.

[carbon dude oxide]

Loving the new segment, i do have a question though, how do you determin the value of the caps for each stage?

[JuiceKing]

Another thumbs up! I like this kind if video best.

[perfect_disturbance]

Great video keep the fundamentals Fridays coming they are great for those of us with limited electronics experience.

[mswhin63]

Dave, Well done. Fundamentals Friday I believe are far better than most of the other segments. Maybe it just me but keep them going warts and all. 

[Pascalken]

Hi,

If was wondering about the efficiency of the multiplier.

The thing is this: if you charge a capacitor with a step voltage half of the energy is lost in the internal resistance of your step function generator (or any resistance in series with your ideal capacitor).

An illustration of this is:
Take a fully charged capacitor (W=C.V^2/2) an connect it in parallel with an empty capacitor same value (W=0).
After the circuits settles you get Vc half of voltage of the charged capacitor.
Total energy is than on both capacitors: 2x C(V/2)^2/2  or CV^2/4
Disipated energy is also CV^2/4

Hydraulic equivalent is one empty jar coupled to a full jar with a (small) tube and a tap. When you open the tap water settles to half height, and losses are in the tube....

If you want to charge a capacitor without losses you need an inductance in series and then the voltage rises up to twice the step-voltage, at that point  the charging current becomes zero and you need to disconnect the capacitor or it will continue to oscillate and discharge again (storing the energy back into the inductance). This disconnection is simply the same diode as the first diode in the cascade.

Since all the energy goes from the generator by means of charging capacitors to the load, I was wondering if you could confirm that the efficiency is lower than 50% (including the losses of the generator).

I was also thinking (in regard to my second paragraph) that it should be possible increasing the efficiency by means of an inductor in series with the output of the generator.

I don't have the means to verify this myself and I would really like to know.

PS I love your fundamental Friday idea! Nice alliteration too.

[Oracle]

good idea doing this new segment.
Thanks Dave!

[lgbeno]

I like the new segment, honestly I think that tear down Tuesdays are getting overplayed.  If it is a matter of capacity/work, I think I would prefer doing the series on alternating weeks or something like that.  Then again tear downs probably get more YouTube hits because it appeals to a bigger audience.

Mailbag Monday is great though, especially when people send in their projects and dave fires them up instead just sending broken junk for tear downs.  Does that take a lot of effort to produce?

Btw, my all time favorite eevblogs are the design series ones.  FF is step back towards those vids.

[EEVblog]

Mailbag Monday is great though, especially when people send in their projects and dave fires them up instead just sending broken junk for tear downs.  Does that take a lot of effort to produce?

Yes, if you send in a product, then firing it up and testing it and talking about can take a lot of work.
The Digilent Analog Discovery for example. Or a micro starter board or something that would require installing the software, figuring out how to use, doing something useful with it, screen captures etc.

[G7PSK]

Heres why it's called Cockroft Walton voltage multiplier.

http://www.cockcroft.ac.uk/public/CERNCourierDecember07_Cockcroft.pdf

http://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_generator

[bitwelder]

I also appreciated the new Fundamental Friday segment.
It seems to works nicely as a Followup Friday for particularly interesting Teardown Tuesdays 

[KedasProbe]

Some magic happens

The magic is that you created space on your whiteboard 
(to put something in parallel with the diode instead of the capacitor.)

[king.oslo]

Great idea Dave. This fundamental Friday is long over due. Got a couple of observations for you: 1. When you plan the video, try and refine the teaching as much as you can: Chop off all the stuff you dont need: For example, if you had been working with 20Vpp input on the whiteboard, you wouldn't have had to explain your diode losses because it would have been very small, and the tutorial would have come out even clearer! 2. In stead of worrying too much about the length of the video, I would worry that my audience is following. I imagine when one of the newbies don't understand a concept, they may as well go watch something they understand. So in teaching, I think it's all about taking your time, and making sure most people understand. You could for example had taken the time to quickly mention how the capacitor works. Adds just 10 sec good video Dave!M

[jancumps]

.... When you plan the video..

[glatocha]

How about use the Schotky Diodes?
The loss should be much less. Maybe can be use for some small battery powered devices.

[cibola]

Since this thread seems to have become the thread of choice for comments on Fundamentals Friday and desired topics, here is a summary of a longer message I posted in EEVblog » Blog Specific » Suggestions

-- Fundamentals Friday  --->> Two Thumbs Up!
-- Suggested Topics --->> Simple circuit elements, theories of operation, pattern spotting
-- Opportunities:
     1. Ideal for short videos (five to ten minutes)
     2. Mix it up between simple fundamentals and more advanced topics.
     3. Perfect for off-the-cuff style and little or no prep, or video editing.
     4. Build up a permanent "Fundamentals Knowledge Base" in EEV Forum
     5. Attract a new audience that is desperately searching the internet for just such fundamentals (not coincidentally. increasing your YouTube stats and, potentially, your subscriber base).
     6. Sell more Tee Shirts!

[larry42]

Nice video and it made me delve into trying to understand the circuit properly despite being a 10year RF design veteran (I skipped EE undergrad, hence the hole in my knowledge of this circuit). I didn't like the hand-wavey "assume the capacitor is fully charged to start off with".

This assumption can be avoided if you start with the negative cycle on the Vin...

[caga]

I just had a question regarding the multiplier. If I had an output load say a resistor 2ohms , and the output voltage was say 8 V.

Then I = 8/2 = 4A .
Now does the circuit affect the current capability to be output to the load ?
Or can we simply use something else for the currents source ?

[GeezerWhiz]

Here's an unusual C-W app!  We needed to build 2 cosmic ray telescopes to operate on 2 space craft (the first to leave our Solar System).  There were 3 photomultipliers which needed a bit over 1000 VDC each.  Vacuum chamber testing revealed super bad corona discharge problems generating high system noise.  Since each PMT had 10 dynodes, each needing a 100 VDC difference from its neighbors, we made a 100 VAC 100 KHz power supply feeding a 10 stage C-W generator on each tube.  When C-Ws were carefully potted onto each PMT, all corona problems went away!

NASA said we'd probably have data till 100,000,000 miles out, and we did.  So they sent back our Ground Support Equipment which pulled our data out of the stream.  Over 14 years later, we got an emergency call to return our GSE because we had made it around the Sun and baby was catching up with Earth again.  Our Cosmic Ray Anisotropy package was still working perfectly and we got an entire additional data set that was unanticipated.

So, Huzzah!  Huzzah!  for the Cockcroft-Walton Multipliers!