EEVblog #469 - Cockcroft-Walton Multiplier

[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.