Boost Converter Efficiency Improvements

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No, Bill's right Joerg, it does exist.

Here is a scan of it, from that book he's always going on about...

(really good book actually).

Perhaps it's called something else now.

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John Devereux
Reply to
John Devereux
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They may call it that way but it isn't an Ayrton-Perry winding. What is in those two pictures is simply the old trick of winding around a toroid and then shortly before reaching 360 degrees start winding backwards.

The windings all have the same orientation in terms of their magnetic field, unlike in an Ayrton-Perry winding where their fields cancel.

The real Ayrton-Perry style is as shown in the lower right picture in here, it has little to no inductance:

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

That is amazing! Jim Williams got down to 100uV - sounds like you went down another 60dB or so.

Can you give any hints how you managed to do it?

Reply to
JW

I'll bite... what is the angle grinder for? Making heatsinks? Customizing the ferrite cores? Helping to remove parts that have melted down and stuck to the bench?

Matt Roberds

Reply to
mroberds

LOL

Reply to
tm

No, not that. If one needs large heatsinks the switcher isn't high enough in efficiency. I use it a lot for making custom metal parts, gapping ferrite (crudely, for experimental use), making slots, large holes, and so on. Also for fast sizing and deburring, where my bench top grinder slows down too much because it lacks the horsepower.

Yes, but if I have the time for set-up and later the clean-up I use a wet tile saw. A lower cost hardware store model but with a high-quality diamond blade in it. However, it is a pain in winter because it can only be done with the garage door open and the spin direction towards the driveway. When it's hot outside I sometimes stand in front of it and let the water mist rain on me.

:-)

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

h

Sure thing. I put a capacitance multiplier in series with the output, taking the AC feedback from the SMPS output and the DC from the cap multiplier in the same way you do when you put a resistor in series with an amplifier output to avoid instability from capacitive loading. It costs a volt or so, which reduces the efficiency, but cleans up the ripple amazingly.

Getting the input ripple current down that low required a low-Z RC network between the snubber and the main supply. I posted it in this very boutique a couple of years ago, iirc.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

One correction, sorry--it was more like a 3-W supply, roughly 80 mA at

36V. That does make it a bit easier!

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

If anyone wants to build something similar, the BCX70K is an excellent device for a cap multiplier in low power situations. Mainly because of its favorable noise performance at low frequencies. Best of all, it can be had for around 3c in reels.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Hey, that's my favorite NPN! Its beta spread is only about 2:1, so you can do things with them that infuriate various old gits.

BCX71 is the PNP.

But we only pay 2.2 cents for BCX70s.

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John Larkin                  Highland Technology Inc 
www.highlandtechnology.com   jlarkin at highlandtechnology dot com    
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Reply to
John Larkin

I've done so, but you are strangely unwilling to get hold of a copy of "Coa xial AC Bridges" by Rayner and Kibble. Amazon offers two "new" and five use d copies, and there might be one available in an academic library near you.

It would probably be cheaper than buying the book - I've got the enamelled copper wire so I'd only have to buy the toroid.

Not counting the Ayrton-Perry variable inductor, which I didn't know about when I wrote that.

The search string Ayrton-Perry astatic inductor gave several hits, most of the them admittedly picking up the Ayrton-Perry variable inductor, which is something different again, Apparently it can also be made astatic

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The Wiley Survey of Instrumentation and Measurement by Stephen A. Dyer has drawing at figure 5(b) on page 351 which seems to be a version of the Ayrto n-Perry inductor, though it's not identified as such.

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Bill Sloman, Sydney
Reply to
Bill Sloman

Thanks. Very good description - it's easy to see how that can filter the output ripple from the SMPS. As a rough guess, if the SMPS ripple is 5mV, and the filtered output is 100nV, the reduction is 20*log(5e-3/100e-9) =

94dB. That's pretty good. You must have an excellent setup to be able to measure voltages down in the nanovolt region.

But what about the switching transients from the SMPS fllowing on the ground plane? How do you keep them from going everywhere? Do you slow the edges like Williams did?

My problem with switching noise on the ground plane is you can short the scope probe tip to ground and still measure 10's of millivolts! Do you put your measuring system in a cookie tin like Williams?

While waiting for your answer, I was trying to think how you might go about doing it. I was thinking a small pnp set up to drop a volt or so might work as a high impedance source. A large cap to ground would supply the peak current needed by the SMPS, but the current supplied to the pnp would remain constant.

So the trick would be to generate a high impedance output with a fairly small voltage drop. Sort of the opposite of an emitter follower which gives a low impedance output.

That makes a BIG difference! Thanks.

Reply to
JW

haha, yes, perhaps it is just that book that calls it that.

The online references do seem to be to non-astatic variable inductors.

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John Devereux
Reply to
John Devereux

't

d

They don't have to be non-astatic - one of the references I dug up claimed that even the variable inductor could be made astatic, which is interesting - presumably if all the coils are paired in the right way the external fie lds cancel while the internal fields can interact enough to provide the var iability.

Pity Ayrton died before anybody could take a brain scan - his brain might h ave been even more interesting than Einstein's.

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Bill Sloman, Sydney
Reply to
Bill Sloman

Even if it adds in the usual risk of simulation - every mathematical model is a simplification, and some of them turn out to be over-simplifications.

Stroboscopic SEMs have been around for a while, My ex-boss, Graham Plows, got his Ph.D. for developing one

(G.S.Plows, "Stroboscopic Scanning Electron Microscopy", Ph.D.Dissertation, Cambridge University; 1969)

though he did invent voltage contrast electron microscopy at the same time.

Plows Graham Stuart, Nixon William Charles: Electron beam apparatus. Plows Graham Stuart Sep, 15 1971: GB1246744

Plows Graham Stuart, Nixon William Charles: Electron beam apparatus. Plows Graham Stuart Apr, 15 1970: GB1187901

Optical photo-cathodes did allow very brief "on" times - you knew exactly when your imaging electron had left the anode ... if you'd managed to emit even one.

You can use differential pumping to make the gun area less dirty, but you need moving parts and lubricants in the scanning chamber ...

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Bill Sloman, Sydney
Reply to
Bill Sloman

It was for a downhole application, an ultrastable laser. It had to fit inside a 2-inch cased drillhole, so the maximum OD of the package plus housing was 38 mm. Accordingly I put the SMPS things on 28-mm diameter circular boards, stacked in little cast-iron cups with stepped ODs to improve the magnetic coupling. The grounds connected only via the FFC supply cable. (There was a small flat on each board so that the flexes could get past without pinching.)

That wasn't the cheapest way to go, but in this application I'd have seen sidebands on the laser if the ripple voltage were much larger than that. If it had gone into production, we could have used steel stampings instead, but unfortunately the start-up ran out of dough first.

It's a common problem in the ultrasensitive instruments business that your gizmo can see stuff that none of your test equipment can. An optocoupler running into a lock-in amp would have been good enough, assuming that the switching frequency were sufficiently stable, which coming from a hysteretic buck, it probably wasn't.

I have a bunch of NOS 70-mm film cans that I got from Surplus Shed many moons ago. They work just like JW's cookie tin. I also have about 1000

15-nF feedthrough caps from the former Soviet Union, which solder very nicely into holes in the film cans. I couldn't do a lot of my front-end designs without something like that.

Yes, that's called a two-terminal simulated inductor, and was first used way back in the early '60s. You put a cap between E and B, and a resistor from E to C. Probably people did the same sort of thing with firebottles at some point as well.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

Then post it. As a drawing or alink with a drawing, like is customary here.

Yeah, right, you cannot prove your point and so you want to make others buy a book. That has about the same quality as saying "Well, then search the web for it yourself".

Books are full of misnomers (and more gross errors as well), one lone book proves nothing. Ayrton and Perry would most certainly have published or patented an "inductanceless inductor" if it existed. But it doesn't exist.

You only need a pencil, a sheet of paper and a scanner.

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"Restricted: You have reached your viewing limit of this book"

Great. Anyhow, the trackback or bootlace winding technique, if that's what you mean, has nothing to do with the Ayrton Perry winding technique. It will not cancel the inductance, which would not make much sense in an inductor in the first place anyhow.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Books have all sorts of misnomers in there. Often just an innocent error and reviewers might not catch all of them because they can't be famuiliar with 100% of the covered technologies. Sometimes it's more gross though. My dad ran into some unexplainable discrepancies during his master's thesis project. Until he found out that a widely accepted formula (!) was wrong. It had been introduced in one publication and then was, ivory-tower style, cited and copied in lots of other publications. So often that it was at some point regarded as some sort of law of nature. Yet it was clearly long.

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Resistor goes from B to C, of course. (I posted this correction earlier, but it doesn't seem to have shown up.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

You do some of the most amazing things! I'm still not clear on what happens to the switching noise on the ground wires. Did you do anything to slow the fast edges?

Did the cast-iron cups connect to the outside case? That might have helped isolate one section from another.

Maybe some built-in dither to spread the spectrum:)

I'll see if I can find it in one of the forums.

As you pointed out the resistor goes from C to B. That's what I ended up with in LTspice. It also needs a decent cap from C to ground. It seems to work, but probably only suitable for low current applications. It also needs some consideration for turnon surge and protection against source shorts to ground. My interest would be to keep switching noise out of sensitive circuits, such as YIG synthesizers for microwave applications. I'm coming to the conclusion it may be better if there is a way to avoid using a SMPS altogether.

Reply to
JW

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