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Re: Boost Converter Efficiency Improvements
On 06/24/2013 11:59 AM, JW wrote:
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All the ground transients are contained inside the cups.  Ripple on the  
supply and ground traces is in the low nanoamps.

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I used to try pretty hard to avoid SMPSes, but at this point they're  
pretty much a necessary evil.  Toroids are a big help.

I can't find the exact circuit at the moment, but it was something like  
this with an extra cap multiplier stage.  IIRC I decided to leave the  
second stage out, since the ripple current was in the low nanoamps  
anyway.  The heater was a bunch of 0603 resistors on a flex,  
indium-soldered to a thermal shield made of anodized, annealed aluminum  
foil for fast response.

Not the most efficient thing in the world, but interesting in some  
respects.  The FB loop may need a bit of recompensating--I gave up after  
about 15 ms of simulated time.

Cheers

Phil Hobbs


Version 4
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TEXT -224 896 Left 2 !.tran 0 100m 0 50n
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3.4 3.5 3.6 3.8
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TEXT 504 680 Left 2 !.param Rsnub60%00
TEXT 864 680 Left 2 !.param Csnub22%p
TEXT 496 760 Left 2 !;.step param Csnub list 180p 200p 220p 270p 330p  
390p 470p
TEXT -800 664 Left 2 !.MODEL BAV70 D \n + IS = 3.2E-009 \n + N = 1.85  
    \n + BV = 125.9    \n + IBV = 2.906E-007      \n + RS = 1.1      \n  
+ CJO = 4.957E-013      \n + VJ = 0.54     \n + M = 0.03      \n + FC =  
0.5      \n + TT = 0\n + EG = 1.1      \n + XTI = 3
TEXT 568 -104 Left 2 ;Heater (47 47k in parallel)
TEXT -552 136 Left 2 ;Catch diode decoupling
TEXT 504 904 Left 2 !.options plotwinsize=0


--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Boost Converter Efficiency Improvements
On Monday, June 24, 2013 1:29:56 PM UTC-4, Phil Hobbs wrote:
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<Big snip>  


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You know, after much kicking and screaming, I now kinda like SMPS.  Especially,
when they are external, with the supply over there and the circuit here.  
It's pretty easy to filter out the high frequency stuff, and there's never the
60 Hz magnetic pickup problem I use to always get with internal linear supplies.

George H.    
  
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<and snipping the nice LTspice circuit.>

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Re: Boost Converter Efficiency Improvements
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Wow! a 48V square wave at 1MHz, with 140mA sawtooth. I just looked at the  
first couple of hundred uS, but I am astounded. If you can keep the  
switching transients out of the ground(s), there may be hope for humanity  
after all.

I racall one of my HP spectrum analyzers had to resort to dithering the  
SMPS frequency to get the spurs low enough so they wouldn't show in the  
noise floor. I'm sure they spent a great deal of effort in shielding and  
circuitry before they finally gave up and accepted dithering.
  
And you just waltzed in and did it! Amazing.

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Re: Boost Converter Efficiency Improvements
On 06/24/2013 04:39 PM, JW wrote:
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"Waltzed in" might be a bit cavalier--more like "clomped in wearing  
belt, suspenders, crash helmet, foul weather gear, and a portable air  
raid shelter". ;)

  I relied on separate 4-layer boards in individual bomb-proof steel  
shield cans, toroidal coils with a compensation turn on the board to  
cancel the solenoidal part of the field, flat flex cable going through  
very small slots in the steel shield, a very tight layout, and lotsa  
bypasses.  One of the nice things about low power supplies is that the  
layout can be really really tight.

Plus I haven't shown any pictures of the actual gizmo, because I haven't  
got any--the company ran out of dough, as I said.  The prototype laser  
worked great, but didn't have all this down-hole stuff finished, more's  
the pity.  As I said when I walked in on this thread, I'm just coming up  
to speed on SMPSes myself.

Cheers

Phil Hobbs


--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Boost Converter Efficiency Improvements

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What! No Ghostbusters to back you up?

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Most of my HP gear is sealed in aluminum cans (better conductivity than  
steel), often double-shielded coax or hardline, feedthroughs all over the  
place, and they still ran into problems with switching transients.

At the beginning of transient analysis in your circuit, capacitor C6 in  
the Catch Diode Decoupling has a 120mA sawtooth with about 2nS fall time.  

You added 2pF parallel capacitance to the 68uH, L1. According to some  
specs on different style inductors, the SRF of a 68uH is from 10MHz to  
15MHz. So 2pF is about right. Even if the fall time increases to 4nS, it  
still has harmonics well into the VHF range. The energy will happily flow  
along any unshielded wires to other parts of the circuit.

In addition, capacitor C1, 330nF on the other end of L1 has a 120mA p-p  
sawtooth at 1MHz. That's a lot of energy and would be extremely difficult  
to prevent it from going everywhere.

No doubt the current swing decreases when the voltage across the 47k load  
resistors reaches the final value, buut there is still plenty of 1MHz  
stuff floating around. I am baffled at how you can get that down to  
nanovolt levels, even with all the precautions you take.
  
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There must be plenty of other companies drilling holes in the ground.  
Would your system be any use in fracking? If you could get some company  
interested in following up, you stand to make a fortune. If the original  
company has gone bankrupt, you might be able to get the rights for a song  
if you don't have them already.
  
I'm sure everyone here would wish you the best of luck!

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Re: Boost Converter Efficiency Improvements
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Oops - not sawtooth. Triangle waveform. 120mA p-p is a lot of energy!

Re: Boost Converter Efficiency Improvements
On 6/24/2013 6:54 PM, JW wrote:
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Steel has the advantage of a large mu with lots of loss at high  
frequency.  Plus it's cheeep.

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Yeah, but my simulation will beat anybody's actual hardware. ;)  (Maxim  
#1 of PowerPoint Engineering)

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There's not much of anywhere for it to go, though.  Faraday cages and  
all that.

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I'm not sure that the nanovolt part (the two-stage cap multiplier) would  
have worked with everything in the same box.  I mostly cared about the  
nanoamp part, because the heater blanket would completely surround all  
the sensitive sensor and control electronics, and I really wanted to  
avoid any inductive coupling.
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Thanks.  It's a pretty specialized business, doing downhole geophysical  
measurements, and really the only customers are the big oil services  
companies.  (The start-up was funded by one of those, but my NDA  
prevents me saying which one, or exactly what the measurement was.)

One of the things about that business is that there's an enormous amount  
of engineering lore, learned by a mixture of (a) hard experience and (b)  
folks pulling stuff out of their lower abdomen and telling other folks.  
  I have a lot of respect for the people in that business, which is a  
difficult one on very many levels, but it's really hard to know where  
real experience ends and the other stuff begins.

We were planning to use a thermoacoustic refrigerator to make an optical  
bench that would stay at around 25C even with a 175C ambient.  
Thermoacoustic fridges are incredibly tough--they're made entirely of  
metal, and the only moving part is the gas.  However, the customer  
wouldn't have anything to do with the idea, apparently on account of  
some misadventures with Stirling fridges in the dim distant past.

Assuming that had worked, it could have been used for a huge variety of  
measurements.  The two main issues with downhole stuff are, first, that  
it has to work at a 175C ambient, and second, that it has to survive  
being banged around really, really badly, every single day.

Thermoacoustic fridges would have fixed #1 more or less completely, and  
not made #2 any worse than it already was.

Maybe another time!

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Boost Converter Efficiency Improvements
Phil Hobbs wrote:
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it's
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and
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almost a
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any
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uses
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inductors, who
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it.
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Welcome to the *PHUT* boom KABLOUIE club :-)


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I had to get into switchers, big time, in the early 90's. What I obtained:

a. Good face and eye protection.

b. A large fire extinguisher (no, that's not a joke).

c. A bench kill switch for power (all power).

d. Several pounds of ferrite parts.

e. A big angle grinder.

f. The 1990 "Unitrode IC Data Handbook". That was pretty much the only
switcher book I ever had, Unitrode was "the" place where the experts
hung out. Meantime they were swallowed by TI and it is possible that the
collection of app notes in there is available as PDF.

I have heard that a book by Pressman is considered the master book for
EEs getting into switchers these days but I don't have it. Regarding
university or academic literature about SMPS, I was never very
impressed. But this site is great if you want to kick around architectures:

http://schmidt-walter.eit.h-da.de/smps_e/smps_e.html

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements
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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


Re: Boost Converter Efficiency Improvements

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LOL

Re: Boost Converter Efficiency Improvements
snipped-for-privacy@att.net wrote:
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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.


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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/

Re: Boost Converter Efficiency Improvements
On 2013-06-23 17:34, John Larkin wrote:
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[...]
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it.
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process
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The French have a nice expression for this: 'La langue de bois'.
Politicians are usually good at it too.

Jeroen Belleman

Re: Boost Converter Efficiency Improvements

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it.
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process
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As long as it's our fault, they don't have to take all our parts back and
replace them with the improved ones.


--  

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

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Re: Boost Converter Efficiency Improvements
John Larkin wrote:
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[...]

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and
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almost a
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Only on badly designed chips. LTC's are among the best, but even there I
found bloopers, missing leading-edge blanking and such. Sometimes I take
care of cross-over myself, with two resistors, a cap and one diode per
side and then through a muscular gate driver chip. One only has to be
careful that the added prop delay won't cause the leading-edge blanking
to become ineffective.

Whenever I can I design switchers synchronous. Never had much of an EMI
problem but they sure are efficient.

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uses
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who
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That's why things like soft-start also have to be cut short. Or with
"trickle-on" primary switchers one has to send a huge jolt into the VCC
cap so they start before the computer developed cobwebs.


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Are you writing a book?


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Never seen any funnies or unruly behavior with that as far as I can
remember. And I have also used them as pulsers and in all sorts of odd
situations.


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process
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That's one of the things I like about LTC, they are honest and they fess
up when they screwed up. Like when I found a boo-boo in the design of
the LT6700 series. It resulted in an apology, thankfulness, and
immediate corrective action. In today's corporate world that is
remarkable. I have seen very different behavior in larger semiconductor
companies.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements
wrote:

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and
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almost a
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any
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uses
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inductors, who
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process
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We may just go digital on this cap charger boost thing.

https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Digital_Boost_Controller.JPG

It can do arbitrarily cute algorithms and takes a lot less parts than
using a dedicated analog controller. The uP will likely be cheaper
than an analog controller chip, too.

The fet source current sensing may not be necessary, but I think it
simplifies the control algorithm. Might need a gate driver, but
probably not.




--  

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
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Re: Boost Converter Efficiency Improvements
John Larkin wrote:
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[...]

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process
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https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Digital_Boost_Controller.JPG
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If it doesn't have to be fast and agile this can be done by uC. I just
did 1/2 of one converter with a uC. Unfortunately that one also had
scores of other jobs. It was a situation where an analog loop was simply
too primitive and slow. Sure enough we ran out of horsepower and had to
resort to a simpler algorithm. My experience is: If you think you need a
uC of a certain size, take one at least two sizes bigger. Bigger is
better, at least when it comes to fast PWM or SMPS jobs.


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Cycle-by-cycle current sense is a royal pain with uC. They are too slow
and even their built-in comparators are too sluggish. And forget about
leading edge blanking so that lowpass has to do it all.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements
wrote:

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process
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https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Digital_Boost_Controller.JPG
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Right: we weren't planning on cycle-by-cycle control. But if we review
the situation say, every 50 or 100 usec maybe, easy on a 50 MHz ARM or
something, that's still faster than most analog feedback loops. It's
unlikely anything will go bad wrong in 100 usec.

If we know the gate drive waveform and we know the averaged fet
current, we know the peak current. We really know everything we need.
There's just this little cultural gap between the analog designer and
the C programmer. He's about 30 feet North of here.

Somebody could do some nice consulting business around digital power.
Get a few uP eval kits, an open-source compiler, build a few
breadboards, accumulate a library of simple apps and subroutines, set
up a web site. The most expensive thing would be a Rigol oscilloscope.


--  

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
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Re: Boost Converter Efficiency Improvements

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and
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"continuous process
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https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Digital_Boost_Controller.JPG
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Well, I want to adjust the PWM duty cycle to keep the cap charging approximately
constant-power. One easy way is to servo the PWM off the average source current,
which is a control loop of sorts. Then efficiency might be optimized by making
the frequency a function of the load cap voltage. Something like that.


--  

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

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Re: Boost Converter Efficiency Improvements
John Larkin wrote:
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[...]

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approximately
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current,
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Or, since you have to monitor the cap voltage anyhow, and assuming a
somewhat constant input voltage rail:

Provide a simple math function or LUT in the uC that changes the duty
cycle to the voltage of the cap at any given time.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements

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approximately
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current,
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making
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That would work: don't bother to measure fet current, just map cap voltage into
optimum-efficiency PWM settings. The uP would fit into a 6 pin SOT23. There are
still some advantages to measuring fet current too, and we'll probably wind up
with a uP with more pins than six.

This digital power thing is interesting. If you look at the recent analog
switcher controller chips, they are immensely complex (hard to understand
exactly what they do) and need tons of external parts. The complexity creates
quirks, too. I was going to use one LTC dual-phase switcher in a laser driver,
to regulate current, but it has mandatory current foldback, so it won't start
up.  


--  

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

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