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Re: Boost Converter Efficiency Improvements

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https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Boostback_1.jpg
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typ of
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LT Spice has probably sold a billion dollars worth of chips.

Here's a variant on a boost converter. A standard boost would have a huge
current surge at powerup, charging the caps directly through the inductor and
diode. I was trying to fix that and came up with the thing below. It's almost a
sepic, but the inductors are coupled. C5 isn't necessary but eliminates any
leakage inductance effects. It has more copper loss than a plain boost, but uses
the core about as well. It can use one of the common dual-winding inductors, who
really do have K of 0.99.

This sims at 5 PPM of real time.


Version 4
SHEET 1 1920 940
WIRE -304 32 -368 32
WIRE -176 32 -240 32
WIRE 1296 32 1232 32
WIRE 1424 32 1360 32
WIRE -368 144 -368 32
WIRE -304 144 -368 144
WIRE -176 144 -176 32
WIRE -176 144 -224 144
WIRE 176 144 -176 144
WIRE 464 144 176 144
WIRE 656 144 464 144
WIRE 896 144 784 144
WIRE 1088 144 1040 144
WIRE 1232 144 1232 32
WIRE 1232 144 1152 144
WIRE 1296 144 1232 144
WIRE 1424 144 1424 32
WIRE 1424 144 1376 144
WIRE 1504 144 1424 144
WIRE 1552 144 1504 144
WIRE 1664 144 1552 144
WIRE 656 176 656 144
WIRE 784 176 784 144
WIRE 896 176 896 144
WIRE -368 256 -368 144
WIRE 1552 256 1552 144
WIRE 1664 256 1664 144
WIRE 1424 272 1424 144
WIRE 656 320 656 256
WIRE 752 320 656 320
WIRE 896 320 896 256
WIRE 896 320 816 320
WIRE 1040 320 1040 144
WIRE 1040 320 896 320
WIRE 176 352 176 144
WIRE 1232 368 1232 144
WIRE 656 384 656 320
WIRE -368 400 -368 336
WIRE 1424 400 1424 336
WIRE 1552 400 1552 336
WIRE 1664 400 1664 336
WIRE -176 416 -176 144
WIRE 16 416 -176 416
WIRE 464 416 464 144
WIRE 464 416 336 416
WIRE 656 432 656 384
WIRE -128 512 -384 512
WIRE 16 512 -64 512
WIRE 400 512 336 512
WIRE 544 512 480 512
WIRE 608 512 544 512
WIRE 1232 528 1232 448
WIRE 1232 528 1040 528
WIRE -384 608 -384 512
WIRE -144 608 -384 608
WIRE 16 608 -64 608
WIRE 656 608 656 528
WIRE 656 608 336 608
WIRE 656 640 656 608
WIRE 1232 656 1232 528
WIRE -384 704 -384 608
WIRE -336 704 -384 704
WIRE -192 704 -272 704
WIRE -144 704 -192 704
WIRE 16 704 -64 704
WIRE 464 704 336 704
WIRE 656 768 656 720
WIRE -384 784 -384 704
WIRE 464 816 464 704
WIRE 928 816 464 816
WIRE 1040 816 1040 528
WIRE 1040 816 928 816
WIRE 1232 816 1232 736
WIRE 176 832 176 768
FLAG 1424 400 0
FLAG 1552 400 0
FLAG 1504 144 VP
FLAG 656 768 0
FLAG -384 784 0
FLAG 1232 816 0
FLAG -368 400 0
FLAG 1664 400 0
FLAG 176 832 0
FLAG 928 816 FB
FLAG -192 704 VCOMP
FLAG 656 384 DRAIN
FLAG 544 512 GATE
FLAG 784 176 0
SYMBOL ind2 640 160 R0
WINDOW 0 -70 40 Left 2
WINDOW 3 -80 83 Left 2
SYMATTR InstName L1
SYMATTR Value 8.2
SYMATTR Type ind
SYMATTR SpiceLine Rser=0.06
SYMBOL schottky 1088 160 R270
WINDOW 0 91 33 VTop 2
WINDOW 3 79 35 VBottom 2
SYMATTR InstName D1
SYMATTR Value 10MQ060N
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL cap 1408 272 R0
WINDOW 0 -66 -4 Left 2
WINDOW 3 -65 32 Left 2
SYMATTR InstName C1
SYMATTR Value 5
SYMBOL res 1536 240 R0
WINDOW 0 -51 29 Left 2
WINDOW 3 -56 62 Left 2
SYMATTR InstName R1
SYMATTR Value 5K
SYMBOL cap -64 496 R90
WINDOW 0 -8 65 VBottom 2
WINDOW 3 -35 2 VTop 2
SYMATTR InstName C2
SYMATTR Value 100p
SYMBOL res 1248 464 R180
WINDOW 0 77 76 Left 2
WINDOW 3 65 38 Left 2
SYMATTR InstName R2
SYMATTR Value 290K
SYMBOL res 1216 640 R0
WINDOW 0 -65 37 Left 2
WINDOW 3 -74 76 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL voltage -368 240 R0
WINDOW 0 48 47 Left 2
WINDOW 3 53 80 Left 2
SYMATTR InstName V2
SYMATTR Value 9
SYMBOL current 1664 256 R0
WINDOW 0 -44 90 Left 2
WINDOW 3 -287 220 Left 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName I1
SYMATTR Value PULSE(0 1 5m 1u 1u 20u 5m)
SYMBOL nmos 608 432 R0
WINDOW 0 129 47 Left 2
WINDOW 3 80 83 Left 2
SYMATTR InstName M1
SYMATTR Value FDS4559_N
SYMBOL res 640 624 R0
WINDOW 0 61 41 Left 2
WINDOW 3 56 77 Left 2
SYMATTR InstName R5
SYMATTR Value 0.05
SYMBOL PowerProducts\LT3757 176 560 R0
SYMATTR InstName U1
SYMBOL res -48 592 R90
WINDOW 0 69 80 VBottom 2
WINDOW 3 41 30 VTop 2
SYMATTR InstName R7
SYMATTR Value 10K
SYMBOL res -48 688 R90
WINDOW 0 72 79 VBottom 2
WINDOW 3 44 27 VTop 2
SYMATTR InstName R12
SYMATTR Value 5k
SYMBOL cap -272 688 R90
WINDOW 0 72 52 VBottom 2
WINDOW 3 44 7 VTop 2
SYMATTR InstName C4
SYMATTR Value 2n
SYMBOL ind2 880 160 R0
WINDOW 0 50 40 Left 2
WINDOW 3 46 78 Left 2
SYMATTR InstName L2
SYMATTR Value 8.2
SYMATTR Type ind
SYMATTR SpiceLine Rser=0.06
SYMBOL cap 816 304 R90
WINDOW 0 70 29 VBottom 2
WINDOW 3 76 28 VTop 2
SYMATTR InstName C5
SYMATTR Value 1
SYMBOL res 496 496 R90
WINDOW 0 70 75 VBottom 2
WINDOW 3 43 29 VTop 2
SYMATTR InstName R3
SYMATTR Value 50
SYMBOL res 1280 160 R270
WINDOW 0 -36 55 VTop 2
WINDOW 3 -38 53 VBottom 2
SYMATTR InstName R6
SYMATTR Value 1m
SYMBOL cap 1360 16 R90
WINDOW 0 67 32 VBottom 2
WINDOW 3 70 32 VTop 2
SYMATTR InstName C3
SYMATTR Value 10m
SYMBOL res -320 160 R270
WINDOW 0 -40 53 VTop 2
WINDOW 3 -44 53 VBottom 2
SYMATTR InstName R8
SYMATTR Value 1m
SYMBOL cap -240 16 R90
WINDOW 0 65 32 VBottom 2
WINDOW 3 72 29 VTop 2
SYMATTR InstName C6
SYMATTR Value 10m
TEXT 1416 720 Left 2 !.tran 0 5m 0 1n uic
TEXT 1368 592 Left 2 ;D140 BOOST CONVERTER D
TEXT 1416 656 Left 2 ;JL  June 22 2013
TEXT 712 248 Left 2 !K L1 L2 0.99


--  

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

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Re: Boost Converter Efficiency Improvements
On Sunday, 23 June 2013 13:18:29 UTC+10, John Larkin  wrote:
:  
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my  
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rs,  
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<snip>

Start-up is interesting. Only simulating the first 5 msec does give a sligh
tly optimistic picture. V(drain) was creeping up at 5msec, so I ran the sim
 a second time, for 10msec, and U1 turned itself off again at 5.5msec. and  
back on again at 6.6msec, off at 7.12msec and on again at 7.65msec.

U1 was still switching at 10msec, but the circuit was not entirely settled  
down. I was tempted to run a third time, it for 20msec, but it's your can o
f worms ...

--  
Bill Sloman, Sydney


Re: Boost Converter Efficiency Improvements
John Larkin wrote:
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https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Boostback_1.jpg
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a typ of
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it's
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Not sure if it's that much but in my case (or my clients') alone it's in
the six digits by now. LTSpice takes a ton of risk out of designs.


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a
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It is a SEPIC. Most of my SEPICs have coupled inductors, aside from
smaller magnetics that let's you play with the EMI footprint:

http://www.ti.com/lit/an/slyt309/slyt309.pdf

The real deal would be to design one that's synchronous. LTC has a
synchronous boost chip but I haven't yet figured out a way to
efficiently use that as a synchronous SEPIC. It is possible, of course,
but the schematic gets very busy and big. Never had enough available
real estate to do that.


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uses
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who
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Dual cores have less air gap, it's tough to get small flyback
transformers that are substantially better than k=0.95.

The LT3757 is a nice chip. I used it a lot, including for some very
unorthodox non-switcher circuits.

[...]

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements

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a typ of
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5:1
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OK, I re-invented the sepic converter.

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I've developed an aversion to synchronous switchers. Too many of them have
created astounding EMI problems. The crossover is inherently nasty.

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uses
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I tried charging a 1000 uF cap in the sim. It ran for 10 hours, created a 10
gbyte .raw file, and it was only halfway up to my target voltage. I stopped it.
Got to finish my book, anyhow.

LT3757 is a nice chip. Have you seen any funnies? It has enough external
components to let me tune everything, but it's not too smart like some other
chips.

We recently had a few failures in LTM8023's. We sent one back to LTC and
insisted on a failure analysis. The results finally came back:

1. It's our fault.

2. They will change their die attach method as part of their "continuous process
improvement" program.


--  

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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<snip>
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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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I've done several fairly simple SMPS designs, which worked fine, but now
I'm going to have to get good at it.  My usual way of doing that sort of
thing is to get a good upper level undergraduate text and read it like a
novel, maybe do some of the exercises, and then just start in doing the
work.

Ideally it would cover the ins and outs of the major converter families,
and talk about when and why you'd use one or another, and what to watch
out for.  (A lore book, in other words.)

Any suggestions?  (Amazon reviews of Maniktala's books are very
positive, but he seems to have written about 5 of the same book.)

Thanks

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Boost Converter Efficiency Improvements
On Sun, 23 Jun 2013 11:48:28 -0400, Phil Hobbs

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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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but uses
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inductors, who
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it.
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I don't have any books on switchers. I guess I've just learned stuff from data
sheets and appnotes and other guys and experimenting.

Some lore:

Iron powder cores can get really hot.

Switching speeds in IC converters are getting crazy, a couple ns rise/fall. The
amps/second are getting scary. External fets are good because you can add gate
resistors to slow things down.

Synchronous switchers can be really nasty. My un-favorite waveform:

https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/LM3102_Switcher_Rise.JPG

I just spun a PCB to take out a couple of LTC3411's that were making more RF
than a customer liked in his system. The big spectral lines were harmonics of
the switcher frequency, in the 5-9 MHz range.

LTM8023s are nice and quiet. As are the older National Simple Switchers.

PCB loop currents really matter.

Ferite beads around switchers are often useful if you have any low-level stuff
on the same board.

You can charge pump off switching nodes, or make voltages off windings added to
the main inductor.

Continuous mode is great.

Tantalums explode. Polymer alums and ceramics don't.  

Switchers have negative input impedances, so can have startup problems. Some
wall-warts can't kick off some switchers. Use soft-start if it's available, and
reset it!

It's fun to make your own switchers.


There must be a lot more.


--  

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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it's
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and
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almost a
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any
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but uses
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inductors, who
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it.
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They can also spectacularly disintegrate. I learned that lesson as a
teenager, trying to squeeze 1200 watts of RF through a T200-2 because I
"invested" the money for the 2nd core I should have stacked on into a
crate of Pilsener beer. The result ... *KABOOM*


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Couldn't it be dithered?


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And nothing beats 4oz copper :-)


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Yup. And those make for interesting conversations in design reviews.


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Having seen orange and green clouds from exploding tants, I wonder
whether I might have breathed stuff that has already shortened my life
span ...


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Switchers can make other switchers go totally berserk even after start-up.


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Some of it is etched as scars into the Formica of my lab bench.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements
John Larkin wrote:
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but it's
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huge
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inductor and
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almost a
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any
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but uses
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10
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it.
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other
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Thanks, I've gleaned quite a few pointers from you and others on SED.  
The switchers I've made previously were either roll-my-own hysteretic
bucks or LM2594-based bucks and inverters.  Probably the most fun one
was a hysteretic buck regulator for driving heaters in a
high-performance temperature control loop for a passive-cavity
stabilized laser.   I got about 30W out of it with nanovolt ripple and
nanoamp current noise injection into the upstream supply.  Good
medicine, but of course the peak efficiency was only about 80%.

I've become a fan of using computer wall warts for instrument power,
because they have easily enough output for just about anything I do, and
they're cheap and reliable.  Since they produce 16-20V, the switcher
efficiencies aren't too bad, and using some nice Coilcraft dual-winding
toroids I have a range of things I can do with them without dying from
interference.    

I read a good book on photocathodes the other day, and learned a lot.  I
really like doing that.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Boost Converter Efficiency Improvements
On Sun, 23 Jun 2013 13:10:53 -0400, Phil Hobbs

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but it's
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all
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but uses
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data
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One idea I had was to taper a fiber really small and deposit a photocathode on
the end. Shoot a lot of light into the fiber, and you get a really small
electron emitter, like for a cheap student SEM.



--  

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

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oscillators, but it's
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That sort of thing has been done in the optical microscope world, e.g.
in Eric Betzig's papers on near-field scanning optical microscopes
(NSOMs) from the late 1980s and early '90s.

Around the same time, some of my fellow IBM Yorktown folks (Jean-Marc
Halbout and co.) used photocathodes deposited on fibre facets
illuminated by picosecond lasers, to make stroboscopic SEMs.

It's a cute idea.  The basic issue IIUC is that even way up in the gun,
SEM vacuums are too dirty for caesium-activated photocathodes to last
very long.

Cheers

Phil

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Boost Converter Efficiency Improvements
On Monday, 24 June 2013 04:10:44 UTC+10, Phil Hobbs  wrote:
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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.  
  
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> > >> >> >> coupled. ...
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> >> >> voltage. I stopped it.  
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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.
  
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You can use differential pumping to make the gun area less dirty, but you need
moving parts and lubricants in the scanning chamber ...

--  
Bill Sloman, Sydney


Re: Boost Converter Efficiency Improvements

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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?

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

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

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements

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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.


--  

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

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Re: Boost Converter Efficiency Improvements

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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?
  
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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.
  
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That makes a BIG difference!
  
Thanks.

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Re: Boost Converter Efficiency Improvements
On 6/23/2013 9:50 PM, JW wrote:
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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.

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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.
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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


--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Boost Converter Efficiency Improvements
On 06/24/2013 08:59 AM, Phil Hobbs wrote:
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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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Re: Boost Converter Efficiency Improvements

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

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

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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.

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