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Re: Boost Converter Efficiency Improvements
On Sun, 16 Jun 2013 08:37:03 -0700, John Larkin

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Oh, the other issue is that it will probably need snubbing, which
costs efficiency. A single-inductor continuous-mode boost converter
doesn't need a snubber.


--  

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
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Re: Boost Converter Efficiency Improvements
On Tue, 18 Jun 2013 11:57:00 -0700, John Larkin

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<SNIP>

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Yes, I saw that mentioned somewhere else in the thread. I went for a  
250V FET, thinking it would be able to cope without any snubbing. The  
highest voltage I'm seeing is only 135V though. And then only for  
10ns, right after switch off, before it settles back to 110V or so.

I'll post a trace in ABSE, under this subject heading.


Dave.


Re: Boost Converter Efficiency Improvements
Le Tue, 18 Jun 2013 20:58:21 +0100, David Jordan a écrit:

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You don't need any snubber for a two inductor boost too. At least the one  
you use with 2 rectifying stages. That is with a properly wired circuit  
(low parasitic inductances).

How did you connect your scope probe?
The 25/30V overshoot might be a measurement artefact due to your probe  
5-6" ground lead (check the resonnant frequency which probably is circa  
100MHz)


--  
Thanks,
Fred.

Re: Boost Converter Efficiency Improvements
On Tue, 04 Jun 2013 21:15:43 +0100, David Jordan wrote:

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Two diodes in a SEPIC?  The SEPIC schematic that I'm familiar with only  
has one.

??

--  
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
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Re: Boost Converter Efficiency Improvements
wrote:

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I posted the schematic earlier in the thread. It's a multiplying SEPIC
so the big difference is the 2nd inductor is connected to the output  
of the first stage, rather than ground.

In this case, the first stage boosts 12V to 100V and the second stage  
adds another 100V on top of that. The peak voltage across the FET and
diodes is only 100V but the capacitor in the 'middle' takes a beating.

Have a look at Linear's AN-1126. Figures 6 to 8 show the progression
quite nicely.


Dave.


Re: Boost Converter Efficiency Improvements
On Wed, 05 Jun 2013 20:22:57 +0100, David Jordan wrote:

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Have you considered just ganging two boost converters?  About the only  
extra component you'd have would be another FET.

Boost from 12 to 50 or so, then from 50 to 200.

--  
Tim Wescott
Control system and signal processing consulting
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Re: Boost Converter Efficiency Improvements
On Wed, 05 Jun 2013 14:56:22 -0500, Tim Wescott

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That does work but I need to make the output capacitor on the first  
converter quite large to keep the 50V stable. I also end up with two  
loops to control and the 2nd converter has a very low duty cycle,  
which I'm trying to avoid. If the load current was reasonably constant
I could possibly run one at a fixed duty cycle.

It splits the ratio down to 2x 1:4 rather than a single 1:16 which is  
nice but it makes things a bit more complex in the software driving  
it.

If the load current suddenly drops to zero, or there's a short, I  
don't want it to go *phut*. At the moment, If the output voltage rises
to, say, 10V above the setpoint, I've lost control because the load  
current has suddenly dropped. This takes a few milliseconds to happen  
which is plenty of time for the software to notice and cut off the FET
drive until it's back within range. It'll do a sort of burst mode  
control with very low loads.

I don't like the idea of burst mode control with two interacting  
converters.


Dave.


Re: Boost Converter Efficiency Improvements
David Jordan wrote:
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That's the trick, run one of them hog-tied. But put in a governor, one
that only comes on if it starts over-revving.


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Best to put in a governor. Whenever you use SW loops to control a
switcher there should always be a redline limiter anyhow. I have seen it
too often, someone whips out a cell phone, turns it on, the uC gets
perturbed and loses it, a spindle drive runs the sled past the limit
switch, way past ... *KABLAM*


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It's been done before. But in the design review it results in initial
utterances of disgust :-)

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements
wrote:

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<SNIP>

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Probably a good idea. I was going to put a shunt in the FET source to  
cut the gate drive on overcurrent (if the SW leaves the drive pin high
for too long) but I could also do a similar thing if the output  
voltage rises way too high.

For real fun, you want to try using a uC to control a buck regulator  
that supplies the power *for* that uC from a much higher voltage rail.
Startup is the best bit :-) I breadboarded in once and sort of got it  
working, but never dared use it.


Dave.


Re: Boost Converter Efficiency Improvements
David Jordan wrote:
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I've seen worse: 115V AC (!) was supplied to a port pin, via a resistor,
cap or something. The parasitic substrate diode acted as a zero-Dollar
rectifier. The voltage was not regulated but was kept within an allowed
band via executing dummy code during times where the uC would normally
be almost idle, so that the uC presented an almost constant load.

The problem: Nobody told me. So here I was, touching the OSC-IN pin with
a scope probe, the crystal hicced up ... *BAM* ... had a crater in the
uC :-)

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements
Le Thu, 06 Jun 2013 14:53:18 -0700, Joerg a écrit:

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LOL!
Good one but I fail to see how this capacitively coupled supply could  
stand the first mains transient.

Hey, if you carefully choose the uC (latch-up wise) you can even use it  
for a free crowbar protection :-)


--  
Thanks,
Fred.

Re: Boost Converter Efficiency Improvements
Fred Bartoli wrote:
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There was an electrolytic on the other side. Also, they ran the uc at
the lower voltage limit with a slow clock.

Of course this does not help in some of the markets I have to develop
for. Like islands where sometimes Felipe gooses a recalcitrant generator
by reaching in and pushing the throttle by hand.


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I was amazed how much abuse such a little uC can take.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements
On Tue, 04 Jun 2013 21:15:43 +0100, David Jordan

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Here's a little step-up converter that I plan to use in a laser driver, to
charge a capacitor bank. It's a tapped-inductor "boostback" circuit. LT Spice
claims about 85% efficiency. I included the transformer resistances but no core
loss or leakage L. The snubber costs a per cent or so. Needs a little tuning,
but looks good. The L and the IC are both tiny.


Version 4
SHEET 1 1840 680
WIRE -320 144 -384 144
WIRE -176 144 -240 144
WIRE -48 144 -176 144
WIRE 112 144 32 144
WIRE 240 144 192 144
WIRE 304 144 240 144
WIRE 432 144 384 144
WIRE 592 144 512 144
WIRE 640 144 592 144
WIRE 752 144 704 144
WIRE 848 144 752 144
WIRE 1008 144 848 144
WIRE 1088 144 1008 144
WIRE 1136 144 1088 144
WIRE 592 176 592 144
WIRE -384 256 -384 144
WIRE 1008 256 1008 144
WIRE 1136 256 1136 144
WIRE -176 272 -176 144
WIRE -80 272 -176 272
WIRE 80 272 -80 272
WIRE 592 288 592 256
WIRE -176 304 -176 272
WIRE 752 304 752 144
WIRE 848 304 848 144
WIRE 80 336 80 272
WIRE 240 336 240 144
WIRE 592 384 592 352
WIRE -384 400 -384 336
WIRE -80 400 -80 272
WIRE 0 400 -80 400
WIRE 1008 400 1008 320
WIRE 1136 400 1136 336
WIRE -176 416 -176 368
WIRE 752 448 752 384
WIRE 752 448 320 448
WIRE 848 448 848 368
WIRE 848 448 752 448
WIRE 1040 464 1008 464
WIRE 1056 464 1040 464
WIRE 0 496 -80 496
WIRE 752 496 752 448
WIRE 1008 496 1008 464
WIRE -80 528 -80 496
WIRE 752 608 752 576
WIRE 1008 608 1008 576
WIRE -80 624 -80 592
WIRE 160 624 160 560
FLAG 1008 608 0
FLAG 1008 400 0
FLAG 1136 400 0
FLAG 1088 144 VP
FLAG 160 624 0
FLAG -80 624 0
FLAG 752 608 0
FLAG 592 384 0
FLAG -176 416 0
FLAG -384 400 0
FLAG 1040 464 EFF
SYMBOL ind2 96 160 R270
WINDOW 0 -35 52 VTop 2
WINDOW 3 -43 51 VBottom 2
SYMATTR InstName L1
SYMATTR Value 2µ
SYMATTR Type ind
SYMBOL ind2 288 160 R270
WINDOW 0 -36 59 VTop 2
WINDOW 3 -40 61 VBottom 2
SYMATTR InstName L2
SYMATTR Value 18µ
SYMATTR Type ind
SYMBOL diode 640 160 R270
WINDOW 0 -40 28 VTop 2
WINDOW 3 -44 29 VBottom 2
SYMATTR InstName D1
SYMATTR Value ES1D
SYMBOL cap 992 256 R0
WINDOW 0 -59 -5 Left 2
WINDOW 3 -56 28 Left 2
SYMATTR InstName C1
SYMATTR Value 1µ
SYMBOL res 1120 240 R0
WINDOW 0 -51 29 Left 2
WINDOW 3 -53 67 Left 2
SYMATTR InstName R1
SYMATTR Value 1K
SYMBOL res -64 160 R270
WINDOW 0 -38 53 VTop 2
WINDOW 3 -44 54 VBottom 2
SYMATTR InstName R3
SYMATTR Value 0.25
SYMBOL PowerProducts\LT3467 160 448 R0
SYMATTR InstName U1
SYMBOL cap -96 528 R0
WINDOW 0 -55 18 Left 2
WINDOW 3 -60 53 Left 2
SYMATTR InstName C2
SYMATTR Value 20n
SYMBOL res 736 288 R0
WINDOW 0 -54 41 Left 2
WINDOW 3 -67 76 Left 2
SYMATTR InstName R2
SYMATTR Value 400K
SYMBOL res 736 480 R0
WINDOW 0 61 43 Left 2
WINDOW 3 56 79 Left 2
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL cap 832 304 R0
WINDOW 0 57 22 Left 2
WINDOW 3 49 56 Left 2
SYMATTR InstName C3
SYMATTR Value 3.3p
SYMBOL res 576 160 R0
WINDOW 0 -47 53 Left 2
WINDOW 3 -57 89 Left 2
SYMATTR InstName R5
SYMATTR Value 4K
SYMBOL cap 576 288 R0
WINDOW 0 -51 25 Left 2
WINDOW 3 -63 60 Left 2
SYMATTR InstName C4
SYMATTR Value 22p
SYMBOL cap -192 304 R0
WINDOW 0 -50 18 Left 2
WINDOW 3 -60 50 Left 2
SYMATTR InstName C5
SYMATTR Value 10m
SYMBOL res -336 160 R270
WINDOW 0 -38 55 VTop 2
WINDOW 3 -41 53 VBottom 2
SYMATTR InstName R6
SYMATTR Value 10m
SYMBOL voltage -384 240 R0
WINDOW 0 48 47 Left 2
WINDOW 3 53 80 Left 2
SYMATTR InstName V2
SYMATTR Value 9
SYMBOL bv 1008 480 R0
WINDOW 0 -88 57 Left 2
WINDOW 3 -229 181 Left 2
SYMATTR InstName B1
SYMATTR Value V = 100 * ( V(VP)**2 / 1000 ) / ( I(R6) * 9 )
SYMBOL res 416 160 R270
WINDOW 0 -36 54 VTop 2
WINDOW 3 -41 54 VBottom 2
SYMATTR InstName R7
SYMATTR Value 1.2
TEXT 192 96 Left 2 !K L1 L2 1
TEXT 456 616 Left 2 !.tran 1m
TEXT 80 48 Left 2 ;Coilcraft LPR4012-103DMLB
TEXT 376 512 Left 2 ;D140 BOOST CONVERTER
TEXT 424 560 Left 2 ;JL  June 21 2013


--  

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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core
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Sure? When I ran it R5 showed 140mW, which would come to around 5%. Why
not just let the inductor ring out?


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What kind of transformer are you using for L1/L2?

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements

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core
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The ringing might be an EMI issue. I'll probably put the snubber parts on the
layout (maybe another one on the fet drain?) in case they are needed.

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It's a Coilcraft part. The part number is on the schematic. Tiny little thing.

C1 is 4400 uF in real life. Charging that up will simulate in a bit over 5
hours, 1 second of real time. I could build one and test it a lot faster than
that.

I can't trust this sim anyhow.  

https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Boostback_1.jpg

The LTC data sheet gives the max switch current limit as 2.5 amps, with a typ of
1.8.  




--  

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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Spice
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core
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Usually not for radiated, it's typically under 30MHz and has little
energy in the radiated field. For conducted you need good line filtering
anyhow because of the switch current chop and its harmonics.


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http://www.coilcraft.com/pdfs/lpr4012.pdf

Cool, thanks for the hint! Can't get pricing right now. They have this
pathetic "system" where if their cookie has been erased you have to
enter name, address, shoe size and whatnot to get the price. Over and
over again.


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That's also what happens if the switcher chip is not a behavioral model
like LTC's are. It'll be more accurate but sometimes I had the office
temp rise several degrees, just from the PCs. That's ok in January but
not so much in August (got to get a 2nd evap cooler here).


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I think it's fairly realistic if you correct k and maybe add some
parasitics in there. Datasheet says k=0.85.


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of
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It looks like your design is in the healthy range. Got to correct k to
the datasheet value though. Also, you'd probably use a larger soft-start
cap in real life.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements
Joerg wrote:
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Spice
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core
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thing.
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of
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Minor addition: The winding resistances for the indutor you chose are
0.6ohms and 3.71ohms. Instead of providing extra resistors you can enter
them in the inductor itself and click the "make visible" check box.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Boost Converter Efficiency Improvements

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Spice
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core
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the
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thing.
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than
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typ of
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I'm looking into doing a simple single-inductor boost, reasonable at my 5:1
boost ratio. It's much simpler, less junk to snub, no leakage inductance!


--  

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

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Re: Boost Converter Efficiency Improvements
On Sat, 22 Jun 2013 15:01:18 -0700, John Larkin

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to
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Spice
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no core
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the
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thing.
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than
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typ of
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Simulating switchers isn't as bad as simulating crystal oscillators, but it's
close.


--  

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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https://dl.dropboxusercontent.com/u/53724080/Circuits/Power/Boostback_1.jpg
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typ of
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At 5:1 I'd definitely do that. I use direct step-up for anything up to
10:1, sometimes more, depending on how much power the switcher has to
deliver.


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LTSpice is really nice for that job. Of course, that means that for all
not cost-critical applications I use LTC chips. Which I guess was the
purpose why they gave us LTSpice.

--  
Regards, Joerg

http://www.analogconsultants.com/

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