another goofy boost converter architecture

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Sort of a hybrid of a flyback and a sepic. I call it a skeptic converter.

I don't trust the efficiency calculation, especially when it goes over 100%.


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TEXT 1184 576 Left 2 !.tran 0 4m 0 10n uic
TEXT 1168 480 Left 2 ;SKEPTIC CONVERTER
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TEXT 160 808 Left 2 ;USE LM393



--  

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

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Re: another goofy boost converter architecture
On Wed, 03 Jul 2013 21:53:35 -0700, John Larkin

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Interesting equation for efficiency ?>:-}
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: another goofy boost converter architecture
John Larkin wrote:
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Patent it, quickly! :-)

The reason for that are the very large caps C3 and C6 which are not in
your efficiency calc. If you take those out or set them to 50pF or
something, it's all in the green. Peaks at 92% on the ramp-up but then
efficiency really goes to pots as the output voltage comes up.

[SPICE file]

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: another goofy boost converter architecture
wrote:

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That sure is a strange looking expression for efficiency.  Where did
that come from?  Wouldn't efficiency be a long average of output power
divided by a long average of input power.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: another goofy boost converter architecture
Jim Thompson wrote:
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Yeah, technically you have to integrate. But with switchers it does not
require long averages if one does not use large caps in there. I found
that my simple non-integrated values jibe quite well with the circuit
later once it comes from the assemblers.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: another goofy boost converter architecture
wrote:

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Still a weird equation.  Who dreamt (or nightmared) that?

In PSpice Probe (post-processor) one uses the "avgx" function and
average over a cycle (if you like).
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: another goofy boost converter architecture
wrote:

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Power_out / Power_in sounds like "efficiency" to me.



Re: another goofy boost converter architecture
On Thu, 04 Jul 2013 12:18:24 -0700, John Larkin

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But I*V is _instantaneous_ power, not average over a cycle, or over
some longer period.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: another goofy boost converter architecture
On Thu, 04 Jul 2013 13:32:01 -0700, Jim Thompson

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Makes no sense. I average it over the period of interest.

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My numerator and denominator are what the 9 volt supply has to furnish
and what the load (a cap, in this case) absorbs. I want to see
efficiency as a function of time, during charging, because that's what
I want to see.  

The filters on the input and output current make them plot nicely.
Real-life power supplies do, after all, have input and output bypass
caps. My customer's battery won't see the mosfet instantaneous
current; he cares about the current he can measure, and the total
energy he has to furnish, which is the data I'm generating.

I could add a bypass cap across the 9V source if that would make you
happy.  




Re: another goofy boost converter architecture
On Thu, 04 Jul 2013 14:11:11 -0700, John Larkin

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You totally missed (or evaded) the point.  Is anyone surprised?
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: another goofy boost converter architecture
On Thu, 04 Jul 2013 17:19:39 -0700, Jim Thompson

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You never say anything concrete. And nobody is surprised.

Post a equation that you think reports efficiency.



Re: another goofy boost converter architecture
On Thu, 04 Jul 2013 18:14:08 -0700, John Larkin

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I did already.  Wimp.  Wimp. Whine, Whine.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: another goofy boost converter architecture
On 7/4/2013 4:11 PM, John Larkin wrote:
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Well, John, make sure your "period of interest" includes energy returned  
as well as energy supplied.

John S


Re: another goofy boost converter architecture
wrote:

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What does that mean?




Re: another goofy boost converter architecture
On 7/4/2013 8:16 PM, John Larkin wrote:
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What is the load and the "period of interest"? (Your turn now).


Re: another goofy boost converter architecture
On 7/4/2013 8:16 PM, John Larkin wrote:
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I think I should back out of this thread. I do not understand your  
definition of efficiency because you have no load on your simulation. I  
always thought that efficiency was Pout/Pin. Since Pout is close to zero  
(steady state) your efficiency cannot be very good.

Good luck.




Re: another goofy boost converter architecture
On 7/4/2013 8:16 PM, John Larkin wrote:
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Well, sort of this...

Use the following for your behavioral source for efficiency:

V= 100 *idt( I(R6) * V(VP)  /  ( I(R8) * 9 ))/time

It does not go over 100%. If you see a flaw in the math, please ping me.

Cheers,
JohnS


Re: another goofy boost converter architecture
wrote:

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At time T in the sim, that gives the average of efficiency since
startup. That's not what I want to see; I want to see the "realtime"
efficiency vs time curve. If course, some amount of time averaging is
required to get a usable plot, which is why I have filtering.

Your equation has a gotcha too. 1 mw/1mw makes the same contribution
to the efficiency integral as 1w/1w, which doesn't seem fair to me.
The actual averaged efficiency might better be (integrated energy out)
/ (integrated energy in). That would be the ratio of two integrals,
not the integral of one ratio. But again, that's not what I want to
see.

There is no unambiguous, clearly right definition of efficiency here.
My equation is what I want to see.



Re: another goofy boost converter architecture
On Fri, 05 Jul 2013 17:20:19 -0700, John Larkin

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Your equation "clips" products greater than 120 or more negative than
zero.  What kind of gimmick is that?

The integral needs to encompass at least one cycle.  Your
"integration" is way short.

Unfortunately LTspice doesn't implement one of PSpice's Probe
niceties, AVGX... average over t=X.
        
                                        ...Jim Thompson
--  
| James E.Thompson                                 |    mens     |
| Analog Innovations                               |     et      |
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Re: another goofy boost converter architecture
On 7/5/2013 7:20 PM, John Larkin wrote:
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Okay.

ISTM that a better metric to determine how happy I would be with it, if  
it were mine, would be watt-seconds in the output capacitor divided by  
watt-seconds supplied by the source, calculated over the charging interval.

For curosity, I did that and I see that it puts 4.6 w*s into the output  
capacitor while using 5 w*s from the source. That would be about 92%  
efficient. Not bad.

Anyway, not my project, so have fun.




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