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Re: charge pump/boost converter
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well, a buck and a buck-boost are kind of similar  

                   ====
  (1)----.  .--+---mmmm-+--(3)  
         ----  |        |    
         ---.  |        |    
            |  |        |        
        `----------magic
           |        |
           `--|<----+--(2)
            
            
  "magic" senses the voltage between 2 and 3 and drives
  the switch apropriately, possibly with a vcc input  
  from 1 also, I expect it's an off-the shelf switcher chip.
    
            
--  
umop apisdn


Re: charge pump/boost converter
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Of course, the same is true of the $1.50 eBay buck converters. To make a negative supply, you ground the output apply power between there and the +in wire, and let it pump its 'ground' pin negative. (You knew that already.)

Cheers

Phil Hobbs

Re: charge pump/boost converter
On Wed, 22 Jul 2015 01:27:44 -0700 (PDT), Phil Hobbs

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Does that always work? I hadn't thought it through.

Given this horrible flu thing that I have, there are lots of things
I'm not thinking through. I think I'll draw a schematic; that's easy.




--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: charge pump/boost converter
Den onsdag den 22. juli 2015 kl. 19.37.31 UTC+2 skrev John Larkin:
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it is shown in some datasheets/appnotes

http://www.digikey.com/en/articles/techzone/2012/oct/generating-negative-output-from-positive-input-voltage

-Lasse  


Re: charge pump/boost converter
On 07/22/2015 01:37 PM, John Larkin wrote:
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I do it a fair amount with 150 kHz Simple Switchers (my fave) and have  
never had a problem.  You design a buck that goes from Vin-Vout to  
-Vout.  The two issues are:

1. The voltage stress on the IC is Vin-Vout rather than Vin

2. The feedback pin isn't ground referenced, so you can't put a cap  
multiplier inside the DC loop, which I like to do when I can.  (You use  
split feedback, as with driving a capacitive load with an op amp and  
series resistor.)  There are bandaids for this, of course, e.g. hanging  
a TLV431 on the cap multiplier.

Get well soon!

Cheers

Phil Hobbs



--  
Dr Philip C D Hobbs
Principal Consultant
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Re: charge pump/boost converter

It's well past midnight for me, sorry excuse, but a cap multiplier inside a DC loop in a buck or boost , what the heck is that?  

Cheers

Klaus  

Re: charge pump/boost converter
On 7/23/2015 7:22 PM, Klaus Kragelund wrote:
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Capacitance multipliers are amazingly good at cleaning up SMPSes, but  
they're a bit squishy on the DC regulation.

If you close the DC loop of an LM2594 (or something like that) around  
the emitter of the cap multiplier, and the AC loop around from the  
switcher's output, you get the best of all worlds: decent efficiency and  
very very low noise.

It's pretty simple: normal buck + cap multiplier, FB pin driven by a  
resistor from the cap multiplier output (to keep the regulation  
reasonable) and a capacitor from the FB pin to the SMPS output (to keep  
the loop stable).


Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: charge pump/boost converter
On Friday, July 24, 2015 at 2:04:50 AM UTC+2, Phil Hobbs wrote:
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Ok, but for the efficiency, you loose some power in the capacitance multiplier. Like those made for class A amplifiers, right?

Cheers

Klaus

Re: charge pump/boost converter
On 7/24/2015 9:18 AM, Klaus Kragelund wrote:
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Don't know about class A amplifiers, at least if you mean audio.  A cap  
multiplier is just an emitter follower hung on an N-pole RC lowpass.

For what I do, the tradeoff is generally between losing a bit of  
efficiency on a switcher, or having to use a shunt-regulated cap  
multiplier as a linear regulator, because switcher noise is intolerable.

As I often repeat, "there's SMPS quiet and then there's instrument quiet."

Cheers

Phil Hobbs


--  
Dr Philip C D Hobbs
Principal Consultant
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Re: charge pump/boost converter
On 7/24/2015 9:26 AM, Phil Hobbs wrote:
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Oh, and if you're desperate for that last half a volt, you can use a  
low-sat NPN and source a little current into the RC from the input  
supply.  That'll reduce the dropout voltage.  You do have to keep enough  
headroom for V_CEsat plus the peak-to-peak ripple.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: charge pump/boost converter
On Tuesday, July 21, 2015 at 6:21:55 PM UTC+2, John Larkin wrote:
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73-2-ND/4006941
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_oscillator1.htm
  
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If it existed.

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We were talking about transformers rather than inductors. Even with inducto
rs one has to be aware that a small 100uH inductor will saturate or burn ou
t rather earlier than a larger (and more expensive) part. If you know enoug
h to be aware of self-resonant frequencies, the situation gets even more co
mplicated.

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If you put in a little more effort you might be able to find a coil winder  
who didn't take weeks.
  
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We were talking about transformers, rather than inductors. Even so "tons" i
sn't a useful measure.
  
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If they provide the performance you need, fine. +48V from +5V USB doesn't s
eem to be a mass market application.

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This thread doesn't seem to have thrown up a specific "standard switcher" f
or bitrex's application.
  
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Vapour-ware is so much easier to generate.

--  
Bill Sloman, Sydney

Re: charge pump/boost converter
On Tuesday, July 21, 2015 at 5:52:30 PM UTC+2, Phil Hobbs wrote:
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3-2-ND/4006941
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oscillator1.htm

Then you probably need to learn a bit more about the ranges of cores and fo
rmers available off the shelf.

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Obviously. But neither you nor John do much of that.

Transformers and inductors offer rather a lot of variables, so getting one  
right for a particular application isn't "micro-optimisation".

John Larkin wanted a tune-able inductor which he could have had wound onto  
an off-the-shelf former for an off-the-shelf core that came with a tuning s
lug (I gave him links to both), but he found that too hard.

Transformers for low volume production aren't mass-produced, and there are  
plenty of small winding shop that will make them for you pretty cheaply, or
 at least wind the wire onto formers. They'll probably clip the cores aroun
d the wound formers for very little more.

--  
Bill Sloman, Sydney

Re: charge pump/boost converter
On 7/18/2015 8:39 AM, bitrex wrote:
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Interesting! Anyone know how quiet is the power coming out of a USB port  
(vs load)?

Re: charge pump/boost converter
On 7/18/2015 12:38 PM, John S wrote:
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I don't think there is any spec on that other than the voltage tolerance  
of 4.75 to 5.25 volts.

--  

Rick

Re: charge pump/boost converter
On Sat, 18 Jul 2015 09:39:34 -0400, bitrex wrote:

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Boost or flyback, and if noise is an issue then make 50V and follow it  
with a linear regulator.

--  
www.wescottdesign.com

Re: charge pump/boost converter
On 7/18/2015 1:02 PM, Tim Wescott wrote:
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Linears only reduce noise in their active bandwidth, often no more than  
100 kHz.

--  

Rick

Re: charge pump/boost converter
On 7/18/2015 3:02 PM, rickman wrote:
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A shunt-regulated cap multiplier can do a _lot_ better.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: charge pump/boost converter

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That's usually good enough.  When it isn't, there are things like TI's
LP38798, which extend that another decade or more.  After that, use a
passive filter.


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