charge pump/boost converter

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For a hobby project, I'd like to be able to generate +48 volts or so  
from +5 volt USB.  Current requirements are small, maybe 15 mA or so?  
I'd like uh, low noise (I don't have an exact spec so this is just kind  
of existential at this point), so maybe a charge pump would be in order  
rather than a boost switcher?

Does anyone make a charge pump IC that I could feed an external clock  
to, with outputs suitable for running something like a Dickson pump?  
Maybe that would be too many stages to go from +5 to +48...

Re: charge pump/boost converter
On 7/18/2015 8:39 AM, bitrex wrote:
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My guess is that it would take 11 stages, possibly more.

Re: charge pump/boost converter
On 07/18/2015 10:25 AM, John S wrote:
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You can get modules that do most of that for a buck and a half on eBay.  
http://tinyurl.com/q2qkn2u will do 5->24V, and then a homemade  
single-stage charge pump will get you 48V.

Cheers

Phil Hobbs



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Dr Philip C D Hobbs
Principal Consultant
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Re: charge pump/boost converter
On 7/18/2015 10:51 AM, Phil Hobbs wrote:
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Oh wow, those are great.  They're cheap enough that I could just slap  
them into a "finished" product...


Re: charge pump/boost converter

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They do not have an isolated output. So connecting them in series to make 48  
volts will not work.


Re: charge pump/boost converter
On 7/18/2015 2:36 PM, Tom Miller wrote:
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Right, which is why I suggested the charge pump.  Of course the OP could  
get a buck converter module (about the same dough) and connect it to  
make -24, then work off the difference.

Cheers

Phil Hobbs

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

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That's a good idea.

Just a diode and capacitor need flipping.

And correct the feedback.



Re: charge pump/boost converter
On 7/18/2015 4:04 PM, Tom Miller wrote:
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Not even.  You ground the 'output' pin, and take the negative output  
from the 'ground' pin.  It pumps its 'ground' down by itself.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
Principal Consultant
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Re: charge pump/boost converter
On Saturday, July 18, 2015 at 11:33:21 AM UTC-7, Tom Miller wrote:
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The converters John suggested are isolated, you can stack them in series.
Phil only suggested using one non-isolated, then a charge pump.
So, they are not suggesting to stack the non-isolated converters.

Re: charge pump/boost converter
On Sun, 19 Jul 2015 09:54:42 -0700 (PDT), snipped-for-privacy@gmail.com
wrote:

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$1.49 with free shipping from China. That's crazy.



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And you can stack them on top of the +5 supply, to get another 5 volts
for free.


--  

John Larkin         Highland Technology, Inc
picosecond timing   laser drivers and controllers

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Re: charge pump/boost converter
A $1.50 boost and a $1.50 buck connected as an inverter gives the effect of stacking two of the fancier ones, using the isolation of the USB brick. Of course it may not work if the OP needs to use the 5V in the same circuit.  

Cheers

Phil Hobbs

Re: charge pump/boost converter
On 7/19/2015 2:04 PM, Phil Hobbs wrote:
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I am going to need +5/-5 and +48 unfortunately...

Re: charge pump/boost converter
On Sunday, July 19, 2015 at 2:26:18 PM UTC-7, bitrex wrote:
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Perhaps one cheap non-isolated and one expensive stack-up isolated.  A bit expensive, but still much cheaper than what you can build with discretes.

Re: charge pump/boost converter
On 7/19/2015 5:39 PM, snipped-for-privacy@gmail.com wrote:
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If I turn this hobby product into an actual product, space is also at a  
premium.  The current requirements of the -5 volt rail are modest - a  
while back someone pointed out a circuit that used a MAX232 to generate  
a negative rail for an entire board.  How would the "stack-up isolated"  
work?

Re: charge pump/boost converter
On Sunday, July 19, 2015 at 2:44:24 PM UTC-7, bitrex wrote:
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Yes, have John ('s suggestion) sitting on top of Phip ('s suggestion).  John would be totally isolated from the rest (Sorry, John, it's just a joke).  A Max232 can also generate the negative rail (probably -7 to -10) then regulate it to -5V.

Re: charge pump/boost converter
On Sun, 19 Jul 2015 14:59:32 -0700 (PDT), snipped-for-privacy@gmail.com
wrote:

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Snarl. Snap.


The same series of CUI bricks has a 5 to +-5 version. Or use an
LM2662.



--  

John Larkin         Highland Technology, Inc
picosecond timing   laser drivers and controllers

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Re: charge pump/boost converter
On Saturday, July 18, 2015 at 7:51:24 AM UTC-7, Phil Hobbs wrote:
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Easier to use a different chip (LM2585 has a slightly different pinout,
but almost exactly the same function as that XL6009, and goes to 60V).

Re: charge pump/boost converter
On 2015-07-18 6:39 AM, bitrex wrote:
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Too much hassle, too many stages. I'd use one of the flyback  
transformers they sell for power over Ethernet (PoE) and use it in reverse.

At this roughly 10:1 ratio a boost converter will also work and they are  
often less noisy. If you can cloc-drive it from or synchronize it to an  
ADC clock or something.

--  
Regards, Joerg

http://www.analogconsultants.com/

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

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Two of these

http://www.digikey.com/product-detail/en/PDS1-S5-S24-M-TR/102-2973-2-ND/4006941

with the outputs in series would work. They are fairly quiet, and you
could add a little filtering to help. At light loads, their output
tends to be a few per cent high. But then, 5 volts from USB may not
really be 5 volts.

For really quiet, consider some sort of sinewave drive step-up
transformer.

A diode-based charge pump would make less than 4 volts per stage, so
that would take a lot of parts.





--  

John Larkin         Highland Technology, Inc
picosecond timing   laser drivers and controllers

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Re: charge pump/boost converter
On Saturday, July 18, 2015 at 5:50:11 PM UTC+2, John Larkin wrote:
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A Baxandall Class-D oscillator - one step-up transformer and one inductor - would work well. MOS-FET transistors do a bit better than bipolar transistors, but Baxandall's paper rather pre-dates them.

http://sophia-elektronica.com/0344_001_Baxandal.pdf

http://sophia-elektronica.com/Baxandall_parallel-resonant_Class-D_oscillator1.htm

--  
Bill Sloman, Sydney

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