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...
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.
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.
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John Larkin Highland Technology, Inc
picosecond timing laser drivers and controllers
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.
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.
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.
or - would work well. MOS-FET transistors do a bit better than bipolar tran sistors, but Baxandall's paper rather pre-dates them.
lator1.htm
The 1959 Baxandall class_D oscillator isn't "failed". To quote from my web- site "The circuit is probably best known from Jim Williams' series of appli cation notes for Linear Technology, on high frequency inverters for driving cold cathode back-lights used in laptop computers (application notes AN45, AN49, AN51, AN55, AN61, AN65)." These apparently were Linear Technology's most popular application notes for quite a while.
It has been claimed that Jim Williams got the circuit from England, without the Baxandall label.
I do have a low distortion variant of the class-D oscillator, with a curren t mirror rather than the feed inductor, but that's not the low distortion o scillator I'm working on at the moment.
You are distinctly public-spirited in regularly reminding us that you are a n idiot, but you really don't have to do it quite as often as you do.
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