high voltage charge pump

Anyone familiar with a high voltage charge pump designed as a step down power supply? The voltage is between 175 & 200. Numerous high voltage versions exist using inductors, (Onsemi has one that is "self supplied" which is attractive) but not a one that works with just a capacitor. Are there any out there I've missed?

Hul

Reply to
Hul Tytus
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Capacitor step-up supplies are called Cockcroft-Walton generators and a similar form are Marx generators. An inverse version of the circuit can do step-down. We encountered a fellow, Steve Cerwin, who promoted that form. Crazy, we thought, but went ahead anyway, and wrote it up for the AoE x-Chapters, section 9x.15.5, page 439. Capacitors are charged in series, but discharged in parallel. We show a circuit that does 120 Vac to 24 Vdc, using six capacitors, and 14 diodes, awk! The output current is stepped up, of course. But, just because you can do it, that doesn't mean you should.

--
 Thanks, 
    - Win
Reply to
Winfield Hill

AFAIR the step down cap supplies is not that bad

7 stages or more sounds like a nightmare, but since individual voltage is low, the process can be low voltage and thus cheap

That said, I am yet to see one that can compete with inductor step down

Cheers

Klaus

Reply to
Klaus Kragelund

Win - In this case, the existing power supply is between 175 & 200 volts. The needed supply is 12 volts. Similar to a nonisolated dc supply from a 115 volt ac line I suspect there is such a device on the market, but proper search terms are required.

Hul

W> >

Reply to
Hul Tytus

You're going the wrong way, Klaus. Take a look at the message to win.

Hul

Klaus Kragelund wrote:

Reply to
Hul Tytus

Of course there is, but it'll most likely be transformer based (an inductor will have too poor a duty cycle). No capacitive circuits, such as I mentioned will be found. (There is low-power AC-to-DC, using a single cap, which we cover in some detail, but that's another story).

What you're forgetting is that most AC offline to low-V DC converters start with a bridge rectifier.** In the case of 120Vac, they're internally working from about 170Vdc on their bulk capacitor. Many work up to 230Vac, which more than covers your range. They convert down to all types of DC voltages. But they're happy with DC as an input. So you simply hook up your DC source to one of these "AC supplies", and hey, Bob's your uncle.

** Inspect to be sure there's a input bridge rectifier
--
 Thanks, 
    - Win
Reply to
Winfield Hill

The level-shifting required to make switches for the whole voltage range is one problem, and the high inrush currents when capacitors are connected (like, only limited by the switch resistance) is another. Microscopic switches can get hot FAST. Inductance solves the inrush problem, but once you go with power inductors, the capacitors aren't required.

Reply to
whit3rd

I'm imagining a wooden drum with brass shim contacts, a bank of paper caps and a small motor. Probably feeding a CLC filter, and thence to a post-WW1 radio.

NT

Reply to
tabbypurr

I don't think so

See example:

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Page 25, 48V to 12V switched capacitor high efficiency solution.

A 200V DC type might exist

Reply to
Klaus Kragelund

c.pdf

Page 89 of this excellent danish thesis :-)

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_Fan_20180422_Orbit.pdf

380V to 95V (4:1). Add a couple of more stages, and your ratio is solved. T his is not easy stuff though, plenty of easy solutions are available. Pick any:

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Reply to
Klaus Kragelund

The advantage is at low power. I built a 6 stage capacitive divider 48V to 5V at max 10 microamperes input (on-hook POTS 48V). Microamp inductor based buck converters do not appear to be easy.

piglet

Reply to
Piglet

There was the Harris HV2405 in the late 1980s but that was AC input - it charged the capacitor on the leading portion of the ac line waveform and disconnected when it exceeded the output voltage. Won't work from a DC supply.

Did you specify if the HV input is AC or DC and how much current is demanded at 12V?

piglet

Reply to
Piglet

Klaus, if you come across one spec'd to the higher voltage, let me know.

Hul

Klaus Kragelund wrote:

Reply to
Hul Tytus

Easy! Just run them discontinuous at low pulse rate. Many switcher chips will automatically go into burst mode at low load, too.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
jlarkin

Right, the problem is underspecified.

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John Larkin         Highland Technology, Inc 

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Reply to
jlarkin

Input varies between 150 & 200 volts dc. Current is at the 12 volt output is

60 ma. There will probably be a 6 volt negative output also but that will cause little added circuitry. Simply stated, 2 npn's, 1 pnp, 6 resisters & 2 1nf capacitors comprise the device. That''s doable but cumbersome in pcb real estate and design time. An integrated package would be a neater fix.

Hul

Piglet wrote:

Reply to
Hul Tytus

Schematic? A charge pump may be no more efficient than resistors.

People usually bottom-post on usenet. Mixed posting gets confusing.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
jlarkin

in my experience the only types of charge pumps which aren't dreadful are CW multipliers to make high voltages at very small currents, and the types that come in IC packages that can use techniques like fractional conversion to improve their efficiency/regulation and can use internal switches that have had their parameters tuned to suit the chip application.

Every other time I thought I'd use a roll-your-own charge pump for something I've ended up going inductor-based because naive charge pumps made with logic or discretes suck harder IRL than the by-the-book calculations would lead you to believe

Reply to
bitrex

Using one capacitor and one diode to boost e.g. 3.3V logic output square wave to ~4.something to reliably drive a white or blue LED at a few mA is OK too but it's not really high-investment charge pump design here

Reply to
bitrex

Something like this works...

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but the boost ratio is small and efficiency doesn't matter much.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
jlarkin

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