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What's a "charge pump"?

Very generally, the idea of charging capacitors and carrying the charges here and there. You can, for example, charge a number of capacitors in parallel from, say, a 9 volt battery, then disconnect them and rearrange in series and get N*9 volts, at least for a while. Simple diode-capacitor circuits (voltage doublers or multipliers) can be considered charge pumps, too. A Marx generator is an extreme charge pump.

PLLs sometimes use "charge pump phase detectors" which shoot short current blips, hunks of charge, into a capacitor to pump its voltage up or down.

I guess it's any circuit that depends on quantized charge to define its operation. This, like a lot of other circuit terms, is fairly vague.

John

Reply to
John Larkin
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--- It won't, because no matter how "powerful" the packets are, they've only got 5V from the supply across them, so you're stuck with 5V.

BUT...

You _could_ charge up a bunch of capacitors in parallel, and then hook them up in series, and discharge them into the cap you want to whack up to 15V, like this:

CHARGE

+5V---+-----+-----+-----+-----+-----+ | | | | | | [C1] [C2] [C3] [C4] [C5] [C6] | | | | | | GND---+-----+-----+-----+-----+-----+

DISCHARGE

+--[C1]--[C2]--[C3]--[C4]--[C5]--[C6]--+ | | | | +---------------->[C7]
Reply to
John Fields

Helo,

whats a charge pump, what does it do and how does it work? Is it true it can be used to step-up DC volatages?

tnx,

Steve

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Fat, sugar, salt, beer: the four essentials for a healthy diet.
Reply to
Steve Evans

Oh yeah Ive heard of diode voltage multipliers someplace.

So say I've only a pretty crappy low voltage available, like 5V say, and I want to momentarily whack a capactior up to say 15V, could I do it by pumping a short but powerful 'packet' (or *packets* ) of charge from the 5V source into it? Would the capactior store the excess charge in the form of excess voltage accross its plates if you get what i mean?

tnx

--

Fat, sugar, salt, beer: the four essentials for a healthy diet.
Reply to
Steve Evans

Steve Evans wrote: >

Another way to do this is with an inductive spike. Inductors like to keep current flowing through them. Thus, if you get current flowing, and then cut it off suddenly, the voltage at the point you cut it off will spike due to the sudden extra electrons (or lack thereof).

This is how DC-DC boost converters work. They have an oscillator that turns on and off current through an inductor, and tap the point where the inductor and transistor meet (the point with the voltage spikes) with a diode pointing away from the junction. They then charge up a capacitor with the 'packets' of charge that the inductor keeps sending in, regardless of the voltage. A feedback mechanism turns off the oscillator when the voltage reaches the point the circuit is designed to get to.

The amount of power that can be taken from a circuit like this is defined by the frequency and duty cycle of the oscillator, the inductance of the inductor, and the voltage across it when charging.

You can buy these dc-dc converters off the shelf for various voltages, or build them pretty easily. White light LEDs require about 4V to light, but they can be lit from a single 1.5V AA battery using a simple circuit like this.

--
Regards,
   Robert Monsen

"Your Highness, I have no need of this hypothesis."
     - Pierre Laplace (1749-1827), to Napoleon,
        on why his works on celestial mechanics make no mention of God.
Reply to
Robert Monsen

yes, it IS possible to get 12V from 5V, i've done it in a circuit needing

+12V/-12V for a few mA supply and only having 5V available you'll need an oscillator circuit giving a 0-to-5V wave (say a 555 circuit or something similar), and one voltage doubler for every output Carefull, using a TTL output is NOT enough due to the diode-drops and TTL usually going only swinging from 0.8 to 3V

(view in notepad using fixed font)

|| +--||------------+-------| |--+--o +12V | | |/| | | --- | | / | | || --- | +--||--+---| |---+ | | | |/| --- --- | | --- --- | --- | | | / | | | --- === === | | | | | o | +5V | | | |/| +--||------------+-------| |--+--o -12V | | || | | --- | | / | | |/| --- | +--||--+---| |---+ | | | || --- --- o | --- --- (osc) --- | | o / | | | --- === === === | ===

Oh yeah Ive heard of diode voltage multipliers someplace.

So say I've only a pretty crappy low voltage available, like 5V say, and I want to momentarily whack a capactior up to say 15V, could I do it by pumping a short but powerful 'packet' (or *packets* ) of charge from the 5V source into it? Would the capactior store the excess charge in the form of excess voltage accross its plates if you get what i mean?

tnx

--

Fat, sugar, salt, beer: the four essentials for a healthy diet.
Reply to
peterken

Alternatively you could get a high voltage (up to several hundred volts, albeit with very low current capability), by using any simple oscillator driving a miniature mains transformer in reversed mode.

Here's an example:

formatting link 

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Terry Pinnell
Hobbyist, West Sussex, UK
Reply to
Terry Pinnell

Tnx, Terry, thats not quite what I was getting at. lets say I wanted to contrive a VCO where controle voltages of 4.3,

10.25, and 18.35V were needed at certain intervals; would a charge pujmp do the trick? is it accurate enough from a 5V source to bump up that much precisely? 
--

Fat, sugar, salt, beer: the four essentials for a healthy diet.
Reply to
Steve Evans

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