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I would like to use a charge pump to step up a 1.5V AAA battery to >7V. The charge pump itself is already constructed and works fine when I test it with a 5V input. At this point I'm providing the clock signals using a microcontroller. However, the microcontroller can't operate at 1.5V, and eventually I'd like to power the microcontroller from the output of the pump. I am not sure what would be the best way to provide the two out of phase clock signals that the pump requires. I've had some success constructing a multivibrator using capacitors, resistors and MOSFETs, as shown on p. 16, Fig 1-26 here:

http://books.google.ca/books?id=-sE7JVywygQC&pg=PA15&dq=multivibrator+mosfet&hl=en&sa=X&ei=AXR_U_PnDs3foASw1YG4Dg&redir_esc=y#v=onepage&q=multivibrator%20mosfet&f=false

This works fine from a 5V source, but getting it to run successfully from a battery is proving more difficult. I can see that there are various low-voltage multivibrator ICs available, but these are pretty big and seem like overkill for such a simple application.

So, how would one usually go about providing the clock signals for a low input voltage charge pump?

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  • \$\begingroup\$ Using MOSFETs means that you need a supply voltage that's greater than their threshold voltage. But the same circuit built with NPN BJTs should work at 1.5V (with some care). \$\endgroup\$ – Dave Tweed May 23 '14 at 18:32
  • \$\begingroup\$ The link to the page doesn't work - the page says something like "The viewing limit has been reached". Please consider copying, trimming and pasting the schematic into your question or to a sustainable page so that someone can paste it up for you. \$\endgroup\$ – Andy aka May 23 '14 at 18:45
  • \$\begingroup\$ @DaveTweed, thanks. I'm now thinking that perhaps a better option might be to use an IC boost regulator to get from the voltage supplied by the battery to 3V, and then use the charge pump to get from 3V to >7V. The circuit needs a voltage regulator anyway, and the 3V boost regulators don't seem to cost much more. \$\endgroup\$ – foldl May 23 '14 at 19:05
  • \$\begingroup\$ @Andyaka Sorry that the link didn't work. The circuit on that page is just a standard astable multivibrator. There's a schematic e.g. here virtual.cvut.cz/dyn/examples/examples/electronic/mosmulti \$\endgroup\$ – foldl May 23 '14 at 19:07
  • \$\begingroup\$ If you're willing to use an IC, then there are several off-the-shelf solutions that will take you directly from 1.5V to 7V, with regulation. Check out vendors like Linear Technology, Texas Instruments and Maxim. \$\endgroup\$ – Dave Tweed May 23 '14 at 19:48
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I'd consider using a boost regulator to take you to a voltage suitable for your micro. For instance: -

enter image description here

All the devices above can produce 5V AFAIK and once you have your micro running you can drive the charge pump circuit.

Finding a booster that works from about 1V and takes you to 7V is a little tricky, that's why I opted for this method.

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