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I recently bought a 12V small computer fan(about 1"X1") and it was running rather slow when I checked it with a 9V. The package says that the fan requires 12V to run at an optimized speed, so is there a way/circuit that I can use/make that increases the voltage from 9 to 12?

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  • \$\begingroup\$ What you are looking for is a dc-dc step-up converter. I hope you don't try to feed your fan with a 9V block battery? \$\endgroup\$ – Botnic Nov 7 '15 at 17:27
  • \$\begingroup\$ ebay.com/bhp/dc-dc-adjustable-step-up \$\endgroup\$ – Botnic Nov 7 '15 at 17:28
  • \$\begingroup\$ @Botnic hehe at least it's cheap as dirt \$\endgroup\$ – Enthurzan Nov 7 '15 at 17:31
  • \$\begingroup\$ The bigger bottleneck is the current that the 9V battery can provide. Boosting to 12V will only make that problem worse. \$\endgroup\$ – Passerby Nov 7 '15 at 18:47
  • \$\begingroup\$ The battery is not going to stay at 9V either when under load. I'd estimate the fan will draw 0.1A @ 12 V (1.2W) and your 9V battery is unlikely to exceed 0.05A @ 8V (0.4W). 8xAA battery might be a better solution. A NiMH battery easily delivers that that 0.1A. \$\endgroup\$ – MSalters Nov 7 '15 at 19:45
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Use an inverting buck regulator to create -3V and wire your fan between -3v and +9V. Maybe one of these: -

enter image description here

It's got a -5V output but that can be made -3V by choosing appropriate values for R3 and R4

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As others have said, a 9V battery won't produce enough current to power a small computer fan. Using any type of step-up circuitry is only going to increase the current demand on the battery. Even if you could get it to work, you'd get only 3-4 hours runtime at most. The short answer is that a 9V battery just doesn't have enough juice to power a computer fan.

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"Simple Switchers" (brand name) are easy to use, buck or boost, very efficient switch mode power supplies - boosting the output current should be easy, but I'll let the experts answer that, otherwise I'll get into hot water.

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The simplest answer is to return the fan you bought, and get one intended to run from 9 V.

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    \$\begingroup\$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. \$\endgroup\$ – jippie Nov 8 '15 at 15:29
  • \$\begingroup\$ @Jip: Actually, it properly addresses the overall problem, just not the single solution the OP is envisioning. \$\endgroup\$ – Olin Lathrop Nov 8 '15 at 22:07
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You can try putting the 9V battery and 2AA(1.5V) battery in series to produce 12V. Or you can try making a boost converter circuit which is a bit more complicated but will step-up or step-down your voltage in a circuit. You can learn more about boost-converters here.

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