How to Get 8 Volts out of a 7805 Regulator

If you're building a portable, and you need to get 8 volts for one reason or another, you have several options. You can use 8 volts' worth of batteries, track down a 7808 regulator, or you can do what I do and build a regulator circuit around a 7805. I actually based this off of my own tinkering and a page I found on the internet. You can find a link to this article at the bottom of the page if you want to find out why this works, the math involved, and other resistor values you can use to get different voltages. Since I know you want to get it over with and build the board, here's how.

Materials Required:

  • 7805 Regulator (RS Catalog # 276-1770) - $1.59
  • 220 ohm resistor (RS Catalog # 271-1111) - $0.99 /pk of 5
  • 470 ohm resistor (RS Catalog # 271-1115) - $0.99 /pk of 5
  • Wire
  • PC board (optional)


Tools Required

  • Soldering stuff (iron, solder, helping hands, sponge...)

 

To make things easier I put together this diagram using Skyone's component drawings, because my drawing skills are on par with my cat's.

It's really pretty simple. First solder one end of each resistor to the ground side of the regulator. Then, connect the 220 ohm resistor's other end to ground. Now connect the 470 ohm resistor's loose lead to the regulator's normal regulated output.

When you apply power to the regulator, and have the 220 ohm resistor grounded, you should be able to get 8 volts out of the spot where the 470 ohm resistor connects to the regulated output. If not, check your ground and your wiring.

And as always, check to make sure the voltage is correct before you try to power anything important off this!

That about takes care of this quickie tutorial. Here's the link to the detailed page.
Rason.org

Happy portablizing!
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Text Copyright 2006 bicostp http://bicostp.portablesofdoom.org do not copy without permission or I will turn green and eat you.