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Want to by variable power supply

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Ian:
HI
I am looking to by a variable power supply that has like 1amp of power and 0-12v or so. It would be nice if it had a meter to show voltage. thank you

Zero999:
I'd build one using the LM317.

The problem is it's generally limited to 1.25V minimum but there are ways round this, here's an example:
http://www.silicontronics.com/index.php?action=ezportal;sa=page;p=19

Jon Chandler:
Here's a link to an LM-317-based design I built using an 18-volt switcher as the source.  It only goes do to 1.25 volts but it's pretty handy for the cost.

Mr J:

--- Quote from: Hero999 on December 27, 2010, 11:08:08 pm ---I'd build one using the LM317.

The problem is it's generally limited to 1.25V minimum but there are ways round this, here's an example:
http://www.silicontronics.com/index.php?action=ezportal;sa=page;p=19

--- End quote ---

there is an easier way :) I love the 317, check out the data sheet at  http://www.national.com/profile/snip.cgi/openDS=LM317

Okay you have to change r1 to get 12 volts

some math:

Vout = 1.25 (1+R2/R1)

Define Vout = 12V, R2 5K Pot, R1 is unknown

12V = 1.25 (1+5K/R1)

12/1.25 = (1+5K/R1)

9.6 = 1+5K/R1

9.6 - 1 = 5K/R1

8.6 = 5K/R1

R1= 5K/8.6

R1=581 ohms, (use a 560 it's a standard value, it will give you 12.41Vout)

you can use any pot as long as you keep the ratio of r2/r1 the same. I would also suggest a 10 or 25 turn precision pot, it makes it easier to get the voltage you want dead on.

for a meter I would use the PM-128E (e is the enhanced version you can use with a common ground to supply the meter) http://www.web-tronics.com/panelmeter.html

Mr J:
let me know if you need a full schematic, I can draw one up in gEDA.

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