Power supply :
DC Power Supply 1.25V to 25V
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DC power supply
Switching Regulator
Variable Regulator
Macbook power supply
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This power supply is based on the LM317 Variable Regulator.
The input of the regulator needs to be around 28 Volts DC and
it will output a DC voltage from 1.25vdc to 25 vdc.
To adjust the output voltage simply turn the 5k ohm pot.
The regulator will supply 1.5 amps of current.
Source : http://home.maine.rr.com/randylinscott/apr20.htm