If I want this battery eliminator to always put out 1.5v, what resistor would I need to use in place of the 5K pot? Please see schematic. http://photos.yahoo.com/scubapair

:If I want this battery eliminator to always put out 1.5v, what resistor would I need to use in place of the 5K pot? Please see schematic. http://photos.yahoo.com/scubapair

Either 5K or zero. I'd say Zero as Vout = Vref(1+R2/R1)IadjR2. Vadj is a semi-constant 1.25V according to NS data found here: http://www.national.com/ds/LM/LM117.pdf

Hope this helps.

Z-

Vout = 1.25V (1 + Radj/220) = 1.5V
Radj = (1.5-1.25) 220 = 55 ohms

BUT: this ckt has a 24-V AC input, which is quite high if all you want is 1.5-V DC output. It will cause the regulator to get unnecessarily hot. Best to reduce the AC input voltage to perhaps 5V.

:If I want this battery eliminator to always put out 1.5v, what resistor would I need to use in place of the 5K pot? Please see schematic. http://photos.yahoo.com/scubapair

Also, the 5K pot is way to high in value to get 1.5V without being much too touchy.

Need to revise the value of the 220-ohm resistor and/or add a trimmer to the fixed cap.

Not a real good idea to take a ckt like this and try to modify it without thinking it all through.

:Vout = 1.25V (1 + Radj/220) = 1.5V
:Radj = (1.5-1.25) 220 = 55 ohms
:
:BUT: this ckt has a 24-V AC input, which is quite high if all you want is 1.5-V DC output. It will cause the regulator to get unnecessarily hot. Best to reduce the AC input voltage to perhaps 5V.
:
::If I want this battery eliminator to always put out 1.5v, what resistor would I need to use in place of the 5K pot? Please see schematic. http://photos.yahoo.com/scubapair

:If I want this battery eliminator to always put out 1.5v, what resistor would I need to use in place of the 5K pot? Please see schematic. http://photos.yahoo.com/scubapair

Correction, you said 1.5, not 1.25...Make that around 33-40 ohms. Always allow for a slight difference unless you use precision resistors...

Z-