schematic power supplies 18v

[ANDYEFFECT]

schematic power supplies 18v

does anybody have schematic PS for 18volts? 
 
can I modify GGG ultra clean of 9 to 18v? 
 
thankful. 
André

[kusi]

hi,

have a look at the LM317 datasheet and calculate  r2a/b  for Ua=18V.  (www.google.de => " LM317 datasheet" )
whats the secondary-voltage of your transformer?


greetings KHE

[ANDYEFFECT]

hi,

have a look at the LM317 datasheet and calculate  r2a/b  for Ua=18V.  (www.google.de => " LM317 datasheet" )
whats the secondary-voltage of your transformer?


greetings KHE

yes, more which of the two resitores I change for smaller value? R2a or R2b (you look at schematic below) 

http://www.generalguitargadgets.com/diagrams/ultra_clean_ps_sc.gif

 
thankful.

[kusi]

hi andy,

you have to increase the totally resistance of R2!

lets calculate it;

R1a and R1b are paralell, the totally resistance of this two is R1= 1/((1/R1a)+(1/R1b)) = 240.9 Ohm
R2a and Rab are parallel, the totally resistance of this two is R2= 1/((1/R2a)+(1/R2b)) = 1,545k Ohm

now, have a look at the datasheet; www.datasheetcatalog.com/ datasheets_pdf/L/M/3/1/LM317.shtml

Ua= Uref *(1+(R2/R1))*Iadj.*R2

Ua= Outputvoltage, you want 18V
Uref= Reference-voltage, 1,25V (=>datasheet)
R1= 240 Ohm
Iadj = ~0mA
R2 = ??

formula change over to R2:

R2= (Ua*R1)/Uref-R1 = (18V*240 Ohm)/1.25V -240 Ohm = 3216 Ohm

now, this is not a standart vaule, so you can use resistors in parallel to become a vaule neary 3.216kOhm, or you use
a 2,7k R wiht a 500 Ohm Trimm-pot in series to adjust Ua.

greetings KHE

[jxoco]

the input to the regulator circuit has to be over 18 volts.

so, the 12v transformer won't do...

[kusi]

that is logic, i think (and hope) andy know that...