                   BUILDING A 12 VOLT POWER SUPPLY 

Components:


120v  MOV
T1    18 volt @ 2 amp. transformer    (Radio Shack # 273-1515)
BR1   Bridge rectifier, 4 Amp. @ 50 PIV (Radio Shack # 276-1146)
      (You may substitute 4 rectifier diodes in bridge configuration)
C1    4700 F  @ 35 v. electrolytic capacitor   (Radio Shack # 272-1022)
C2    1000 F  @ 25 v. electrolytic capacitor   (Radio Shack # 272-1019)
C3    .1 F @ 25 v. disc ceramic capacitor      (Radio Shack # 272-135)
7812 voltage regulator                    (Radio Shack # 276-1660 assortment)
     (optional, see note)
120 volt, 1 amp. fuse
3-wire line cord
sw     DPST toggle switch
Jacks and connectors
Perf board or project board
Enclosure

Ŀ          
                       7812 12-volt VOLTAGE REGULATOR
Ŀ    
     Ŀ
            

          
   7812                 front view
          
                       Pin 1 = input
              Pin 3 = ground
                   Pin 2 = output
     
     
     
     
  1   3   2 

 
 

Ŀ
     FULL WAVE     
 Bridge Rectifier     BR1
                   
+       AC        -

                
                
                
                
                

 





12-volt Power Supply schematic


    switch     T1                       
AC /ıĿ    ac         +         1Ŀ2
black   fuse )(Ĵ 7812 +12v out
     Ŀ  )(  bridge                       
---- MOV   )( rectifier   +      3       +    +
grn   )(              C1             C2    C3
             )(    BR1                               
AC )(Ĵ-                           
white             ac         Ŀ
                                   gnd                             gnd




Note: The 7812 regulator may be omitted if the unregulated output is approx. 
      in the 10 - 15 volt range.  The filter caps ARE necessary.                                                                   

Warning: Use all appropriate precautions around the 120v AC input when 
         testing with the power on.  AC power line voltage is dangerous
         and can be lethal!  If you are a novice at this, get assistance
         from an electronics technician or experienced hobbyist.
