+/-15V supply shorting?

Discussion in 'The Projects Forum' started by abhaymv, Mar 14, 2014.

  1. abhaymv

    Thread Starter Active Member

    Aug 6, 2011
    104
    4
    Hello,

    I'm using the circuit shown in the figure to produce a +/- 15 V supply for powering some op amps. I tested this circuit using a center tapped transformer without any load connected to it. The circuit seems to draw too much current. A 6 A fuse blew, which definitely shouldn't be happening. I implemented this circuit in breadboard and PCB, but the results stayed the same. However, my PSpice simulation says I should be getting a +/- 15 V output.

    Narrowing it down, I am getting the +15 V section (when I tried a partial implementation) but the -15 V section seems to be the source of the problem. What am I doing wrong? :confused:
     
  2. ericgibbs

    Senior Member

    Jan 29, 2010
    2,499
    380
    hi,
    With a CT transformer you dont need two bridge rectifiers, you are effectively shorting thru your double bridge.

    E
     
    abhaymv likes this.
  3. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,773
    1,103
    Your bridge rectifiers are fighting each other. You only need one, like this:-
     
    abhaymv likes this.
  4. abhaymv

    Thread Starter Active Member

    Aug 6, 2011
    104
    4
    Thanks! I'll try them out! :)

    Although I still don't completely get how the bridge rectifiers clash... is it because the ground line both sources and sinks current? (In my understanding of the circuit?)
     
  5. #12

    Expert

    Nov 30, 2010
    16,252
    6,751
    It's the connection at C1 and C2. You have one bridge sending its negative there and the other bridge sending its positive there, and they are also connected through the transformer. Too many current paths!

    You need to simplify. It only takes 4 diodes to do this job.
     
    abhaymv likes this.
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,773
    1,103
    Consider the half-cycle when the bottom of L3 is +ve and the top of L2 is -ve. There is a short circuit via D6 and D9.
     
    abhaymv likes this.
  7. abhaymv

    Thread Starter Active Member

    Aug 6, 2011
    104
    4
    Umm... :eek: Whoops...
     
  8. crutschow

    Expert

    Mar 14, 2008
    12,988
    3,226
    The PSpice simulation likely worked because the short circuit just created a very large current but the voltage was still okay, since the components are ideal (diodes that can carry infinite current and not blow). If you look at the diode currents you will likely see very large values.
     
    abhaymv likes this.
Loading...