I am trying to understand center tap and full wave rectification and struggling with flow of current. My understanding of center tap is that, voltages will be 180 out of phase for the 2 parts in secondary. So I have tried to create circuit (Fig 1 attached) with that understanding. 2 questions

  1. Is the direction of current in part 1 and Part 11 in Fig 1 correct?

  2. If 1 above is correct, then when we attach 2 diodes as in Fig 2, we wont get full wave rectification as both diodes will be forward and reverse baised at the same time.

I know I am missing something but cant put my finger to it.

enter image description here

  • 1
    $\begingroup$ This is really one for the Electrical Engineering SE. $\endgroup$ – Guy Inchbald May 20 at 14:38
  • $\begingroup$ @GuyInchbald I answered the question because at this level it is not really much of engineering. It belongs to the kind of question that you would get about conservation of angular momentum and then you also explain the basic concepts of a gyroscope, not their design but rather the principle of keeping direction. $\endgroup$ – hyportnex May 20 at 14:46

You might note, that in figure 1, you have a short circuit from top to bottom. On the sketch, you might want to reverse the current in the bottom loop. In the transformer, current flows only one direction at each instant. With the diodes, current can flow through only one at a time.

  • $\begingroup$ if I reverse the direction in botton loop @R.W.Bird , that will solve my rectification dilema, but if it do that, it wont be 180 out of phase with one in top circuit which i thought is what a center tap does.? $\endgroup$ – user31058 May 20 at 14:54
  • $\begingroup$ They are out of phase at the center tap. In Fig. 1 you have drawn them in phase at that point. Try adding the phase on the primary, that might make it clearer for you. $\endgroup$ – Guy Inchbald May 20 at 15:02
  • $\begingroup$ If the induced voltage is trying to push (positive) current up in the secondary of the transformer, that makes the upper terminal positive and the bottom one negative relative to the center tap. They are out of phase. With the diodes in place, current can flow in the upper loop, but not in the bottom loop. $\endgroup$ – R.W. Bird May 21 at 13:32

In Figure 2 with the ideal diodes you are indicating the possible direction of the nonzero current during either half-cycle, but those half-cycles are not simultaneous but rather consecutive. So if in one half-cycle the upper branch is conducting then the lower branch has zero current. In the next half-cycle the lower branch will conduct with zero current in the upper branch, but notice that the load current direction is the same as in the previous half-cycle, hence the name "full-wave rectifier".


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