Physics Electronics MDCAT 2017
PMDC Verified Question 482 of 494
In the following figure what happens for the positive half cycle of the input?

D1 D2 D3 D4
A
\( D_1 \) and \( D_3 \) conducts
B
\( D_1 \) and \( D_2 \) conducts
C
\( D_3 \) and \( D_4 \) conducts
D
\( D_2 \) and \( D_4 \) conducts
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: \( D_1 \) and \( D_3 \) conducts
Concept:

In a standard full-wave bridge rectifier, diodes conduct in diagonally opposite pairs depending on the instantaneous polarity of the alternating input voltage.

Solution:

  • During the positive half-cycle of the AC input voltage, the terminal polarity forward-biases the first pair of diagonally opposite diodes, labeled \( D_1 \) and \( D_3 \) in the diagram.


  • Simultaneously, the opposite pair (\( D_2 \) and \( D_4 \)) is reverse-biased and blocks current.


  • Therefore, \( D_1 \) and \( D_3 \) conduct during the positive half-cycle.


Why other options are incorrect:

  • Option D: \( D_2 \) and \( D_4 \) conduct during the alternating negative half-cycle.
  • Options B and C: Adjacent pairs (such as \( D_1 \) & \( D_2 \), or \( D_3 \) & \( D_4 \)) cannot conduct simultaneously in a bridge rectifier as they would cause an input short circuit.

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