Question

A simple laboratory power supply consists of a transformer, bridge rectifier and a filter capacitor. It drives a suitable load. If due to some reason one of the diodes in the rectifier circuit becomes open, then
A. Output voltage of the power supply falls to zero.
B. Output voltage of the power supply decreases to some non-zero value.
C. a.c. ripples in the output increases
D. Ripple frequency decreases

Answer 1

Recall the concept of diodes used in the circuits. Recall what the main function of the diode is. Check what happens if one of the diodes in the rectifier circuit becomes open like how it affects the output voltage of the power supply, does it affect the a.c. ripples or ripple frequency.

Complete answer:
-We have given that a simple laboratory power supply consists of a transformer, bridge rectifier and a filter capacitor. It drives a suitable load.One of the diodes in the rectifier circuit becomes open due to some reason.
-As diodes are the components in the circuit allowing the current to flow through them towards the output of the power supply. Hence, if one of the diodes becomes open, the output voltage has to be zero. So there is no chance of increasing the a.c. ripples in the output or decreasing the ripple frequency without electric current in the circuit.Hence, the options B, C and D are incorrect.
-The diodes are the devices prepared using semiconductor materials. The diodes act as a gate for current. They allow the flow of electric current through them in the positive part of the AC cycle and restrict the flow of electric current in the negative part of AC cycle.The diodes not only restrict the current in the negative part of the cycle but also redirect this current in the proper direction.
-Hence, it one of the diode in the rectifier circuit becomes open due to some reason they supply of the electric current stops suddenly as diodes are the main components directing the current in proper direction.Therefore, if one of the diodes in the rectifier circuit becomes open then the output voltage of power supply becomes zero.

Hence, the correct option is A.

Note: The students may think that the output voltage of the power supply decreases but does not become zero when one of the diodes in the rectifier circuit is open as there are some remaining charge carriers in the series of the diodes. But this is only for a short time. Finally, the voltage of the power supply becomes zero.