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Difficulty: MediumDiodes

A direct-current (DC) solar charging circuit contains a standard silicon diode connected in series between the solar panel and a 12-volt battery. Which of the following best explains the primary function of this diode when the solar panel is not producing voltage at night?

  1. A
    It converts the direct current from the battery into alternating current to power the solar panel.
  2. It prevents the battery from discharging backward through the dark solar panel.Answer
  3. C
    It allows bidirectional current flow so the panel and battery maintain identical voltage levels.
  4. D
    It steps up the battery voltage to continuously supply power to the solar cells.

Answer

It prevents the battery from discharging backward through the dark solar panel.
A semiconductor diode permits electrical current to flow in only one direction (from anode to cathode under forward bias). When darkness falls, the solar panel's output drops to zero while the storage battery remains charged at 12 V. This higher potential at the cathode places the diode in reverse bias, creating an open circuit condition that prevents the battery from discharging through the solar panel.

Step-by-Step Solution

1
Analyze the circuit state under nighttime conditions.
The unilluminated solar panel produces 0 V, while the connected storage battery maintains approximately 12 V.
Determining the relative electric potentials at the diode terminals identifies its biasing condition.
2
Determine the bias state of the series diode.
The cathode connected to the battery positive terminal is at a higher potential than the anode connected to the panel, placing the diode in reverse bias.
A semiconductor diode conducts current only when its anode is more positive than its cathode by at least the forward barrier potential.
3
Identify the resulting circuit behavior.
The reverse-biased diode exhibits extremely high resistance, preventing current from leaving the battery.
This blocking action prevents the battery from draining energy into the internal resistance of the dark solar panel.

Key Concept

Unidirectional Current Flow and Reverse-Bias Blocking
Estimated Time:1m 0s
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Topics

Diodes

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