Zener Diodes

The given question involves analyzing the I-V characteristics of an electronic device to determine its type. The options provided are:

1. A solar cell
2. A transistor which can be used as an amplifier
3. A zener diode which can be used as a voltage regulator
4. A diode which can be used as a rectifier

To solve this, we need to analyze the given I-V characteristics graph:

• The graph shows that the current remains constant after a certain reverse voltage is reached. This is a distinctive feature of a Zener diode.
• A Zener diode operates in the reverse breakdown region, where it maintains a constant voltage across it despite changes in current. This property is used for voltage regulation.

Now, let's reason through the options:

• Solar cell: The I-V characteristic of a solar cell typically shows a current generation with illumination, which is not present here.
• Transistor as an amplifier: Transistors have different characteristic curves for different configurations, and this I-V curve does not match any transistor mode.
• Zener diode as a voltage regulator: The depicted graph matches the behavior of a Zener diode in the reverse breakdown region, making this option correct.
• Diode as a rectifier: Rectifiers typically show forward-biased characteristics, which are not displayed here.

Therefore, the correct option is a Zener diode which can be used as a voltage regulator.

This choice is confirmed by the graph showing the constant current in reverse bias, indicative of a Zener diode's voltage regulating behavior.

To determine the output voltage in the given circuit, we need to analyze the circuit considering the ideal diode case. In an ideal diode scenario, the diode conducts perfectly when forward-biased (zero voltage drop across it) and does not conduct at all when reverse-biased (infinite resistance).

1. Initially, consider diode . Since it is forward-biased with , it will conduct, allowing current to pass through it without any voltage drop.
2. Next, examine diode . The cathode of is connected to ground, making the anode potential higher than ground when the circuit is active. This results in being reverse-biased.
3. As is conducting and is not conducting, the voltage at the output is the same as the cathode of the conducting diode , causing it to be .

Finally, observe the resistor connected to the output; it is also connected to . With both connections at the same potential, there is no potential difference, leading the output voltage to be .

Thus, the correct answer is:

This problem describes a Zener diode voltage regulator circuit. We need to determine the load current ( ) and the load resistance ( ) based on the given circuit parameters and conditions.

Concept Used:

The operation of this circuit is based on the properties of a Zener diode and fundamental circuit laws.

1. Zener Diode as a Voltage Regulator: When operated in the reverse breakdown region, a Zener diode maintains a nearly constant voltage across its terminals, known as the Zener voltage ( ). In this circuit, the load resistor is connected in parallel with the Zener diode, so the voltage across the load is regulated to be equal to the Zener voltage, i.e., .
2. Ohm's Law: This law relates voltage (V), current (I), and resistance (R) as .
3. Kirchhoff's Laws:
   • Kirchhoff's Voltage Law (KVL): The sum of voltage drops around a closed loop is zero. For the input loop, the input voltage drops across the series resistor ( ) and the Zener diode.
   • Kirchhoff's Current Law (KCL): The total current entering a junction is equal to the total current leaving it. The current from the source ( ) splits into the Zener current ( ) and the load current ( ).

The key equations are:

Step-by-Step Solution:

Step 1: List the given circuit parameters.

• Unregulated DC input voltage,
• Zener voltage,
• Series resistance,
• Given condition: Zener current is 4 times the load current, .

Step 2: Calculate the total current ( ) flowing from the source through the series resistor .

The Zener diode maintains a constant voltage of 5 V across the load. Therefore, the voltage drop across the series resistor is the difference between the input voltage and the Zener voltage.

Using Ohm's law, we can find the total current :

Converting this to milliamperes (mA):

Step 3: Use Kirchhoff's Current Law (KCL) and the given condition to find the load current ( ).

According to KCL, the total current splits into the Zener current and the load current .

We are given the condition that . Substituting this into the KCL equation:

Now, we can solve for using the value of we calculated:

Final Computation & Result:

Step 4: Calculate the load resistance ( ).

The voltage across the load resistance is the regulated Zener voltage, . We can find the load resistance using Ohm's law with the load current we just found.

First, convert the load current back to Amperes:

Now, calculate :

Therefore, the load current and load resistance are:

We are given:

• Supply voltage
• Series resistor
• Zener breakdown voltage
• Load resistor

Step 1: Behavior of the Zener diode
Since the applied voltage is greater than the breakdown voltage of the Zener diode ( ), the Zener diode enters the breakdown region and maintains a constant voltage of across itself.
Step 2: Voltage across the load resistor
The Zener diode and the load resistor are in parallel. Therefore, the voltage across the load resistor is also:
Step 3: Current through the load resistor (measured by the ammeter)

Step 4: Ammeter Reading
The ammeter is in series with the 400 load resistor and thus measures the current through it.
Therefore, the reading of the ammeter is: