*Question E7D05:
Which of the following types of linear voltage regulator operates by loading the unregulated voltage source?*  

*Correct Answer is  D: A shunt regulator*  

### AI Response: (may contain errors)  

To understand why the correct answer is a shunt regulator, let's break down the options:

### Correct Answer: D - A shunt regulator

- **Explanation**: A shunt regulator operates by diverting excess current away from the load to maintain a constant output voltage. It does this by "loading" the unregulated voltage source, effectively shunting the excess voltage to ground. This allows the output voltage to remain stable despite variations in input voltage or load current.

### Why the Other Choices are Incorrect:

- **A: A constant current source**  
  - **Explanation**: A constant current source is designed to provide a fixed current regardless of the load resistance. It does not regulate voltage and does not operate by loading the voltage source.

- **B: A series regulator**  
  - **Explanation**: A series regulator controls the output voltage by varying the resistance in series with the load. It does not load the unregulated voltage source; instead, it adjusts the voltage drop across itself to maintain a constant output voltage.

- **C: A shunt current source**  
  - **Explanation**: A shunt current source is similar to a constant current source and is not specifically designed to regulate voltage. It provides a constant current to the load but does not operate by loading the voltage source in the way a shunt regulator does.

### Summary of Key Points:

- **Shunt Regulator**: Loads the unregulated voltage source to maintain a constant output voltage.
- **Constant Current Source**: Maintains a fixed current, not voltage.
- **Series Regulator**: Adjusts voltage drop in series with the load, not by loading the source.
- **Shunt Current Source**: Provides constant current, not voltage regulation.

This understanding will help you differentiate between these types of regulators and their functions, which is crucial for the Extra Class exam.