*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)  

A shunt regulator operates by loading the unregulated voltage source to maintain a constant output voltage. Here's how it works and why it's the correct answer:

### Correct Answer: D: A shunt regulator

1. **Shunt Regulator Operation**:
   - A shunt regulator maintains a stable output voltage by diverting excess current away from the load and through a parallel (shunt) path.
   - It effectively "loads" the unregulated voltage source by adjusting the current through the shunt path to keep the output voltage constant.
   - This is useful in applications where the load current varies, and a stable voltage is required.

### Why Other Choices Are Incorrect:

- **A: A constant current source**:
  - A constant current source is designed to provide a steady current regardless of the voltage across it. It does not regulate voltage by loading the source.

- **B: A series regulator**:
  - A series regulator controls the output voltage by varying the resistance in series with the load. It does not load the unregulated voltage source in the same way a shunt regulator does.

- **C: A shunt current source**:
  - A shunt current source is not a standard term in voltage regulation. It might imply a current source in parallel, but it does not describe a voltage regulation method.

### Key Concept:

- **Shunt Regulator Formula**:
  - The basic operation can be described by Ohm's Law and the concept of parallel resistance:
  $$ V_{\text{out}} = V_{\text{in}} - I_{\text{shunt}} \times R_{\text{shunt}} $$
  - The shunt regulator adjusts $I_{\text{shunt}}$ to maintain $V_{\text{out}}$ constant.

Understanding these concepts will help you identify the correct type of voltage regulator based on its operation and application.