*Question E7D15:
What is the purpose of a step-start circuit in a high-voltage power supply?*  

*Correct Answer is  D: To allow the filter capacitors to charge gradually*  

### AI Response: (may contain errors)  

The correct answer to the question about the purpose of a step-start circuit in a high-voltage power supply is:

**D: To allow the filter capacitors to charge gradually.**

### Explanation of the Correct Answer:
- **Step-start circuits** are designed to limit the inrush current when the power supply is turned on. This is particularly important for high-voltage power supplies where large filter capacitors are present.
- When power is first applied, if the capacitors were to charge instantly, it could lead to a very high inrush current that might damage components or cause arcing in switches or relays. 
- By gradually increasing the voltage applied to the capacitors, the step-start circuit allows them to charge slowly, reducing the risk of damage.

### Why the Other Choices are Incorrect:
- **A: To provide a dual-voltage output for reduced power applications**  
  - This is incorrect because a step-start circuit does not change the voltage output; its primary function is to manage the charging of capacitors, not to provide multiple voltage levels.

- **B: To compensate for variations of the incoming line voltage**  
  - This is also incorrect. While power supplies may have voltage regulation features, a step-start circuit specifically addresses inrush current and capacitor charging, not line voltage variations.

- **C: To prevent arcing across the input power switch or relay contacts**  
  - Although preventing arcing is a benefit of controlling inrush current, the primary purpose of a step-start circuit is to manage the charging of filter capacitors. The prevention of arcing is a secondary effect rather than the main function.

### Summary:
- A step-start circuit is crucial for safely managing the initial charging of filter capacitors in high-voltage power supplies, thereby preventing excessive inrush current and potential damage to the system.