*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)  

A step-start circuit in a high-voltage power supply is designed to allow the filter capacitors to charge gradually. This is important because it prevents a large inrush current when the power supply is first turned on, which could otherwise damage components or cause circuit breakers to trip.

### Explanation of the Correct Answer (D)

- **Gradual Charging of Capacitors**: When a power supply is turned on, the filter capacitors initially appear as a short circuit because they are uncharged. A step-start circuit limits the initial current, allowing the capacitors to charge slowly to their full voltage. This reduces stress on the power supply components and extends their lifespan.

### Why the Other Choices are Incorrect

- **Choice A: Dual-voltage output for reduced power applications**  
  A step-start circuit does not provide dual-voltage outputs. Its purpose is not related to output voltage levels but to manage the initial current surge.

- **Choice B: Compensate for variations of the incoming line voltage**  
  Step-start circuits do not adjust for line voltage variations. Voltage regulation is typically handled by other components, such as voltage regulators or transformers.

- **Choice C: Prevent arcing across the input power switch or relay contacts**  
  While reducing inrush current can help prevent arcing, the primary purpose of a step-start circuit is to manage the charging of capacitors, not specifically to prevent arcing.

### Useful Rule of Thumb

- **Inrush Current Limiting**: A step-start circuit often uses resistors or inductors in series with the power supply input to limit the initial current. After a short delay, these components are bypassed, allowing normal operation.

Understanding the role of a step-start circuit helps ensure the reliable and safe operation of high-voltage power supplies by managing the initial power-on conditions.