Question
What is the purpose of a step-start circuit in a high-voltage power supply?
Answer Options
- A) To provide a dual-voltage output for reduced power applications
- B) To compensate for variations of the incoming line voltage
- C) To prevent arcing across the input power switch or relay contacts
- D) To allow the filter capacitors to charge gradually
Correct Answer: D
Explanation
A high-voltage power supply, such as those used for vacuum tube RF amplifiers, typically uses large filter capacitors to smooth the rectified DC. When the supply is first turned on, these discharged capacitors look like a dead short to the transformer, causing a massive, instantaneous inrush current that can damage rectifiers, fuses, or circuit breakers.
A step-start circuit is a soft-start mechanism designed to allow the filter capacitors to charge gradually. This is typically done by inserting a large, temporary current-limiting resistor in series with the transformer primary when the supply is first energized. After a few seconds, once the capacitors are substantially charged, a relay bypasses the resistor for normal, low-loss operation.
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