Cold Start

Power supply equipment may experience a temporary current exceeding specifications at startup, known as inrush current, which requires countermeasures. Inserting a resistor to suppress inrush current is a simple and low-cost method, but it has the disadvantage of reduced efficiency due to resistive loss. One way to overcome this drawback is a cold start method that uses a thermistor with the characteristic that its resistance decreases as temperature rises. In a cold start, the high resistance at low temperature suppresses inrush current at startup, and as the temperature increases to the operating level, the resistance decreases to reduce losses. However, if power is restored immediately after a shutdown due to a short power outage after reaching operating temperature, there is no cooling time for the thermistor, resulting in a large inrush current that may adversely affect the equipment.