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When electrical equipment powers on, it often experiences a sudden surge of current — known as inrush current — that can be several times higher than the steady-state operating current. This surge may damage sensitive components, blow fuses, or shorten the life of your system. That’s where NTC inrush current limiters come into play.

What Is Inrush Current?

Inrush current is the initial surge that flows into a device when power is first applied. It occurs because uncharged capacitors act like short circuits and magnetic components like transformers draw high magnetizing current at startup.

Common problems caused by inrush current include:

• Component overheating or burnout.
• Blown fuses.
• Transformer stress.
• Reduced equipment reliability.

How NTC Inrush Current Limiters Work?

NTC (Negative Temperature Coefficient) thermistors are temperature-sensitive resistors. Their resistance decreases as temperature increases. NTC thermistors offer dual-stage protection:

1. At startup: The thermistor is cold and provides high resistance, limiting inrush current.

2. During operation: As current flows through the thermistor, it self-heats. The resistance drops, allowing normal current flow with minimal power loss.

This makes NTC thermistors a cost-effective and space-saving solution compared to traditional fixed resistors or complex relay-based circuits.

Typical Circuit Integration.

NTC inrush current limiters are typically placed in series with the load and power input. This placement makes them ideal for:

• Switching power supplies.
• Motors.
• Transformers.
• High-capacitance input circuits.

⚠ Important Note: Do not use NTC thermistors in parallel, as current imbalance may cause overheating or failure.

Key Selection Parameters.

When choosing an NTC inrush current limiter, engineers should consider:

• Maximum Steady-State Current: Must be higher than the device’s operating current.
• Cold Resistance (R25): Determines how much the inrush current is suppressed.
• Maximum Energy Rating (Joules): The limiter’s ability to absorb startup energy.
• Thermal Derating: Ambient temperature affects performance — adjust specs accordingly.
• Self-Heating Temperature: Some devices can reach up to 250°C — consider spacing and insulation.

Application Examples.

NTC thermistors are widely used across industries:

• Lighting: Fluorescent, halogen, and LED lamps.
• Home appliances: Kitchen equipment with motor startup protection.
• Industrial power supplies: AC-DC converters, EV chargers.
• Transformers: To suppress initial current spikes

At Shiheng Electronics, we offer a full range of NTC inrush current limiters with power ratings from 1.5W to 36W and continuous current handling up to 50A AC — tailored for a wide range of applications.

Need help selecting the right part for your design? Contact us today for datasheets, samples, or technical support.