PTC Thermistors vs. NTC Thermistors for Inrush Current

PTC-Thermistor

Today we’re going to cover how you can improve inrush current protection for your equipment, machinery or system using NTC and PTC thermistors. Inrush current affects a wide range of products. It becomes further complicated by systems that switch on and off quickly, such as welding equipment and HVAC systems. This post will give you a brief overview of the topic. For more information, you can read the full article here.

What is Inrush Current?

Inrush current describes a spike in current that occurs when equipment is powered on.

Why Manage Inrush Current?

If the spike in current is allowed to pass through the system it can reduce the effective operating life of equipment and potentially damage the system (see below). Fortunately, NTC and PTC limiting can properly manage this.

Embedded Inrush Current Limiter

An uncontrolled flow of inrush current can damage the diode bridge and link capacitor, disabling the conversion of AC to DC current. This can lead to system failure.

What is NTC-based Limiting?

NTC stands for Negative Temperature coefficient. The NTC thermistor provides variable resistance based on temperature. As temperature increases, the resistance drops from high to low and allows current to pass through.

NTC thermistors are the most commonly used thermistor. They fit a wide range of applications including: automotive, military, industrial, and emissions controls.Various items around your home contain NTC thermistors including your oven, air conditioning, and fire detector.

 

PTC and NTC Graph

For an NTC thermistor, as temperature increases, resistance decreases. For a PTC thermistor as temperature increases, resistance increases.

What is PTC-based Limiting?

PTC stands for Positive Temperature Coefficient. The PTC thermistor also provides variable resistance based on temperature. As temperature rises, resistance increases from low to high and blocks the spike in current.

Typically, NTC-based limiting is used for most applications. However, there are certain scenarios that require a PTC thermistor over an NTC thermistor. These include equipment with a near-zero reset time, extreme temperature conditions, and systems that experience frequent shorts.

If you have a specific question about managing inrush current, don’t hesitate to contact our engineers. We are friendly and only an email or phone call away!

Thanks for reading! 

References:

Special Thermistors Limit Inrush Current

How to Stop Inrush Current

 

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