Why do household appliances like rice cookers and electric kettles automatically switch to a “keep warm” function after cooking, or stop heating when the water reaches boiling point? The answer lies in a small but crucial component—the thermistor, which helps monitor and control the temperature in these devices.
A thermistor is an electronic component that is highly sensitive to temperature. Due to its high sensitivity, wide operating temperature range, small size, stability, and ease of use, thermistors are widely applied in electronic devices.
Thermistors can be categorized into two types based on their temperature coefficient: NTC thermistors (Negative Temperature Coefficient) and PTC thermistors (Positive Temperature Coefficient).
NTC thermistors decrease in resistance as temperature increases.
PTC thermistors, on the other hand, increase in resistance as the temperature rises.
Although NTC and PTC thermistors look similar and serve similar functions, they operate very differently. Some people may mistakenly use the wrong type, leading to issues.
What Happens When You Use a PTC Thermistor Instead of an NTC Thermistor?
Let’s consider a rice cooker as an example:
Normally, the rice cooker uses an NTC thermistor to sense the temperature of the inner pot. When cooking begins, the pot’s temperature is low, so the NTC thermistor has a high resistance.
As the rice cooker heats up and the temperature rises to 100°C (the boiling point), the NTC thermistor’s resistance drops rapidly.
The control circuit detects this sharp drop in resistance, interprets it as the food being cooked, and sends a signal to cut off the heating power, switching to the “keep warm” mode.
But if the rice cooker uses a PTC thermistor instead:
As the temperature rises, the PTC thermistor’s resistance increases.
The control circuit receives this signal and may mistakenly think the rice cooker is still at a low temperature, leading it to continue heating.
This results in the rice cooker overheating and potentially burning the food. In severe cases, it could even cause a fire.
This is the dangerous consequence of mixing up NTC and PTC thermistors. To avoid such issues, it’s essential to understand the difference between these two types when selecting thermistors for your devices.
This article is provided by JYH HSU (JEC) Electronics. JEC is a research, development, production, and sales-oriented company specializing in manufacturing and selling various electronic components such as capacitors and resistors.
Post time: Oct-22-2025