Epoxy bead coating · Ø 2.6 mmPins

Black epoxy drop, two thin legs; a larger disc-shaped PTC beside it
Epoxy drop body, a few mm; PTC disc types are larger · Example shown: 10 kΩ NTC, epoxy drop (MF52 type)

Resistors

Thermistor (NTC/PTC)

In simple terms

What is this?

A small bead whose opposition to electricity changes with temperature.

What is it for?

An NTC drops in resistance when it heats up, which is how temperature is measured; a PTC instead throttles back when it heats up and protects the circuit.

Where do you see it?

In the temperature sensing of digital thermometers, heaters and fans.

How do you spot it?

A small drop or disc with two legs; NTC or PTC may be printed on it.

Caution:

Don’t mix up NTC and PTC; it can heat up from its own current and throw off the measurement.

Technical definition

A resistor whose resistance changes noticeably with temperature. An NTC lowers its resistance as it warms and is mostly used for temperature measurement. A PTC raises its resistance sharply above a certain temperature and acts as protection like a fuse.

At 25 °C10 kΩ

B value3950 K

Tolerance±1%

Schematic symbol IEC and ANSI differ

IEC 60617: the drawing style used in Türkiye and Europe.

Pins 2

1Pin 1Has no direction1

2Pin 2Has no direction2

Features typical

Nominal resistance: 10 kΩ (25 °C)
B value: 3950 K (25/50 °C)
At 50 °C: ≈3.6 kΩ
Tolerance: ±1% · ±5%
Behavior: NTC: resistance falls when heated
Operating range: −40 … +125 °C (typical)
Example part: NTC 10 kΩ, B = 3950 K (MF52 type)

Common mistakes

Self-heating the thermistorIf you pass a large current, the thermistor heats itself and you measure wrongly. Use a high resistor such as 10 kΩ in the divider.

Assuming it is linearAn NTC’s resistance does not change linearly with temperature. Calculate temperature with the B equation or the manufacturer’s table.

Mixing up NTC and PTCA PTC increases its resistance as it heats up. If you put a PTC in a measurement circuit, the result changes in the opposite direction.

Test with a multimeter

Test whether this part is good with the multimeter on the measurement screen.

Take a measurement

Where it is used

Digital thermometerFan or heater controlBattery temperature monitoringInrush current limiting (power NTC)

Try it in the Lab