NTC thermistors for

inrush current limiting

Leaded and coated disks

Series/Type: B57235S0***M0**

Date: May 2013

© EPCOS AG 2015. Reproduction, publication and dissemination of this publication, enclosures hereto and the

information contained therein without EPCOS' prior express consent is prohibited.

EPCOS AG is a TDK Group Company.

1) For details on the capacitance Ctest please refer to "Application notes", chapter 1.6.

Wide resistance range

Small space requirement

Manufacturer's logo, NTC and resistance value

stamped on

UL approval (E69802)

Resistance tolerance <20% and alternative lead

configurations available on request

Delivery mode

Resistance tolerance ∆RR/RR±20 %

Rated temperature TR25 °C

Dissipation factor (in air) δth approx. 9 mW/K

Thermal cooling time constant (in air) τcapprox. 60 s

Heat capacity Cth approx. 540 mJ/K

Electrical specification and ordering codes

R25

Imax

(0...65 °C)

Ctest1)

230 V AC

µF

Ctest1)

110 V AC

µF

Rmin

Ordering code

Test Standard Test conditions ∆R25/R25

heat, steady state

Relative humidity of air: 93%

Duration: 21 days

Termal schock IEC

Lower test temperature: 55 °C

t: 30 min

Upper test temperature: 170 °C

t: 30 min

Time to change from lower to

upper temperature: < 30 s

Number of cycles: 10

Endurance IEC

Ambient temperature: 25 ±5°C

Number of cycles: 1000

capacitance test

Ambient temperature: 25 ±5°C

Capacitance = Ctest

Number of cycles: 1000

The self-heating of a thermistor during operation depends on the load applied and the

applicable dissipation factor.

When loaded with maximum allowable current/power and the specified dissipation factor is

taken as a basis, the NTC thermistor may reach a mean temperature of up to 250 °C.

The heat developed during operation will also be dissipated through the lead wires. So the

Data book 2012". The complete application note can be downloaded from

1.4 Load derating

The power handling capability of an NTC thermistor cannot be fully utilized over the entire temper-

ature range. For circuit dimensioning the derating curve given below provides information on the

extent to which the current must be reduced at a certain ambient temperature (TA).

Derating curve for types S237, P11 and P13

Figure 1

TA= Ambient temperature > 25 °C

Tmax = 170 °C

1.6 Maximum permissible capacitance

ing to IEC 60539-1:

Figure 3

Test circuit for evaluating the maximum permissible capacitance of an NTC thermistor

Vload Load voltage [V]

Ctest Test capacitance [µF]

RSSeries resistance [RS=1Ω]

VNTC Voltage drop across the NTC under test [V]

are given in the data sheets.

1 Taping of radial leaded ICL NTC thermistors according to the

specified lead spacing

Dimensions and tolerances

Lead spacing F = 5.0 mm (taping to IEC 60286-2)

for the following types: S153, S235 and S236

Lead spacing F = 7.5 mm (taping based on IEC 60286-2)

for the following types: P11, P13, S237, S238 and S364

Electrode must not be scratched before/during/after the mounting process.

Contacts and housings used for assembly with thermistor have to be clean before mounting.

During operation, the inrush current limiters surface temperature can be very high. Ensure that

adjacent components are placed at a sufficient distance from the thermistor to allow for proper

cooling of the NTC inrush current limiters.

Ensure that adjacent materials are designed for operation at temperatures comparable to the

surface temperature of the thermistor. Be sure that surrounding parts and materials can

withstand this temperature.

Make sure that inrush current limiters are adequately ventilated to avoid overheating.

Avoid contamination of thermistor surface during processing.

terminals). For measurement purposes (checking the specified resistance vs. temperature), the

component must not be immersed in water but in suitable liquids (e.g. Galden).

In case of exposure of the NTC inrush current limiters to water, electrolytes or other aggressive

media, these media can penetrate the coating and reach the surface of the ceramic. Low-ohmic

or high-ohmic behavior may occur due to the formation of an electrolyte with metals

(silver/lead/tin from metallization or solder). Low-ohmic behavior is caused by electrochemical

migration, high-ohmic behavior by dissolving of the electrode. In either case, the functionality of

the NTC inrush current limiters can not be assured.

Be sure to provide an appropriate fail-safe function to prevent secondary product damage

caused by malfunction (e.g. use a metal oxide varistor for limitation of overvoltage condition).

Imax Maximum current within stated temperature range

INTC NTC current

Pmax Maximum power within stated temperature range

Rmin Minimum resistance

RRRated resistance

∆RR/RRResistance tolerance

RSSeries resistance

RTResistance at temperature T

(e.g. R25 = resistance at 25 °C)

T Temperature

V Voltage

Vload Load voltage

VNTC Voltage drop across an NTC thermistor

δth Dissipation factor

τcThermal cooling time constant

Abbreviations / Notes

* To be replaced by a number in ordering codes, type designations etc.

nevertheless expressly point out that such statements cannot be regarded as binding

statements about the suitability of our products for a particular customer application.

As a rule, EPCOS is either unfamiliar with individual customer applications or less familiar

with them than the customers themselves. For these reasons, it is always ultimately incum-

bent on the customer to check and decide whether an EPCOS product with the properties de-

scribed in the product specification is suitable for use in a particular customer application.

failure before the end of their usual service life cannot be completely ruled out in the

current state of the art, even if they are operated as specified. In customer applications

requiring a very high level of operational safety and especially in customer applications in

third parties in the event of malfunction or failure of an electronic component.

tailed questions, please contact our sales offices.

publication may change from time to time. The same is true of the corresponding product

sion of the "General Terms of Delivery for Products and Services in the Electrical In-

dustry" published by the German Electrical and Electronics Industry Association

(ZVEI).

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