NTC thermistors for
inrush current limiting
Leaded and coated disks
Series/Type:
B57235
Date:
March 2006
EPCOS AG 2006. Reproduction, publication and dissemination of this publication, enclosures hereto and the
information contained therein without EPCOS' prior express consent is prohibited.
1) For details on the capacitance C
test
as well as on the parameters k and n refer to "Application Notes", chapters 2.6 and 2.7.
Applications
Switch-mode power supplies
Features
Useable in series connections up to 265 V
rms
Coated thermistor disk
Kinked leads of tinned copper wire
Wide resistance range
Small space requirement
Cost-effective
UL approval (E69802)
Options
Resistance tolerance <20% and alternative
lead configurations available on request
Delivery mode
Bulk (standard),
cardboard tape, reeled or in Ammo pack
Dimensional drawing
Dimensions in mm
Approx. weight 0.8 g
General technical data
Climatic category
(IEC 60068-1)
55/170/21
Max. power
(at 25
C)
P
max
1.8
W
Resistance tolerance
R
R
/R
R
20
%
Rated temperature
T
R
25
C
B value tolerance
B/B
3
%
Dissipation factor
(in air)
th
approx. 9
mW/K
Thermal cooling time constant
(in air)
c
approx. 60
s
Heat capacity
C
th
approx. 540
mJ/K
Electrical specification and ordering codes
R
25
I
max
(0...65
C)
A
No. of
R/T char-
acteristic
B
25/100
K
C
test
1)
230 V
F
C
test
1)
110 V
F
Param.
for R(I)
1)
k
Param.
for R(I)
1)
n
Ordering code
5
4.2
1202
2800
200
800
0.710
1.30
B57235S0509M000
6
4.0
1202
2800
200
800
0.757
1.30
B57235S0609M000
8
3.5
1203
2900
200
800
0.814
1.32
B57235S0809M000
10
3.0
1203
2900
200
800
0.879
1.32
B57235S0100M000
Inrush current limiters
B57235
ICLs
S235
Page 2 of 6
Please read Important notes and
Cautions and warnings at the end of this document.
Reliability data
Test
Standard
Test conditions
R
25
/R
25
(typical)
Remarks
Storage in
dry heat
IEC
60068-2-2
Storage at upper
category temperature
T: 170
C
t: 1000 h
< 10%
No visible
damage
Storage in damp
heat, steady state
IEC
60068-2-78
Temperature of air: 40
C
Relative humidity of air: 93%
Duration: 21 days
< 5%
No visible
damage
Rapid temperature
cycling
IEC
60068-2-14
Lower test temperature:
55
C
Upper test temperature: 170
C
Number of cycles: 10
< 10%
No visible
damage
Endurance
I = I
max
t: 1000 h
< 10%
No visible
damage
Cyclic
endurance
I = I
max
, 1000 cycles
On-time = 1 min
Cooling time = 6 min
< 10%
No visible
damage
Transient
load
Capacitance = C
test
Number of cycles: 1000
< 5%
No visible
damage
Cautions and warnings for ICLs
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
contact areas, too, may become quite hot at maximum load.
When mounting NTC thermistors you have to ensure that there is an adequate distance between
the thermistor and all parts which are sensitive to heat or combustible.
Inrush current limiters
B57235
ICLs
S235
Page 3 of 6
Please read Important notes and
Cautions and warnings at the end of this document.
Cautions and warnings
General
See "Important notes" at the end of this document.
Storage
Store thermistors only in original packaging. Do not open the package before storage.
Storage conditions in original packaging: storage temperature
25
C ... +45
C, relative
humidity
75% annual mean, maximum 95%, dew precipitation is inadmissible.
Do not store SMDs where they are exposed to heat or direct sunlight. Otherwise, the packing
material may be deformed or SMDs may stick together, causing problems during mounting.
Avoid contamination of thermistors surface during storage, handling and processing.
Avoid storage of thermistor in harmful environments like corrosive gases (SOx, Cl etc).
After opening the factory seals, such as polyvinyl-sealed packages, use the SMDs as soon as
possible.
Solder thermistors after shipment from EPCOS within the time specified:
SMDs: 12 months
Leaded components: 24 months
Handling
NTC thermistors must not be dropped. Chip-offs must not be caused during handling of NTCs.
Components must not be touched with bare hands. Gloves are recommended.
Avoid contamination of thermistor surface during handling.
Soldering
Use resin-type flux or non-activated flux.
Insufficient preheating may cause ceramic cracks.
Rapid cooling by dipping in solvent is not recommended.
Complete removal of flux is recommended.
Mounting
When NTC thermistors are encapsulated with sealing material or overmolded with plastic
material, the precautions given in chapter "Mounting instructions", "Sealing, potting and
overmolding" must be observed.
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 thermistor's surface temperature can be very high (ICL). Ensure that
adjacent components are placed at a sufficient distance from the thermistor to allow for proper
cooling ot the thermistors.
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 thermistors (ICLs) are adequately ventilated to avoid overheating.
Avoid contamination of thermistor surface during processing.
Inrush current limiters
B57235
ICLs
S235
Page 4 of 6
Please read Important notes and
Cautions and warnings at the end of this document.
Operation
Use thermistors only within the specified operating temperature range.
Use thermistors only within the specified voltage and current ranges (ICLs).
Environmental conditions must not harm the thermistors. Use thermistors only in normal
atmospheric conditions.
Contact of NTC thermistors with any liquids and solvents should be prevented. It must be
ensured that no water enters the NTC thermistor (e.g. through plug 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).
Avoid dewing and condensation.
Be sure to provide an appropriate fail-safe function to prevent secondary product damage
caused by malfunction (e.g. use VDR for limitation of overvoltage condition).
Inrush current limiters
B57235
ICLs
S235
Page 5 of 6
Please read Important notes and
Cautions and warnings at the end of this document.
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