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# F-452 View Datasheet(PDF) - SEMITEC Corporation

 Part Name Description Manufacturer F-452 SURGE ABSORBERS , SENSORS AND MODULES , THERMISTORS SEMITEC Corporation F-452 Datasheet PDF : 44 Pages
 First Prev 21 22 23 24 25 26 27 28 29 30 Next Last Thermal time constant
If ambient temperature of a thermistor is changed
to T1 from T2 suddenly, temperature of the thermistor
changes slowly.
The time constant means the time when temperature
of the thermistor reaches 63% of the temperature
difference.
Residual resistance
If current is flowed through a thermistor, any heat
will be generated in the thermistor by which its
resistance will be decreased, however, a decrease
of a resistance will be stabilized at a saturation
resistance value which is determined by impressed
electric power and a dissipation constant. The
residual resistance value means maximum
saturation resistance value when the maximum
permissible current is flowed through the thermistor.
Temperature coefficient
The temperature coefficient of a thermistor is
expressed by the following equation ;
Ϫ
B
T2
( % / Њ C)
Dissipation factor
If small voltage is applied to a thermistor, small
current will flow which produce enough heat in the
thermistor. Dissipation factor is electric power
which make 1Њ C raise by heat in a thermistor.
ϭ
P
t
(mW/ Њ C)
P is applied electric power.
t is rised temperature of the thermistor.
Maximum permissible current
If the maximum permissible current flows to a
thermistor at 25ЊC, temperature of the thermistor
rises to 200ЊC, (160ЊC). When ambient temperature is
above 25ЊC, the maximum permissible current shall be
over reduced as the maximum permissible current
reduction curve.
New Power Thermistor MARK
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200
Ambient temperature (ЊC)
Power Thermistor
1.2
1.1
1.0
0.9
0.8
W TYPE
0.7
0.6
D TYPE
0.5
0.4
0.3
0.2 Ϫ10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160
Ambient temperature (ЊC)
Reliability tests
MARK
Dry heat test
Test sample is exposed in air at 200ЊC for 1,000
hours. R25/R25 Ϯ20%
Damp heat test
Test sample is exposed in atmosphere of 95%RH at
40ЊC for 1,000 hours. R25/R25 Ϯ10%
Test sample is applied the maximum rating current
in air at 25ЊC for 1,000 hours. R25/R25 Ϯ20%
Change of temperature
Test sample is given 10 times of the following
temperature cycle,
Ϫ40ЊC for 30 minutes room temperature for 5
minutes
200ЊC for 30 minutes room temperature for 5
minutes.
R25/R25 Ϯ10%
POWER THERMISTOR
Dry heat test
Test sample is exposed in air at 160ЊC for 1,000
hours. R25/R25 Ϯ10%
Damp heat test
Test sample is exposed in atmosphere of 95%RH at
40ЊC for 1,000 hours. R25/R25 Ϯ10%
Test sample is applied the maximum rating current
in air at 25ЊC for 1,000 hours. R25/R25 Ϯ10%
Change of temperature
Test sample is given 10 times of the following
temperature cycle,
Ϫ30ЊC for 30 minutes room temperature for 5
minutes
160ЊC for 30 minutes room temperature for 5
minutes.
R25/R25 Ϯ10%
Resistance-temperature characteristics
The theoretical characteristics of a thermistor is expressed by following equation.
R1 ϭ R2 exp
B
1
T1
Ϫ
1
T2
R1 is the zero-power resistance at absolute temperature T1
R2 is the zero-power resistance at absolute temperature T2
B is constant which depends on the material used to
make the thermistor. Unless otherwise specified, all
values of B are determined from measurements made
at 25ЊC and 85ЊC.
MARK
100
B : 3150K
10
1.0
0.1
0.01
200 160
100
50 25
0
Ϫ25
Temperature (ЊC)
MARK
100
B : 2900K
10
1.0
0.1
0.01
200 160
100
50 25
0
Ϫ25
Temperature (ЊC)
Power Thermistor B : 3250K
20.0
10.0
5.0
3.0
2.0
1.0
0.5
0.3
0.2
0.1
0.05
0.03
0.02
160
100
50
25
0
Ϫ30
Temperature (ЊC)
22