NTC POWER THERMISTOR, SCK SERIES Meritek NTC THERMISTOR-INRUSH CURRENT LIMITING DEVICES
Meritek NTC Power Thermistor (SCK) devices are made of a specially formulated metal oxide ceramic material which is capable of suppressing high inrush current surges. SCK devices, being of relatively high resistance, shall limit the inrush current for I - 2 seconds during which time the device decreases in resistance substantially to a point where its voltage drop is negligible. The devices are especially useful in power supplies (see Fig A) because of th e extremely low impedance of the capacitor being charged, of which the bridge is usually subjected to an exceedingly high current surge at turn on point.
FEATURES * High inrush current restriction effect. * Small power loss in stationary state. (Normally IW or less than 50W power.) * High thermal and electrical stability. * Wide selection of electrical characteristics. * Special coating material: gray silicone.
NTC THERMISTOR CHARACTERISTICS To choose for application or take as referable parameters, the NTC thermistors are usually decided by the following three fundamental characteristics: * Temperature-Resistance Characteristic: The resistance value of NTC thermistor is decreased while the ambient temperature or itself temperature is increased. (see Fig.D)
APPLICATIDN As shown in Fig. B, the current surge can be eliminated by placing a NTC thermistor in series with a filament string. Yet, if the resistance of one NTC thermistor does not provide sufficient inrush current limiting functions for your application, two or more may be used in series or in separate legs of the supply circuit(Fig. A). Notic that , the thermistor cannot be used in parallel since one unit will tend to conduct nearly all the current available. Thus, SCK thermistor may be used in the AC(point AI or A2) or the DC(point DI or D2) locations in the circuit.(See Fig. A) The resistance of NTC thermistors is designed higher than the total resistance of filaments when the circuit is turned on. As current begins flowing, the thermistor shall immediately "self-heat". Then, in I - 2 seconds, its resistance will be reduced to a minimum and become insignificant to the total resistance of a circuit. With the same concept, current surges in electric motors can be held to a minimum. Fig. C shows a typical DC motor's turn on surge before and after the application of a SCK thermistor to the circuit.
• • • • •
o
Nominal resistance at 25 C (Ω) Zero-power resistance (Ω) Tolerance on the resistance nominal ∆R25/R25=15%(L),20%(M) o Material constant(Sensibility index)( K) o Temperature coefficient of resistance(% C)
R25 RT
B
α
T
O.01
NTC POWER THERMISTOR, SCK SERIES Meritek
Voltage-Current Characteristic:
PARAMETERS DEFINITION
When operating in small current (see Fig.E), the low power will Not allow the NTC thermistor self-hot, thus its resistance value is thus maintained constant and displayed with a linear curve (in conformity with Ohm-law V/R=I ). If the current is increased, the NTC thermistor will follow Joule-efficiency(P=V x I ) and make itself self-heated, resulting in a decreasing resistance value current and voltage are then inversely related.
Thermistor A thermistor is a thermally sensitive resistor whose primary function is to exhibit a change in resistance accompanying a change in temperature.
Negative Temperature Coefficient (NTC) Thermistor NTC thermistor is a thermistor whose the zero-power resistance decreases while itself temperature is increased.
Inrush current Inrush current is the initial surge of current that results when power is first applied to a load having a low starting impedance, such as a discharged capacitor, a cold lamp filament, or a stopped motor, etc.
Inrush current limiter
• • •
Thermal dissipation coefficient(mW/oC) δ Maximum steadystate current(A) Imax Resistance at maximum current(Ω) RImax
Temperature-Time Characteristic: As shown in Fig. F which explains the time needed to reach the thermal equilibrium of NTC components with the environment. This characteristic depends on two important parameters as outlined below. If a step change in temperature is applied to a component e.g. from high(T1) to low(T0) temperature, the energy lost by the component(-HdT) is equal to the energy dissipated by it (δ (T-T0) dt ). -HdT= (δ (T-T0) dt This equation yields:T-T1=( T0T1) X e 1/4 , t =H/δ
O.02
Specially designed and constructed NTC thermistor may be used as an inrush current limiters. Meritek’s inrush current limiter(SCK) is available in a wide range of current handling and zero-power resistance value combinations.
Zero-power resistance( Rt ) The zero-power resistance is the direct current resistance value of a thermistor measured at a specified temperature "T" with a power dissipation by the thermistor low enough that any further decrease in power will result in less than 0. I percent change in resistance.
Maximum steady-state current (Imax.) The maximum steady-state current is the rating of the maximum current, normally expressed in amperes (A), allowable to be conducted by an inrush limiting NTC thermistor for an extended period of time.
Resistance at maximum current (Rlmax.) The resistance at maximum current is the approximate resistance of an inrush current limiting thermistor, expressed in ohms(Ω), when it is conducting its rated maximum steady state current.
NTC POWER THERMISTOR, SCK SERIES Meritek
Thermal dissipation coefficient( δ )
Surge energy
The thermal dissipation coefficient is the ratio, normally expressed in milliwatts per degree C (mW/oC), at a specified ambient temperature, of a change in power dissipation in a thermistor to the resultant body temperature change. (δ =VXI/∆T)
Surge energy is the maximum energy of pulses. The thermistor is capable of tolerating surge energy more than 1000 times with the resistance changing rates within ± 10%. This energy varies with voltage and capacitance.
Thermal time constant( t ) The thermal time constant is the time required for a thermistor to change 63.2 percent of total difference between its initial and final body temperature when subjected to a step function change in ambient temperature under zeropower condition and is normally expressed in seconds.
Material constant(B) The material constant of a NTC thermistor is a measure of its resistance at one temperature compared to its resistance at a different temperature. Its value may be calculated by the formula shown below and is expressed in degrees kelvin (oK ). The reference temperature used in this formula for determining material constant rating of Meritek’s thermistor is 298.15'oK and 323.15 oK B=Ln(R1/R 2)/( 1/T1-1/T2 )
o
Storage temperature range:- 40 to +125 C o Operating temperature range:- 30 to +125 C
DERATING CURVE OF SURGE CURRENT LIMITING THERMISTOR The maximum power of a thermistor will decrease with the change of ambient temperature.(See Fig.G)
Temperature coefficient of resistance (α α) The temperature coefficient of resistance is the ratio at a specified temperature, T, of the rate of change of zero-power resistance with temperature to the zeropower resistance of the thermistor. The temperature coefficient is commonly expressed in percent per degree C(%/oC). α =I /R dR/dT
O.03
NTC POWER THERMISTOR, SCK SERIES Meritek
Zero Power Resistance o at 25 C (W)
Max. Steady State Current o at 25 C (A)
Approx. Resistance at Max. Current o at 25 C ( mW )
Thermal Dissipation Constant o ( mW/ C )
Thermal Time Constant ( Sec. )
Operating Temperature o (C )
SCK05-052
5
2
429
14
17
-40~+150
SCK05-101
10
1
1126
15
17
-40~+150
SCK05-20X3
20
0.3
5560
14
22
-40~+150
SCK08-042
4
2
441
17
31
-40~+170
SCK08-053
5
3
261
17
36
-40~+170
SCK08-063
6
3
283
17
38
-40~+170
SCK08-082
8
2
520
16
36
-40~+170
SCK08-102
10
2
542
17
38
-40~+170
SCK08-152
15
2
548
15
38
-40~+170
SCK08-201
20
1
1544
17
41
-40~+170
SCK08-30X
30
0.5
4094
16
33
-40~+170
SCK10-2R55A
2.5
5
120
18
46
-40~+170
SCK10-034
3
4
156
18
45
-40~+170
SCK10-035
3
5
119
18
45
-40~+170
SCK10-044
4
4
161
16
40
-40~+170
SCK10-054
5
4
180
17
33
-40~+170
SCK10-083
8
3
278
17
43
-40~+170
SCK10-103
10
3
297
17
46
-40~+170
SCK10-122
12
2
512
18
50
-40~+170
SCK10-123
12
3
301
18
50
-40~+170
SCK10-133
13
3
356
18
49
-40~+170
SCK10-152X
15
2.5
442
17
51
-40~+170
SCK10-162
16
2
604
18
55
-40~+170
SCK10-162X
16
2.5
442
16
45
-40~+170
SCK10-202
20
2
646
17
54
-40~+170
SCK10-252
25
2
674
17
52
-40~+170
SCK10-302
30
2
700
17
50
-40~+170
SCK10-472
47
2
720
18
49
-40~+170
SCK10-501X
50
1.5
1170
18
48
-40~+170
SCK10-502
50
2
813
18
48
-40~+170
SCK10-801
80
1
2236
17
53
-40~+170
SCK10-1001
100
1
2318
17
45
-40~+170
SCK10-1201
120
1
2406
19
54
-40~+170
Part No
O.4
NTC POWER THERMISTOR, SCK SERIES 13 ∅ & 15 ∅
Meritek
Zero Power Resistance o at 25 C (W)
Max. Steady State Current o at 25 C (A)
Approx. Resistance at Max. Current o at 25 C ( mW )
Thermal Dissipation Constant o ( mW/ C )
Thermal Time Constant ( Sec. )
Operating Temperature o (C )
SCK13-1R37
1.3
7
70
17
49
-40~+200
SCK13-2R55
2.5
5
117
17
61
-40~+200
SCK13-2R56
2.5
6
94
17
48
-40~+200
SCK13-055
5
5
166
18
75
-40~+200
SCK13-084
8
4
206
17
65
-40~+200
SCK13-104
10
4
217
17
66
-40~+200
SCK13-124
12
4
217
17
66
-40~+200
SCK13-153
15
3
343
18
66
-40~+200
SCK13-163
16
3
348
16
68
-40~+200
SCK13-203
20
3
410
20
76
-40~+200
SCK15-1R38
1.3
8
64
21
59
-40~+200
SCK15-1R58
1.5
8
62
21
66
-40~+200
2
8
78
20
63
-40~+200
2.5
8
75
20
63
-40~+200
SCK15-037
3
7
91
21
73
-40~+200
SCK15-046
4
6
117
20
62
-40~+200
SCK15-048
4
8
87
27
76
-40~+200
SCK15-056
5
6
121
20
66
-40~+200
SCK15-057
5
7
98
20
65
-40~+200
SCK15-065
6
5
159
20
74
-40~+200
SCK15-075
7
5
161
20
79
-40~+200
SCK15-078
7
8
108
28
57
-40~+200
SCK15-086
8
6
130
20
68
-40~+200
SCK15-105
10
5
178
20
79
-40~+200
SCK15-125
12
5
185
19
59
-40~+200
SCK15-152
15
2
704
21
77
-40~+200
SCK15-154
15
4
261
19
79
-40~+200
SCK15-164
16
4
261
19
79
-40~+200
SCK15-204
20
4
283
18
90
-40~+200
SCK15-253
25
3
425
21
76
-40~+200
SCK15-303
30
3
461
20
90
-40~+200
SCK15-403
40
3
511
22
83
-40~+200
SCK15-404
40
4
360
22
86
-40~+200
SCK15-473
47
3
501
20
77
-40~+200
SCK15-802X
80
2.5
693
19
71
-40~+200
SCK15-1202
120
2
1010
19
65
-40~+200
Part No
SCK15-028 SCK15-2R58
O.05
NTC POWER THERMISTOR, SCK SERIES 20 ∅
Meritek
Zero Power Resistance o at 25 C (W)
Max. Steady State Current o at 25 C (A)
Approx. Resistance at Max. Current o at 25 C ( mW )
Thermal Dissipation Constant o ( mW/ C )
Thermal Time Constant ( Sec. )
Operating Temperature o (C )
SCK20-0R78
0.7
8
59
28
96
-40~+200
SCK20-0R715
0.7
15
35
29
122
-40~+200
1
20
20
25
73
-40~+200
SCK20-2R512
2.5
12
60
29
104
-40~+200
SCK20-2R515
2.5
15
46
29
103
-40~+200
SCK20-058
5
8
93
28
101
-40~+200
SCK20-0510
5
10
82
29
123
-40~+200
SCK20-0512
5
12
66
29
124
-40~+200
SCK20-106
10
6
173
32
100
-40~+200
SCK20-108
10
8
122
29
119
-40~+200
SCK20-128
12
8
106
24
130
-40~+200
SCK20-138
13
8
106
24
130
-40~+200
SCK20-206
20
6
190
28
107
-40~+200
Part No
SCK20-0120
Dimensions:
O.6
Unit: mm
Disc Ø
D max
L min
d
P
Tmax
05
6.5
31
0.8 ± 0.02
4 ± 0.6
5
08
9.5
31
0.8 ± 0.02
5 ± 0.8
5
10
11.5
31
0.8 ± 0.02
5 ± 0.8
5
13
14.5
30
0.8 ± 0.02
7.5 ± 1.1
6
15 20
16.5 21.5
29 26
1.0 ± 0.02 1.0 ± 0.02
8 ± 1.2 8 ± 1.2
6 6
NTC POWER THERMISTOR, SCK SERIES Meritek
• R-T CHARACTERISTIC
5∅
8∅ 1000
1000
RESISTANCE - TEMPERATURE
RESISTANCE - TEMPERATURE
CURVE OF 8 φ SERIES
CURVE OF 5φ SERIES
100
RESISTANCE - OHM
RESISTANCE - OHM
100
SC K -2 0X 3 SC K -1 01
10
SC K -0 52
SC SC KK 201 -1 SC 52 K SC -1 02 K 08 SC 2 SC KK 053 -0 42
10
1
1
0.1 -30 -20
-10
0
10
20
30
40
50
60
70
80
90
0.1
100 110 120 130 140 150
-30 -20 -10
0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
TEMPERATURE
•
TEMPERATURE
V-I CHARACTERISTIC CURVE
5∅
8∅ 10
1Ω
0.05
0.1
0.2
0.5
1
2
5
10
20
Ω 05 0.
Ω
SC
K
-0
0.2
50
100
0.1 0.01
Ω
0.02
01 0.
S SC CKK- 20 S SC CK- 152 1 1 K S - 0 SC CK- 082 2 K- 053 04 2
0.0 1Ω
K
52
-1
01
SC SC
0.02
0.2 Ω
0.
0.0 2Ω
02
0.0 5Ω
0.1 Ω
3 0X
1
K
-2
0.1 Ω
0.2 Ω
VOLTAGE (V)
0.5 Ω
0.5 Ω
2Ω
5Ω
Ω
10
Ω
20
Ω
50
0Ω
10
20
1Ω
2Ω
5Ω
Ω
10
Ω
20
Ω
50
0Ω 10
0Ω 20
W
VOLTAGE (V)
50
W
W
20
10
5W
2W
1W
2
0.5
0.1 0.01
W 0.5
W
1
0.2
W 0.2
5
5W 0.0
W
05
2
0.5
W 0.1
50
W
W
20
10
2W
1W
5W
5W
0.
2W
0.
1W
0.
0.
5
0Ω
10
0.05
0.1
0.2
0.5
1
2
5
10
20
50
100
CURRENT (A) CURRENT (A)
O.07
NTC POWER THERMISTOR, SCK SERIES Meritek
• R-T CHARACTERISTIC
10 ∅
13 ∅
10000 1000 RESISTANCE - TEMPERATURE RESISTANCE - TEMPERATURE
CURVE OF 10φ SERIES 1000
C U R V E O F 1 3φ S E R I E S
100
SC K SC -12 K 01 SC -80 K- 1 50 1X SC S C K2 K 0 SC - 1 6 2 2 SC KSC K-0 103 K- 83 05 SC 4 K2R 55 A SC K01 5
10
RESISTANCE - OHM
RESISTANCE - OHM
100
SC K SC -203 K SC -15 3 SC K K -104 -08 SC 4 K -0 55
10
SC K -2R 56
1
SC K -1R 37 1
0.1
0.01
0.1 -30 -20 -10
0
10
20
30
40
50
60
70
80
9 0 100 110 120 130 140 150
-30 -20 -10
0
10
20
30
TEMPERATURE
•
10 ∅
V-I CHARACTERISTIC CURVE
80
90 100 110 120 130 140 150
1Ω
0.2 Ω
0.5 Ω
2Ω
5Ω
Ω
10
Ω
20
Ω
0Ω
0Ω 20
50
0.0 5Ω
0.1 Ω
0.0 2Ω 0.0 1Ω
Ω 01 0.
K-
1R SC
K-
SC K01 5
SC
37
Ω
10 56
Ω 05 0. 0.
0.5
2R
VOLTAGE (V)
0.2 Ω 0.1 Ω
02
1 S SC CKS K 20 SC CK -153 3 K 1 SC - 0 K- 084 4 05 5
1Ω 0.5 Ω
2Ω
5Ω
Ω
10
Ω
20
Ω
50
0Ω 10
0Ω 20
SC KS 20 S CK 2 SC CK- -16 10 2 K SC 3 K- 083 05 SC 4 K2R 55 A
W
SC SC K- K SC 80 -12 1 K01 50 1X
50
W
W
20
2
0.2
0.2
0.5
1
CURRENT (A)
O.08
10
0.1
5W
0.05
2W
0.02
1W
0.1 0.01
W 0.5
0.2
W 0.2
5
5W 0.0
0.5
W 0.1
W
VOLTAGE (V)
70
13 ∅
50
W
W
20
10
5W
2W
1W
W 0.5
W 0.2
5W 0.0
1
60
10
W 0.1
2
50
TEMPERATURE
10
5
40
2
5
10
20
50
100
0.1 0.01
0.02
0.05
0.1
0.2
0.5
1
CURRENT (A)
2
5
10
20
50
100
NTC POWER THERMISTOR, SCK SERIES Meritek
• R-T CHARACTERISTIC
15 ∅
20 ∅
1000
1000 RESISTANCE - TEMPERATURE
RESISTANCE - TEMPERATURE CURVE OF 15φ SERIES
CURVE OF 20 φ SERIES 100
100
RESISTANCE - OHM
10
K-
47
3
RESISTANCE - OHM
SC
S S CK SC CK-2 -403 K 5 SC -20 3 K- 4 SC 164 K
SC -10 SC K-0 5 K- 75 05 SC 6 K0 37 SC S K
CK -2R -1R 58 SC 58 K1R 38
1
10
SC K20 6 SC K10 8 SC K05 12 SC K2R 51 5
SC K01 20
1
0.1
0.1
0.01 -30
0.01 -20 -10
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150
-30 -20 -10 0
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
TEMPERATURE
TEMPERATURE
•
V-I CHARACTERISTIC CURVE
15 ∅
20 ∅
1Ω
2Ω
5Ω
10 Ω
20 Ω
0Ω
0Ω
10
1Ω
0.1 0.01
0.02
0.05
0.1
0.2
2Ω 0. 0.0 5Ω
0.1 Ω
0.0 2Ω
6
0.1 0.5
1
2
5
10
20
50
0.0 1Ω
8 SC
0.2
SC K01 20
0.2
SC K05 SC 12 K2R 51 5
K-
0.5
SC
0. 01 Ω
K-
20
0. 02 Ω
1
SC
K SC -1 05 S C K-0 K 75 S -0 SC C 5 K K 6 -2R - 0 58 SC 37 K -1 SC R5 K 8 -1 R3 8
SC SC K-4 03
0.5
SC K -2 SC K-2 53 K 04 -16 4
SC
K
-4
1
2
10
73
0. 05 Ω
0. 1Ω
2
VOLTAGE (V)
0.2
Ω
0.
0.5 Ω
W
W
5Ω
2Ω
5Ω
Ω
10
Ω
20
Ω
50
0Ω
0Ω
10
20
W
W
05
05
VOLTAGE (V)
50
20
W 10
5W
2W
1W
W 0.5
0.
5
W 0.2
W
W 0.1
50
W
W
20
10
2W
1W
5W
5W
0.
0.
2W
1W
0.
0.
5
50 Ω
10
20
10
100
0.01
0.02
0.05
0.1
0.2
0.5
1
2
5
10
20
50
100
CURRENT (A) CURRENT (A)
CURRENT (A)
O.09
