g
NTC THERMISTORS: TYPE CL
NTC DISCS FOR INRUSH CURRENT LIMITING
DESCRIPTION:
Disc thermistor with uninsulated lead-wires.
FEATURES:
• Low cost solid state device for inrush current
suppression
• Excellent mechanical strength
• Wide operating temperature range: -50°C to 175°C
• Suitable for PCB mounting
• Available as a standard with kinked leads and on
tape and reel to EIA RS-468A for automatic insertion
TYPE
Fig. 1
CL-11
CL-21
CL-30
CL-40
CL-50
CL-60
CL-70
CL-80
CL-90
CL-101
CL-110
CL-120
CL-130
CL-140
CL-150
CL-160
CL-170
CL-180
CL-190
CL-200
CL-210
Max*
Steady
Res @ State
Disc
25°C Current Dia.
±25% AMPS (Max)
(ohms) (RMS)
(in.)
0.7
1.3
2.5
5
7
10
16
47
120
0.5
10
10
50
50
5
5
16
16
25
25
30
12
8
8
6
5
5
4
3
2
16
3.2
1.7
1.6
1.1
4.7
2.8
2.7
1.7
2.4
1.7
1.5
0.77
0.55
0.77
0.77
0.77
0.77
0.77
0.77
0.93
0.93
0.40
0.40
0.45
0.45
0.55
0.55
0.55
0.55
0.55
0.55
0.40
Lead
Disc
Thick. Spacing
(Ref.)
(Max)
(in.)
(in.)
0.22
0.21
0.22
0.22
0.26
0.22
0.22
0.22
0.22
0.22
0.17
0.17
0.17
0.17
0.18
0.18
0.18
0.18
0.18
0.18
0.20
0.328
0.328
0.328
0.328
0.328
0.328
0.328
0.328
0.328
0.328
0.250
0.250
0.250
0.250
0.328
0.328
0.328
0.328
0.328
0.328
0.250
Lead
Dia.
AWG
18
18
18
18
18
18
18
18
18
18
24
24
24
24
22
22
22
22
22
22
24
Cx (max)**
µFarads
Equation constants for
resistance under load ***
@120
VAC
@240
VAC
X
2700
800
6000
5200
5000
5000
5000
5000
5000
4000
600
600
600
600
1600
1600
1600
1600
800
800
600
600
200
1500
1300
1250
1250
1250
1250
1250
1000
150
150
150
150
400
400
400
400
200
200
150
0.50
0.60
0.81
1.09
1.28
1.45
1.55
2.03
3.04
0.44
0.83
0.61
1.45
1.01
0.81
0.60
1.18
0.92
1.33
0.95
1.02
Approx. Res. Under Load at %
Max. Rated Current
Y
Current
Range
Min. I / Max. I
25%
50%
75%
100%
-1.18
-1.25
-1.25
-1.27
-1.27
-1.30
-1.26
-1.29
-1.36
-1.12
-1.29
-1.09
-1.38
-1.28
-1.26
-1.05
-1.28
-1.18
-1.34
-1.24
-1.35
4.0≤ 1≤ 12
3.0≤ 1≤ 8.0
2.5≤ 1≤ 8.0
1.5≤ 1≤ 6.0
1.5≤ 1≤ 5.0
1.2≤ 1≤ 5.0
1.0≤ 1≤ 4.0
0.5≤ 1≤ 3.0
0.5≤ 1≤ 2.0
4.0≤ 1≤ 16
0.7≤ 1≤ 3.2
0.4≤ 1≤ 1.7
0.4≤ 1≤ 1.6
0.2≤ 1≤ 1.1
1.0≤ 1≤ 4.7
0.8≤ 1≤ 2.8
0.5≤ 1≤ 2.7
0.4≤ 1≤ 1.7
0.5≤ 1≤ 2.4
0.4≤ 1≤ 1.7
0.3≤ 1≤ 1.5
14
.25
.34
.65
.96
1.09
1.55
2.94
7.80
.09
1.10
1.55
5.13
5.27
.66
.87
1.95
2.52
2.63
2.74
3.83
.06
.09
.14
.27
.40
.44
.65
1.20
3.04
.04
.45
.73
1.97
2.17
.27
.42
.80
1.11
1.04
1.18
1.50
.04
.06
.09
.16
.24
.26
.39
.71
1.75
.03
.27
.46
1.13
1.28
.16
.27
.48
.69
.60
.70
.87
.02
.04
.06
.11
.16
.18
.27
.49
1.18
.02
.18
.34
.75
.89
.11
.20
.33
.49
.41
.49
.60
OPTIONS:
DATA:
• For kinked leads, add suffix “A”
• For tape and reel, add suffix “B”
• For tape and reel, add suffix “AB”
• Other tolerances in the range 0.7Ω to 120Ω
• Other tolerances, tolerances at other temperatures
• Alternative lead lengths, lead materials, insulations
*maximum rating at 25ºC or
Iderated =
Diss.
Time
Const. Const.
(mW/°C) (sec.)
25
15
25
25
25
25
25
25
30
30
8
4
8
4
15
9
15
9
15
9
8
100
60
100
100
120
100
100
100
120
120
30
90
30
90
110
130
110
130
110
130
30
√(1.1425–0.0057 x TA) x Imax @ 25°C
for ambient temperatures other than 25ºC.
**maximum ratings
***R0=X1Y where X and Y are found in the table above
g
NTC THERMISTORS: TYPE CL
NTC DISCS FOR INRUSH CURRENT LIMITING
RI
-tº
TYPICAL POWER SUPPLY CIRCUIT
INRUSH CURRENT LIMITERS IN
SWITCHING POWER SUPPLIES
•
•
The problem of current surges in switch-mode power supplies
is caused by the large filter capacitors used to smooth the ripple in the rectified 60Hz current prior to being chopped at a
high frequency. The diagram above illustrates a circuit commonly used in switching power supplies.
•
•
•
In the circuit above the maximum current at turn-on is the
peak line voltage divided by the value of R; for 120v, it is
approximately 120 x 公2/RI. Ideally, during turn-on RI should be
very large, and after the supply is operating, should be
reduced to zero. The NTC thermistor is ideally suited for this
application. It limits surge current by functioning as a power
resistor which drops from a high cold resistance to a low hot
resistance when heated by the current flowing through it.
Some of the factors to consider when designing NTC thermistor as an inrush current limiter are:
Maximum permissible surge current at turn-on
Matching the thermistor to the size of the filter
capacitors
Maximum value of steady state current
Maximum ambient temperature
Expected life of the power supply
Maximum Surge Current
The main purpose of limiting inrush current is to prevent
components in series with the input to the DC/DC convertor
from being damaged. Typically, inrush protection prevents
nuisance blowing of fuses or breakers as well as welding of
switch contacts. Since most thermistor materials are very
nearly ohmic at any given temperature, the minimum no-load
resistance of the thermistor is calculated by dividing the peak
input voltage by the maximum permissible surge current in
the power supply (Vpeak/Imax surge).