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11
307C Overcurrent Thermistors
Vishay Cera-Mite
Document Number: 23089
Revision 14-May-02
ceramite.support@vishay.com
PTCR Overcurrent Protection
FEATURES:
Sizes For Your Application - Hold currents from 5 mA to 1.5 A are available
in sizes from 4 to 22mm.
Better Protection, Maintenance Free - PTCRs reset after an overcurrent
situation. Protection levels may be set lower than possible with fuses, without
worrying about nuisance trips.
Resetting, Non Cycling - Functioning as a manual reset device, PTCR
overcurrent protectors remain latched in the tripped state and automatically
reset only after voltage has been removed. This prevents continuous cycling,
and protects against reclosing into a fault condition.
Simplified Mounting - PTCRs may be mounted directly inside end use
equipment. Unlike fuses, no bulky fuseholder or access for user replacement
is required.
Ceramic Material Selection - Various curie materials are available to tailor
hold and trip current operating points.
Repeatable, No Hysteresis - After resetting, ceramic PTCRs return to the
initial resistance value, providing repeatable, consistent protection levels.
Unlike polymer type PTCRs, Vishay Cera-Mite devices exhibit no resistance
hysteresis application problems.
Telecom Line Balance - In telecom circuits matched pairs are used to
maintain line balance. Unlike polymer PTCRs, ceramic devices maintain
balance after resetting.
A NEW DIMENSION
The Positive Temperature Coefficient
Resistor's (PTC thermistor) unique property
of dramatically increasing its resistance
above the curie temperature makes it
an excellent candidate for overcurrent
protection applications. Overcurrent
situations in electronic devices occur
due to voltage fluctuations, changes in
load impedance, or problems with system
wiring. PTC thermistors monitor current in
series connected loads, trip in the event
of excess current, and reset after the
overload situation is removed, creating a
new dimension of flexibility for designers.
APPLICATIONS:
Telecommunication Products
Electronic Power Supplies
Automotive Motor Protection
Industrial Control Systems
In a typical current limiter application, the PTC device is connected in series
with a load impedance (Fig P-1). When current (I) flows, internal I
2
R losses
attempt to increase the PTCR's temperature. To maintain the low resistance
"on" state, stabilization must occur below the switching temperature, where
the heat generated (I
2
R) is balanced by heat lost due to radiation and
conduction.
Hold current (I
H
) is the maximum continuous current at which a PTCR can
be maintained in a low resistance "on" state while operating at rated ambient
temperature (typ 25C). To prevent nuisance tripping, choose the rated hold
current to be greater than the normal current expected.
Since heat dissipated by the device is proportional to the ambient temperature,
hold current must be derated for ambients higher than 25C according to
the following relationship:
Hold Current (I
H
) = D( T
SW
- T
A
)
R
PTC
Where:
D = Dissipation Constant
(varies based on disc
size, wire type, &
coating
material)
T
S W
= Switching (Curie)
Temperature
of
PTCR
Material
T
A
= Ambient
Temperature
R
P T C
= Resistance of PTCR
at
25C
Fig P-1
Typical PTC Current Limiter Application
This relationship is shown in Fig P-2,
which provides hold current (I
H
) derating
estimates for ambient temperatures in
excess of 25C. Five curie materials
illustrate the design flexibility offered by
ceramic PTCR's.
Fig P-2
PTC Thermistor Overcurrent Protectors
Ambient Temperature Derating of Hold and
Trip Currents
LOAD
PTC
V
AC
or
DC
Ambient Temperature (C)
-10 0 10 20 30 40 50 60 70 80 90 100 110 120
70C Curie Material
80C Curie Material
90C Curie Material
105C Curie Material
120C Curie Material
P
ercent Der
ating
140%
120%
100%
80%
60%
40%
20%
0%
APPLICATION DATA
Document Number: 23089
Revision 14-May-02
www.vishay.com
12
307C Overcurrent Thermistors
Vishay Cera-Mite
ceramite.support@vishay.com
How Various Physical Parameters Influence a PTCs:
PARAMETER VOLTAGE & CURRENT CAPABILITY HOLD CURRENT & TRIP TIME
Disc Diameter (D) Increased diameter will increase voltage Increased diameter will increase
and current ratings. hold current and lengthen trip time.
Disc Thickness (T) Increased thickness will increase Increased thickness will increase
voltage rating; may or may not hold current and lengthen trip time.
increase current rating.
Curie (Switch) (T
SW
) Typically, lower switch temperature Higher switch temperature
Temperature materials have higher voltage/ materials increase hold current
current capability. and lengthen trip time.
Resistance (R
25
) Higher resistance will increase Lower resistance will increase hold
voltage capability. current and lengthen trip times.
Thermal Loading Increased thermal loading typically Increased thermal loading increases
(Heat Sink) reduces the maximum interrupting current. hold current and lengthens trip times.
Wire Leads Wire leads added to a PTCR pellet act as Depends on thermal conductivity of
a thermal load resulting in reduced wire used. Copper will increase
maximum interrupting current. hold current and trip time.
Coating Material Applying coating to a leaded PTCR has Applying coating to a leaded PTCR
minimal effect on voltage/current ratings. increases hold current/trip time 10-20%.
APPLICATION DATA
TRIPPING ACTION DUE TO OVERCURRENT
During normal operation, the PTCR remains in a low base
resistance state (Fig P- 3, Region 1). However, if current
in excess of hold current (I
H
) is conducted, I
2
R losses
produce internal self heating. If the magnitude and time of
the overcurrent event develops an energy input in excess of
the device's ability to dissipate heat, the PTCR temperature
will increase, thus reducing the current and protecting the
circuit.
PTC current limiters are intended for service on telecom
systems, automobiles, or the secondary of control transform-
ers or in similar applications where energy available is limited
by source impedance. They are not intended for application
on AC line voltages where source energy may be high and
source impedance low.
The current required to trip (I
T
) is typically specified as two
times the hold current (2 x I
H
). I
T
is defined as the minimum
rms conduction current required to guarantee thermistor
switching into a high resistance state (Fig P- 3, Region 2) at
a 25C ambient temperature.
Ambient temperature influences the ability of the PTCR to
transfer heat via surface radiation and thermal conduction at
the wire leads. At high ambient temperatures, less energy
input (via I
2
R ) is required to reach the trip temperature. Low
ambients require greater energy input. Approximate derating
effects are shown in Fig P- 2.
Since the tripping operation is due to thermal change, there
is a time-trip curve associated with each device. At relatively
low magnitudes of overcurrent, it may take minutes for the
device to trip. Higher current levels can result in millisecond
response time. Trip time (t) can be calculated as follows
kM(T
S W
- T
A
)
Trip Time (t ) =
I
2
R - D(T
S W
- T
A
)
Where:
k = coefficient of heat absorption = 0.603 J/g/ C
M = mass of PTCR = volume x 5.27x10
- 3
g/mm
3
R = zero power resistance of PTCR at 25C
Fig P-3
CERAMIC MATERIALS
The temperature at which the PTCR changes from the
base resistance to high resistance region is determined by
the PTCR ceramic material. Switching temperature (T
SW
)
described by the boundary between regions 1 & 2 (Fig P- 3),
is the temperature point at which the PTCR has increased
to two times its base resistance at 25C ambient (R
SW
= 2
x R25). Design flexibility is enhanced by Cera-Mite's wide
selection of ceramic PTCR materials with different switching
temperatures (Fig P- 4).
Fig P-4
Table 2
SELF RESETTING - NON CYCLING - REPEATABLE
After tripping, the PTCR will remain latched in its high
resistance state as long as voltage remains applied and
sufficient trickle current is maintained to keep the device
above the switching temperature. After voltage is removed,
the PTCR resets (cools) back to its low resistance state and
is again ready to provide protection.
PHYSICAL DESIGN CONSIDERATIONS
Diameter (D) - Common diameters range from 4 to 22mm.
Thickness (T) - Typical thickness ranges from 1 to 5mm.
Curie (Switching) Temperature (T
SW
) - See Fig P- 4.
Resistivity (
) -
Determined during sintering process; combined
with pellet geometry results in final resistance
based
on:
R
25
= zero power resistance at 25C =
T
Area
PTCR Overcurrent Protection
Vishay Cera-Mite offers
a wide selection of
ceramic PTC materials
providing flexibility for
different ambient
temperatures. Close
protection levels are
possible by designing
resistance and physical
size to meet specific
hold current and trip
current requirements.
Curie Temperature C (5)
Resistance Ratio
100K
10K
1K
100
10
2.0
1.0
0.1
55

C
70

C
80

C
90

C
105

C
120

C
PTC
RESISTANCE
REGION 2
HIGH
RESISTANCE
REGION 1
BASE
RESISTANCE
R vs. T Operating Characteristics
PTC
Temperature
T
SW
25C
10
R
25
R
SW
=
2 x R
25
100
1000
10000
100000
Resistance (log scale)
www.vishay.com
13
307C Overcurrent Thermistors
Vishay Cera-Mite
Document Number: 23089
Revision 14-May-02
ceramite.support@vishay.com
PTCR Overcurrent Protection
VISHAY
HOLD (I
H
) TRIP (I
T
) RESISTANCE SWITCH SIZE (D) CERA-MITE
CURRENT CURRENT R
25
TEMP. NOMINAL PART
mA mA Ohms C mm NUMBER
110 220 30 105 6.5 307C1127
100 200 15 70 8 307C1128
100 200 20 80 8 307C1126
110 220 18 80 8 307C1268
120 240 15 80 8 307C1129
140 280 15 105 8 307C1435
110 220 15 70 9.5 307C1134
130 260 15 80 9.5 307C1130
140 280 9 70 9.5 307C1436
150 300 10 80 9.5 307C1437
Note 1 Note 2 Note 3
Fig P-5
Fig P-6
PTC THERMISTORS FOR
TELECOMMUNICATIONS
PTC Thermistors provide protection
for large digital switches. Vishay Cera-
Mite has pioneered this field with
ceramic PTC thermistors working
closely with major telephone equip-
ment and telephone protection
manufacturers. The requirements are
dynamic, as switch makers continually
strive to protect at lower levels. Vishay
Cera-Mite participates with industry
standard technical committees to
establish common definitions and
understanding of this new tech-
nology.
Over-voltage
Pressure
Contact
Line
Tip
C.O.
Tip
Ground
C.O. Ring
Over-Current
Pressure
Contact
PTCR
Main Switch
C.O. Ring
To Battery
OV
PTCR
C.O. Tip
Leaded PTCR
PTCR
C.O. Tip
C.O. Ring
Line Ring
Line Tip
OV
PTCR
PTC THERMISTOR PELLETS FOR TELECOMMUNICATIONS
Table 2
Fig P-7
Rated Voltage = 60 V
DC
Rated Current = 3A
Maximum Voltage = 220 Vr m s
Fig P-8
Time-Trip Curves for Popular Telecom Pellets
Note 1
Hold and trip currents
are specified at
25C ambient.
Note 2
R
25
is nominal zero power
resistance at 25C with
tolerance of 20%.
Note 3
All pellets have silver elec-
trodes suitable for pressure
contact mounting.
INTERRUPTING CAPACITY ESTIMATES
Under unusual circumstances, telecommunication lines may
be subjected to high surge currents as might occur from
lightning effects or accidental crossing with power lines or
transformer primaries.
Fig P-10 shows trip time curves for higher currents. Estimated
interrupting capability data is also shown in Table 3 and
is expressed as "I
2
t Let Through" based on test data
conducted in accordance with UL 497A and CSA 22.2 No.
0.7-M1985.
The data shown is for reference. Specific short circuit data or
interrupting capability is partially determined by the mounting
means and circuit application.
Fig P-9
Fig P-10
Time VS. Current Curves for High Current Surges (25C)
D
Base
Electrode
T
Silver
Electrode
Solid Ceramic
Disc
2.5mm
Current (Amperes)
Operating Time to 50% Current
0 .05
1 1.5
2
2.5 3
Time (Seconds)
307C1130
307C1129
307C1128
307C1126
307C1127
PTCR
Scope
Time To
R
L
1/2
R
SHUNT
50
- 100 mV
Current (Amperes)
2 4 6 8
10
12 14 16
18
20
10,000
1,000
100
10
Time (Milliseconds)
10 ohm, 80C Pellets for
Diameters (mm
14.5mm
12.5mm
11.0mm
9.5mm
8.0mm
6.5mm
Variable
Voltage
Source
0-600V
60Hz
Current
Probe or
26 AWG
Pair
A = 1.5 sec.
B = 5 sec.
C = 30 min.
A
B
C
PTCR
Current
Limiter
15
85
275
Timed Interrupter
2
t Let Through
100
10
1
0.1
Document Number: 23089
Revision 14-May-02
www.vishay.com
14
307C Overcurrent Thermistors
Vishay Cera-Mite
ceramite.support@vishay.com
PTCR Overcurrent Protection
VISHAY
HOLD (I
H
) TRIP (I
T
) RESISTANCE SWITCH SIZE (D) MAX. CERA-MITE
CURRENT CURRENT R
25
TOL. TEMP. NOMINAL VOLTAGE PART
mA mA Ohms % C mm V
RMS
NUMBER
70 140 100 25 120 6.5 265 307C1418
100 200 20 20 80 8 220 307C1305
100 200 30 20 105 8 220 307C1506
110 220 18 20 80 8 220 307C1354
110 220 25 20 105 8 220 307C1514
120 240 15 20 80 8 220 307C1129
120 240 20 20 105 8 220 307C1296
120 240 25 20 120 8 220 307C1470
130 260 13 20 80 8 120 307C1421
120 240 39 30 120 8.7 250 307C1505
120 240 25 25 105 8.7 250 307C1501
150 300 12 20 90 8.7 110 307C1439
120 240 15 25 80 9.5 220 307C1465
125 250 20 20 105 9.5 220 307C1507
135 270 10 25 80 9.5 220 307C1469
150 300 10 20 105 9.5 220 307C1233
170 340 10 20 105 11.2 220 307C1234
110 220 23 20 80 14.5 300 307C1262
125 250 18 25 80 14.5 265 307C1254
Note 1 Note 2 Note 3
CUSTOM PTCR PELLET
DESIGN CAPABILITY
Vishay Cera-Mite will customize
solid state overcurrent protector
PTCRs to your exact requirements
for telecommunication, power
supply, or general electronic
use. Providing great flexibility to
establish specific voltage, hold
current, time-trip characteristic, and
ambient temperature values.
Each device must be evaluated
and ratings established per appli-
cation. Mechanical packaging
influences performance ratings.
Table 3
RATING CHART FOR CUSTOM PELLETS
DISC DIAMETER (2.5mm THICK) 6.5mm 8mm 9.5mm 11mm 12.5mm 14.5mm
Continuous Voltage Rating (rms)
(proportional to resistance) 100 300 100 300100 300 100 300 100 300 50 - 300
Resistance Range @ 25C (ohms) 10 to 35 7 to 25 5 to 20 4 to 17 2 to 15 1 to 10
Continuous Carry Current (mA)
Ambient 25 to 50C (inversely 60 120 75 175 100 200 110 250 130 400 150 600
proportional to resistance)
Approximate Minimum Power
to Trip or Reset (watts) 0.4 0.5 0.6 0.7 0.8 0.9
Interrupting Capability
A. Repetitive (25 to 300 V
RMS
)
Peak power in watts 600 700 800 900 1000 1100
B. Non-repetitive (for 10 ohm
pellet) I
2
t Let Through 2.5 4.0 7.5 15 20 30
Maximum Safe Interrupting
Voltage (rms) (voltage rating 300 350 400 450 500 600
is proportional to resistance)
Fig P-11
WIRE LEADED PTC
TELECOM THERMISTORS
Resettable current limiters featuring
hold current and voltage ratings for
telecommunication applications.
Fig P-12
TELECOM CURRENT LIMITERS
Rated Voltage = 60Vdc; Rated Current = 3A at rated voltage.
Note 1
Hold and trip
currents specified at
25C ambient.
Note 2
R25 is nominal zero
power resistance
( 25%) at 25C.
Note 3
P/N suffix describes
options including:
Tape & Reel
Wire Size
Wire Style &
Length
Lead Spacing
Coating Material
D
32mm min
4.5mm
max
LS = 5mm
5mm
max
Tinned Copper Wire
22 AWG Standard
20 AWG on D=14.5mm
Pass-Thru Pulse
PTCR
1000
10 x 1000 sec.
1000V peak
Rating applies to pellets with silver electrodes and pressure connections.
TRANSIENT VOLTAGE &
CURRENT
Because of the thermal storage
capacity of the ceramic PTCR,
transient surges do not cause tripping.
The PTCR is considered to be
transparent to these low energy
transients. Fig P-11 shows a typical
test circuit for such transients.
Table 4
www.vishay.com
15
307C Overcurrent Thermistors
Vishay Cera-Mite
Document Number: 23089
Revision 14-May-02
ceramite.support@vishay.com
MAX. DESIGN LIMITS (APPROX.)
D (mm)
COATED V
RMS
I
HOLD
OHMS
17.5 600 40 mA 125
15 950 mA 0.8
19 600 45 mA 100
15 1.1 A 0.7
21 600 55 mA 80
15 1.2 A 0.6
22.5 600 60 mA 70
15 1.3 A 0.5
23.5 600 70 mA 60
15 1.4 A 0.45
25 600 80 mA 50
15 1.5 A 0.4
MAX. DESIGN LIMITS (APPROX.)
D (mm)
COATED V
RMS
I
HOLD
OHMS
5.5 600 5 mA 2000
15 150 mA 13
6.5 600 7 mA 1200
15 200 mA 8
8 600 10 mA 850
15 275 mA 6
9.5 600 13 mA 500
15 350 mA 4
11 600 20 mA 350
15 450 mA 2.5
12.5 600 22 mA 250
15 500 mA 2.0
14.5 600 30 mA 200
15 650 mA 1.5
16 600 35 mA 150
15 800 mA 1.2
PTCR Overcurrent Protection
VISHAY
RATED MAX. HOLD (I
H
) TRIP (I
T
) MAX. RES SWITCH D CERA-MITE
VOLTAGE VOLTAGE CURRENT CURRENT CURRENT R
25
TEMP MAX. PART
VRMS VRMS mA mA A Ohms C mm NUMBER
12 15 130 260 1.1 13 120 5.5 307C1455
12 15 170 340 2.4 6 105 8 307C1308
12 15 600 1200 10 1.2 105 16 307C1311
24 30 130 260 2.3 10 105 8 307C1315
24 30 175 350 3.4 6 105 9.5 307C1429
24 30 600 1200 11 1.3 105 17.5 307C1318
50 60 60 120 0.8 50 105 6.5 307C1321
50 60 120 240 2 12 105 8 307C1323
50 60 150 300 2.6 10 105 9.5 307C1548
50 60 325 650 10 3.5 105 14.5 307C1325
50 60 475 950 12 2 105 17.5 307C1326
120 140 60 120 0.6 50 105 6.5 307C1329
120 140 85 170 0.8 30 105 8 307C1330
120 140 95 190 1.5 39 105 11 307C1302
120 140 115 230 2 27 105 12.5 307C1303
120 140 105 210 1 20 105 9.5 307C1331
120 140 350 700 5 4.5 105 19 307C1333
240 375 20 40 0.2 600 105 6.5 307C1335
240 340 28 56 0.3 300 105 6.5 307C1336
240 310 31 62 0.33 240 105 6.5 307C1337
240 265 34 68 0.34 200 105 6.5 307C1338
240 265 40 80 0.45 125 105 6.5 307C1340
240 320 45 90 0.4 150 105 9.5 307C1339
240 320 55 110 0.5 100 105 11 307C1341
240 265 65 130 0.6 70 105 9.5 307C1342
240 265 90 180 1 45 105 11 307C1343
Note 1 Note 2 Note 3
Table 5
GENERAL PURPOSE PTC THERMISTORS OVERCURRENT PROTECTORS
GENERAL PURPOSE
PTC CURRENT LIMITERS
Designed as resettable current
limiters, PTC thermistors offer an
alter native to conventional over-
current protection devices such as
fuses or circuit breakers.
A wide variety of sizes and current
ranges are available for many
electronic, industrial and automotive
applications. Both standard parts and
custom designs are offered.
Fig P-13
D
4.5mm
max
LS
CL
5mm
max
Tinned Copper Clad Steel Wire
24 AWG when D < 9.5mm
22 AWG when D > 11mm to < 19mm
20 AWG when D > 21mm
CUSTOM CURRENT LIMITER GUIDELINES
Table 6
RANGE CHART FOR CUSTOM WIRE LEADED DESIGN
Conformal coating adds 1.5mm
APPLICATION CONSIDERATIONS:

PTC current limiters are intended for service on
telecom systems, automobiles, or the secondary of
control transformers or in similar applications where
energy available is limited by source impedance. They are
not intended for application on AC line voltages where
source energy may be high and source impedance low.

Fuses and circuit breakers result in total circuit
isolation after tripping. PTC thermistors provide a
current limiting function by switching to a high
resistance mode. Safety consideration must be given
to the potential shock hazard caused by the steady
state leakage current and voltage potential remaining in
the circuit.

Wire leaded PTC current limiting thermistors are intended
for applications which expect a limited number of tripping
operations. Actual life is a function of operating parameters.
For high duty cycle applications, ceramic PTC pellets
mounted in spring contact mechanical housings are
preferred.

Wire size, wire type and coating material can be used to
precisely tailor required operating characteristics.

Options Include: Tape & Reel; Wire Forms; Lead
Spacings.
Resistance is propor tional
to voltage and inversely
propor tional to hold
current (I
H
)
CL - Cut Leads are Standard 4.75 0.5mm
LS - Standard Lead Spacings:
5mm when
D
11mm
7.5mm when D = 12.5 to 17.5mm
10mm when
D
19mm