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307C Overcurrent Thermistors
Vishay Cera-Mite
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
APPLICATION DATA
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 I2R 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 2R) is balanced by heat lost due to radiation and conduction. Hold current (IH) 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:
Percent Derating
This relationship is shown in Fig P-2, which provides hold current (IH) 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
140% 120% 100% 80% 60% 40% 20% 70C Curie Material 80C Curie Material 90C Curie Material 105C Curie Material 120C Curie Material
Hold Current (I H ) = Where: D
D( TSW - TA) R PTC Fig P-1
= Dissipation Constant (varies based on disc size, wire type, & coating material)
Typical PTC Current Limiter Application
PTC
0% -10 0 10 20 30 40 50 60 70 80 90 100 110 120
T SW = Switching (Curie) Temperature of PTCR Material TA = Ambient Temperature R PTC = Resistance of PTCR at 25C
Document Number: 23089 Revision 14-May-02
V
AC or DC
Ambient Temperature (C)
LOAD
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307C Overcurrent Thermistors
Vishay Cera-Mite
PTCR Overcurrent Protection
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 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. 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(TSW - TA ) Trip Time (t) = I 2 R - D(T SW - TA ) 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
PTC RESISTANCE 100000
10000 Resistance (log scale)
1000
REGION 1 BASE RESISTANCE
REGION 2 HIGH RESISTANCE
100
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 (TSW) 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 R 25 ). Design flexibility is enhanced by Cera-Mite's wide selection of ceramic PTCR materials with different switching temperatures (Fig P- 4). Fig P-4
100K
RSW = 2 x R25 R25 10 25C TSW R vs. T Operating Characteristics PTC Temperature
PHYSICAL DESIGN CONSIDERATIONS
Diameter (D) - Common diameters range from 4 to 22mm. Thickness (T) - Typical thickness ranges from 1 to 5mm. Curie (Switching) Temperature (TSW) - See Fig P-4. Resistivity () Determined during sintering process; combined with pellet geometry results in final resistance based on: T R25 = zero power resistance at 25C = Area Table 2
How Various Physical Parameters Influence a PARAMETER VOLTAGE & CURRENT CAPABILITY Disc Diameter (D) Increased diameter will increase voltage and current ratings. Disc Thickness (T) Increased thickness will increase voltage rating; may or may not increase current rating. Curie (Switch) (TSW) Typically, lower switch temperature Temperature materials have higher voltage/ current capability. Resistance (R 25 ) Higher resistance will increase voltage capability. Thermal Loading Increased thermal loading typically (Heat Sink) reduces the maximum interrupting current. Wire Leads Wire leads added to a PTCR pellet act as a thermal load resulting in reduced maximum interrupting current. Coating Material Applying coating to a leaded PTCR has minimal effect on voltage/current ratings. PTCs: HOLD CURRENT & TRIP TIME Increased diameter will increase hold current and lengthen trip time. Increased thickness will increase hold current and lengthen trip time. Higher switch temperature materials increase hold current and lengthen trip time. Lower resistance will increase hold current and lengthen trip times. Increased thermal loading increases hold current and lengthens trip times. Depends on thermal conductivity of wire used. Copper will increase hold current and trip time. Applying coating to a leaded PTCR increases hold current/trip time 10-20%. Document Number: 23089 Revision 14-May-02
10K Resistance Ratio
1K
100
10 2.0 1.0 0.1
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.
55C 80C 90C 105C 120C 70C
Curie Temperature C (5)
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.
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307C Overcurrent Thermistors
PTCR Overcurrent Protection
Vishay Cera-Mite
PTC THERMISTORS FOR TELECOMMUNICATIONS
PTC Thermistors provide protection for large digital switches. Vishay CeraMite has pioneered this field with ceramic PTC thermistors working closely with major telephone equipment 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 technology. Fig P-8
Time-Trip Curves for Popular Telecom Pellets
100 RL RSHUNT 50 - 100 mV 3 18 20
PTCR
Fig P-5
C.O. Ground Tip Line Tip C.O. Ring Over-Current Pressure Contact
Fig P-6
Leaded PTCR
Pressure Contact Over-voltage C.O. Tip PTCR Line Tip OV PTCR Line Ring C.O. Ring To Battery C.O. Tip C.O. Ring PTCR OV PTCR Main Switch
PTC THERMISTOR PELLETS FOR TELECOMMUNICATIONS
Table 2
VISHAY Fig P-7 HOLD (IH ) TRIP (IT) RESISTANCE SWITCH SIZE (D) CERA-MITE Solid Ceramic CURRENT CURRENT R25 TEMP. NOMINAL PART Disc mA mA Ohms C mm NUMBER 110 220 30 105 6.5 307C1127 Base 100 200 15 70 8 307C1128 Electrode D 100 200 20 80 8 307C1126 Silver 110 220 18 80 8 307C1268 Electrode 120 240 15 80 8 307C1129 140 280 15 105 8 307C1435 T 110 220 15 70 9.5 307C1134 2.5mm 130 260 15 80 9.5 307C1130 140 280 9 70 9.5 307C1436 Rated Voltage = 60 VDC 150 300 10 80 9.5 307C1437 Rated Current = 3A Maximum Voltage = 220 Vr ms Note 1 Note 2 Note 3
1/2 Time To
Scope
Time (Seconds)
10
307C1130 307C1129 307C1128 307C1126 307C1127
1
0.1 0 .05 1 1.5 2 2.5 Current (Amperes) Operating Time to 50% Current
Note 1 Hold and trip currents are specified at 25C ambient.
Note 2 R25 is nominal zero power resistance at 25C with tolerance of 20%.
Note 3 All pellets have silver electrodes suitable for pressure contact mounting. Fig P-10
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
15 85 275 A B C PTCR Current Limiter A = 1.5 sec. B = 5 sec. C = 30 min.
Time VS. Current Curves for High Current Surges (25C)
10,000
Time (Milliseconds)
1,000
10 ohm, 80C Pellets for Diameters (mm 14.5mm 12.5mm 11.0mm 9.5mm 8.0mm 6.5mm
100
Variable Voltage Source 0-600V 60Hz
Timed Interrupter
2
Current Probe or 26 AWG Pair
10 2 4 6 8 10 12 14 16
t Let Through
Current (Amperes)
Document Number: 23089 Revision 14-May-02
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307C Overcurrent Thermistors
Vishay Cera-Mite
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 application. Mechanical packaging influences performance ratings.
PTCR Overcurrent Protection
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 Continuous Carry Current (mA) Ambient 25 to 50C (inversely proportional to resistance) Approximate Minimum Power to Trip or Reset (watts) Interrupting Capability A. Repetitive (25 to 300 VRMS) Peak power in watts B. Non-repetitive (for 10 ohm pellet) I 2 t Let Through Maximum Safe Interrupting Voltage (rms) (voltage rating is proportional to resistance) 600 2.5 300 700 4.0 350 800 7.5 400 900 15 450 1000 20 500 1100 30 600 7 to 25 5 to 20 4 to 17 2 to 15 1 to 10
60 - 120 75 - 175 100 - 200 110 - 250 130 - 400 150 - 600
0.4
0.5
0.6
0.7
0.8
0.9
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.
Fig P-11 1000
10 x 1000 sec. 1000V peak
PTCR
Pass-Thru Pulse
WIRE LEADED PTC TELECOM THERMISTORS
Resettable current limiters featuring hold current and voltage ratings for telecommunication applications. Fig P-12
Tinned Copper Wire 22 AWG Standard 20 AWG on D=14.5mm 5mm max 32mm min 4.5mm max D LS = 5mm
Table 4
TELECOM CURRENT LIMITERS
VISHAY Note 1 HOLD (IH) TRIP (I T) RESISTANCE SWITCH SIZE (D) MAX. CERA-MITE Hold and trip CURRENT CURRENT R25 TOL. TEMP. NOMINAL VOLTAGE PART VRMS mA mA Ohms % C mm NUMBER currents specified at 70 100 100 110 110 120 120 120 130 120 120 150 120 125 135 150 170 110 125 140 200 200 220 220 240 240 240 260 240 240 300 240 250 270 300 340 220 250 Note 1 100 20 30 18 25 15 20 25 13 39 25 12 15 20 10 10 10 23 18 Note 25 20 20 20 20 20 20 20 20 30 25 20 25 20 25 20 20 20 25 2 120 80 105 80 105 80 105 120 80 120 105 90 80 105 80 105 105 80 80 6.5 8 8 8 8 8 8 8 8 8.7 8.7 8.7 9.5 9.5 9.5 9.5 11.2 14.5 14.5 265 220 220 220 220 220 220 220 120 250 250 110 220 220 220 220 220 300 265 307C1418 307C1305 307C1506 307C1354 307C1514 307C1129 307C1296 307C1470 307C1421 307C1505 307C1501 307C1439 307C1465 307C1507 307C1469 307C1233 307C1234 307C1262 307C1254 Note 3
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
Rated Voltage = 60Vdc; Rated Current = 3A at rated voltage.
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Document Number: 23089 Revision 14-May-02
307C Overcurrent Thermistors
PTCR Overcurrent Protection
Table 5
Vishay Cera-Mite
GENERAL PURPOSE PTC CURRENT LIMITERS
GENERAL PURPOSE PTC THERMISTORS OVERCURRENT PROTECTORS
RATED VOLTAGE VRMS 12 12 12 24 24 24 50 50 50 50 50 120 120 120 120 120 120 240 240 240 240 240 240 240 240 240 MAX. HOLD (I H ) VOLTAGE CURRENT VRMS mA 15 15 15 30 30 30 60 60 60 60 60 140 140 140 140 140 140 375 340 310 265 265 320 320 265 265 130 170 600 130 175 600 60 120 150 325 475 60 85 95 115 105 350 20 28 31 34 40 45 55 65 90 Note 1 TRIP (I T ) MAX. CURRENT CURRENT mA A 260 340 1200 260 350 1200 120 240 300 650 950 120 170 190 230 210 700 40 56 62 68 80 90 110 130 180 1.1 2.4 10 2.3 3.4 11 0.8 2 2.6 10 12 0.6 0.8 1.5 2 1 5 0.2 0.3 0.33 0.34 0.45 0.4 0.5 0.6 1 RES R25 Ohms 13 6 1.2 10 6 1.3 50 12 10 3.5 2 50 30 39 27 20 4.5 600 300 240 200 125 150 100 70 45 Note 2 SWITCH TEMP C 120 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 105 D MAX. mm 5.5 8 16 8 9.5 17.5 6.5 8 9.5 14.5 17.5 6.5 8 11 12.5 9.5 19 6.5 6.5 6.5 6.5 6.5 9.5 11 9.5 11 VISHAY CERA-MITE PART NUMBER 307C1455 307C1308 307C1311 307C1315 307C1429 307C1318 307C1321 307C1323 307C1548 307C1325 307C1326 307C1329 307C1330 307C1302 307C1303 307C1331 307C1333 307C1335 307C1336 307C1337 307C1338 307C1340 307C1339 307C1341 307C1342 307C1343 Note 3
* Designed as resettable current limiters, PTC thermistors offer an alternative to conventional overcurrent 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
Tinned Copper Clad Steel Wire 24 AWG when D < 9.5mm 22 AWG when D > 11mm to < 19mm 20 AWG when D > 21mm 5mm max
4.5mm max D CL LS
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
CUSTOM CURRENT LIMITER GUIDELINES
Table 6
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.
RANGE CHART FOR CUSTOM WIRE LEADED DESIGN
MAX. D (mm) COATED 5.5 6.5 8 9.5 11 12.5 14.5 16 DESIGN LIMITS (APPROX.) VRMS 600 15 600 15 600 15 600 15 600 15 600 15 600 15 600 15 I HOLD OHMS 5 mA 2000 150 mA 13 7 mA 1200 200 mA 8 10 mA 850 275 mA 6 13 mA 500 350 mA 4 20 mA 350 450 mA 2.5 22 mA 250 500 mA 2.0 30 mA 200 650 mA 1.5 35 mA 150 800 mA 1.2 MAX. D (mm) COATED 17.5 DESIGN LIMITS (APPROX.)
VRMS I HOLD OHMS 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 Resistance is propor tional to voltage and inversely propor tional to hold current (I H ) Conformal coating adds 1.5mm
Document Number: 23089 Revision 14-May-02
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