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307C1336 Datasheet(PDF) 1 Page - Vishay Siliconix |
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307C1336 Datasheet(HTML) 1 Page - Vishay Siliconix |
1 / 5 page www.vishay.com 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 2R 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 (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 25°C). 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 25°C according to the following relationship: Hold Current (I H ) = D( T SW - TA) R PTC Where: D = Dissipation Constant (varies based on disc size, wire type, & coating material) T SW = Switching (Curie) Temperature of PTCR Material T A = Ambient Temperature R PTC = Resistance of PTCR at 25°C 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 25°C. 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 70°C Curie Material 80°C Curie Material 90°C Curie Material 105°C Curie Material 120°C Curie Material 140% 120% 100% 80% 60% 40% 20% 0% APPLICATION DATA |
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