Electronic Components Datasheet Search |
|
307C1308 Datasheet(PDF) 2 Page - Vishay Siliconix |
|
307C1308 Datasheet(HTML) 2 Page - Vishay Siliconix |
2 / 5 page 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 (R25) 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 (IH) 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 IH). IT 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 25°C 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 SW -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/mm3 R = zero power resistance of PTCR at 25°C 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 25°C 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 ( ρ) - Determined during sintering process; combined with pellet geometry results in final resistance based on: R25 = zero power resistance at 25°C = ρT 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°) 100K 10K 1K 100 10 2.0 1.0 0.1 PTC RESISTANCE REGION 2 HIGH RESISTANCE REGION 1 BASE RESISTANCE R vs. T Operating Characteristics PTC Temperature TSW 25°C 10 R25 RSW = 2 x R25 100 1000 10000 100000 |
Similar Part No. - 307C1308 |
|
Similar Description - 307C1308 |
|
|
Link URL |
Privacy Policy |
ALLDATASHEET.COM |
Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |