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AND TEC I INNOVAT O L OGY With Non-Linear Resistors N HN CIRCUIT PROTECTION O 19 62-2012 Resistors - Wide Resistance Range PTC and NTC Thermistors, Through-Hole Varistors TABLE OF CONTENTS Using PTC - Positive Temperature Coefficient Thermistors.................................................02 PTC Overload Protection Principles.....................................................................................02 Using NTC – Negative Temperature Coefficient Thermistors...............................................03 Examples of NTC Circuit Protection....................................................................................03 Rate of Rise Heat Detecting Fire Alarm................................................................................04 Using Through-Hole Varistors..............................................................................................05 Resources • For technical questions contact [email protected] One of the World’s Largest Manufacturers of Discrete Semiconductors and Passive Components Capabilities 1/6 VMN-PL0436-1205 This document is subject to change without notice. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 V i s hay Intertechnolo g y, Inc . I INNOVAT AND TEC O L OGY With Non-Linear Resistors N HN CIRCUIT PROTECTION O 19 62-2012 Using PTC – Positive Temperature Coefficient Thermistors PTC Overload Protection Principles Features Part Numbers • Different voltages in function of the application: 30 V to 60 V, 145 V, 265 V, 600 V • Several mechanical executions: pellets, through hole leaded, SMD • Wide range of trip and hold currents: from 10 mA to 4.5 A minimum trip currents • Wide range of resistance: from 0.3 Ω to 5 kΩ • Small ratio between trip and hold currents (Itrip /Ihold = 1.5 at 25 °C) • High maximum inrush current: up to 30 A • UL approved series General overload protection: • 30 V to 60 V series: PTCCL..H....BE series (UL approved) • 145 V series: PTCCL..H...FBE (UL approved) • 265 V series: PTCCL..H...HBE (UL approved) • 600 V series: PTCCL..H...SBE • SMD series: PTCTZ PTCSS Series (SMD, UL approved) PTCSL Series Telecom protection: • General leaded: PTCTL • SMD: PTCTZ and PTCTT When connected in series with the input of an electrical or electronic circuit load (see Figure 1), such as a small motor or power supply, the PTC thermistor acts as a self-resettable fuse, protecting the circuit against current, voltage and temperature overload conditions. Log R PTC Over-temperature: • Tn 70 ºC to 140 ºC: • Tn 70 °C to 150 °C: Vsupply Load Normal Operating Zone Figure 1 2Rmin Rmin Protecting Zone 100 trip time (s) 25 ºC Temp Ts Log I Resistors - Wide Resistance Range The electrical resistance of ceramic PTC (positive temperature coefficient) thermistors increases exponentially at the so called switching temperature or Ts. This typical characteristic makes PTC thermistors very useful components for several application areas such as voltage and current overload protection, over-temperature protection, inrush current generation, time delay, energy discharge, and as a ceramic self-limiting heating element. As an overload protective element, PTC thermistors are used in a wide range of circuits, including line cards, set-top boxes, and private automated branch exchanges in telecom applications; airbag and temperature control devices in automobiles; power supplies, transformers, DC motors and small domestic appliances; and in other consumer products. 10 Itrip Ihold 1 0.1 0 2000 4000 6000 8000 10000 I (mA) Figure 3 Figure 2 Capabilities 2/6 Vmax Log V In normal operating conditions the PTC resistance is low (see Figure 2), and the current is below its hold value (Ihold). However, an overload will quickly heat up the PTC thermistor until, at around the switching temperature (Ts), its resistance increases rapidly, limiting the current to far below its trip value (Itrip), and so protecting the circuit. The trip time until protection will depend on the level of overload (see Figure 3). VMN-PL0436-1205 This document is subject to change without notice. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 V i s hay Intertechnolo g y, Inc . I INNOVAT O L OGY With Non-Linear Resistors AND TEC N HN CIRCUIT PROTECTION O 19 62-2012 Using NTC – Negative Temperature Coefficient Thermistors Resistors - Wide Resistance Range The electrical resistance of NTC (negative temperature coefficient) thermistors increases as the ambient temperature decreases, and decreases when temperature increases. NTC thermistors are used for overtemperature protection in PCs, power supplies, and motherboards; Li-ion battery protection in fast chargers; and in digital scan cameras, fire and smoke detectors, TCXOs, and other automotive, consumer, and industrial applications. They are generally included in a voltage divider or Wheatstone bridges and can provide a measuring voltage to analog-digital converters. They also allow to control the temperature compensation of displays and regulation of temperature with opamps or more complex ICs. Features for Circuit Protection: • • • • • Leaded and SMD versions in case sizes from 0402 to 1206 Large resistance range: from 3.3 Ω to 470 kΩ Temperature range: - 55 °C to + 155 °C SMD termination: 100 % Sn over Nickel Customized types available upon request Examples of NTC Circuit Protection PC Cooling Fan The output Q of a bistable RS drives the gate of a MOSFET transistor switching a cooling fan on and off. The cooling principle is based on a limit cycle regulation between a chosen low temperature Tlow ( the NTC value at temperature Tlow is equal to Rlow) and a high temperature Thigh (the NTC value at Thigh is equal to Rhigh). The NTC value is compared to fixed resistors of values Rlow and Rhigh. Input R and S depend directly upon this comparison. The cooler fan will work between the moment when R or S go from 0 to 1 . VC RNTC + – + Rhigh + Rlow + – – A A + C – A + C – Fan Motor Temperature – R=1 S=0 THigh R=S=0 R=S=0 (unchanged) S TLow R Q unchanged R=0 S=1 Q Time Q Sensor (pos. a) Q=1 Vcc Heatsink 0 Fan Off Processor Capabilities Socket Sensor (pos. b) Q=0 Q=0 On Time Off Sensor (pos. c) 3/6 VMN-PL0436-1205 This document is subject to change without notice. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 V i s hay Intertechnolo g y, Inc . I INNOVAT 19 62-2012 R10 R3 TR1 R5 Resistors - Wide Resistance Range AND TEC O L OGY With Non-Linear Resistors N HN CIRCUIT PROTECTION O R1 -Θ R9 alarm D4 NTC2 (exposed) DC supply R6 TR2 TR4 TR3 Z1 R7 D1 D2 Z2 TH1 -Θ NTC1 (insulated) R8 R2 C1 C2 R11 R4 Z3 Z4 Rate of Rise Heat Detecting Fire Alarm Rate of rise heat detecting fire alarms operate on the principle of monitoring for a sudden rise in temperature associated with an outbreak of fire, rather than waiting for the temperature to increase to a predetermined fixed limit before activating. They therefore provide a faster response to a fire incident. The detector employs two matched NTC thermistors (NTC1 and NTC2), one of which is semi-protected in the body of the fire-alarm unit, while the other is exposed to the surrounding atmosphere. With a gradual rise and fall in ambient temperature, both sensors track each other fairly closely. With the outbreak of fire however, the exposed thermistor will react to the temperature increase faster than the shielded sensor. This causes an imbalance between the two sensors which in turn triggers the detector output. These detectors also feature an upper temperature limit at which point the detector will respond regardless of rise time. Capabilities 4/6 VMN-PL0436-1205 This document is subject to change without notice. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 V i s hay Intertechnolo g y, Inc . AND TEC I INNOVAT O L OGY With Non-Linear Resistors N HN CIRCUIT PROTECTION O 19 62-2012 Using Through-Hole Varistors VDRs (voltage dependent resistors), or Metal Oxide Varistors (MOV), are used for transient surge suppression. Surge suppression circuits are commonly used in computers, automobiles, telecom and industrial equipment, domestic appliances, and other consumer products. Resistors - Wide Resistance Range Specifications Table Standard Series: VDRS05 to VDRS20 Sizes from 5 mm to 20 mm Vrms from 14 V to 680 V Vdc from 18 V to 895 V Can absorb surges up to 6,500 A UL recognized according UL1449 edition 3 High-Surge Series: VDRH05 to VDRH20 Sizes from 5 mm to 20 mm Vrms from 11 V to 680 V Vdc from 14 V to 895 V Can absorb surges up to 10,000 A UL recognized according UL1449 edition 3 Example of VDR Circuit Protection in PC High Surge Voltage (without VDR) Line Inductance VAB Safe Clamping Voltage (with VDR) 230 V Mains Mains Line Capacitance I VDR VAB PC Fuse Time 3.15 A M Short Fuse 3.15 A Circuit Opens (on motor) Capabilities Washing Machine Motor 400 W 5/6 VMN-PL0436-1205 This document is subject to change without notice. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 V i s hay Intertechnolo g y, Inc . 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