docPolySwitch PPTC Device Principals of Operation
download 
Report Transcription
PolySwitch PPTC Device Principals of Operation
PolySwitch PPTC Device Principals of Operation What they are, How they work, Where to use them Using PPTCs to meet circuit protection requirements Presented by Jim Toth Raychem Circuit Protection Tyco Electronics Proprietary www.circuitprotection.com What a PolySwitch™ Resettable PPTC Device is Raychem Circuit Protection’s PolySwitch™ Polymeric Positive Temperature Coefficient (PPTC) devices are used to help protect against harmful overcurrent surges and overtemperature faults. Like traditional fuses, these devices limit the flow of dangerously high current during fault conditions. The PolySwitch device, however, resets after the fault is cleared and power to the circuit is removed, thereby reducing warranty, service and repair costs. Tyco Electronics Proprietary 77 How a PolySwitch device works UNDER A FAULT CONDITION UNDER NORMAL OPERATION heats up cools down • At the operating current • Many conductive paths • Very low resistance Tyco Electronics Proprietary • Excessive current causes device to heat • Fewer conductive paths • High resistance • Cools down and resets when fault removed 78 Why is a PPTC useful? Employed as series elements in circuit Under normal operating conditions, the PPTC remains low in resistance When a fault occurs, the PPTC heats up and increases in resistance thereby protecting the equipment from fault PPTC resets when power is removed, and fault is cleared, returning to low resistance state . I Log Rs Switched I=V/Rs Resistance of the PolySwitch device increases with temperature Normal I=V/RL Rs V RL RL The PolySwitch device is in series with the load Temperature Tyco Electronics Proprietary 79 PolySwitch PPTC Device Mechanism 10 10 8 0.70 Resistance 6 0.65 4 10 10 2 0.60 0 Thickness 10 M.Heaney 11.92 -2 10 0.55 0 50 100 150 200 Temperature ( C) Tyco Electronics Proprietary 80 PolySwitch Resettable PPTC Device Functionality A PPTC device acts like a fuse, however it is a non-linear thermistor that limits current, so a small trickle current will continue to flow through the circuit Under most conditions the PPTC will not reset until power is removed from the circuit 1Overtemperature and overcurrent protection. fuses are not designed for overcurrent protection, and generally require large currents to trip. 3Periodically attempts to reset until fault and/or power is removed, or resets to low resistance state when bimetal cools. 4Automatically resets to low-resistance state once the fault is cleared and power is removed. 2Thermal Tyco Electronics Proprietary 81 Resistance Relaxation for RXE075 Resistance Relaxation of RXE075 100000 10000 20 °C Rf/Ri 1000 60 °C 100 10 1 0.1 1 10 100 1000 10000 Relaxation Time (Seconds) Tyco Electronics Proprietary 82 Effect of Extended Rapid Cycling Cycle Life at 16V/100A - 5,000 cycles RGE300 0.50 0.45 Resistance ( ) 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Cycle Count Tyco Electronics Proprietary 83 Benefits & Features of PolySwitch™ Resettable PPTC Devices Benefits Reduced warranty and service costs Increased product reliability Superior shock and vibration withstand Wide variety of applications Tyco Electronics Proprietary Features Remotely resettable Testable Solid-state Wide variety of stock and custom form factors Low resistance devices available 84 Typical Applications Computers and peripherals, USB ports, Firewire ports, disk drives Rechargeable battery packs Cell phones, MP3 players, DSC’s Automotive electronics Window and door lock motors, entertainment and GPS systems Telecommunications equipment Faxes, modems, routers, central office switching Electrical equipment Security systems, solenoids, small and medium motors Tyco Electronics Proprietary 85 Sample Application: Automotive Electronics Applications Since 1985, available as surface-mount and radial-leaded devices to help protect: Electronic modules, and junction boxes Power and signal distribution systems Automotive actuators for power windows, mirrors, seat adjusters and door locks Protective devices that can be located strategically throughout the vehicle can help reduce wire harness size and weight Tyco Electronics Proprietary 86 Sample Applications: DC Input Port Protection Standard DC Barrel Jack •PDAs Cell Phones •Digital Cameras •Portable DVD Players •MP3 Players Custom DC Connector •Portable Electronics Tyco Electronics Proprietary 87 DC Input Port Protection: Misconnections The power supply can not be guaranteed DC Barrel Jack with Reversible Polarity +/- , -/+ Variable Voltage Custom-to-Standard Adaptor Tyco Electronics Proprietary Custom Connectors are not immune! 88 Sample Application: POS PolySwitch SMD device Secondary side protection Serial Port TVB270SA & TS250-130 Modem Line Protection PolySwitch Strap device Pack protection PolySwitch LVR device Primary side protection Power Supply Tyco Electronics Proprietary ROV Varistor for Power Supply 89 Sample Application: Industrial Power Management AC Mains OC Protection PolySwitch LVR device Input Power OV Protection ROV Comms I/O OC Protection PolySwitch RXE, miniSMD devices Interface Protection Analog I/O OC Protection PolySwitch RXE/RTE/SMD devices Power Driver Protection TRIAC, MOSFET, SCR OC Protection PolySwitch LVR/RXE/RUE devices Tyco Electronics Proprietary 90 Sample Application: Synergies in Mobile Phones PolySwitch Strap device Battery Pack Overcurrent & Overtemperature Protection PolySwitch LVR device Charger Overcurrent Protection PolySwitch SMD Devices Chip fuses Tyco Electronics Proprietary Power Port OC Protection 91 Sample Application: Washing Machine Solenoid Problem: Washing machine valve failure rate: 0.7%~3% - Resulted in valve or controller board damage Controlled by MCU K 200 G A2 ~220V PolySwitch A1 TRIAC Tyco Electronics Proprietary LOAD 92 Visit us at www.circuitprotection.com and check out our complete Circuit Protection solutions PESD devices Fuses GDTs and ROVs Portable electronics PolySwitch Device family Wide Variety of form factors Tyco Electronics Proprietary Telecom 93 Q&A Session Begins Now Resources & Links: http://www.ttiinc.com/object/seminar_cp_resources.html
