PPTC device technology has been widely used in overcurrent and overheating circuit protection designs for portable appliances, mobile phones, computers and telecommunication equipment. The new standard for passive components introduced by the Automotive Electronics Technology Committee has promoted the application of polymer positive temperature coefficient device (PPTC) circuit protection technology in the automotive industry. New automotive designs are targeting electronic circuits and motorized accessories such as power windows, power seats, sunroof controls and telematics to reduce costs and improve reliability and functionality.
Motor drives and controls are subject to some harsh working environments and are required to operate continuously and reliably. On-site failures are inevitable, and choosing the right circuit protection strategy will help ensure product reliability and keep repair costs to a minimum for manufacturers and customers. Using PolySwitch? polymer positive temperature coefficient (PPTC) resettable circuit protection devices provided by Raychem Circuit Protection, a more robust and reliable product architecture can provide protection against some common faults in motor drive and control systems.
PolySwitch polymer PTC devices are available in leaded, shaft, sheet, disc and surface mount packages. The small size of the polymer PTC device helps save valuable circuit board space, and because it has a resettable function, it can be placed in a location that is not accessible to the user, which is significantly different from traditional fuses that need to be placed in a location that is easily accessible to the user for replacement. Because the polymer PTC device is a solid-state device, it can also withstand mechanical shock and vibration, providing reliable circuit protection for a variety of different applications.
Power protection
PolySwitch devices have long been used for overload and short circuit protection at the DC output of power supplies. With the development of the LVR series, PolySwitch devices are now available in the AC main circuit at the input of the power supply. This product puts the AC line transformer and other line-side equipment under the protection of the PolySwitch device product family. These products can provide protection for the power supply when the neutral line is accidentally disconnected or the AC line voltage is applied to the 24 VAC input. LVR devices are suitable for power systems with a maximum input current of up to 400 mA at 120VAC and 240VAC voltages. Power systems with higher current can place PolySwitch devices in the output circuit on the secondary side to protect against power failures caused by overcurrent conditions.
RXE input/output interface protection
Many drives and controls are equipped with communication and data interfaces for information transfer between system components. The wiring for these interfaces is sometimes laid side by side with the AC or DC power cables. These harnesses can short-circuit due to normal wear and tear, accidents, installation wiring errors, or mishandling at the central distribution box. If the power cable and the communication wire short-circuit, the PolySwitch device can protect any system connected to the shorted line from damage to the communication interface. In some cases, this phenomenon may affect many systems. The role of the PolySwitch device in protecting the interface can significantly reduce the downtime and repair costs of common equipment failures.
Overheat protection
Since PolySwitch devices can respond to the temperature rise caused by external heat and heat generated by internal current, and can establish a thermal connection with high-voltage equipment, it can provide overheat protection for high-voltage equipment. This thermal connection can be achieved by arranging these devices in contact with or close to high-voltage equipment.
The contact method allows the PolySwitch device to easily make physical contact with the equipment, thereby improving the protection effect. The transformer is a good example of such equipment. The PolySwitch device can be tied to an external coil or casing to establish a thermal connection. The PolySwitch device can be incorporated into the circuit during design so that it can send a warning to the controller when the transformer overheats, and the system will stop operating immediately.
The close proximity method is suitable for the protection of power semiconductor components and works best when a small surface mount PolySwitch device is on the same copper base plate as the power device. This is a low-cost thermal contact method that allows the PolySwitch device to operate when the temperature exceeds its operating point, while notifying the power device that it should stop operating when it is in an overheated state.
In this application, there is a certain degree of thermal delay, so this protection scheme cannot protect high current components and power devices that fail within milliseconds. However, for most overload conditions, this configuration can provide protection for power devices.
Motor stall protection
Moving machinery is subject to jamming or breaking faults that can cause the motor to stall. Continuing to supply power when the motor is stalled can result in damage to the motor and/or destruction of the drive. Placing a PolySwitch device in series with the motor drive protects the motor and drive electronics from system failures in a stalled or overloaded condition. Once the fault is cleared (and power is removed), the system can resume normal operation without the need for maintenance or replacement of parts. For many years, PolySwitch devices have been the most commonly used solution in the automotive industry to protect seats, windows, and other motors. Using PolySwitch devices in these applications requires consideration of the value of the series resistor and the maximum hold current rating of the device. Maximum operating current at room temperature is 15A at 16V and 9A at 30V.
In these applications, PolySwitch devices can allow the motor drive and controller systems to continue to operate when these systems experience external faults due to overcurrent or overtemperature conditions. The benefit is a robust and reliable product that can protect the system when other components fail.
Application of PolySwitch Devices in Automotive IEEE 1394 Networks
In the automotive industry, the increasing connection between family lifestyle and automobile is in the ascendant. The standardized global interface developed by the American Automotive Multimedia Interface Association (AMI-C) can easily connect to various consumer electronic devices and facilitate the rapid installation of these devices. The network known as the IEEE 1394 serial bus in the consumer electronics industry is designed with the transmission of multimedia content as the goal. This additional standard for the automotive industry is called IDB-1394 and was developed by the "1394 United Automotive Industry Group".
IDB-1394 is designed for high-speed multimedia applications, that is, quickly transmitting large amounts of information in the car. This open standard allows portable electronic devices to connect and interact with the vehicle network, establishing a communication channel between the two.
The power interface needs to provide overcurrent protection, and the power supply standard used in the existing automotive system was promulgated many years ago. Since the customer convenience port (CCP) is used to transmit signals and power supply, it must be protected to prevent short circuits or damage to downstream devices due to various faults, such as poorly contacted cables or connectors when inserted into the product. This situation may occur frequently, so the short-circuit protection of the central control panel must be effective and reliable.
Application Overview
As shown in the figure, the architecture of the in-vehicle network can be divided into an embedded network and a customer convenience port (CCP). The current technical specifications define the embedded plastic optical fiber (POF) in-vehicle network as a specification similar to the existing MOST (Media Oriented System Transmission) technology. However, the former's architecture is more stable, can provide higher data transmission rates, and is easier to implement. This network can connect various electronic devices, such as DVD players, video display screens, navigation systems, radio receiving equipment, communication equipment, such as wireless phones or emergency automatic remote communication and information processing technology terms, and other multimedia applications.
This video-audio network includes a Customer Convenience Port (CCP) that allows passengers to connect their own CD players, game consoles and other 1394-bus devices and peripherals to the network using cables that can be used both at home and in the car.
Circuit protection requirements
In a hot-swap automotive environment, there is an obvious potential for short-circuit damage as customers frequently connect and disconnect peripherals to the power interface. The power interface requires overcurrent protection, and the existing power standards used in current automotive systems were developed many years ago. Since the user convenience interface is used to transmit signals and power, it must be protected to prevent short circuits or damage to downstream devices due to various faults, such as poorly connected cables or connectors when plugged into the interface. This situation may occur frequently, so the short-circuit protection of the central control panel must be effective, reliable, and preferably resettable.
Current limiting can be accomplished using resistors, fuses, switches, or polymer positive temperature coefficient (PPTC) devices. Resistor protection is rarely used because it creates an excessive voltage drop under normal current conditions. One-time fuses are possible, but they are easily damaged and must be replaced after a failure. Bimetallic switches are limited in that they are repeatedly made and can cause contact welding failures. In many automotive applications, the best protection is a polymer positive temperature coefficient (PPTC) device, which presents a low impedance under normal operating conditions and a high impedance when a fault condition occurs.
PolySwitch polymer positive temperature coefficient devices are widely used in IEEE 1394 applications, often providing resettable circuit protection for computers, peripherals and portable electronic devices. In automotive multimedia applications, such devices are often used to provide circuit protection for the input and output interfaces of GPS positioning devices, CD changers, audio and other electronic peripherals.
Protect GPS (Global Positioning System) components, CD changers, stereos and other electronic peripherals connected to the car network:
Above: PolySwitch devices help circuit designers meet safety requirements for circuit design and provide circuit protection for power interfaces, remote electrical communication devices and portable devices connected to the vehicle network.
PPTC devices are similar to traditional fuses in that they can limit dangerously high currents when a fault occurs and persists, but they are different in that they can reset themselves after the fault is cleared and/or the circuit power is disconnected. Another advantage is that polymer positive temperature coefficient devices are relatively small and can be mounted directly on circuit boards and can be installed in electronic modules, junction boxes, and power distribution center components.
In-vehicle products that use common electronic industry standards can help customers upgrade their cars with new products. A common bus also helps automakers solve the problem of technological obsolescence caused by technological advancement and continuous advancement of automotive design cycles. In hot-swappable automotive environments, there is a clear potential for short-circuit damage because customers often connect and disconnect various peripherals at the power interface. Polymer positive temperature coefficient devices provide an effective overcurrent protection solution for this problem. This resettable circuit protection device also helps manufacturers produce safe and reliable products to meet regulatory requirements and reduce product warranty and repair costs.
The IDB-1394 standard interface allows users to use hot-swappable devices, and overcurrent protection for power interfaces and portable devices on multimedia networks must be reliable and economical. The low impedance, fast disconnect response time, small size and resettable function of the PolySwitch series devices help circuit designers design safe and reliable products to meet the requirements of regulatory agencies and reduce warranty costs.
The advantages of PolySwitch products also include manufacturing characteristics compatible with large-scale electronic assembly technology, and a wide range of products to choose from, providing greater design flexibility.
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