In traditional automotive applications , fused-protected electromechanical switches have been widely used in high-load applications due to the high safety requirements of in-vehicle circuits. However, this system solution also has certain limitations. Mechanical relays are prone to wear and contact errors during long periods of operation. At the same time, this system solution does not have Pulse Width Modulation (PWM) and requires additional diagnostic and protection devices. In the event of a circuit failure, the fuse needs to be replaced, and the temperature characteristics of the fuse tend to be higher than the wiring. At low temperatures and short periods of time, the strong current generated by the instantaneous short circuit is still very harmful to the system. Therefore, traditional relay and fuse solutions are not the best choice, whether based on cost or technical considerations. For these reasons, automotive systems have gradually reduced the use of fuses and relays, and more and more smart power devices have entered the next generation of automotive systems.
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At the "2007 Infineon Automotive Body Electronics Solutions Seminar" held in Shenzhen recently, Jing Jiefei, Automotive Electronics Systems Application Engineer, Automotive, Industrial and Diversified Electronics Marketing Division, Infineon Technologies (China) Co., Ltd. (Jean- Philippe Boeschlin) pointed out: "Because of the technical and cost advantages of smart power devices, their applications in automotive systems will become more widespread. Intelligent power devices can easily use PWM control with frequencies up to 80- 150Hz, while the traditional fuse and relay solutions can not use this control method, can not meet the actual requirements of the system." In the automotive system to choose intelligent power devices for five reasons, Infineon experts will tell us.
The system cost is low, it is really low cost!
When it comes to system cost issues, Jing Jiefei stressed: "Although the cost of relays and fuses is lower than that of smart power devices, due to its low reliability and high failure rate, the overall system cost will rise. Therefore, when calculating the cost, you cannot consider a single device, but should consider it comprehensively.†He said that the traditional relay circuit must use a thicker wire because it needs to be blown to protect the overcurrent circuit. As a result, not only will the weight of the entire system increase, but the cost will also increase. The circuit using the power device does not need to be equipped with a fuse, so the thin wire can be used to control the load, which not only reduces the weight of the system, but also effectively reduces the system cost.
Get rid of the bondage and really achieve miniaturization
Jing Jiefei also compared the dimensions of several options. The system with relay and fuse is large in size, with a large heat sink on the top; while the ordinary smart power device is much smaller, it still needs to be equipped with a heat sink; if the on-resistance is very A small new generation of intelligent power devices will completely get rid of the shackles of the heat sink and truly realize the miniaturization of the system. Moreover, since the power device itself has perfect protection functions (overvoltage protection, overcurrent protection, overload protection, short circuit protection, over temperature shutdown, open circuit detection, etc.), the fuse and some discrete components are eliminated, thereby reducing The volume of the controller; at the same time, the fault diagnosis function can be realized, not only can know which device is faulty, but also know what causes the error and is more conducive to maintenance.
Easy to achieve low power consumption and no noise without pre-driver
Since the microcontroller cannot directly drive the relay, it is necessary to install a pre-drive device and have a fixed dissipated power when it is turned on. The intelligent power vehicle circuit can be directly controlled by a single-chip microcomputer, and its power dissipation is small. And the circuit is basically no noise, but it is difficult to achieve this with a relay scheme. For example, wipers and power seat control systems have high requirements for this.
High and low reliability
Jing Jiefei also used the PROFET device as an example to introduce the high reliability of the intelligent power device to the participating engineers. He said: From 2002 to 2006, Infineon delivered a total of 800 million PROFET devices with a failure rate of 0.18 dmp, which means that there are only two failed devices in every 10 million PROFET devices. The relay is beyond the reach of the relay. Related data shows that the failure rate of relays is almost 10 to 100 times that of smart power devices. Smart power devices are undoubtedly the most sensible choice in environments with high standards and high reliability requirements such as automobiles. At the same time, the traditional relay control wiring is complicated, causing serious electromagnetic interference, which will also reduce the reliability of the entire system, and also bring many problems to assembly and maintenance.
Flexible parameter adjustment
In the overload protection circuit, since the characteristics of the fuse are constant, it cannot be adjusted accordingly according to the actual situation of the circuit. The overload protection circuit using intelligent power devices embodies unparalleled superiority. It can calculate the current sampling data through the single-chip microcomputer and software, and control and adjust the relevant data according to the desired effect, so as to judge whether the circuit needs overload protection at this time, which can greatly improve the flexibility of the overload protection circuit.
As the degree of intelligentization of automobiles increases, the demand for new control functions continues to rise, such as central door locks, window lifts, rearview mirror adjustments, sunroof control, seat adjustment, and ignition delay control. Etc, so the requirements for the entire control system are getting higher and higher. I believe that based on the above five considerations, smart power devices will be the smart choice for automotive electronics systems engineers!
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