最近车灯客户都有了新的EMC需求，远近光切换的电磁吸铁需要测试7637的5B波形，很多成熟的产品拿去测试，输入口的TVS保护二极管都被烧坏，工程师找了很多原因，找到雷卯电子讨论解决方案。

雷卯电子仔细分析了下产品结构和电路，电磁吸铁本身是一个不带IC的电路结构，相当于一个电感，随便任何高压，都不会损坏，但在日本车型最早的设计中还是在电路前端加了保护器件，一般为插件或贴片两种。如图是最早的插件保护保护设计，此方案简单，不需要PCB板，但是装配人工费用高，最新的版本为贴片的器件，极大提高了装配效率和减低了成本：

在雷卯电子实验室做EMC测试时，确实去掉保护的二极管，整个电磁吸铁不会打坏，测试正常，但是工程师忽略了一个问题，既然是一个电感，他会有储能作用，每个波形测试完成，会对发射电压端反向输出电压，而且波形时间越长，经过示波器波形的抓取发现这个能量很大，在汽车上，对输出电压的点击是个很大的损伤，所以整灯模块对这个测试要求是有必要的。

经过客户供货的，星宇，小糸，帕萨特，Q5，荣威750系列等各车厂不同的7637-5B需求，做了不同的设计验证，选用雷卯电子5.0SMDJ系列的车规级TVS满足了测试需求。

在客户有空间的产品上，采用了更高功率的SM8S系列，SM10S系列产品，确保了可靠性。

【5.0SMDJ】

Description

The 5.0SMDJ series is designed specifically to protect sensitive electronic equipment from voltage transients induced by lightning and other transient voltage events.

Features

◆ 5000W peak pulsepower capability at 10 x 1000μs waveform, repetition rate (duty cycle):

0.01%

◆ Glass Passivated chip junction

◆ For surface mounted applications to optimize board space

◆ Low profile package

◆ Built-in strain relief

◆ Low incremental surge resistance

◆ Excellent clamping capability

◆ Plastic package has UL flammability classification 94V-O

◆ Fast response time: typically less than 1.0ps from 0 Volts to BV min

◆ Typical IR less than 5uA above 22V

◆ High temperature soldering: 260°C/40 seconds at terminals

◆ IEC-61000-4-2 ESD 15KV(Air),8KV(Contact)

◆ ESD protection of data lines in accordance with IEC 61000-4-2(IEC801-2)

◆ EFT protection of data lines in accordance with IEC61000-4-4(IEC801-4)

Applications

TVS devices are ideal for the protection of I/O Interfaces, VCC bus and other

vulnerable circuits used in Telecom, Computer, Industrial and Consumer electronic

applications.

Maximum Ratings and Electrical Characteristics

(TA=25℃ unless otherwise noted)

Notes:

1. Non-repetitive current pulse, per Fig.3and derated above TA=25℃ per Fig. 2. 2. Mounted on copper pad area of 0.31x0.31” (8.0 x 8.0mm) to each terminal.

3. Measured on 8.3ms single half sine wave or equivalent square wave for unidirectional

device only, duty cycle=4 per minute maximum

Notes:

For bidirectional type having VRWM of 20 volts and less, the IR limit is double.

For parts without A (VBR is ± 10% and VC is 5% higher than A parts

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