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符合汽車排放要求的電源轉換技術
了解汽車電源轉換器中使用的 EMI 緩解技術,以符合排放要求。
Power Conversion Techniques for Automotive Emissions Requirements: Introduction to automotive EMC
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This video series explores power conversion techniques for complying with automotive emissions requirements. In this first video, we discuss the motivation for reducing electromagnetic interference, EMI, in vehicles, the topics covered in this video series, and some general challenges with powering automotive system.
So why are car makers concerned about emissions and immunity? Well, let's consider an example scenario where you're trying to listen to the AM radio in your car as you drive. Unfortunately, the power converters used to supply the adaptive cruise control system in this example are generating a lot of unwanted emissions or noise right in the frequency band of the radio station you're trying to listen to. And you can't hear it clearly.
Now if it's just music, this will probably be annoying. But what if you're trying to get important weather or road conditions information? This could be quite disruptive. Also, what if this scenario was flipped? What if the radio system was generating noise that interfered with the adaptive cruise control system? Well, that could be quite deadly. So it's for reasons like this that there are strict limits on emissions in vehicles.
In this video series, we will explore how to design for electromagnetic compatibility, or EMC. We'll discuss various sources and types of emissions, especially in power converters. And we will look at the CISPR 25 EMI standard and how it applies to automotive power conversion.
In the next section, we will explore various methods and techniques to mitigate emissions in power conversion systems. This includes filtering, component selection, board layout, and various circuit techniques.
We'll conclude with a case study that shows how to pass CISPR 25 Class 5 for a specific 13.5 volt input to 3.3 volt at 5 amps output. And a picture of the example converter is shown on the right. To help us contextualize the presentation material in the following video clips, let's briefly cover some general design challenges for automotive power converters.
First off, you need a wide input voltage range for the nominal 12 volt rated off-battery converters because they can go as low as around 4 volts to as high as about 40 volts, due to warm and cold cranks, and load dumps and things like that, which requires higher voltage rated FETs, as well as unique control methods.
These converters also experience considerable vibration mechanical stress, which means that certain low EMI power stage construction methods aren't available. And there can be cases where you may have two capacitors placed at 90 degrees, which can increase the equivalent series inductance.
There's a wide temperature range that these converters need to operate, from minus 40 C to 125 C. And you can't always use a fan to cool them off. A lot of manufacturers also like to be able to visually inspect solder joints, and this can lead to a preference for leaded packages, which can increase EMI.