小功率便携式音频产品(含Charger和DC-DC)的辐射发射超标对策

Measures to Excess Radiated Emission of Low-power Portable Audio Products(Including Charger and DC-DC)

小功率便携式电子产品,目前常用锂电池和Boost(Buck)芯片给MCU、Audio以及显示屏等器件供电。此类产品通常使用适配器供电,设计要求充电部分工作时,必须通过测试并符合EMC标准。一般来说,为了提高系统工作效率,锂电池充电芯片都是基于开关工作方式,类似一个开关电源;另外,可能其他的开关电源芯片在同时工作,器件均为开关工作方式,提高了工作效率,同时引入了辐射问题,这也是电子产品设计过程中的常见问题。本文基于一个产品设计实例(用BQ24133单电池充电电路和LM3478升压电路),对设计过程中曾经遇到的辐射难题进行了详尽的分析。确定骚扰源,找出耦合路径,最终给出解决问题的方法,以供大家作参考。

As for low-power portable electronic product,devices,like MCU,Audio and display screen,are powered by lithium battery and Boost(Buck) chip.They are often powered by adapters,requiring passing the test and according with EMC standard when the charging part is working.In general,in order to improve working efficiency,the charging chip of lithium battery is based on switch working mode,similar to a switching power supply.Besides,maybe other switching power chips are working at the same time,all of which are in switch working mode,improving working efficiency and introducing problems of radiation.This is a common problem during the design of electronic product.In this paper,there is a detailed analysis of radiation problems that have ever been met when designed according to an instance of product design-using BQ24133 single cell charging circuit and LM3478 boost circuit.The research will determine disturbing source,find out coupling path.Finally,solutions are presented for reference.