This design guide discusses the design methods for reducing conducted EMI in TOPSwitch power supplies to below the typical regulatory limits. Proper design of the transformer, PCB layout and EMI filter can not only reduce conducted EMI, but suppress radiated EMI and improve the power supply’s EMI immunity.
This application note explains how to lower conducted electromagnetic interference (EMI) in offline switch‑mode power supplies that use Power Integrations' TOPSwitch devices. It discusses the relevant EMI standards for North America, the EU and Germany, measurement techniques with LISN, and safety considerations.
The guide also provides practical advice on transformer design, PCB layout, EMI filter component selection (including X2 capacitors and Y‑type safety capacitors), and typical filter topologies. Design examples and test data illustrate how to meet FCC, EN55022 and VDE0871 limits while keeping costs low. This manual is written in Chinese.
| 200 V Aluminum Electrolytic Capacitor | 200 V rated |
|---|---|
| 400 V Aluminum Electrolytic Capacitor | 400 V rated |
The guide follows IEC950 safety requirements for insulation and protection against electric shock.
Use short leads and keep PCB traces as short as possible; place filter components close to the TOPSwitch device.
A single‑stage EMI filter (first‑order common‑mode and differential‑mode attenuation) offers the smallest size and lowest cost.