Power adapter electromagnetic interference solution

Issue Time:2006-08-31
Electromagnetic Interference (EMI) refers to any electromagnetic phenomenon that occurs when a conductive or electromagnetic field is accompanied by a voltage or current that can degrade the performance of a device, device, or system, or cause adverse effects.

Power adapter electromagnetic interference, the main aspects of the engineer to consider are: circuit measures, EMI filtering, component selection, shielding and printed circuit board anti-interference design. For engineers designing adapters, the problem of electromagnetic interference is a key issue that has always existed in the design. So how to solve this problem? To solve the electromagnetic interference problem of LED drive power, you can start from the following aspects.

1. Soft switching technology: Adding inductance and capacitance components to the original hard-switching circuit, using the resonance of the inductor and capacitor to reduce the du/dt and di/dt in the switching process, so that the voltage drop before the switching device is turned on before the current The rise or fall of the current before the turn-off precedes the rise of the voltage to eliminate the overlap of voltage and current.

2. Switching frequency modulation technology: By modulating the switching frequency fc, the energy concentrated on fc and its harmonics 2fc, 3fc... is dispersed to the frequency bands around them to reduce the EMI amplitude at each frequency point.

3, the choice of components: select components that are not easy to produce noise, difficult to conduct and radiate noise. Of particular note is the selection of winding components such as diodes and transformers. A fast recovery diode with low reverse recovery current and short recovery time is ideal for high frequency rectification of the power supply.

4. Reasonable use of electromagnetic interference filter: One of the main purposes of EMI filter, power grid noise is a kind of electromagnetic interference, which belongs to radio frequency interference (RFI), and its conducted noise spectrum is roughly 10KHz~30MHz, up to 150MHz. .

Under normal circumstances, the differential mode interference amplitude is small, the frequency is low, and the interference caused is small; the common mode interference amplitude is large, the frequency is high, and the radiation can be generated by the wire, and the interference caused by the interference is large. The most effective way to reduce conducted interference is to install an EMI filter in the power input and output circuits.

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