Hi

Can any one explain how emi filter work.

Thnaks
Robert

 

What type? Where is it applied?

 

by putting inductance in series with the circuit, and capacitance in shunt. the inductance resists the high frequency current and the capacitance takes it to ground.

 

You may find more EMI/RFI suppressor engineering info on one of the manuf. sites such as Corcom etc.
Max.

 

An EMI filter is just a passive filter, typically composed of L and C elements, designed to suppress (filter), as much as practical, a wide range of frequencies that can be troublesome if they either enter a circuit (induced) or leave a circuit (generated). They are normally connected in series with any signal or power lines going into and out of the circuit.

 

EMI filter is a high reactive component. EMI is produced externally by cosmic energy, such as solar flares, appliances and power cords. EMI filter has two types of components that work together to suppress these signals: capacitors and inductors. their are number of type emi filters, that are work on different mechanism. I know about Radius Power Inc. they are one of the providers of emi filter. you can get more info from their website...

 

There are two "current components" to be EMI-filtered at the input of your converter:

First, your converter input current has a current ripple due to switching. So you put a single- or multistage LC-filter. This is called a differential-mode filter.

Second, because you switch your power switches, the voltage potential of the power chips makes big voltage jumps with the switching frequency. The chips are close to the heat sink, and there will be currents through the stray capacitances of the interface chip - insulation - heat sink. So you ground the heat sink and you make a LC-filter (with capacitors on ground), single- or multistage, which provides a return path of this current. Then this current does not go into the grid. This is called common-mode filter.

Fig.1 and Fig.9 in http://www.pes.ee.ethz.ch/uploads/tx_ethpublications/APEC2010_Hartmann_FinalVersion_01.pdf show these two filter components combined as it is often done.

 

All the filters that you will ever see, besides all the ones that you won't work the same way. Some frequencies are passed through the filter, some frequencies are attenuated, and some frequencies are passed and attenuated. These frequency bands are referred to as the passband, the stopband, and the transition band. No smoke, no mirrors, and nothing up my sleeve.