 Hello everyone, my name is Dheeraj Jain and I'm from WIRTH Electronics. Thanks for joining the webinar. The title of today's webinar is EMI Mitigation. The agenda for the webinar is as follows. Introduction, the need for a filter, components and technologies, choosing a component for a filter, how to destroy a filter and some tips. Let's take an example of a AC-DC power supply from ST-Micro. It's a 3 kilowatt, 3-channel interlit PFC. In the front end of this power supply, it has an EMI filter and rectification, which is fed to the 3-channel interlit PFC to provide the desired DC voltage and current. This is run or controlled by the digital controller from ST-Micro, which is ST NRG PF01. This digital controller is getting the power from auxiliary power supply, which is coming out of the DC output of the front end supply. Now the question comes in, why we need the EMI filter? Why we really care about EMI? You may have experienced the noise issue when you are listening, AMFM radio or on a call. This can be annoying. There are other cases where this can be high revenue, property or life loss. Imagine in the case of vehicle accident, due to EMI issue, the airbag does not open. This can be deadly. They are EMC directives from the agencies so that the end product is safe for the end user. Now let's look into the economic perspective for EMI. We suggest considering EMI from the early stage. It looks high in the beginning, but you can notice that the overall cost is low considering the rework at the time of production. It can delay the launch and at the cost significantly. Let's take a practical example from one of our customer who was designing ACDC power supply. Let's see how his configuration looks like. He has an input, he has a switch and then he plays a filter because he finds the place over here and then he connected the filter to the power supply or the ACDC stage and DCDC stages. You can see that there are a lot of wires going around which are behaving like an antenna at high frequency. What we are creating here, we are creating a big noise path. For any power supply for any design, it is important that we are not creating antennas by ourselves. So after this making this power supply, the customer run the EMC testing and you can see that it failed the EMC. He has seen all the noises at one sec first harmonic, second harmonic, third harmonic and this is one of the reasons that customer failed the test. By seeing the previous example, we are sure that we need a filter. We need a EMC filter. Do EMC filter is a black magic or something? The answer is no. If we know what are the causes for those noises, we can create a EMC filter which can help to get rid of noise. So it's very important to know what are the issues, what type of noise it is and then we'll move to the next stage that what type of filter you need it. So noise move to the next section which is the need for a filter. There are two types of noise in the transmission modes. One is a differential mode noise or there is a common mode noise. The differential mode noise is the noise which flows from one phase or one line to other line. In this case, earth path is not affected. Now if we talk about common noise where the noise is flowing in both the lines in the same direction and the return path is to the earth. That makes a big difference between the differential mode noise and common noise. Let's take a typical design filter where you have X cap, Y caps, common mode choke and also a resistor which is a bleeding resistor which is a high value like in a mega ohms or so. Now the question is how the differential mode noise or common mode noise works in the system or in this filter. As we know from the last slide the differential mode noise will flow in the different opposite direction. So the equivalent diagram or the equivalent circuit for differential mode will be like this. Now let's see what the common mode filter will look like. Here the noise is flowing in the same direction and it flows to the earth. So now it will have a different equivalent circuit. EMI is defined as unwanted signals and can be in the form of conducted or redid emissions. Conducted EMI is where the noise travels along the electrical conductors and redid EMI is where the noise travels through the air as magnetic fields or radio waves. You can see that conduct interference is mirror from 150 kilohertz to 30 megahertz but for redid it's over 30 megahertz. Components and technologies. Let's see the structure of a common mode choke. As you can see in the center is a toroidal core and it has two windings. Based on the type of mode differential mode or common mode they will exhibit different behavior for the choke. In the case of differential mode noise or if you can see when the noise is in the opposite direction the flux will also generate in the opposite direction. What is that do? Because since they are in the opposite direction they will cancel each other and it means there will be no magnetization. In this case the coil or the choke will behave as a resistor or impedance network. In the case of common mode which is different than differential mode the noise is flowing in the same direction and because of this we can see that the flux or magnetic flux is also in the same direction. It means it will magnetize and the attenuation of the common mode signal is through reflection and absorption. Now let's talk about the winding style. There are two types of winding styles very common. One is the bi-filler winding other is sectional winding. As you can see for bi-filler winding the leakage inductance is small compared to sectional winding. Because of low leakage for the bi-filler there is a low differential mode impedance and this is good for wideband application. In the sectional winding which has a high leakage it has a high differential mode impedance and which is good for high isolation application. These are the real pictures of some of the design of the windings. You can see in the sectional you can see that it has a different winding. The winding is done differently. These are two examples where you can see that and the bi-filler where two windings are coming together and it's a winding like this. Because of the winding style in the common mode you can see that if you are the bi-filler or sectional the impedance will not change much which is differential different for differential mode where you can see that the sectional has a high impedance compared to the bi-filler winding. Choosing a component for a filter. So the question is what I am filtering? Here this is a simple basic typical EMI filter. You can see here we have common mode choke and caps. Now the question comes in how I can know that I have a differential mode noise or common mode noise? There is one of the easy way you can do is we have called snap-on ferrite where the ferrite is put in two pieces and it has been placed in the plastic which can give you good idea that you have a common mode noise or differential mode noise. There are few steps which can help you on that. Let's say in the step one you want to see if it's a common mode noise. What you can do is you can put both the lines in this snap-on ferrite and do the EMC testing. If EMI is reduced then we know it's a common mode noise. If not then we can go on step two which is you can put one line in the snap-on ferrite and other line outside and by running the EMI testing if you find that EMI is reduced then it's a differential mode noise otherwise you have a wrong ferrite for the noise frequency. Let's take an example. Customer is looking for 1,000,000 common mode jokes. We can offer different options which can be based on code material or it can be based on the type of construction. The two main material which are used are nanocrystalline or manganese zinc. Nanocrystalline give the white band impedance or attenuation compared to manganese zinc which has a higher peak than nanocrystalline but it has a narrow band. You can notice in this graph that for the same core material we have a different attenuation. This is because in one we are using the sectional winding and since we are using sectional winding it has a low parasitic capacitance which help to provide a high attenuation. In the case of nanocrystalline as I mentioned it has a wide band. You can notice the bottom gray that you have a wide band of attenuation. For example if customer has a request of let's say looking for 30 or more than 30 dB attenuation at 1 MHz nanocrystalline is not a good choice but if customer has a request or have a need of more than 20 dB from let's say 0.5 MHz to 50 MHz we can offer this nanocrystalline material or nanocrystalline common mode choke. Depends on the need there are different solutions can be provided. In the case of differential mode attenuation which is more reactive or impedance based it very much depends on the shape number of turns material in a small term we can say is parasitics because they will have a different behavior and these are not the ideal component. You can notice that they have a different resonance at different frequencies. How to destroy a filter? It is very important that use the right filter. Why we are using the filter for? What does EMI filter does? The EMI filter is used to unbalance the impedance which help to reduce the high frequency noise. For example if you need the attenuation of 50, 60 or over more dB you cannot just use only the single order inductor or single order filter. You need to use the second order which can be LC or LRC followed by two stage filter or four stage filter. The other things what type of noise you are having. Either you have a differential mode noise or common mode noise. It is if you for the differential mode use the common mode it will not help. It can help to reduce a bit but it will not be very effective or vice versa. The other thing is very important is what type of orientation you have. For example in the first case you have a high impedance and on the output side of the filter you have a low impedance. It will make more sense that you put a capacitor on the input side and inductor on the output side. Why? Because what the cap is doing it is acting as a short circuit or providing a low impedance. This will make the impedance imbalance because on the input side of the filter you have a high impedance and the cap is providing the low impedance. The noise will pass through this cap. On the other side the inductor will allow BC or low frequency current. The inductor will block the harmful unwanted high frequency current. So this will help to reduce the noise and it will allow it will not allow the noise to pass through the system. In the other case where you have a very low impedance and you have very high impedance on the output of the filter it will not be wise to use the capacitor because capacitor will not will balance not unbalance this design. So it is important it will make sense that in case of cap you can just use the inductor. This will make an unbalance in the design and it will be helpful as a filtration. The other thing is why my filter is not working. You can see in the on the left hand side you have a SMPS or switching mode power supply you have a secondary stage there and you have a filter. You can see in this case there are a lot of wires going up. We are creating a lot of wire loops, ground loops and what is the possibility because high frequencies these wires will act as an antenna and amplifying the noise from the filter to the SMPS which is not correct. We need to make sure that we need to keep those filter stage SMPS far from each other. So you can see on the right side where you have a filter and two wires going to the SMPS and from SMPS is going to the other other stage. You have to make sure that a design is as clean as possible so that you are not creating antenna or the ground loops in this cases. The other thing is for differential mode operation it is very important to know what is the saturation of inductors. You don't want that during the differential mode your inductors are carrying more current than this one because if you they saturate they will behave very differently. The other things is the parasitic is very important in differential. In the idle word you will not see it but in reality every component have their own resonance and they will create a different resonance at different frequencies for this particular design. The other thing is important is the parasitic of the layout. In this case you can see you have a capacitor which are connected to ground but you are putting a long wires there. They will act as antenna. They can create a parasitic. Longer the wire they will have a own leakage inductance and they will create a noise in the design. So it is better that either you connect through wire vias or have a small wire or small loop as possible. The next thing is the potting material. It is very important that you use the right potting material for the design. For example for Magnesink we usually use the silicon based potting material and nano christen we usually have a plastic around it and then you can use the potting material. If you don't use the right potting material what it can do is that it can push or it can put a pressure on the core which will change the impedance or it will change the inductance value. Over the time because of the heat and everything the pot can fail. So it is very important, it is very important that you are putting the right core as you can see that with the pressure of the potting material on the core it can have a different behavior and because of this your performance will have a different results. Now let's talk about some of the tips. Here you can see that you have a different stages. You have a stack of PCBs, you have other stage it can be PFC stage, it can be a DC-DC stage and then you have another stage of PFC. Now there are different ways now we have to connect them to the ground. One way is you create it like this but nobody does that but as a beginner people will think oh yeah this is easy let's make the ground loop but what we are doing is here we are creating a lot of ground loops here which is wrong because this will as I mentioned before also this loops will have the leakage parasitics and everything as an antenna they can emit the noise. We need to come with the star type of connection which is this way where you bring all the PCB grounds together and connect into the star connection. This will make the design more clean and it will be easy to connect all the wires together. It will help to reduce the EMOIN noise better. The other is on the IC pins somebody thought, somebody think yeah let's put the wire under the IC which is nice because then nobody can see the wire it looks more cleaner but the issue is not that. The issue comes in that let's say you have from ground you have a current flowing through the IC pin but what about the cab which is also connected it will have its own current loop they can create they can create a parasitic and also can be creating a noise because now cab has a longer current path which will emit the noise. So what we can do about is we can bring the vias in between as a parallel vias or connect in a way where we can have a small loop as possible. The best is to have a multiple vias or parallel vias and connect them. This will help to make design cleaner and also help to reduce the noise. In this example you can see the IC has a multiple grounds. You can see ground there are three grounds here in this case and this all these grounds are connected using the copper layer and all are connected. This is not recommended. Why? Because we have to understand that every millimeter of copper layer we are adding increase the leakage inductance of one nano Henry. So you can imagine that how much parasitic we will increase if we connected in this way. This will increase the number of antennas this will have a lot of antennas and this will create a noise. This is not recommended. The best way is on the right side where you are bringing the vias and connected all the ground individually. This will make the loop smaller and also it will help to make sure that we are not creating non unwanted antennas or the noise by itself. It is very important to have the right ground reference. This is one of the way by doing it through through connections vias or the parallel connection we can avoid those interference. The idea behind is to avoid antennas or extra loops which will create a EMC noise by having those several layers connected in parallel will help to remove or reduce the EMC noise. This is very important for a PCB point of view. In this case you can see on the left hand side you have a signal line in between VCC and ground. The VCC and ground next to each other will create a parasitic capacitance. What it will do is that it will create the signal interference between the voltage or the load signals other interference from each other. This will make the system unstable. This we need to avoid how we can avoid this is bring this ground in between VCC and signal. So what we are doing is we are sandwiching the ground layer in between the VCC and signal. This will help to remove those parasitic and also make the signal or the power with no interference. The recommended layer thickness is maximum is 100 micro m but recommended is 50 to 60 or 60 to 80 micro m. It is very important that you should have a high solid ground layer. When you are plugging in a cable two things will happen. There is a risk of ESD jumping onto the connector. Also the cable is a very good antenna for common mode noise both for receiving and transmitting. Both ESD and common mode noise are equal to PE chassis ground. Connecting your PCB to chassis ground is a very good idea then to give those disturbance a clear way back. However, you should not just place this connection anywhere. Placing it far away from the origin gives both ESD and the common mode current a chance to influence or damage your application. That's why you place this steel spacer as close to the IO port as possible like this. We can put a ceramic Y safety cap to have a low RF impedance coupling to chassis while maintaining DC isolation. For common mode emission then will act as short and keep the common mode loop small. The incoming common mode current and the ESD are both diverted away from our electronics. It is very important to take care and make sure the connections are with the low impedance and as small as possible. Thank you. If you have any questions, please reach out to your local worth electronics contacts and they will be able to help you. Have a great day. Bye.