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Thread: IR2153 SMPS high frequency noise issue on touchscreen device.

  1. #11
    Here is my PCB.

    In this picture you will see two coils in between the output capacitors. I kept that space to connect an output common mode inductor, didn't used though. I didn't recreate the schematic because it was already done by Mr. Silvio. Links are given bellow:
    Main post:
    PCB and Schematics:

  2. #12
    .... Silvio's Avatar
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    I am sorry to say that I find the spacing between the mains and also the high voltage DC is not adequate. The spacing for the mains traces should be 3mm minimum and for the 320v traces this should be a minimum of 4mm. Take a look at my PCB and notice. This is done for your own safety DC voltage will easily gap with some dust and humidity. I also see that you again omitted the Y capacitors in the input filter (4.7nF x1000v) these are important to complete the filter. You also omitted the safety capacitor between Primary and secondary windings. In my schematic you will notice that the high voltage ground is grounded via 2.2nf to chassis at 2 different points. The secondary center grounds are also grounded to chassis via the earthing point and the stand off nuts that tie the pcb with the metal chassis of the amplifier box. We sometimes not ground directly but use a low value resistor such as 10 ohms or so to lift the ground point a little and this will eliminate any ground loops especially when using long leads to microphone circuits.

    I also see that you did not leave enough space between the high voltage traces and the secondary voltages traces.

    I see also a second common mode choke which in my opinion is not needed. If you are still using the IR2153 this works at nearly 50% duty and minimum noise is generated. The smps is not regulated and hence an output choke is not really needed. The 5uH inductors will be enough. I would rather include a 0.1uf ceramic capacitors between the secondary voltage rails to center ground and also will include space for 1uf film capacitors in parallel with them. This will smooth out any noise generated.

    As a rule of thumb keep high current traces away from small signal traces. Avoid passing traces under the transformer. The transformer generates a lot of magnetic fields and try to stay away from it as much as possible. Keep your paths as short and thick as possible and do not run with them all over the PCB this is not good practice they serve as antennas to noise and pick it up.

    I hope this will help you out with a better pcb design

    Regards Silvio
    Last edited by Silvio; 03-11-2020 at 09:17 PM.

  3. #13
    Hi Mr. Silvio, this is the board I posted earlier, and there I mentioned about the capacitors. Currently they are soldered underneath the board. I know it is risky, but don't worry, it's just for test purpose. I'm not going to use this psu regularly.
    The second common mode choke is not used. I kept that space because I thought it might help. They are now shorted with jumpers.
    And all about the traces? I know it's a complete disaster. I'm still learning, hope you will understand

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