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Induction Problem in Microcontroller

Discussion in 'Microcontrollers, Programming and IoT' started by rmrps, Mar 29, 2015.

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  1. rmrps


    Mar 29, 2015
    Hi Friends I am using Pic32mx460f512L controller my problem is when i switch off and on 230vac ceiling fan pic32 controller get disturbed and some times its get resetted i am tracing the power supply 24vac input via oscilloscope some unwanted hormonics coming from the 230v ac source when switch off and on 230vac fan i think i have to correct my power supply with best filter please give me your guidance to resolve this issue with best filter i have attached my power supply design please help to overcome induction problem[​IMG]
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Welcome to electronicspoint.

    While this cascade of voltage regulators may look like a good idea it actuall yis a waste of energy. The peak voltage at the capacitor after the rectifier will be approx. 32V (24V*sqrt(2)-2*0.6V). Your output is 3.3V, therefore all in all ~29V are lost in the regulators, distributed among the 5 ics. But sorry, that's not what you've been asking for.

    The electrolytic capacitors used are good for low frequency noise suppression. It is (almost always) a good technique to use a smaller capacitor (ceramic or film) in parallel for high frequency noise suppression. A very common value is 100nF.
    Also note that the LM3940 requires an output capacitor that meets certain requirements (datasheet, page 9ff).

    The 100mH inductor in series between the 5V and the 3.3V regulator may not be a good idea. The combination of L and C may make the regulators susceptible to ringing and the inductor may act as an antenna (depending on its construction), picking up noise e.g. from the fan.

    My recommendation:
    • add a 100nF film or ceramic capacitor parallel to each electrolytic capacitor.
    • Add a capacitor at the output
    • remove the inductor
    • check your wiring(layout for any loops that may act as antennas, minimize the loops
    • ensure a good ground (thick wire, wide traces)
  3. rmrps


    Mar 29, 2015
    thanks for the reply
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