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Choke Placement

Simple question, with probably a very simple answer, but I cannot seem to wrap my head around it.

It is my understanding that the purpose of chokes in a dimming module (D20 let's say) is to limit the "slam" of current to the load fillament to reduce noise. If that "slam" is coming from the SCR firing midway through the AC sinewave, why then would the chokes be wired before the "dimming" process instead of after? In my mind, it makes more sense for the chokes to be after the SCR's so they would filter the current that the SCR's are producing.

 

Thanks!

Parents

  • The choke and the SCR are in series, and therefore the current must pass through the choke and it will limit the rate-of-change-of-current (the cause of filament buzz) no matter where it lies between live busbar tap-off and neutral return.

    Think of the wire as a 'water pipe'.

    There are other reasons why it goes 'before' the SCR, such as limiting the amount of switching noise conducted back to the mains supply etc.

Reply

  • The choke and the SCR are in series, and therefore the current must pass through the choke and it will limit the rate-of-change-of-current (the cause of filament buzz) no matter where it lies between live busbar tap-off and neutral return.

    Think of the wire as a 'water pipe'.

    There are other reasons why it goes 'before' the SCR, such as limiting the amount of switching noise conducted back to the mains supply etc.

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