rc snubber circuit

Discussion in 'The Projects Forum' started by khaled ragab, Jan 23, 2013.

  1. khaled ragab

    Thread Starter New Member

    Aug 5, 2011
    12
    0
    hello,
    i making a control circuit that have lcd, and some selectors to control ac coil contactors the problem is that the ac input voltage stepped down and the control circuit dc voltage become negative or also stepped down and the lcd get blanked when i turn off the selector.
    i know that i need to put an rc snubber over the coil of the contactors,but can i put a capacitor at the output of the regulator to maintain the voltage until the coil spark is over.
    or is there is any other solution rather than rc snubber
     
  2. DickCappels

    Moderator

    Aug 21, 2008
    2,648
    632
    Its not quite clear why the control circuit [power supply voltage] would become negative.

    Are you driving the coil with AC or with DC?

    Would you please post a schematic of what you already have?
     
  3. Duane P Wetick

    Active Member

    Apr 23, 2009
    408
    19
    If you are switching the DC off an inductive load, the voltage will appear to reverse; that is going negative. What is happening is that the inductive load is now the source and being an inductor, it wants to keep the current flowing in the same direction before being switched off. A free wheeling diode should be placed across the inductive load to protect the switching device. The diode will circulate the current thru the inductor until dissipated. Just add some polarity symbols in your circuit and you will begin to understand this concept.

    Cheers, DPW [Everything has limitations...and I hate limitations.]
     
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