Reducing Noise

Discussion in 'General Electronics Chat' started by Dritech, Jan 14, 2014.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Hi,

    While doing research, I found that one method for reducing noise is to connect the load ground directly to the power supply ground. Does this also apply for the positive supply? Also, can the relay coill cause noise in a circuit? If yes, how can I reduce it?

    Thanks in advance.
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    When switching a high-current, or inductive load from a low-level circuit (e.g. microprocessor), it best to separate both the positive and negative feed wire from the PCB containing the low-level circuit, and instead run both those wires directly to the power supply.
     
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  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I generally bond all power supplies to earth ground at a common point.
    Many who control say a AC motor via an SSR from a port on a PC. wrongly think they are galvanically isolating the AC motor from the P.C. where as usually the case is that the PC power supply is connected to earth ground and so is the AC motor through the neutral.
    So a good way to eliminate ground loops etc is to bond both at one place.
    In the case of the relay, a BEMF diode should be placed across the coil, reversed biased.
    Max.
     
  4. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
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    Thanks for the reply. Can noise be present at the base of the transistor as well or does the transistor act as an isolator, hence preventing noise at the microprocessor I/O pin?
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The base current is likely one to two orders of magnitude less than the current being switched, so the transistor acts as a pretty good isolator.

    If you want more isolation, you can use an opto-isolator between the noise sensitive circuit and the the switch.

    If you need more isolation still, use a separate power supply to run the noise-sensitive circuit and the high-current circuit....
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    What I do is remember the wires in the circuit are not superconductors but resistors, albeit small resistors, but resistors non the less. Plus the have inductance too... both generate a real voltage drop.

    So when looking for a place to connect a "high" current device (high is always relative) see where it will do the least harm. That is generally close to the power supply itself.
     
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