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Determine Power Supply Requirements for Simple Circuit

Discussion in 'Power Electronics' started by wyred451, Nov 23, 2018.

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  1. wyred451


    Nov 23, 2018
    I would like to build a circuit consisting of a power supply, flashing light, and a reed switch. The purpose of the circuit is for the light to flash when the door the reed switch is connected to is opened. The light is rated for 12 volts and a current of 120 +/- 15 mA. How do I use that information to determine the voltage and amperage requirements of the power supply. I'd like to use an existing power supply such as USB charger and customize it for my needs.

    Thank you in advance.
  2. BobK


    Jan 5, 2010
    You need a 12V supply capable of at least 120 ma. To avpid stressing it, use pne that can supply 150 ma or more.

    If you want to use a USB charger, ypu wpuld need a boost converter to 12V, unnecessarily complicating the project.

    The 5V supply would need to be capable of about 450 ma or more, allowing for the boosted voltage and inefficiency.

  3. Minder


    Apr 24, 2015
    Usually 12vdc Wall-Wart's are plentiful, less work than converting the 5v, IMO..
  4. kellys_eye


    Jun 25, 2010
    Get hold of a flashing red LED (they do exist) instead of the 12V lamp and then you can use your USB charger.
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