running lm3915 with AC current

Discussion in 'General Electronics Chat' started by zazas321, Nov 29, 2015.

  1. zazas321

    Thread Starter Member

    Nov 29, 2015
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    3
    I tryed to run my 10 led vu meter with AC 10V,2A adaptor and I heard cracking sound, the lm3915 got very hot and apparently its not even working even with my 9V battery anymore.. Can anyone explain why this circuit wont work with alternating current? whats bad about it :eek: I mean i know the differences between alternating and direct current in the theoretical way but i cant use it the practical things:(
     
  2. #12

    Expert

    Nov 30, 2010
    16,343
    6,828
    That chip is not designed for its power supply voltage to become more negative than its ground pin. Try feeding it AC for a power supply and it's going to die suddenly.:eek:
     
  3. wayneh

    Expert

    Sep 9, 2010
    12,153
    3,059
    Well, you just learned one thing about the practical differences between AC and DC: Things meant for DC will be destroyed by AC!
     
  4. dl324

    Distinguished Member

    Mar 30, 2015
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    Now you know it matters and can use this experience as an opportunity to learn from your mistake.
     
  5. zazas321

    Thread Starter Member

    Nov 29, 2015
    99
    3
    Yeah definately thats some good experience. So u guys mean lm3915 cant go any more down than 0V or it will be destroyed?
     
  6. dl324

    Distinguished Member

    Mar 30, 2015
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    Most parts won't tolerate reversed power connections.
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    Exactly.
    If you apply a reverse voltage to most IC power pins it forward biases the substrate isolation diode and large currents will flow, zapping the IC.
    Most semiconductors require a steady DC voltage of one polarity and not AC voltage which is constantly varying and reverses polarity every half cycle.
    Only a few devices are designed to directly operate with AC voltages such as SCRs and TRIACs.
     
  8. zazas321

    Thread Starter Member

    Nov 29, 2015
    99
    3
    Cool guys, thanks so much for quick answers! :)
     
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