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 Voltage stays on when power is removed 

Last post Wed, Oct 19 2011 7:45 AM by jmh1022. 4 replies.
Started by jmh1022 18 Oct 2011 08:43 AM. Topic has 4 replies and 1415 views
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  • Tue, Oct 18 2011 8:43 AM

    • jmh1022
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    • Everett, WA
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    • Points 45
    Voltage stays on when power is removed Reply
    Hello all, I designed a prototype circuit for my MSP430 and other components. It is powered by two voltage regulators and a current source. What confuses me is that after I remove the battery power (4.2V) from the circuit, it does not turn all the way off. V+ drops to 500mV and then drops so slowly that it seems permanent. After 5 minutes, it's still 350mV. Is this normal behavior? I am a newly graduated bioengineer trying to do the job of an EE, so I'm sorry if this is a totally stupid question. I have no idea what is happening! I have an experimenter's board from TI (that I copied very closely for my circuit, especially the decoupling capacitors). I am tempted to just add a huge resistor between V+ and V-, but I figured that that would be a bad plan. Any help is much appreciated!
    • Post Points: 35
  • Tue, Oct 18 2011 9:14 AM

    • alokt
    • Top 25 Contributor
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    • Noida, Uttar Pradesh
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    Re: Voltage stays on when power is removed Reply
    It's difficult to comment without having a look at schematic. Do you have any large capacitor connected at output? This kind of behaviour is generally seen when you have large energy storage element at output with very light load.

    Hope this helps.=
    • Post Points: 20
  • Tue, Oct 18 2011 9:37 AM

    • jmh1022
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    • Everett, WA
    • Posts 3
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    Re: Voltage stays on when power is removed Reply
    I think that my capacitors are normal-sized for this circuit, but I may not be the best judge of that. I posted the schematic. Thanks!
    • Post Points: 5
  • Tue, Oct 18 2011 8:32 PM

    • alokt
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    RE: Voltage stays on when power is removed Reply
    I think slow discharge is due to absence of any resistance (also known as bleeder resistance) to discharge capacitors connected with power supply output terminals. At shutdown, this would be RC discharge and hence decay of voltage would be progressively slow.
    • Post Points: 20
  • Wed, Oct 19 2011 7:45 AM

    • jmh1022
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    • Everett, WA
    • Posts 3
    • Points 45
    Re: RE: Voltage stays on when power is removed Reply
    That would make sense. Is this normal behavior, or what do other circuits have to prevent it?
    • Post Points: 5
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Started by jmh1022 at 18 Oct 2011 08:43 AM. Topic has 4 replies.