How to protect from damaging circuit during engine start ?

Discussion in 'Power Electronics' started by fsq, Jul 1, 2018.

  1. fsq

    Thread Starter New Member

    Jul 1, 2018
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    Hi, I assembled indicator beacon using led, ne555 and cd4017. It is propelled by 12V from a cigarette socket in a car. ICs sometimes get damaged, when beacon is plugged during engine start. I assume that problem is either spikes or reverse voltage. How to build simple protection ?
     
  2. AlbertHall

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  3. Hymie

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    Mar 30, 2018
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    Gone are the days when I added all sorts of electronics to vehicles I owned – but that was in the days of no lights on reminder, no intermittent wipers, no alarm, no electronic ignition system etc.

    Most of the time I would protect the added circuit feeding the +12V through a diode with a large electrolytic capacitor providing smoothing and minimising the voltage drop in the circuit, while engine cranking.
     
  4. danadak

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  5. Hymie

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  6. danadak

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    https://www.mouser.com/applications/automotive-circuit-protection/

    Regards, Dana.
     
  7. DickCappels

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    Aug 21, 2008
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    Other techniques include using parts rated at higher than usual voltages, such as regulators that can handle large spikes and varistors across the power supply. TVS diodes are probably a more modern solution.
     
  8. Bordodynov

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    May 20, 2015
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    See
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  9. shortbus

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  10. Hymie

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    Mar 30, 2018
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    Many ICs will die if the voltage on certain pins exceeds that of the supply.

    Engine cranking may result in a sudden drop in the supply voltage to the IC, but other IC pins may be held up by charged capacitors within the circuit – destroying the IC.
     
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  11. Bordodynov

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    For example: when using LM317, a diode is added to avoid damage to the chip.
     
  12. fsq

    Thread Starter New Member

    Jul 1, 2018
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    I've just added ceramic capacitor and diode, hope it'll help.
     
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