Overvoltage protection circuit

Discussion in 'The Projects Forum' started by John5788, May 26, 2009.

  1. John5788

    Thread Starter Active Member

    Apr 2, 2009
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    im searching for some ideas for overvoltage protection on an analog signal to a microcontroller.

    the intended signal is analog from 0V - 5V, but I would like to protect it up to 13V with some sort of circuit.

    my first idea was to use a voltage divider circuit, but the downside to that is that I would lose resolution for my signals

    I was looking into some TVS diode, but i've never used something as such before.

    anyone have any good suggestions?
     
  2. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
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    A TVS is good for protecting against overvoltage and ESD. If you are not worried about ESD and are just limiting voltage you can also use a zener diode to limit the output of the analog stage to your desired limit.

    The cause of the over-voltage condition can greatly determine the scheme to solve the issue. You would need to provide more details.
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    Here is a schematic that is often used inside the IC's for input protection.

    [​IMG]

    Greetings,
    Bertus
     
  4. John5788

    Thread Starter Active Member

    Apr 2, 2009
    54
    0
    If i wanted to take the zener diode route, would I just do something simple like this:

    [​IMG]

    Say the zener voltage was 5.1V. If i received anything higher than 5.1V, then the diode would start shorting to ground through the resistor? is this a good reliable design? I just want to be able to protect up to ~13V.

    the cause of over voltage condition would just be accidentally wiring the input voltage to 13V instead of actually supplying it with a 0V - 5V analog signal, nothing complicated.
     
  5. CDRIVE

    Senior Member

    Jul 1, 2008
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  6. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
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    Like this ....
     
  7. John5788

    Thread Starter Active Member

    Apr 2, 2009
    54
    0
    nice thanks, that works. only problem is the resistor gets slightly hot when running 13V through it, but thats ok, the circuit is protected from overvoltage.
     
  8. StayatHomeElectronics

    Well-Known Member

    Sep 25, 2008
    864
    40
    Assuming your using the values in the above discussion, the maximum power of the resistor is

    P = V^2 / R = (13 - 5.1)^2 / 220 = 0.28 Watts

    If you parallel two resistors at twice the value (440 ohms or closest value) or use two resistors in series at half the value (110 ohms or closest value) you should be able to run the overvoltage indefinitely. That is assuming you are using 0.25 W resistors.
     
  9. CDRIVE

    Senior Member

    Jul 1, 2008
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    I think RS still sells 1/2W resistors.
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    An oldie but goodie...

    [​IMG]
     
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