Voltage protection circuit ?

Discussion in 'General Electronics Chat' started by curry87, Jan 5, 2011.

  1. curry87

    Thread Starter Member

    May 30, 2010
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    Looking for a simple over voltage protection circuit that will kill the supply if the voltage rises to as much as .5v above normal voltage which is a regulated stable 5v dc and draws 200 ma at peak.The circuit is very voltage sensitive and any higher voltages than 5.5v will damage components.
     
  2. steinar96

    Active Member

    Apr 18, 2009
    239
    4
    1 way would be puting a 5.1V zener diode connected to the positive terminal of the supply and ground and use a proper sized fuse before the zener. This means that when the voltage goes above 5.1V the zener breaks down and starts drawing enough current to blow the fuse. Only thing to keep in mind is that the zener must be able to handle the fuse current and fur the duration it takes for the fuse to die.

    an alternative solution would be an electronic (transistor one) but that might be a little more involved.
     
  3. curry87

    Thread Starter Member

    May 30, 2010
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    What math is required to ensure the supply is cutoff fast enough so that damage is not done,will using a single transistor to source the load + zener setup be plenty fast enough ?
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    No feedback - no slewing rate delay. Simple transistor bias.

    When the voltage of the selected zener is exceeded, output is turned off until the voltage returns to normal levels.
     
  5. timrobbins

    Active Member

    Aug 29, 2009
    318
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    Curry, are you able to cope with a voltage drop of some level between the power supply and the load? Such a voltage drop may be non-linear and affect the voltage regulation that the load sees.

    Is the load likely to cause an over-voltage (ie. does it have inductance, or does it have transient load changes that could cause power supply heartache), or is it just the power supply that may go over-voltage due to a fault or poor regulation.

    Does the load need to keep operating, as a priority, or can the protection circuit cut or clamp power with no consequences, for any kind of fault/glitch?

    Ciao, Tim
     
  6. JDT

    Well-Known Member

    Feb 12, 2009
    658
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    The classic circuit is a "crowbar" using a SCR. You need to have some way of shutting down the PSU when it trips. A fuse is one way but a fuse drops quite a lot of voltage. Better to use the electronic current limit on the power supply.
     
  7. curry87

    Thread Starter Member

    May 30, 2010
    101
    0
    Ideally no, the load has to see as close to 5v as possible from the output of the 5v voltage regulator no more than 0.05v drop between the supply and load is just about acceptable.

    No inductances but a smoothing 10uf is placed between output of the voltage regulator and 0v.

    The load can be cutoff at any time without warning the faster the better if voltage rail creeps to around 5.5v.
     
  8. curry87

    Thread Starter Member

    May 30, 2010
    101
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    In this circuit ive got the load getting cutoff when the voltage rises to 5.1v if the load has max safe voltage of 5.2, 5.3v and the npn transistor that is sinking it is in cutoff mode but still passing 227pA will the load still be damaged from it even if its passing very low current?
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
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    What is the load? If it is a device, what does the data sheet say?

    Realistically, can it be affected by under a microwatt of power? The load normally takes 1 watt of power, if the figures of 5 volts and 200 ma are correct.
     
  10. tom66

    Senior Member

    May 9, 2009
    2,613
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    Another solution may be the LTC4365 - which handles overvoltage protection up to 60V and reverse battery protection down to -40V. Unfortunately it's only SMD and requires some external components including a fet.
     
    Last edited: Jan 9, 2011
  11. curry87

    Thread Starter Member

    May 30, 2010
    101
    0
    The load is made up of a pic micro controller a lcd display and a am reciever module all rated at around 5.5v maximum.The input voltage into the 5v regulator could be as high as 20v so needed a circuit that will cut the supply if there was a short across the regulator or if the regulator failed for some reason.
     
  12. tom66

    Senior Member

    May 9, 2009
    2,613
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    Don't worry about it. PICs can take 7V although they won't last longer than a few months in that state, and they can take 12V for about 10 seconds. Set your OVP circuit at 6V-7V or so.
     
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