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Two ways to fry a component

Discussion in 'Electronic Basics' started by Midnight Oil, Oct 7, 2005.

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  1. Midnight Oil

    Midnight Oil Guest

    Many components I have seen have 2 ratings on them: volts and amps. I
    am guessing that they put these two ratings on there because there are two
    ways to "break" the component:

    1) The voltage rating indicates how much "push" or force you can apply to
    the device before it breaks. Even if you have a small amount of current
    flowing through the device, if you apply too much push, it will break.
    Like a door in a house, even if there is just one person going through the
    door, if they are a very strong person and they push too hard on the door,
    the latch will snap.

    2) The current rating. If you apply a safe amount of push (voltage), but
    you have a lot of current going through the device, it will break in
    another way. Like the doorway analogy. If you have a bunch of weak people
    running through the door, there isn't a lot of pressure, so the latch
    won't snap, but with the crowd rushing through, the doorway will break.

    So, when hooking up a device in a circuit, you need to observe both
    ratings. Like the doorway, you want to be sure that someone too strong
    doesn't go through and break the latch, and you also want to be sure not
    too many people go through at once and break the doorway down. Two
    different scenarios.

    Is my understanding correct?

    - Jamie

    The Moon is Waxing Crescent (18% of Full)
  2. Ralph Mowery

    Ralph Mowery Guest

    Electronic devices may actually have 3 ratings that can 'break' them. If
    too much voltage is applied the device will break down or arc over. Too
    much current and the device melts. Also if the voltage and current are
    under the limit but the product of them (watts) the device will melt. Most
    simiconductors must get rid of the excess heat that is produced. That is
    partly why the power devices are mounted on large heat sinks.
  3. PeteS

    PeteS Guest

    There are lots of voltage and current ratings for parts.

    There's usually a current rating per pin on connectors, (as well as a
    voltage rating which does not refer to the same thing). On ICs, there
    is usually a current and voltage rating on IO ports when used as an
    output or an input (how much it can source or sink - current - and the
    maximum voltage permitted on the pin as an input usually). There are
    many, many other voltage and current ratings (to say nothing of power
    ratings and derating information).

    In many (most?) cases, the two are not referring to the same thing.

    Your post is mixing things apparently out of context, and in
    electronics, context can be everything.

    Get a specific part and ask about it - all will be explained by the
    usenet denizens :)


  4. For many components, the current rating is the current the device will
    draw at the recommended voltage.

    For switches, and relay contacts, the current rating is the maximum
    current that the contacts should be asked to carry or switch.

    For fuses, the current rating is the maximum current the fuse should
    carry without blowing, and the voltage rating is the maximum voltage
    that should appear across the fuse if it does blow. If you use a 32
    volt fuse on a 120 V circuit, it is likely to arc for some time,
    rather than blowing cleanly.

    Peter Bennett, VE7CEI
    peterbb4 (at)
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  5. Jasen Betts

    Jasen Betts Guest

    Immagine a revolving door or turnstile, with too many people passing through
    the people move so fast that the bearings overheat and the turnstile falls
    off (failed device is short circuit) or the bearing seize up (failed device
    is open circuit)

    current damage (too many amps) is usually caused by the resistive
    overheating of some part of the device.

    voltage damage is typically caused by the insulation failing inside
    the device and then either causing overheating or leaving a
    permanent hole in the insulation so current flows where it shouldn't
    pretty much

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