Two ways to fry a component

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 :)



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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)

Reply to
Midnight Oil

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.

Reply to
Ralph Mowery

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  
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Reply to
Peter Bennett

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

Bye. Jasen

Reply to
Jasen Betts

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