Voltage ratings on components

Voltage ratings are in the 'It depends' category.

For most devices, you should read the data sheet for the specific statement of just what the voltage rating implies. For some parts, the rating is understood to mean specific things.

The voltage rating of an electrolytic cap, for instance, is usually taken to mean it's rated 'Working Voltage' - i.e. the voltage it can withstand continuously in normal operation (although I would never use a 10V electrolytic in a 9V system...)

For semiconductors, it may mean the normal (highest) rated working voltage, or (depending on context) it may mean the absolute max rating.

So the answer is - find a voltage rating that you are unsure of, read the datasheet, and if it's still not clear, ask - someone here should know what it means.

Your LED rating may refer to either it's maximum forward voltage drop (probable) or it's reverse voltage rating (possible but unlikely).



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I have a question about the meaning of voltage ratings on electronic components. Does the voltage rating mean it is the maximum voltage you can apply to a device before it melts down? Or does it have a more subtle meaning?

For instance, if I have an LED with a 5V rating on the package, do the put that on there to say "If you apply more than 5 volts of pressure on this component, it will 'snap' inside and all the magic smoke will come out."

Or, is there another meaning behind it that engineers use?

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Reply to
Midnight Oil

For some components (Transistors, Capacitor, resistors...) the voltage rating is a maximum recommended operating voltage.

For ICs, the data sheets will often list a recommended operating voltage and a maximum voltage beyond which the device may be damaged.

For light bulbs and relay coils (and probably your "5 volt" LED) the stated voltage is the recommended operating voltage. (Normally, a bare LED requires a current limiting resistor in series - an LED spec'd at

5 volts probably has an internal limiting resistor, suitable for operation on 5 volts.)
Peter Bennett, VE7CEI  
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Reply to
Peter Bennett

Maximum, *recommended*? You sound like you're talking about TOOBS!

That's more like it.. ;-)

Yeah transistors should be lumped here.. I have yet to meet a transistor that doesn't explode over its limit (or at least act like a zener, i.e. avalanche effect).

To the OP: for things like resistors, you have three intersecting limit curves, depending on wattage and value. The straight bounding limits are current (I don't know what a typical 1/4 or 1/2W resistor is rated for) and voltage, which depend on the physical size of the device as an absolute rating. For instance, 1/4W resistors are rated as 250V or so, while 1/2W resistors are good for 400V and 1Ws are good for 600V. But in almost all cases, the curved limit of power wins out: for example, a 100k 1/2W resistor is at maximum dissipation at 224V, well below the voltage limit for that package.

What you get is, for resistors of yea wattage within whatever range of resistance, you only have to worry about power. For resistors below some fractional value, the current limit goes into effect. For values above some large value (for 1/2W, around 330k), the voltage limit is imposed before you can reach full power.

For values outside of the dissipation-limited zone, you can still burn out the resistor by exceeding the limit, BUT, because the resistance is so low or so high, you can never technically "burn" it out (by which I mean, exceed dissipation rating).

And all this applies moreso for semiconductors, which are often, in effect, variable resistors. ;-)


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Reply to
Tim Williams

that's pretty much what it means

on a LED that's probably the maximum reverse voltage the manfacurer guarantees it for, I've seen LEDs witstand as much as 12V (in the reverse direction) without failing.

it's basically the design limit of the part. all good parts will exceed the design limit by some extent. those that don't are often relabled and sold as a less robust part.

Bye. Jasen

Reply to
Jasen Betts

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