Mr RB
Well-Known Member
I pretty much agree, but I can think of at least one example. By reversing your inductor example, consider an uncharged capacitor. We can (and should) charge the capacitor with a current source, and in that first instant, there is no voltage. The field (and voltage) is a result of the charges getting on the plates. Of course, in that instant when even those first electrons are moved, an electric field is present, but it is the charge movement that generates a net electric field which manifests the potential voltage. ...
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Thanks for replying. I expected a capacitor argument in rebuttal and understand your point about the "charge movement" but I don't think it is a perfect inversion of the voltage-first argument. With the inductor we can start from zero and apply an instantaneous voltage, which will eventually cause a current. With a capacitor how do you apply an "instantaneous current" to its two pins? No current can flow between two pins UNLESS there is a voltage differential.
Or for a clearer example that the inductor what about a spark gap or ionised gas device like a neon bulb? Enough voltage must be applied before the device is eventually "activated". I would classify that as a voltage activated device, and it is roughly comparable to a LED or PN junction that requires enough voltage to activate it to cause it to function, and once activated the amount of current then determines the effect. Likewise the bandgap point raised by Mr_Al above.
So in a face off of current vs voltage activated/operated/controlled I think the vast majority of electronic devices are really voltage controlled, especially if the context is general electronics where we are more concerned with HOW we control a component, rather than what might be happening inside a component from a pure physics viewpoint.
But I would still describe something like a LED as "current controlled" to a beginner as the important thing for them to know when controlling a LED is to make sure they get the current right!
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