Power, Voltage, Current Supplies

Question

I am confused by the use of these three terms in conjugation with supplies.

I read somewhere that the prime objective of the circuit is to provide power rather than voltage? What exactly does that mean. Isn't \$Power = IV\$? So saying that you're supplying power rather than voltage is another way of saying supplying a large current. If so why not just say so. Why beat around the bush when saying a current supply is far more intuitive than a power supply?

So what does this cryptic sentence mean: "Supplying power to the load." Do they mean a large current or a large voltage?

Answer 1

In general, the term "voltage supply" refers to a constant voltage supply, and "current supply" (or "current driver") refers to a constant current supply. Both are power supplies, they just try to regulate different things.

Typically* "supplying power to the load" means supplying the voltage that the load is rated for, and letting it draw whatever current it wishes or intrinsically does. It doesn't have to be a large voltage or current, but the point is to supply energy, instead of communicating by sending a signal, which usually involves only a tiny current.

*It's also a pretty vague saying that could refer to something different than what I wrote above.

Answer 2

A load requires current to operate, and current requires voltage to propagate. Supplying power is simply shorthand for saying that current is being supplied and voltage is being applied to a given load.

So, saying "supplying power to x" is somewhat more accurate than saying "supplying current to x" because you can't really have current without voltage. (You can have voltage without current though, or infinitesimally small currents, when the voltage is insufficient to overcome resistance. But since current is required to do any work, it's rather pointless.)

Answer 3

This is a really good question, as this terminology could seem very confusing. The idea of any type of supply is to deliver power to the load by either forcing current into one of the terminals or applying voltage across the terminals. Now if you have a voltage source, it is designed so that no matter what load you connect to it, it will do it's best to keep a constant voltage supplied across its terminals (regardless of the current that is drawn from it). On the other hand, if you have the current source, it will allow the voltage across the terminals to vary so that it can source the same current into the + terminal at all times. Now in practice it is impossible to guarantee these things for "any" load, but for most well-behaved loads this should be true. Hope this answers your question :)