Definition: Active & Passive Deivce

Dear all,

Actually, diode is an active or passive device? As I found the definition of the Active Device is
"active device: A device that requires a source of energy for its operation and has an output that is a function of present and past input signals. Note: Examples of active devices include controlled power supplies, transistors, LEDs, amplifiers, and transmitters. "

Is it correct? Then diode is active or passive?

thanks

wccheng

The definition you have mentioned is possibly correct in one sense.
Actually an active device is a device that seem to be supplying power on it's own.
For example you take the case with transistors. They doesn't produce any power on their own. But, they can be visualised as a constant current sources. They simply utilise the power from the biasing battery and they supply it to the loads. Where as a resistor cannot do that. Hence resistors, capacitors and inductors are passive devices.A diode can rightly be called an active component.

It is nearly always a source of emf, but its important property could be that it is sending a signal of some kind.

where as a passive deviceis a device incapable of current gain or switching, such as a resistor or capacitor.

Think of transistor, it will have a current gain.
For instance think of a resistor, it's state does not change after you connect a power supply. But, for a diode or a transistor lot many changes take place in their states after the connection of a source in the circuit. Moreover their states also depend on the way in which they are biased(connected to the sources).

Well after some thought I came with a definition of active devices as one in which the flow of current depends on the polarity of voltage applied across it where as in case of passive device, the flow of current does not depend on polarity of voltage applied across it.

Think about it.