Q. Mention some characteristics of transistors?

· When a NPN transistor is working, there is always a constant 0.6 volt drop between the base and emitter, i.e., the base is always ~ 0.6 volts more positive than the emitter-

· There is no output at the collector, until the base has reached ~ 0.6 volts and the base is drawing current, i.e., any signal that appears at the base that is not up to ~ 0.6 volts is never seen at the collector.

· The base requires a current, not a voltage to control the collector current.

· The collector is a current source: it does not source a voltage.

· The collector appears to output a voltage when a resistor is connected between it and power source.

· The collector is at high impedance when compared to the emitter.

· The transistor can output an amplified signal either from the collector or the emitter (or both).

· When operating with a collector resistor (RL): the output voltage from the collector is an amplified voltage.

· When operating with only an emitter resistor (Re): the output voltage from the emitter is not an amplified voltage, because it is always ~ 0.6 volts, below the input (base) voltage--hence the name voltage follower. But because the emitter can source large amounts of current to the "LOAD," it can be said as CURRENT amplification.

· The collector--being high impedance--cannot drive a low impedance load.

· The emitter--being low impedance--can drive a low impedance load.

· The voltage gain from the collector is greater than one (Gv > 1).

· The voltage gain from the emitter is less than one (Gv < 1).

· Both the collector and the emitter: output ~ the same power: E x I = P.