the same as the base minus Vbe drop. used for more power transfer
This is a particular transistor amplifier configuration. In general, the input signal is applied to the base, the collector is connected to a supply voltage, and the output is taken between the emitter and power supply common. One of the characteristics of the emitter follower is the output voltage "follows" the input, but the output is reduced by the Vbe voltage (the voltage drop between base and emitter, approximately 0.7 V for a silicon bipolar transistor).
I think you mean a common emitter amplifier, which is an amplifier of voltage. Emitter-follower or common collector amplifiers are used to match impedances, or to amplify power or current. The emitter-follower is a type of common emitter circuit that has a resistor between the emitter and ground. The output signal is taken from the point between the emitter and its resistor.
Because of the geometry of the common collector configuration, changes in base voltage appear at the emitter. Said another way, what happens at the base pretty much happens at the emitter, and the emitter can be said to "mirror" or "follow" the base. The emitter is a follower of the base, and the name emitter follower appeared and was used.
The voltage gain of an emitter follower is theoretically 1. In practice, due to losses, it is marginally less than one.
.7v less than unity for DC operation but unity for AC.
The (Class C, Common Collector) Emitter Follower is used to amplify the available current from a voltage driving circuit that might be disturbed by the load impedance. If the actual voltage value is important, the emitter follower is often teamed up with an opamp which sets the emitter voltage based on the input voltage.
A: Any transistor of either polarity can be used as an emitter follower, The purpose of an emitter follower is to provide current to the load since it cannot provide any voltage gain
The question does not quite make sense. It sounds like you are asking why does changing the emitter resistor in a class C common collector amplifier not affect the output voltage? If so, the answer is that the common collector is an emitter follower, meaning that the emitter will follow the base, less the base-emitter junction voltage, within the limits of hFe. The resistor is simply there to ensure output biasing when the base voltage goes low.
A: Voltage follower imply that the output will follow the input without any gain.
See an analog design textbook for some specific examples but the gist of emitter follower's purpose in life is to transform a high output resistance signal source to achieve a signal with lower output resistance.
Disadvantages of CE amplifier:1. It has a high output resistance.2. It responds poorly to high frequencies.3. It has high thermal instabilities.4. It's voltage gain is very unstable.
The output of a common emitter stage is inverted, it is not out of phase.