The voltage gain of an emitter follower is theoretically 1. In practice, due to losses, it is marginally less than one.
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
.7v less than unity for DC operation but unity for AC.
The advantage of the emitter follower is that it has a positive gain of 1.
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.
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.
A darlington emitter follower is two transistors operating as one. Both collectors are tied together. The emitter of the first is connected to the base of the second. The darlington exhibits very high gain. If hFe, for instance, on each transistor was nominally 100, the effective hFe would be nominally 100 squared, or 10000. The emitter follower is a common collector configuration where the emitter tracks the base, offset by the base-emitter forward junction voltage. In a darlington, there are two junctions in series, so the effective junction voltage is about 1.4V. Voltage gain of the darlington, like any emitter follower, is one, or unity. Current gain, however, is limited only by the power supply, the transistor, and effective hFe. In the darlington configuration, current gain is effectively considered to be large enough to be thought of as "infinite".
A: Voltage follower imply that the output will follow the input without any gain.
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.
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.
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).
The three basic transistor connection configuration modes are common emitter, common base, and common collector. In the common emitter configuration, the emitter terminal is common to both the input and output circuits, providing high voltage gain. The common base configuration has the base terminal common to both circuits, offering high frequency response but low voltage gain. Finally, the common collector configuration, also known as an emitter follower, provides current gain and high input impedance while maintaining unity voltage gain.
In a voltage follower, voltage gain is 1, with an offset of VB-E, and current gain is hFe, limited, of course, by the available current in the supply and by the rating of the transistor.