Colector resistance in an emitter follower circuit serves to place a limit on how much current can be supplied by the transistor. Often, the resistor is sized so that a short circuit in the load does not cause the transistor to fail.
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.
The collector voltage is not necessarily approximately zero when a transistor has a collector-emitter short. It depends on whether or not there is an emitter resistor.A typical collector-emitter circuit has two resistors, one in the collector and one in the emitter. One or both of them might be zero, i.e. not present, depending on design requirements. The collector-emitter junction represents a third resistor, the value of which is dependent on base-emitter vs collector-emitter current ratios and hFe.If the collector-emitter junction is shorted, then this circuit degrades to a simple voltage divider, or single resistor, and the collector-emitter voltage differential will be approximately zero. Simply calculate the voltage based on the one or two resistances.Results could be different than calculated, if the resistors are small in camparision to the shorted impedance, and it could be different depending on the base to emitter or collector relationship in that fault state, though the latter case is usually negligible due to the relatively high resistances of the base bias circuit.
In a common emitter amplifier, the base-emitter current causes a corresponding collector-emitter current, in the ratio of hFe (beta gain) or collector resistance over emitter resistance, which ever is less. Since this ratio is usually greater than one, the differential collector current is greater than the differential base current. This results in amplification of the base signal. As you increase the base-emitter current, the collector-emitter current also increases. This results in the collector being pulled towards the emitter, with the result that the differential collector voltage decreases. This results in inversion of the base signal.
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 advantage of the emitter follower is that it has a positive gain of 1.
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.
The gain of a class A, common emitter BJT amplifier, a fairly standard configuration, is defined as collector resistance divided by emitter resistance, or as hFe, whichever is less. Assuming that we are operating in a linear mode, and hFe is not a limiting factor, then the emitter resistance being greater than the collector resistance simply means that the gain is less than one.
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: The ratio of emitter/collector resistance is the gain. by adding a capacitor on the emitter the AC parameters will shift as a function of frequency
It is not. You have something confused.
A capacitor has lower resistance (impedance) as frequency increases. Adding an emitter capacitor effectively lowers the emitter resistance as frequency increases. Since gain in a typical common emitter amplifier is collector resitance divided by emitter resistance, this decrease in emitter resistance will increase gain as frequency increases.
it depends on the type of the circuit you are analyzing..it could be a voltage divider, emitter follower, be specific on what type of circuit and maybe i can help you aobut this question.
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
yes , it has high resistance between collector and emitter on the off state.
Limit current through emitter, Often the resistance is the load itself. So the restatnce limits current on what otherwise would act as a voltage follower.
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.
The collector voltage is not necessarily approximately zero when a transistor has a collector-emitter short. It depends on whether or not there is an emitter resistor.A typical collector-emitter circuit has two resistors, one in the collector and one in the emitter. One or both of them might be zero, i.e. not present, depending on design requirements. The collector-emitter junction represents a third resistor, the value of which is dependent on base-emitter vs collector-emitter current ratios and hFe.If the collector-emitter junction is shorted, then this circuit degrades to a simple voltage divider, or single resistor, and the collector-emitter voltage differential will be approximately zero. Simply calculate the voltage based on the one or two resistances.Results could be different than calculated, if the resistors are small in camparision to the shorted impedance, and it could be different depending on the base to emitter or collector relationship in that fault state, though the latter case is usually negligible due to the relatively high resistances of the base bias circuit.