Input Resistance − Input resistance is defined as the ration of change in base – emitter voltage (ΔV BE) to the corresponding change in base current (ΔI B) at constant collector – emitter voltage. Hence, coupling capacitor Cc isolates the DC of one stage from the next stage and allow the passes of AC signal only. If this capacitor is not used, the RC will come in parallel with the resistance R1 of the next stage and alter the biasing network of next stage. If this capacitor is not used, the amplified AC signal will flow through RE and cause a voltage drop across it and reduces the output voltage.Ĭoupling Capacitor (C c) − The coupling capacitor couples one stage of amplification to the next stage. If this capacitor is not used, then signal source resistance will come across R2 and change the bias.Įmitter Bypass Capacitor (C E) − This capacitor is used in parallel with RE to provide a path of low reactance to the amplified output AC signal. This capacitor allows only AC signal to flow and isolates the signal source from the resistance R2. Input Capacitor (C in) − An electrolytic capacitor is used to couple the signal source to the transistor base. The function of the biasing circuit is to establish a proper operating point otherwise some part of negative half cycle of input signal may be cut off in output. Practical Circuit of Transistor Amplifierĭescription and function of various circuit elements of transistor amplifier −īiasing and Stabilisation Circuit − The resistance R1, R2 and RE form the biasing and stabilisation circuit of the amplifier. Therefore, amplified output is obtained across the load. This causes reduced output voltage in opposite direction. The increased collector current causes a high voltage drop across the collector load resistance (R C).ĭuring the negative half cycle of the input signal, the forward bias across the emitter – base junction is decreased. Hence, from the n – types emitter more electrons flow to the collector through the base. Circuit Diagram of Transistor Amplifierĭuring Positive half cycle of the input signal, the forward bias across emitter – base junction is increased. In this way, a weak signal applied to the input circuit amplified in the output circuit, hence the transistor acts as an amplifier. Since the collector current flowing through a high load resistance RC produces a large voltage across it. Due to transistor action, same change occurs in the collector current. Since the input circuit has low resistance (because of forward biased), hence a small change in signal voltage causes a huge change in emitter current. This DC voltage is known as Bias Voltage and its magnitude is such that it always makes the emitter – base junction forward biased regardless of polarity of signal. For this, a DC voltage VBB is applied in the input circuit in addition to signal. In order to achieve desired amplification, emitter – base junction must remain forward biased. The weak signal is applied between the emitter – base junction and output is taken across the load connected in the collector circuit. A transistor can increase the strength of a weak signal and hence it can be used as an amplifier in a circuit.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |