Question

Explain npn transistor as an amplifier in common emitter mode 12 pu answer

Answer 1

Transistor as an amplifier

• Amplifier – It is a device which is used for increasing the amplitude of the alternating voltage, current or power

• Amplifier using n-p-n transistor in common emitter configuration is shown below:
• Circuit Diagram:

• The emitter is common to both the input and output circuit
• The input circuit is forward biased with the battery VBB and the output circuit is reverse biased with the battery Vcc
• RL is the load resistor connected in the collector circuit
• Input and output:
• Working:

• Case 1 – No AC signal voltage is applied to the input circuit
• When no AC signal voltage is applied to the input circuit, let the emitter current, base current and collector current be IE, IB and Ic
• By applying Kirchhoff’s law, we know, IE = IB + Ic
• From the output circuit, we find, VCC = VCE + Icily Hence, VCE = VCC - IcRL
• Case 2 – When AC signal voltage is applied to the input circuit

• There will be a change in the emitter-base voltage and hence the emitter current
• As emitter current changes, collector current changes
• In equation, VCE = VCC - IcRL as the collector current changes, the collector voltage VCE changes accordingly as VCC is fixed
• The change in the collector voltage appears to be amplified output of the input variation
• Current and Voltage gain

• The change in the output current by the input current is called current gain indicated by βac
• βac = Change in Ic / Change in IB = ic / ib

• The change in the output voltage by the input voltage is called voltage gain indicated by Av
• Av = vo / vi = δVCE / r δIB where r is the input resistance

• = - βac RL / r

• The negative sign indicates that the output voltage is opposite with the phase of input voltage

• Power gain

• The power again is the product of the current gain and voltage gain.
• Ap = βac * Av
• The power gain is also defined as the ratio of change in output power to the change in input power

Answer 2

Answer:

I don't know the answer so I am sorry