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EXPERIMENT 2 Common Colector Amplifier EENG-251-01 Electronics 2 Lap Instructor: Vraka Maria Author Name: Leandrou Vasilis School of Sciences and Engineering Department of Engineering University of Nicosia Nicosia, Cyprus Table of Contents OBJECTIVES ..................................................................................................................... 1 BACKGROUND THEORY ............................................................................................... 1 EQUIPMENT and COMPONENTS USED ......................................................................... EXPERIMENTAL METHOD AND PROCEDURE ......................................................... 3 Part 1 ................................................................................................................................... 3 Part 3....................................................................................................................................5 Part 4....................................................................................................................................6 DATA ................................................................................................................................. 8 Data discussion ............................................................................................................... 9 Error Analysis ................................................................................................................. 9 CONCLUSIONS............................................................................................................... 10 ii OBJECTIVES This report aims to: First purpose is to count the open circuit voltage gain, input and output resistance of the common collector amplifier. To consider the common collector amplifier by using the small signal equivalent model. Show the use of the common collector as a buffer between a high impedance source and a law impedance load. BACKGROUND THEORY The common collector amplifier is very important to the BJT because it has very high input resistance, high current gain, very small output resistance and approximately unity voltage gain that make the emitter follower an ideal buffer between a high impedance source and a low impedance load. A small signal ac equivalent circuit can be use to calculate the gain, input and output resistance of the common collector amplifier. The open circuit voltage gain Av of the emitter follower amplifier can be calculate by using the equation The input resistance rin, can be calculate bu using the equation 1 rin= R1// R2// β(re + RE // rs) The output resistance rout can be calculate by using the equation: rout= RE// (re+(R1//R2// rs) / β) EQUIPMENT and COMPONENTS USED 2N2222 silicon transistor DC power supply Analog signal generator Resistors: 1-100kΩ, 2-47kΩ, 1-12kΩ, 1-10kΩ, 1-1kΩ, 1-470MΩ Capacitors: 2-10μF Potentiometers: 1-50kΩ, 1-200kΩ Dual Trace Oscilloscope 2 EXPERIMENTAL METHOD AND PROCEDURE Part 1 The following circuit was connected in order to determine the β of the transistor. RB RC VRC VBE Fig 1 β circuit The voltage across the collector resistor VRC and the based to emitter voltage VBE was measured. The β was calculated using the following formula: VRC = 7.28V VBE =0.63V β= ( VRC )( RB ) ( RC )( VCC - VBE ) 3 β= 7.28x1.51MΩ . =162hfe 4.7KΩx(15-0.63) The measurement of β was found 157hfe. For the second transistor: VRC = 2.96V VBE =0.61V β= 2.96x1.51MΩ . =66hfe 4.7KΩx(15-0.61) The measurement of β was found 60hfe. Part 2 The following circuit was connected to measure the voltage gain Av, input resistance rin and the output resistance rout of the common collector amplifier. . fiq 2 common collector amplifier 4 The signal generators frequency was set to 10 KHz and then was adjusted until Vo= 0.1Vp-p. The input voltage vin was measured and the phase relationship vin and Vo. The open circuit voltage Av is Vo / vin. vin = 34.7mV Vo = 35.4mV Av = 1.02 To measure the output resistance rout, a 200 Ω potentiometer was connected as a rheostat between the output capacitor and the ground. The potentiometer was adjusted until the Vo was 0.5m Vp-p. Then the potentiometer was removed and measured. rout= 7.1 Ω To measure the input resistance rin, the signal generator was reconnected and 50KΩ potentiometer was connected as a rheostat between the input capacitor and the signal generator. The potentiometer was adjusted until vL = 0.5mVp-p. Then the potentiometer was removed and measured. rin= 7.31KΩ 5 Part 3 The following circuit was connected to demonstrate the effect of loading on a common emitter amplifier. Fiq 3 effects of loading Vs was set 0.1Vp-p at 10 kHz. VL was measured and VL / Vs were calculated. vL = 15.5mV vS= 35.35mV vL / vS= 0.43 6 Part 4 The following circuit was connected to demonstrate the use of a common collector stage to a buffer a low impedance load from high output resistance of the common emitter amplifier. Fiq 4 common collector stage to buffer Vs was set 0.1Vp-p at 10 kHz. VL was measured and VL / Vs were calculated. vL = 0.305V vS= 35.35mV vL / vS= 8.62 7 DATA At part 1 β1= 162hfe β2= 66hfe At part 2 vin = 34.7mV Vo = 35.4mV Av = 1.02 rout= 7.1 Ω rin= 7.31KΩ At part 3 vL = 15.5mV vS= 35.35mV vL / vS= 0.43 At part 4 vL = 0.305V vS= 35.35mV vL / vS= 8.62 8 Data discussion The common collector amplifier is very important to the BJT because it has very high input resistance rin= 7.31KΩ, high current gain, very small output resistance rout= 7.1 Ω and approximately unity voltage gain Av = 1.02 that make the emitter follower an ideal buffer between a high impedance source and a low impedance load. When we demonstrate the effects of loading common emitter amplifier the vL / vS= 0.43 but when we demonstrate the use of a common collector stage to a buffer a low impedance load from high output resistance of the common emitter amplifier vL / vS= 8.62 Error Analysis Theoretical Measured % Error Av 1.18 1.02 13.55 VL/VS 0.45 0.43 4.4% 9 CONCLUSIONS The open circuit voltage gain, input and output resistance of the common collector amplifier were measured. The use of the common collector as a buffer between a high impedance source and a law impedance load was demonstrated. The common collector amplifier is very important to the BJT because it has very high input resistance rin= 7.31KΩ, high current gain, very small output resistance rout= 7.1 Ω and approximately unity voltage gain Av = 1.02 that make the emitter follower an ideal buffer between a high impedance source and a low impedance load. When we demonstrate the effects of loading common emitter amplifier the vL / vS= 0.43 but when we demonstrate the use of a common collector stage to a buffer a low impedance load from high output resistance of the common emitter amplifier vL / vS= 8.62 To measure the input resistance rin, the signal generator was reconnected and 200Ω potentiometer was connected as a rheostat between the input capacitor and the signal generator. The potentiometer was adjusted until the voltage is the half of vL. To measure the output resistance rout, a 10 KΩ potentiometer was connected as a rheostat between the output capacitor and the ground. The potentiometer was adjusted until the voltage is the half of Vo. 10