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Common-Emitter/Common- Collector Characteristics 5 Reference Electronic Devices and Circuits, Sixth Edition: Section 4-4. Common- Emitter Characteristics: Section 4-5. Common-Collector Characteristics Objectives 1. To construct input and output characteristics for the common emitter and common collector biasing arrangements based on laboratory measurements. 2. To determine the current gain of the common-emitter and common-collector configurations. Equipment List 1. 2N2222 silicon transistor or the equivalent 2. DC power supply 10V) 3. Resistors: 11 k 2, 1-100 22 4. Potentiometers: 1-1 MS, 1-10KQ (preferably 10-turn) 5. 2 VOM Discussion The two transistor bias methods discussed in this experiment are the common-emitter and the common collector, or emitter follower As discussed in Experiment 4, the common terminal is the one that will be common to input and output in an ac amplifier, le ac grounded. The different bias configurations will affect the various parameters of the ac amplifier. These parameters will be discussed in a later experiment. The transistor bios arrangement used most frequently for signal amplification is called the common emitter configuration, in which the 35
EXPERIMENTS.COMMON-EMITTER.COMMON COLLECTOR CHARACTERISTICS emitter terminal is grounded. In the common-emitter configuration, the input current and voltage are 1g and Va respectively. The output current and voltage are le and V, respectively. The ratio of collector current to base current is called the current gain, B: HE B - The relationship between B and a is: ot Figure 1 shows the input characteristics of the common-emitter biasing configuration. These characteristics display the relationship between base current and base-to-emitter voltage for a constant collector- to emitter voltage: Figure 1 The common-collector configuration is important because it can be used for an amplifier requiring high input resistance and low output resistance-often called a buffer.
EXPERIMENT 5 .COMMON-EMITTERCOMMON-COLLECTOR CHARACTERISTICS Figure 2 shows the input characteristics of the common-collector biasing configuration. These characteristics display the relationship between base current and collector-to-base voltage for a constant Va: CER CY 0.7 Figure 2 Figure 3 shows the output characteristics of the common-emitter configuration. The common-collector output characteristics are similar, except the vertical axis is l (1 - ). These characteristics display collector (or emitter) current versus collector-to-emitter voltage, for each particular amount of base current: Figure 3
EXPERIMENTS.COMMON.EMITTER.COMMON.COLLECTOR CHARACTERISTICS Procedure 1. To determine the input characteristics of the common-emitter configuration, connect the following circuit: VEJOV 1002 Ik M 10 ΚΩ 1 M Figure 4 2. Adjust the I M.2 and 10 k potentiometers to set Va and we as shown in Table 1 Measure and record the voltage across the k2 resistor, for each combination of Ve and Yar in Table 1. To set V Ve for smaller values, it may be necessary to increase the values of the potentiometers by adding series resistance. It may also be necessary to use two VOMs in order to keep Vc constant. Grand 3. To determine the output characteristics of the common-emitter configuration, set the 10 k potentiometer in the circuit of Figure 4 to its maximum setting. This will cause Vas to decrease to approximately o V. Then adjust the 1 MQ potentiometer to set I, to 10 A (note that when Van is 10 mV. l, is 10 HA). Next adjust the 10 K2 potentiometer for all values of Voin Table 2 making sure that I remains constant. 3
EXPERIMENTS.COMMON ESITTER COMMON COLLECTOR CHARACTERISTICS 4. Measure and record in Table 2 the voltage VR across the 100 92 resistor for each combination of Ve and I, in Table 2. 5. To measure the input characteristics of the common-collector configuration, connect the following circuit: 10V 1 1 MON 100 hann Figures 10 ΚΩ 6. By carefully adjusting the 1 MQ and 10 ka potentiometers, set the voltages V and Va as shown in Table 3. Both Va and V are very sensitive to the potentiometer settings. 7. Measure and record in Table 3 the voltage Vos across the i ka resistor, which can be used to calculate the currently