Experiment 1, Plotting Common- Emitter Characteristic Curves

1 Experiment 1, Plotting Common- Emitter Characteristic Curves For more courses visit show the basic method for Plotting Characteristic Curves of a typical NPN transistor give you experience working with the Common- Emitter (CE) amplifier configuration Common- Emitter Characteristic Curves show how a particular transistor type will react to variations in collector- Emitter voltage, collector current and base current. Once these variations are known, it is possible to develop a complete picture of how well a transistor will operate in a given amplifier design. In this Experiment , we will first look at the basic procedure followed to obtain a family of such Curves , and then see what our data actually tells us A typical set of Characteristic Curves is shown on the next slide. Such a group of lines is usually referred to as a family of Curves , because more than one line is drawn on the graph Each line shows how the collector current (IC) varies as the collector- Emitter voltage (VCE) is changed, while the base current (IB) is held constant The horizontal axis, of the graph, is divided into various values of VCE, while the vertical axis includes various values of IC Each line represents all possible combinations of VCE and IC for a particular value of base current Note that each curved line is marked with the base-current value.

2 The values shown in the previous figure are for an NPN transistor. (Voltages and currents used with PNP transistors will have the same shape, but will have the opposite polarity) CE Characteristic Curves are plotted by setting the base current (IB) to some specific value, and then measuring the change in IC as VCE changes The circuit in the following slide show how this can be accomplished: R1 is used to set the base current IB to various specific values, while R4 sets VCE as desired. (R2 and R4 protect the transistor from excessive base and collector currents, respectively) The following steps are to be used for gathering curve data R1 to set IB to the desired value s between 10 mA and 30 mA indicated on the ammeter in base circuit VCE to the lowest desired value IC with the ammeter in the collector circuit (Ckt) VCE to the next higher voltage steps 3 and 4 until IC has been measured at all desired values of VCE (at the specific base current) the base current to the next desired value steps 1 through 6 until all data has been measured You will gather data about the Characteristic Curves of a typical NPN transistor, in this Experiment .

3 Once all data has been collected, you will plot the data points on a graph, to assemble a family of Curves . It is important that you take your time to make accurate measurements and accurately plot the data points. You will be using this graph for the other experiments in this lesson. 1 330 W, Watt Resistor (orange, orange, brown) 1 100 kW, Watt Resistor (brown, black, yellow) 1 1 kW potentiometer (on trainer) 1 100 kW potentiometer (on trainer) 1 MPSA20 NPN transistor (or similar) Note: Your results may be considerably different than those found by CIE. This is because the current gain for each transistor may be quite different . Do not be surprised if your results are not close to ours. on the trainer power and adjust the positive power supply to +15 V. and then turn off the trainers power. a)Be sure not to disturb this setting for the rest of the Experiment . the power off, construct, on the breadboard, the following circuit. a)The transistor Pin out (Lead configuration) is shown at the bottom of the schematic diagram.

4 Sure to wire the transistor correctly so it is not damaged b)Note the two places in the circuit where the ammeter will be inserted. to remove the jumper when inserting the ammeter in the circuit to place the jumper back in the circuit when removing the ammeter the jumpers only applies to the current measurements a)The jumpers are not to be removed when the voltmeter is connected to measure VCE. the base Ckt jumper and place the ammeter to measure IB. c)Note: The meters A and V are illustrated by the schematic symbols on the pictorial diagram. A V the meter to the mA (50 mA) range and turn on the trainer s power R4 to the middle of its rotation and adjust R1 for a base current of 10 mA the ammeter and reconnect the jumper a) Set the meter to the 10V DC range and connect it to measure VCE. b)Adjust R4 to measure O V the meter to measure the collector current (IC) and switch the meter to the 25 mA current range the jumper across the meter and observe the reading a)If necessary, switch to a lower current range to get a more accurate reading the present current value in the first row of the data table under the column headed IB = 10 mA.

5 The meter, and reinstall the jumper in the collector circuit the meter to the 10 V DC range, and connect it to measure VCE. the voltage to exactly 1 V, and repeat the current measurement procedure in step 5. to remove the jumper when making the IC measurement the IC measurement for each VCE value in the data table steps 3 through 7 with each base current value listed in the data table sure the jumper wires are installed when the meter is removed, and disconnected when current readings are taken. the value, in the appropriate space, as you take each collector current reading you have completed all the measurements, turn off the power supply power and refer to the following Characteristics Curve Graph for Exp 1. a)Plot the data points, on the Characteristic curve graph for Exp 1, you have stored in the data table each set of points for a given base current at one time each set of points into a smooth line and mark each line with the appropriate base current dismantling the circuit, mark the transistor you used in some way for identification purposes.

6 A)In later experiments, you will be using several transistors of the same type and you will have to identify the transistor used to make the Curves in this Experiment Our results for this Experiment are shown in the following two slides. Your results should show the same general trend, but don t be concerned if there are considerable discrepancies between our results and yours. The transistor you used can have a current gain of between 40 and 400. Such a wide variation in current gains will affect the shape of the Curves considerably In this Experiment , you measured the characteristics of a typical NPN Transistor-an MPSA20. You compiled your data and plotted the points on a graph to form a family of Characteristic Curves To get your data, you first set the base current on a specific value, and then varied VCE between 0 and 10 V in 1 V increments You then measured the collector current at each VCE setting. When all the readings for a particular base current were made, you changed the base current and repeated the procedure Next you plotted your data on a graph and connected the points to form a family of Curves The lines in the graph should have been nearly parallel, but non-linearities in the transistor may have caused some variations .

7 Your family of Curves could be farther up or down the graph than the Curves shown the plotted Characteristic curve graph, because of the wide variations in current gain between different transistors of the same type Rosenow, K. (2001). Lesson 1432: Common- Emitter Amplifier Characteristics. Cleveland: Cleveland Institute of Electronics. Developed and Produced by the Instructors in the CIE Instruction Department. Copyright 11/2012 All Rights Reserved / Nov. 2012