There is no template document for this laboratory as you have seen what is required in the previous laboratories; however, any of the tables can be cut-and-pasted into your final report. It would be useful if you could have a copy (electronic or otherwise) of the notes on transistors to help you with the responses to the specific questions. The notes are available here as "Lecture Slides on BJTs" Please submit your laboratory write up to: https://loop.dcu.ie/mod/assign/view.php?id=1157953 As there are three digital multimeters required for this laboratory (one with high quality microamp readings) and a variable voltage supply, attendance is compulsory. Lab Objectives:
Equipment:EE223 Electronics Kit, with these components in particular:
Procedure:1. 2N2219 (NPN) Transistor Output Characteristics (IC vs. VCE)The collector current (IC ) of a transistor is mainly dependent upon two variables: the collector-emitter voltage (VCE) and the base current (IB ). This dependency is normally shown as a “family” of graphs: for each of a number of different values of IB , the graph of IC vs. VCE is plotted.
2. Component Assembly and Work-Station Set-up
Figure 1. The 2N2219A Transistor Pin Diagram (note: figure on left illustrates the bottom side of the transistor)
Figure 2. The Common-Emitter Configuration (no meters)
(a) (b)
Figure 3. (a) An example of the internals of a potentiometer. You can see that the W pin is connected to the wiper that turns with the dial over the resistive material. The A and B pins are connected at either end of the material, meaning that when the wiper is turned fully to the left that the resistance between W and A is at the minimum, but the resistance between W and B is at the maximum. (b) shows some different styles of multi-turn potentiometer. The multi-turn potentiometer in your kit allows 15 full 360 degree turns to go from 0Ω to 1MΩ.
Figure 4. The Common-Emitter Configuration (with meters)
3. 2N2219 Transistor Base Current, IB AdjustmentUsing potentiometer RB, set the base current IB to the value in row 1 of the leftmost column of Table 1 below. NB: This is a sensitive adjustment so it’s important to check and reset it constantly as you take the following measurements, to ensure that it is held constant at the indicated value. It may deviate when you alter other variables.
4. Family of Graphs using IC, with values of VCE and IBVary the collector-emitter voltage VCE ¾ the top row of the table below gives a suggested range of values; you may need to include more at some points within this range to produce a reasonable graph ¾ and measure the corresponding values of collector current IC , recording these in row 1 of the table. Some of the readings are very sensitive and take time to settle down. Repeat this procedure for the remaining rows of the table - set a new value for IB, vary VCE through its range, measure and record IC while checking that IB remains constant at the level indicated in the leftmost column (remember that the base current is in micro-amps, while the collector current is in milli-amps)
Table 1 Measurements of Output Characteristics (Place the measured IC value in the boxes) You will need to plot this very carefully for your write-up, but plot each of the curves now and check with one of the demonstrators that you have valid results. So, on the same page and using the same axes, plot a family of graphs: for each value of IB, plot IC (vertical or Y-axis) vs. VCE (horizontal or X-axis), labelling each with the appropriate value of IB. Do this before performing the calculations in the next section of the laboratory. 5. Calculation of Transistor ParametersIn calculating transistor parameters you should take values from the “flat” or active region of the characteristic. Your answers should include the appropriate units. Carefully number each of these questions as 5(a), 5(b) etc. in your final write-up. (a) Estimate the DC current gain hFE = IC / IB where VCE has a constant value of say 9V. Compute for each value of IB from Table 1 and take the mean value. (b) Using the attached datasheet, determine if your calculation in (a) is valid and within range. What is the valid range of hFE at the current temperature (assume 25 Celsius) and with a collector current and collector-emitter voltage in the range that you used. (c) Estimate the small-signal current gain hfe = ΔIC / ΔIB where VCE has a constant value of say 9V again by using the differences between the data in adjacent rows. Compare hFE and hfe. Note: It is possible that the transistor has been damaged by thermal runaway when the current was set to be 150uA and the voltage was set high at the end of the last section. If your transistor is not behaving correctly in the next section then please test the transistor.
6. Basic Common-Emitter Amplifier CircuitIn this part of the experiment we are going to set up a very basic common-emitter amplifier circuit and we are going to design it so that we achieve an optimized operating point when the amplifier circuit is in its quiescent state - i.e. there is no input applied. We are then going to verify that the circuit behaves in this experiment as it should behave in theory.
Set up the circuit as described in Figure 5, where we use a potentiometer on the base and a potentiometer on the collector. When wiring use wires to link all of the components, so that it is easy to replace a wire with the digital multimeter in order to measure current. (Note: you can ignore the dashed lines as you will not be connecting them) Figure 5. The Common-Emitter Amplifier Circuit Procedure steps:
Figure 6. (From the notes) We wish to choose the operating point of the transistor to maximise our possible clean signal output.
Table 2. The Values to be completed from the above procedure
Figure 8. Draw this figure in your write-up replacing the values in green with your actual readings from Table 2.
Table 3. The Values to be Calculated and then Measured
Conclusions:
There is no template document for this laboratory as you have seen what is required in the previous laboratories; however, any of the tables can be cut-and-pasted into your final report. Please submit your laboratory write up to: https://loop.dcu.ie/mod/assign/view.php?id=1157953
|
Laboratories >