* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lab 4: Bipolar Junction Transistors (BJT)
Survey
Document related concepts
Voltage optimisation wikipedia , lookup
Stray voltage wikipedia , lookup
Electrical ballast wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Mains electricity wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Alternating current wikipedia , lookup
Semiconductor device wikipedia , lookup
Zobel network wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Two-port network wikipedia , lookup
Opto-isolator wikipedia , lookup
Buck converter wikipedia , lookup
Distribution management system wikipedia , lookup
Current source wikipedia , lookup
Transcript
Department of Physics, Stanford University Physics 105, Analog Electronics Lab 4.12 Page 1 (Final Version) Lab 4: Scope Probes Intro to Bipolar Junction Transistors (BJT) Read: Meyer Chapter 5, sections 5.1 – 5.2.4 (pp 149-158) PRELAB Part 1.1 A function generator can be modeled as a Thevenin equivalent circuit: an ideal AC voltage source, Vth, in series with an output resistance, Rth. The manual for the HP/Agilent function generator lists its output impedance as 50. Sketch a circuit showing how to measure this output impedance using an external load. Show what you would measure and where and specify the size of load you would use. Think Thevenin and voltage divider. Part 1.2. Your oscilloscope has a stated input resistance of 1M (megohm). As in Part 1a, sketch a circuit to measure this Rin using an added resistance. Show what you would measure; what resistance will you add, and where it will be in the circuit. In addition, the scope input also has a 14pf capacitance (to ground) in parallel with Rin, leading to a frequency-dependent Zin . And, just to make it more fun, coax cables have capacitance. Your “grabber” coax has C ~30 pF/ft, also relative to ground. Sketch the measurement circuit above as a divider including the input R and C of the scope, the C of your coax cable, and a resistance you add to make a divider. Predict the 3dB point of this input circuit. To cancel the frequency effect of the scope and cable, you want to add some C to make a divider with the C of the scope and cable, just like you made a divider with your added R. Hint: remember the relation between C and Zc Part 2. For Lab Manual Exercise 4-6, use the “Current Source” operating curve for the 2N3904 transistor (attached and on Coursework) to estimate the (constant) value of IC using the operating curve data plus the two basic transistor assumptions: VBE = 0.6V and IC = IB. (Hint: you need not calculate IB explicitly; do Kirchhoff’s loops from base-emitter and collector-emitter. You can use the operating curves to estimate and eliminate IB from your equations). +15V Ammeter Load (Decade Resistor Box) +5V 470 2N3904 Use this value of IC to estimate, in , the maximum “load”, shown in Fig L4.6 in the Lab Manual, that will cause the current source to saturate. The purpose of a current source is to put out a constant 820 current regardless of load; the voltage across the load can vary. The max Figure 1 Department of Physics, Stanford University Physics 105, Analog Electronics Lab 4.12 Page 2 load is when IC is no longer constant as the load changes (remember, the transistor saturates when VCE 0). Now replace the 820 resistor in the emitter leg with a 4.7k resistor and repeat the IC estimate and the maximum load estimate. Part 3. Predict VCE and the voltage drop across the bulb when fully lit. See the circuit on the sheet labeled “Switch” attached to this lab. This can be answered by inspection—no calculation needed. Department of Physics, Stanford University Physics 105, Analog Electronics Lab 4.12 Page 3 LAB—DAY 1 PART 1. Impedance Measurements/Scope Probes: (25 pts) 1.1. Measure the output impedance of your function generator using the method outlined in your prelab. you will be adding a resistance to make a voltage divider. Do this at 50 Hz and 1Khz. Is there a difference? Submit: a. sketch/explanation of how you made measurement b. quantitative result of measurement. 1.2. Measure your scope’s input impedance using your prelab method— a. Start with a low frequency, 50Hz (close enough to DC), measure the attenuation to get Rin of the scope. b. Now increase the frequency. You will find the scope reading drops off with frequency. Find this 3dB frequency (one data point, not a full Bode plot). c. Using your Prelab sketch of the input of the scope (1M || 14pF || 30pF/ft of the grabber coax), explain the frequency dropoff. d. How much C should you add in your measurement circuit, and where, to offset the effect of the scope and coax (, ie, make a divider)? e. Build this and document your improvement in the 3dB point. f. Explain this improvement in terms of your voltage dividers and impedances. LAB—DAY 2 PART 2. Meet the Transistor: DC Current Source (25 pts) Care and Feeding of Transistors 2.1 2.2 Use the powered breadboard, which has +15/-15/+5 voltages. Insert the transistor leads straight into adjacent holes on the breadboard, and use wires to bring the circuit to the transistor rather than vice-versa. ie, don’t mangle, bend, fold, spindle, mutilate the leads. +15V Using the diode function on the DMM, check the two diode junctions on a 2N3904 npn transistor: BE, and BC. Measure the forward voltage drops. You should find BE > BC. The collector area is larger than the emitter, which means a lower resistance and hence a lower voltage drop. Use the curve tracer to generate a set of characteristic curves for your 2N3904 transistor; your TA will demonstrate. Use the following settings: VCE = 10V, IC = 10mA. Compare these curves with the curve attached to the back of this lab writeup. If necessary, relabel the axes on the printed curves to match your transistor. (take a photo with your phone to have a record of this in case you need this). Ammeter Load (Decade Resistor Box) +5V 470 2N3904 820 Figure 1 Department of Physics, Stanford University Physics 105, Analog Electronics Lab 4.12 Page 4 2.3 a. Build the circuit of Figure 1. Confirm your prelab calculation for the output current with your load (resistor decade box) at 0 ohms. b. Increase the load in 100 steps until the current source starts to break down, i.e. IC is no longer constant. Do this step quickly and compare to your Prelab prediction. c. Once you’ve found the maximum load, go back to 100 and take the following data at several loads between 100 and your maximum load: IC, VCE, VB . Use one DMM with straight probes, not a BNC-grabber cable, for the latter two measurements—move your DMM probe from one transistor leg to the other. d. Plot these data, as you go, on the transistor curve at the end of the lab. From this, confirm that Kirchhoff’s law is satisfied in the collector-emitter loop while IC is constant, and explain what is happening to the transistor when the current source breaks down. e. Change the 820 resistor in Fig 1 to a 4.7k resistor, and repeat Steps d, e. You will have shown how to extend the “compliance” (read: voltage range over which the circuit operates) of the current source to larger loads. Submit: 1. Sketch of the circuit, indicating which instruments were connected where. 2. Raw data and calculated data to add to curve tracer plot. Calculate ( = hfe) for each data point you show on your plot. Explain how you calculated IB. 3. Prelab calculations for predicted IC, and the maximum load. Compare to measured values. 4. Transistor operating curves (curve tracer) with your actual data added to the plot. Indicate where current source starts to break down (collector current no longer constant). 5. Explain what’s happening on the plot as the load is changed. PART 3. (10 pts) Transistor Switch: +5V +15V Here you will see a transistor operated in saturation, and used as a switch. The usefulness of the transistor switch is that it can use low power signals to turn on and off higher voltage/power loads. Use a #1813 bulb, and connect it to 15V. 1813 bulb 3 While measuring VC and VB , vary the base resistance, R, until the light goes out--this is where the transistor goes out of saturation. Plot your data on the 2N4401 operating curve (appended to the lab). 1k Submit: a. Sketch of circuit, showing what you measured, how you inferred any quantities. b. Transistor operating curves (standard curves attached to lab) with your actual data added to the plot. Indicate where light Figure 2 bulb starts to dim, and where it’s entirely off. c. Explain what’s happening on the plot. Compare range of IB with that of Part 2. 2N4401 Department of Physics, Stanford University Physics 105, Analog Electronics TRANSISTOR SWITCH Lab 4.12 Page 5 Department of Physics, Stanford University Physics 105, Analog Electronics Lab 4.12 Page 6