NPN I-V and DC Characteristics

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1c VCE + VBE + Enter the circuit into your simulator's schematic editor, applying DC voltage supplies to the base and to the collector of the transistor Ic vs. VBE • While setting Vce to a constant value of 5V, sweep the base voltage from 0V to 0.8V in increments of 0.1V. Plot a curve of Ic vs. VBE and place the plot in your lab writeup. • At what value of VBE does current begin to conduct? • What are the values of IB and Ic when VBE = 0.7V? • Based on these numbers, what is your estimate of B? Ic vs. VCE • For three values of VBE (0.6 V, 0.7 V, and 0.8 V), sweep the collector voltage from 0 V to 2 V in increments of 0.1 V. Plot the curves for Ic vs. Vce using a graphing program indicating the value of Vbe next to each curve. • What observations can be made about the curves? . Part 2:Measurements: Assemble the circuit from the figure above, using a power supply to generate the DC voltages. Ic vs. VBE While setting Vce to a constant of 5 V, sweep the base voltage from OV to 0.8V in increments of 0.1V, and measure the collector current using the power supply. (Note that not all power supplies allow you to accurately measure current. If this is the case for your lab setup, you place a small resistor in series with the collector and measure the voltage drop across the resistor.) • Plot a curve of Ic vs VBE At what value of VBE does the current turn on? • Using a small resistor placed in series with the base and collector terminals, measure IB and Ic for VBE = 0.7V Based on these numbers, what is your ß? . C Ic vs. VCE For three values of VBE (0.6 V, 0.7 V, and 0.8 V), sweep the VCE from 0 V to 1 V in increments of 0.1 V, and measure the collector current using the power supply. • Plot the curves for Ic vs. Vce using a graphing program and clearly indicating the value of Vbe next to each curve. Part 3:Post-Measurement Exercise: Simulation vs. Measurement • What are the main differences between your simulated and measured curves? Can you explain the differences? Early voltage, VA • Based on your simulated Ic vs. Vce curves for an active transistor, extract the Early voltage VA. • Does VA change significantly for each value of VBE? • What is the average value of VA Part 4:Design and Simulation Consider the circuit shown below. V+ V+ R1 Rc R2 WW ww RE V. V. Design the circuit such that Ic = 1mA, VB = 0, and Vc = +5V. Use supplies of V+ = -V = 15V. Although there will be variations from transistor to transistor, you may assume a value 100 for B in your calculations. Also assume that VBE = 0.7V. In your lab writeup, perform the following. Hand Calculations • What are IB and IE? Based on these numbers, what is VE? • You now have enough information to calculate Rc and Rc. Are the calculated values available in your kit? Can you achieve these values by combining several resistors? Comment. • Derive the Thevenin equivalent of Rį and R2. What values of Rį and R2 do you need to use to achieve VB = 0 V? Remember that IB #0. Is the problem completely specified? If not, what needs to be specified? Simulations • Simulate your circuit using values of RE, Rc, Rī, and R2 based on you r calculations. Report the values of VE, Vc, VB, IE, Ic, and IB. How closely do they match your calculations? (Remember: The simulator has its own, more complex model of the real transistor, so there should be some small variations.) Prototyping and Measurement • Assemble the circuit onto a breadboard. Using a digital multimeter, measure VE, Vc, and VB. Using a digital multimeter, measure all resistors to three significant digits. . . Post-Measurement Exercise What are the measured values of VBE and VCE? How do they compare to your pre-lab calculations? Explain any discrep- ancies. • Based on the measured values of Vc and Ve and your measured resistor values, what are the measured values of IB, IC and IE based on your lab measurements? Part 5:NPN in Saturation Mode: Redesign the circuit in the figure above such that I c = 1 mA, IE = 1.2 mA, Vc = +2 V, and VCE = 0.2 V. Use supplies of V+ = -V_= 15 V. Note that you must use the saturation model. 3 Hand Calculations • Based on the specifications, calculate Ve and VB. • You now have enough information to calculate Rc and Re. Are the calculated values available in your kit? Can you achieve this value by combining several resistors? Comment. • What is Bforced? What values of Rį and R2 do you need to use? Is the problem completely specified? . Simulation • Simulate your circuit using values of Re, Rc, R1, and R2 based on your calculations. • Report the values of VE, Vc, VB, IE, Ic, and IB. How closely do they match your calculations? Pa 6:Post-Measurement ercise: Prototyping and Measurement • Assemble the circuit onto a breadboard. Using your volt multimeter, measure VE, Vc, and VB. Report them in your lab writeup. Using a digital multimeter, measure all resistors to three significant digits. . . Post-Measurement Exercise • What are the measured values of VBE and Vce? How do they compare to your pre-lab calculations? Explain any discrep- ancies. • Based on the measured voltages and resistor values, what are the measured values of Ib, Ic and IE based on your lab measurements? What is Bforced? LAB 3: NPN I-V & DC Characteristics Lab Due: March 15, 2017 Objective: To Study NPN transistor I-V curves by: • Simulating a transistor to investigate the collector current versus the collector-to-emitter voltage. Implementing a circuit and taking measurements of the Ic vs. Vce curves. . Materials: 1. Laboratory setup, including breadboard 2. 1 NPN transistor (e.g., 2N2222) 3. Several wires and resistors of varying sizes Part 1:Simulation: Consider the circuit shown below. lo Ів INCE UBE =
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Explanation & Answer

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Part 1
The circuit for the simulation is built in LtSpice, and the circuit looks as below:

Figure 1: Simulation circuit in LtSpice
Making Vc=5V and doing a DC sweep analysis on Vbe from 0 to 0.8V in 0.1V increment, we get the
following results:

Figure 2: Ic vs Vbe

As can be seen from the results collector current starts to build up when Vbe reaches 0.7V. The
collector current value obtained at that Vce is Ic=61.17uA.
Base current curve obtained is as follows:

Figure 3: Ib vs Vbe

So, as per the curve Ib=6...


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