Characterization and DC Biasing of the BJT
ECEN 325 - 510
Lab 7: Characterization and DC Biasing of the BJT
Objective:
The purpose of the lab is to investigate the behavior of the bipolar junction transistor. The characteristic NPN and PNP transistors will be designed along with four additional transistors using NPN and PNP junctions. Two of these specific circuits will include a single NPN or PNP junction and the other two circuits will include a cascaded NPN or PNP junction. The circuits should utilize a voltage source and resistors that fit the design parameters. Their behaviors will be compared with simulations, measurements, and calculations.
Data Tables:
The characteristic NPN and PNP circuits will not have data tables due to excel plotting of their current and voltage functions. Comparisons will be drawn in the discussion section.
BJT DC Biasing NPN
Calculated |
Simulated |
Measured | |
V C (V) |
1.5 |
1.51 |
1.53 |
V RE (V) |
2 |
2.03 |
2.03 |
V 2 (V) |
2.7 |
2.69 |
2.69 |
I C (mA) |
1 |
1.01 |
1.01 |
RB1 (kΩ) |
2.3 |
2.3 |
2.3 |
RB2 (kΩ) |
2.7 |
2.7 |
2.7 |
RC (kΩ) |
1.5 |
1.5 |
1.5 |
RE (kΩ) |
2 |
2 |
2 |
BJT DC Biasing PNP
Calculated |
Simulated |
Measured | |
V C (V) |
2 |
1.48 |
1.42 |
V RE (V) |
2 |
1.99 |
1.90 |
V 2 (V) |
2.7 |
2.69 |
2.52 |
I C (mA) |
1 |
0.99 |
0.93 |
RB1 (kΩ) |
2.3 |
2.3 |
2.3 |
RB2 (kΩ) |
2.7 |
2.7 |
2.7 |
RC (kΩ) |
1.5 |
1.5 |
1.5 |
RE (kΩ) |
2 |
2 |
2 |
BJT Current Source Biasing NPN
Calculated |
Simulated |
Measured | |
V C (V) |
1.5 |
1.49 |
1.35 |
V 2 (V) |
2.7 |
2.69 |
2.50 |
V X (V) |
2 |
2.01 |
1.71 |
V Y (V) |
1.2 |
1.19 |
1.04 |
I C (mA) |
2 |
1.99 |
1.94 |
RB1 (kΩ) |
1.15 |
1.15 |
1.15 |
RB2 (kΩ) |
1.35 |
1.35 |
1.35 |
RC (kΩ) |
0.750 |
0.750 |
0.750 |
R3 (kΩ) |
0.250 |
0.250 |
0.250 |
R2 (kΩ) |
1.2 |
1.2 |
1.2 |
R1 (kΩ) |
3.8 |
3.8 |
3.8 |
BJT Current Source Biasing PNP
Calculated |
Simulated |
Measured | |
V C (V) |
1.5 |
1.39 |
1.18 |
V 2 (V) |
2.7 |
2.69 |
2.07 |
V X (V) |
2 |
1.97 |
1.75 |
V Y (V) |
1.2 |
1.19 |
1.06 |
I C (mA) |
2 |
1.85 |
1.57 |
RB1 (kΩ) |
1.35 |
1.35 |
1.35 |
RB2 (kΩ) |
1.15 |
1.15 |
1.15 |
RC (kΩ) |
0.750 |
0.750 |
0.750 |
R3 (kΩ) |
0.250 |
0.250 |
0.250 |
R2 (kΩ) |
1.2 |
1.2 |
1.2 |
R1 (kΩ) |
3.8 |
3.8 |
3.8 |
Discussion:
The calculations, simulations, and measured values for the characteristic PNP lined up very well. However, the characteristic NPN varied slightly. As seen in the IC vs. VCE graphs, the measured valued hit more of an asymptote at 1.2 Ma, whereas the simulated graph hit a maximum value at 1.4 mA. This could be due to a non-ideal PNP BJT which will be discussed further in other measurements. The calculated, simulated, and measured values for the DC sourced NPN BJT varied slightly and the measured values for the DC sourced PNP BJT varied more so. These variations were due to having non-ideal BJT’s and non-ideal resistors. Also, the current from the base was neglected in the calculations because the value was very small. This difference can be spotted greater in the current source BJT’s in the last part of the lab. The calculated, measured, and simulated values for the NPN and PNP current sourced BJT’s varied even more so that did in the DC sourced BJT’s. The BJT and the resistors with their large values and exact undetermined impedances affect the measured values as more are included in the circuit. This error can be minimized from 8%-15% usually to less than 1% with more ideal components and measurement tools.
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