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This page serves as a protocol of measurements on the bipolar NPN transistor 8050S. The measurements were done with the Keithley 2600 Series Sourcemeter which can be controlled with python (Tutorial).

## Common Emitter

In the common emitter configuration the emitter is connected to ground and the collector is connected to a supply voltage. The base current is used control the collector current. For measurements the emitter contact of the transistor was connected to the ground contact of the sourcemeter. The collector was connected to channel A and the base to channel B. For 6 different base currents ($0, 20, 40, 60, 80, 100$ $\mu$A) a sweep of the collector-emitter voltage $V_{CE}$ ($0 - 20$ V) was done and the collector current $I_C$ was recorded. The Python script npn_common_emitter.py was used to record measurements:
The common emitter measurement (data & plot below) lead to unphysical current curves. Repeated measurements lead to the same result. This might be due to the sourecemeter being unable to supply a constant current for small resistances, so a base $12$ k$\Omega$ resistor was introduced.

With the base resistor the common emitter measurement (data & plot below) resulted in the expected output characteristics. The slope in the plot indicates the occurences of the early effect. In the recorded range the current amplification factor $\beta$ is in the range of $220 - 300$ (2nd plot below). From the output characteristics the early voltage $V_A$ can be determined, see the third plot below. Fitting the range from $V_{CE} = 0.3 - 4.7 V$ leads to the best results (best agreement of x-intercepts). The resulting early voltage is $V_A = (-123 \pm 2) V$.
In the common base configuration the base of the transistor is connected to ground. In this configuration the the collector current $I_C$ follows the emitter current $I_E$. It can be used as an impedance converter or a voltage amplifier. For measurements the base contact was connected to the ground contact of the sourcemeter. The collector contact was connected to channel A and the emitter contact to channel B. For 7 different emitter currents ($-0.02, 0, 2, 4, 6, 8, 10$ mA) a sweep of the collector-emitter voltage $V_{CE}$ ($-5 - 10$ V) was done and the collector current $I_C$ was recorded. The Python script npn_common_base.py was used to record measurements:
The common base measurement can be found below. The output characteristic matches the expectations. Below $-0.9$ $V$ collector-base-voltage the collector current is constant due to the set current limit of the sourcemeter. Additionally the current transfer factor $\alpha$ is plotted. It is in the range $\alpha = 0.995-0.998$. Above $8$ $V$ collector-base-voltage there is a slight jump.
To operate the transistor in the so called reverse active mode the collector and emitter contacts have to be swaped. In this case the collector acts as the emitter and vice versa. The corresponding measurement can be found below. Punch-through occurs at a collector-base-voltage of about $V_P = 9\,V$. Above punch-through $I_C$ is constant due to the set current limit of the sourcemeter. At punch-through the depletion regions of the 2 pn-junctions merge and carriers drift through the base without recombining. In reverse-active mode punch-through occurs at a lower voltage since the emitter is heavily doped (usually a lot higher than the base) and the emitter-base junction is reverse biased. So the depletion region grows mostly in the base. Below punch-through the current transfer factor $\alpha$ is in the range $\alpha = 0.95-0.97$. $\alpha$ is the product of the emitter efficiency $\gamma_E$ and the base transport factor $B$. Since $B$ should not change between forward active and reverse active and is at least $0.995$ the "emitter efficiency" of the collector is $\gamma_C \approx 0.95-0.97$