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What is the method for measuring the electrical characteristics of bipolar junction transistors (BJTs) ?

An example of a measurement circuit for electrical characteristics (cut-off current, current gain, saturation voltage) described in the data sheet is shown.
Please refer to the FAQ (What are the electrical characteristics of bipolar junction transistors (BJTs) ?) for the explanation of each item.
The electrical characteristics explained here are described in the data sheet as shown in Table. 1.

The measurement method for each item is shown below. Semiconductor characteristics are greatly affected by temperature. It is necessary to consider fluctuations not only due to room temperature but also due to losses (voltage and current) during measurement. In addition to controlling the room temperature at the time of measurement, please consider the time to apply voltage and current. Pulse measurement is recommended to suppress the temperature rise of the transistor.

Table. 1: Electrical characteristics Bipolar junction transistor (BJT) 2SC2712

1. Collector cut-off current I_CBO: Fig. 1

It is an electrical characteristic paired with the collector-base voltage V_CBO described in Absolute Maximum Ratings. With the emitter open, apply a voltage so that the pn junction between the base and collector is reverse biased, and measure the current. Since the voltage V_CB applied between the collector and the base is the absolute maximum rated voltage, care must be taken so that the voltage value does not exceed the specified value. I_CBO is the leakage current between the collector and the base, so it fluctuates depending on the temperature.

2. Emitter cut-off current I_EBO: Fig. 2

It is an electrical characteristic paired with the collector-base voltage V_EBO described in the absolute maximum ratings. With the collector open, apply a voltage so that the pn junction between the base and emitter is reverse biased, and measure the current. Since the voltage V_EB applied between the emitter and base is the absolute maximum rated voltage, care must be taken so that the voltage value does not exceed the specified value. I_EBO is the leakage current between the emitter and base, so it varies with temperature.

Fig. 1: Collector cut-off current measurement circuit

Fig. 2: Emitter cut-off current measurement circuit

Fig. 3: DC current gain measurement circuit

3. DC current gain h_FE: Fig. 3

Apply the specified voltage V_CE between the collector and emitter and adjust the voltage V_BE between the base and emitter so that the target collector current I_C is obtained. The base current I_B at this time is measured, and the result of the calculation of the following formula is h_FE. 　h_FE ＝ I_C / I_B
Note that h_FE is temperature dependent. (Fig. 4)
As shown in Fig. 5, h_FE changes due to the Early effect. High frequency transistors with narrow base widths will have a larger change.

Fig. 4: h<sub>FE</sub> – I<sub>C</sub> curve (effect of temperature) 2SC2712 — Fig. 4: h_FE – I_C curve (effect of temperature) 2SC2712

Fig. 5: I<sub>C</sub> - V<sub>CE</sub> curve (Early effect) 2SC2712 — Fig. 5: I_C - V_CE curve (Early effect) 2SC2712

4. Collector-emitter saturation voltage　V_CE(sat)： Fig. 6

In the circuit shown in Fig. 6, first apply a voltage of about 0.6 V between the base and emitter with the voltage source V_BE. After that, the collector current I_C is applied while gradually increasing until the specified current is reached. Next, change the base voltage V_BE until the base current I_B reaches the specified value. Measure the collector-emitter voltage V_CE when I_B reaches the specified current. This voltage is V_CE(sat).
If the current source on the collector side is applied while the transistor is off, it may become an abnormally high voltage and destroy the transistor. Set the open-circuit voltage of the current source in advance so that it is less than the collector-emitter voltage V_CEO described in the absolute maximum ratings.
V_CE(sat) is temperature dependent (Fig. 7).

Fig. 6: Collector-emitter saturation voltage measurement circuit

Fig. 7: V<sub>CE(sat)</sub> – I<sub>C</sub> curve (effect of temperature) 2SC2712 — Fig. 7: V_CE(sat) – I_C curve (effect of temperature) 2SC2712

5. Base-emitter saturation voltage　V_BE(sat)： Fig. 8

First, apply a voltage of about 0.6 V between the base and emitter with the voltage source V_BE. After that, the collector current I_C is applied while gradually increasing until the specified current is reached. Next, adjust V_BE so that the base current I_B is the default, and measure the voltage between the base and emitter at this time. This voltage is V_BE(sat).
If the current source on the collector side is applied while the transistor is off, it may become an abnormally high voltage and destroy the transistor. Set the voltage when the current source is open so that it is less than the collector-emitter voltage V_CEO described in the absolute maximum ratings.
V_BE(sat) is temperature dependent (Fig. 9).
This characteristic V_BE(sat) is a spec that makes a pair with collector-emitter saturation voltage (Table. 2).