Simple Measurement of Transistor Performance

(1) Use a multimeter to measure ICEO and β 

The base is open, the black test lead of the multimeter is connected to the collector c of the NPN tube, and the red test lead is connected to the emitter e (the PNP tube is opposite). At this time, the resistance value between c and e is large. Indicates that the ICEO is small, and a small resistance value indicates a large ICEO.

Use your finger to replace the base resistor Rb, and use the above method to measure the resistance between c and e. If the resistance value is much smaller than the base open circuit, it indicates that the β value is large.  

(2) Measure beta with a multimeter hFE file

Some multimeters have hFE files. Insert the triode according to the polar type specified in the table to measure the current amplification factor β. If β is small or zero, it indicates that the triode has been damaged. , Measure the two PN junctions separately with the resistance gear to confirm whether there is a breakdown or open circuit.

The selection of transistors must first meet the requirements of equipment and circuits, and second, it must meet the principle of economy. Depending on the application, the following factors should generally be considered: operating frequency, collector current, dissipated power, current amplification factor, reverse breakdown voltage, stability and saturation voltage drop. These factors have a mutually restrictive relationship. When selecting management, we should grasp the main contradiction and take into account the secondary factors.

The characteristic frequency fT of low-frequency tubes is generally below 2.5MHz, while the fT of high-frequency tubes ranges from tens of megahertz to hundreds of megahertz or even higher. When selecting tubes, fT should be 3 to 10 times the operating frequency. In principle, high-frequency tubes can be substituted for low-frequency tubes, but the power of high-frequency tubes is generally relatively small and the dynamic range is narrow. Attention should be paid to the power conditions when replacing.

Generally hope that the beta should be larger, but it is not the bigger the better. If β is too high, it is easy to cause self-excited oscillation, not to mention that the general operation of the tube with high β is more unstable, and it is greatly affected by temperature. Usually, the β value is between 40 and 100. However, for tubes with low noise and high β value (such as 1815, 9011~9015, etc.), the temperature stability is still good when the β value reaches several hundreds. In addition, for the whole circuit, β should also be selected from the cooperation of all stages. For example, if the front stage uses a higher β, the rear stage can use a lower β pipe; conversely, if the front stage uses a lower β, the rear stage can use a higher β tube.  

The collector-emitter reverse breakdown voltage UCEO should be chosen larger than the power supply voltage. The smaller the penetration current, the better the stability to temperature. The stability of ordinary silicon tubes is much better than that of germanium tubes, but the saturation voltage drop of ordinary silicon tubes is larger than that of germanium tubes, which will affect the performance of the circuit in some circuits. It should be selected according to the specific conditions of the circuit. When dissipating power, a certain margin should be reserved according to the requirements of different circuits.

For transistors used in high frequency amplification, intermediate frequency amplification, oscillators and other circuits, transistors with high characteristic frequency fT and small inter-electrode capacitance should be selected to ensure high frequency conditions. It still has high power gain and stability.

Phototransistor

A triode is similar to a transistor in principle, except that its collector junction is a diode structure. Since the base current can be provided by the photodiode, there is generally no base outer lead (products with a base outer lead are easy to adjust the static operating point).

The output characteristics of the triode are similar to those of the transistor, but the IB in the output characteristic curve of the transistor is replaced by the illuminance of the incident light. When the phototransistor is made into a Darlington form, a large output current can be obtained and some relays can be directly driven.  

(1) Use a multimeter to measure ICEO and β 

The base is open, the black test lead of the multimeter is connected to the collector c of the NPN tube, and the red test lead is connected to the emitter e (the PNP tube is opposite). At this time, the resistance value between c and e is large. Indicates that the ICEO is small, and a small resistance value indicates a large ICEO.

Use your finger to replace the base resistor Rb, and use the above method to measure the resistance between c and e. If the resistance value is much smaller than the base open circuit, it indicates that the β value is large.  

(2) Measure beta with a multimeter hFE file

Some multimeters have hFE files. Insert the triode according to the polar type specified in the table to measure the current amplification factor β. If β is small or zero, it indicates that the triode has been damaged. , Measure the two PN junctions separately with the resistance gear to confirm whether there is a breakdown or open circuit.

The selection of transistors must first meet the requirements of equipment and circuits, and second, it must meet the principle of economy. Depending on the application, the following factors should generally be considered: operating frequency, collector current, dissipated power, current amplification factor, reverse breakdown voltage, stability and saturation voltage drop. These factors have a mutually restrictive relationship. When selecting management, we should grasp the main contradiction and take into account the secondary factors.

The characteristic frequency fT of low-frequency tubes is generally below 2.5MHz, while the fT of high-frequency tubes ranges from tens of megahertz to hundreds of megahertz or even higher. When selecting tubes, fT should be 3 to 10 times the operating frequency. In principle, high-frequency tubes can be substituted for low-frequency tubes, but the power of high-frequency tubes is generally relatively small and the dynamic range is narrow. Attention should be paid to the power conditions when replacing.

Generally hope that the beta should be larger, but it is not the bigger the better. If β is too high, it is easy to cause self-excited oscillation, not to mention that the general operation of the tube with high β is more unstable, and it is greatly affected by temperature. Usually, the β value is between 40 and 100. However, for tubes with low noise and high β value (such as 1815, 9011~9015, etc.), the temperature stability is still good when the β value reaches several hundreds. In addition, for the whole circuit, β should also be selected from the cooperation of all stages. For example, if the front stage uses a higher β, the rear stage can use a lower β pipe; conversely, if the front stage uses a lower β, the rear stage can use a higher β tube.  

The collector-emitter reverse breakdown voltage UCEO should be chosen larger than the power supply voltage. The smaller the penetration current, the better the stability to temperature. The stability of ordinary silicon tubes is much better than that of germanium tubes, but the saturation voltage drop of ordinary silicon tubes is larger than that of germanium tubes, which will affect the performance of the circuit in some circuits. It should be selected according to the specific conditions of the circuit. When dissipating power, a certain margin should be reserved according to the requirements of different circuits.

For transistors used in high frequency amplification, intermediate frequency amplification, oscillators and other circuits, transistors with high characteristic frequency fT and small inter-electrode capacitance should be selected to ensure high frequency conditions. It still has high power gain and stability.

Phototransistor

A triode is similar to a transistor in principle, except that its collector junction is a diode structure. Since the base current can be provided by the photodiode, there is generally no base outer lead (products with a base outer lead are easy to adjust the static operating point).

The output characteristics of the triode are similar to those of the transistor, but the IB in the output characteristic curve of the transistor is replaced by the illuminance of the incident light. When the phototransistor is made into a Darlington form, a large output current can be obtained and some relays can be directly driven.