How to judge the quality of the transistor and distinguish the type and pin?

The triode is a basic and important device we encountered in the study of analog circuits. Everyone must be familiar with the working principle of this device. Definitions such as "high-level turn-on, low-level cut-off", "common-emitter amplifier circuit", "emitter follower", etc. are also commonly encountered in our learning. But in actual work, it is not just knowing these definitions to successfully complete the task, such as "Is this triode good?" and "How to quickly determine the polarity of the triode" These questions are rarely introduced in books, but they are Every electronics practitioner or hobbyist should master it. From the perspective of actual combat, I will introduce three "judgment methods" that must be mastered.

1. Judge the quality of the triode
When we encounter problems in the process of circuit debugging, we often need to judge whether the performance of the tube is good or not. At this time, we can use a three-meter to make the judgment. Adjust the three-meter to the resistance position, and measure the three pins of the triode two by two. A total of six measurements are made. If the resistance value can be measured in two of them, the triode is good, and the other conditions are bad.

Huixin: How to judge the quality of the transistor and distinguish the type and pin?

2. Triode type and pin identification

Adjust the multimeter to the resistance range;

Use the black test lead of the multimeter to contact the No. 1 pin, and the red test lead to the No. 2 and No. 3 pins respectively. Whether there is a resistance value twice;

Use the black test lead of the multimeter to contact the No. 2 pin, and the red test lead to contact the No. 1 and No. 3 pins respectively. Whether there is a resistance value twice;

Use the black test lead of the multimeter to contact No. 3 pin, and the red test lead to contact No. 1 and No. 2 pins respectively. Whether there is resistance value twice;

For the above three groups of measurements, if a certain group of measurements are conducted, the black test lead is in contact with the base, and the transistor is of NPN type;

Using the diode file, the e and c levels can be distinguished;

If none of the three sets of measurements are conducted, use the red test lead as the common terminal, and perform the measurement according to steps 2~4. It is measured that the pin touched by the red test pen that is all conductive is the B pole and the triode. It is a PNP type, and then use the diode file to determine the e and c poles.

Measurement of temperature rise of main power components

The temperature rise measurement mainly includes the measurement of the surface temperature rise of key power components such as MOS switch tubes, transformers, output rectifier diodes and output capacitors. Commonly used measuring instruments include infrared thermometers and thermocouple measuring instruments.


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