How to distinguish the electrode and tube type of a transistor? Do you have any techniques and methods?

How to distinguish the electrode and DIODE type of a transistor? Do you have any techniques and methods?

1、 Visual inspection method

1. Identification of pipe type

Generally, whether the pipe type is NPN or PNP should be distinguished by the model marked on the pipe shell. According to ministerial standards, the second digit (letter) of the transistor model, A and C represent PNPDIODE, B and D represent PNP diodes, for example:

For PNP type low-frequency low-power transistor, 3BX for  NPN type low-frequency low-power transistor

PNP type high-frequency low-power transistor, 3DG type  NPN type high-frequency low-power transistor

For PNP type low-frequency high-power transistor, 3DD for  NPN type low-frequency high-power transistor

For PNP type high-frequency high-power transistor, 3DA for  NPN type high-frequency high-power transistor

In addition, there are internationally popular 9011~9018 series high-frequency low-power DIODE, with the exception of PNP diodes for 9012 and 9015, all of which are  NPN type diodes.

2. Identification of diodes Poles

Commonly used small and medium-sized power transistors have metal circular shells and plastic packaging (semi cylindrical). Figure T305 introduces three typical shapes and electrode arrangement methods.

2、 Using a multimeter to determine the resistance range

There are two PN junctions inside the transistor, which can be used to distinguish the three poles e, b, and c using a multimeter resistance range. In the case of fuzzy model labeling, this method can also be used to distinguish the pipe type.

1. Identification of base electrode

When distinguishing the transistor electrode, the base electrode should be confirmed first. For  NPN DIODE, connect a black lead to the assumed base and a red lead to the other two poles. If the measured resistance is small, it is about a few hundred to several thousand ohms; When the black and red probes are swapped, the measured resistance is relatively high, exceeding several hundred kiloohms. At this point, the black probe is connected to the base electrode. PNP tube, the situation is opposite. When measuring, when both PN junctions are positively biased, the red probe is connected to the base electrode. In fact, the base of low-power transistors is generally arranged in the middle of three pins. The above method can be used to connect the black and red probes to the base respectively, which can not only determine whether the two PN junctions of the transistor are intact (similar to the measurement method for DIODE PN junctions), but also confirm the tube type.

2. Discrimination between collector and emitter

After determining the base electrode, assume that one of the remaining pins is the collector electrode c and the other is the emitter electrode e. Use your fingers to pinch the c and b electrodes respectively (i.e., use your fingers to replace the base resistance Rb). At the same time, contact the two probes of the multimeter with c and e respectively. If the DIODE being tested is  NPN, use a black probe to contact the c pole and a red probe to connect the e pole (opposite to the PNP diodes), and observe the pointer deflection angle; Then set the other pin as the c-pole, repeat the above process, and compare the deflection angle of the pointer measured twice. The larger one indicates that the IC is large, and the tube is in an enlarged state. The corresponding assumptions for the c and e poles are correct.