The method of determining the pins of a transistor using a multimeter
First, pull the three pins of the transistor apart, either front and back or left and right, to a certain distance for easy measurement. This can prevent the test leads from short-circuiting. Set the ohm range of the pointer multimeter to the R×1k range. Measure the resistance between any two pins, both forward and reverse, once each. Take the measurement with the smaller resistance value. The pin connected to the black test lead is the p region, and the pin connected to the red test lead is the n region. Mark them. Then continue to measure the next group and mark them in the same way. If, among the four measurements (two measurements for each pair of pins), there is a common p or n region, then you can determine whether it is an npn or pnp transistor. That is, if there is a common p region, it is an npn transistor; if there is a common n region, it is a pnp transistor. The pin connected to the common region is the base. There is also a situation where the forward and reverse resistances between two pins are almost the same. In this case, these two pins are the emitter region and the collector region. Generally, the above measurements need to be carried out six times (for the three pins, measure each pair of pins both forward and reverse. According to the permutation and combination, six measurements can be made). In this way, you can also determine the condition of the transistor. But sometimes, when measuring any two pins twice, and the measured resistance values are both small, you can determine the polarity with just these two measurements, as shown in Figures 4 and 5. It should be noted that your fingers should not touch the pins!
The basis for this measurement is the content in Figure 2 mentioned above. Both the emitter junction and the collector junction belong to the pn junction, which has the basic characteristics of a pn junction: the forward resistance is small and the reverse resistance is large. After determining the polarity of the transistor, the base is also determined. The next task is to determine the emitter and the collector. At this time, you can use the first sentence in the structure mentioned above.
