Transistor principle and multimeter measurement to determine the pin and model
Step 1: Determine the base and transistor type (NPN or PNP)
The base of a PNP transistor is the common point of two negative electrodes, while the base of an NPN transistor is the common point of two positive electrodes. At this point, we can use the diode range of a digital multimeter to measure the base. For PNP transistors, when the black probe (connected to the negative terminal of the battery inside the meter) is on the base and the red probe is used to measure the other two poles, it is generally a small reading with little difference (usually 0.5-0.8). If the probe is reversed, it is a larger reading (usually 1). For NPN transistors, the red probe (connected to the positive terminal of the battery inside the meter) is connected to the base.
Step 2: Determine the emitter and collector electrodes
If you use a pointer multimeter to this point, you may need to use both hands, and some friends may even use their mouth and tongue, which can be quite troublesome. It is much more convenient to use the HFE mode of a digital meter to measure the DC amplification factor of a transistor. Set the multimeter to the HFE mode, insert the transistor into the small hole of the NPN, and the B pole corresponds to the letter b above. Read the value; Reverse its other two legs and read again. The polarity with the larger reading corresponds to the letter on the table, and the same applies to other transistors!
The method of using a digital multimeter to check the quality of a transistor is as follows:
1. Find the base: Place the digital multimeter in diode mode, connect the red probe to either pin, and use the black probe to sequentially contact the other two pins. If both displayed values are less than 1V or both display the overflow symbol 1, then the pin connected to the red probe is the base b. If the displayed value is less than 1V in two tests and the overflow symbol 1 is displayed in the other test, it indicates that the pin connected to the red probe is not the base. Then use another pin to re measure and find the base
2. Determine the tube type, place the digital multimeter in diode mode, connect the red probe to the base, and use a black probe to touch the other two pins in sequence. If both display 0.5V to 0.8V, the tested tube belongs to NPN type. If overflow symbol 1 is displayed twice, it indicates that the tested tube belongs to PNP type.
3. Distinguish between collector C and emitter e. Taking NPN transistor as an example, place the digital multimeter in HFE mode and use PNP socket. Insert the base B into the B hole, and insert the remaining 2 pins into the C and E holes respectively. If the measured HFE is in the range of tens to hundreds, it indicates that the tube is connected normally and has strong amplification capability. At this time, the collector C is inserted into the C hole and the emitter E is inserted into the E hole. If the measured HFE value is only a few or a dozen, it indicates that the collector c and emitter e of the tested tube are inserted in reverse. At this time, the C hole is connected to the emitter e, and the E hole is connected to the collector c. In order to make the test results more reliable, the base b can be fixed in the B hole, and the collector c and emitter e can be swapped and retested twice, with the larger displayed value as the standard. The pin connected to the C hole is the collector c, and the pin connected to the E hole is the emitter e.
