Multimeter to measure transistor polarity wiring
By using the ohm range of a multimeter, it is possible to distinguish between NPN and PNP transistors. The specific method is to use the Rx1k range of the multimeter, press one pin with a black meter rod, and connect the other two pins with a red meter rod. Figure 1 shows the wiring diagram.
Measure two resistance values of 1R1 and 1R2. Replace the black meter rod with one pin and connect the red meter rod to the other two pins. Measure the two resistance values 2R1 and 2R2; Connect the black meter rod to the third pin and the red meter rod to the other two pins. Measure the two resistance values 3R1 and 3R2
Compare the three sets of measured resistance values. When the two resistance values in a certain set are basically equal, the pin connected to the black meter rod is the base of the transistor. If the two resistance values in this group are the smallest among the three groups, it indicates that it is an NPN transistor; If the two resistance values in this group are at their maximum, it indicates that it is a PNP transistor.
2. Detection principle
NPN type transistor. It has a PN junction with two positive poles connected. When the black meter rod is connected to the base and the red meter rod is connected to the other two pins, the positive pole of the battery in the meter is connected to the black meter rod, which applies a forward bias voltage to the collector and emitter junctions. Therefore, the measured resistance value is basically equal and the minimum value. In the other two detection states, there cannot be two equal and minimum positive values, so it can be determined that it is an NPN type transistor.
Principle of polarity detection of transistor
Two PN junctions are connected to the negative pole, with the black meter rod connected to the base and the red meter rod connected to the other two pins respectively. The internal voltage of the meter applies a reverse bias voltage to the two PN junctions, and the reverse resistance of the two PN junctions is the same. This confirms that the transistor is of PNP type
3.1 Method for distinguishing the collector and emitter of NPN transistor
When distinguishing between NPN and PNP transistors, the base has already been determined. Figure 3 shows the wiring diagram for distinguishing between the collector and emitter of NPN transistors.
Connect either the red or black meter rod to the other two pins outside the base, and then use your lips to simultaneously contact both the black meter rod and the base. The resistance R between the collector electrode and the emitter electrode in the figure is the human body resistance when the lips are in contact. If the pointer deviates to the right by an angle (the resistance decreases significantly), it indicates that the pin connected to the black meter rod is the collector and the other is the emitter.
If the needle does not deflect when the lips come into contact, swap the red and black bars once and measure again using the same method. As long as the transistor is good, there must be a deviation of the needle, which can determine the collector and emitter.
