A simple method for measuring the three pins of a transistor using a multimeter
A transistor is composed of a core (two PN junctions), three electrodes, and a shell. The three electrodes are called collector c, emitter e, and base b. Currently, the commonly used transistor is a silicon planar transistor, which is divided into two types: PNP and NPN. Germanium alloy tubes are now rare. Here, Electrician Home introduces a simple method of measuring the three pins of a transistor using a multimeter.
1. Identify the base and determine the type of transistor (NPN or PNP)
For PNP type transistors, the C and E poles are the positive poles of the two internal PN junctions, while the B pole is their common negative pole. For NPN type transistors, the opposite is true: the C and E poles are the negative poles of the two PN junctions, while the B pole is their common positive pole. Based on the small forward resistance and large reverse resistance of the PN junction, it is easy to determine the type of base and tube. The specific methods are as follows:
Set the multimeter to R × 100 or R × 1K gear. If the red pen contacts a certain pin and the black pen is connected to the other two pins, three sets of readings (two times per set) can be obtained. When one set of secondary measurements has a low resistance value of several hundred ohms, if the common pin is the red pen, it contacts the base, and the transistor type is PNP; If the common pin is a black probe, it is also in contact with the base, and the transistor type is NPN.
2. Distinguish between emitter and collector
Due to the different doping concentrations in the two P or N regions during the production of a transistor, if the emitter and collector are used correctly, the transistor has strong amplification ability. Conversely, if the emitter and collector are used interchangeably, the amplification ability is very weak, which can distinguish the emitter and collector of the transistor.
After identifying the tube type and base b, the following methods can be used to distinguish the collector and emitter.
Set the multimeter to R × 1K gear. Pinch the base pin together with the other pin by hand (be careful not to let the electrodes directly touch). To make the measurement obvious, wet your fingers and connect the red probe to the pin that is pinched together with the base pin, and the black probe to the other pin. Pay attention to the amplitude of the multimeter pointer swinging to the right. Then swap the two pins and repeat the above measurement steps. Compare the amplitude of the needle swinging to the right in two measurements and identify the one with the larger amplitude. For PNP type transistors, connect the black probe to the pin pinched together with the base, repeat the above experiment, and find the one with the larger swing amplitude of the probe. For NPN type transistors, connect the black probe to the collector and the red probe to the emitter. For PNP type, the red probe is connected to the collector and the black probe is connected to the emitter.
The principle of this electrode discrimination method is to use the battery inside the multimeter to apply voltage to the collector and emitter of the transistor, making it have amplification ability. When the base and collector are pinched by hand, it is equivalent to adding a forward bias current to the transistor through the resistance of the hand, making it conductive. At this time, the amplitude of the watch needle swinging to the right reflects its amplification ability, so it can correctly distinguish the starting emitter and collector.
