A simple way to measure the three pins of a triode with a multimeter
The triode is composed of a tube core (two PN junctions), three electrodes and a tube shell. The three electrodes are called collector c, emitter e and base b. Currently, the common triode is a silicon planar tube, which is divided into PNP and There are two types of NPN types. Germanium alloy tubes are now rare. Here, Electrician Home will introduce to you a simple method on how to use a multimeter to measure the three pins of a triode.
1. Find the base and determine the tube type (NPN or PNP)
For the PNP transistor, the C and E poles are the positive poles of the two PN junctions inside, and the B pole is their common negative pole. For the NPN transistor, the opposite is true: the C and E poles are the positive poles of the two PN junctions. The negative electrode, and the B electrode is their shared positive electrode. According to the characteristics of the PN junction with small forward resistance and large reverse resistance, the type of base and tube can be easily determined. The specific method is as follows:
Set the multimeter to R×100 or R×1K. Touch the red pen to a certain pin, and use the black test pen to connect the other two pins respectively. In this way, you can get three sets of readings (twice for each set). When one set of the second measurements is a low resistance value of several hundred ohms, When the common pin is a red test lead, it is touching the base, and the tube type of the triode is PNP type; if the common pin is a black test lead, it is also touching the base, and the tube type of the triode is NPN type .
2. Distinguish emitter and collector
Since the doping concentrations of the two P regions or the two N regions are different when the transistor is produced, if the emitter and collector are used correctly, the transistor has strong amplification capability. On the contrary, if the emitter and collector are used interchangeably, The amplification capability is very weak, so the emitter and collector of the tube can be distinguished.
After identifying the tube type and base b, the following method can be used to identify the collector and emitter.
Set the multimeter to R×1K. Pinch the base and another pin together with your hands (be careful not to let the electrodes touch directly). To make the measurement obvious, you can wet your fingers and connect the red test lead to the pin pinched together with the base. , the black test lead is connected to the other pin, and pay attention to the extent to which the multimeter pointer swings to the right. Then reverse the two pins and repeat the above measurement steps. Compare the amplitude of the meter hand swinging to the right in the two measurements and find the one with the larger amplitude. For the PNP transistor, connect the black test lead to the pin pinched together with the base. Repeat the above experiment to find the time when the watch needle swings the most. For the NPN type, the black test lead is connected to the collector and the red test lead is connected to the collector. is the emitter. For the PNP type, the red test lead is connected to the collector and the black test lead is connected to the emitter.
The principle of this method of identifying electrodes is to use the battery inside the multimeter to apply voltage to the collector and emitter of the triode to give it the ability to amplify. When a hand pinches its base and collector, it is equivalent to adding a forward bias current to the transistor through the resistance of the hand, causing it to conduct. At this time, the amplitude of the hand swinging to the right reflects its amplification ability, so it can be correctly judged. Take out the emitter and collector.
