A transistor, also known as a bipolar transistor or crystal transistor, is a semiconductor device that controls current. Its function is to amplify weak signals into larger amplitude electrical signals, and it is also used as a contactless switch. Triode is one of the basic semiconductor components, which has the function of current amplification and is the core component of electronic circuits. A transistor is a device that produces two PN junctions that are very close together on a semiconductor substrate. The two PN junctions divide the entire semiconductor into three parts, with the middle part being the base region and the two sides being the emitting and collecting regions. There are two types of arrangement: PNP and NPN. Symbol: "Q, VT"

The function of a transistor: amplification, modulation, resonance, switching (1) Current amplification: A transistor is a current control device that uses the base current IB to control the collector current IC and emitter current IE. Without IB, there would be no IC and IE. As long as there is a small IB, there would be a large IC. In an amplification circuit, the characteristic of a transistor is utilized to amplify the signal. (2) Switching function: When the transistor is used as a switch, it operates in two states: cut-off and saturation. In a transistor switching circuit, the collector and emitter of the transistor act as a switch. When the transistor is cut off, the internal resistance between the collector and emitter is large, which is equivalent to the open state of the switch; When the transistor is saturated, the internal resistance between its collector and emitter is very small, equivalent to the on state of the switch

Detection and discrimination of transistor electrodes: Usually, the arrangement of transistor pins can be found in the manual based on the model. If the model is unknown, the resistance range of a multimeter can be used to distinguish the three poles e, b, and c

1. Distinguish the base and tube types and set the multimeter to R × 100 or R × In 1K gear, use a black lead to connect to one pin of the transistor, and a red lead to connect to the other two pins of the transistor until both measured resistance values are very low. The pin connected to the black lead is the base of the NPN transistor; If the above situation does not occur, the red lead should be connected to one pin of the transistor, and the black lead should be connected to the other two pins of the transistor until both measured resistance values are very small, and the pins connected to the red lead are all the base of the PNP transistor

2. Distinguish whether the collector and emitter will be connected to the meter set R × 1K gear, connect two probes to the other two pins of the tube at the same time, use a resistance of several tens of kiloohms or use a wet finger to connect between the base electrode and the assumed collector electrode, and observe the swing of the watch needle; Then use the same method to exchange the probes for measurement once. For NPN type tubes, if the probe swings more, the black probe is connected to the collector of the transistor, and the red probe is connected to the emitter of the transistor; For PNP type tubes, when the probe swings more, the red probe is connected to the collector of the transistor, and the black probe is connected to the emitter of the transistor

3. Distinguishing between germanium tube and silicon tube. By measuring the forward and reverse resistances of two PN junctions with a multimeter, it is possible to determine whether it is a germanium tube or a silicon tube. Generally, the forward resistance of silicon tubes is about 3-20 kiloohms, and the reverse resistance is greater than 500 kiloohms. The forward resistance of germanium tubes is about a few hundred ohms, and the reverse resistance is greater than 100 kiloohms 4. Estimate the amplification factor of DC current. Use the above method to distinguish the collector and emitter, and observe the swing of the watch needle. The larger the swing amplitude of the watch needle, the greater the current amplification factor 5. Estimating the Reverse Leakage Current of a Multimeter Setting R × At 1K gear, open the base electrode and measure the resistance between the collector and the emitter. For PNP tubes, connect the red and black probes to the collector and emitter respectively (NPN tubes are the opposite). The larger the measured resistance value, the smaller the reverse leakage current, and the more stable the performance of the transistor. Usually, silicon tubes are smaller than germanium tubes, high-frequency tubes are smaller than low-frequency tubes, and low-power tubes are smaller than high-power tubes. Note: There are significant differences in the method of using a digital multimeter to distinguish transistors, because for a digital multimeter, the black pen is connected to the negative electrode of the battery inside the meter, and the red pen is connected to the positive electrode. In addition, instead of using an ohmic scale for measurement, a PN junction scale is used for measurement