Basic knowledge and detection methods of transistors

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Basic knowledge and detection methods of transistors [Copy link]

Basic knowledge and detection methods of transistors

1. Basics of transistors The bipolar junction transistor is equivalent to two back-to-back diodePNjunctions. In the forward-biasedEBjunction, holes are injected from the emitter into the base region, most of which can reach the boundary of the collector junction and reach the collector region under the action of the reverse-biasedCBjunction barrier electric field, forming the collector currentIC. In the common emitter transistor circuit, the emitter junction is forward biased in the base circuit, and its voltage drop is very small. Most of the external bias between the collector and emitter is applied to the reverse biased collector junction. Since VBE is very small, the base current is about IB= 5V/50 kΩ= 0.1mA. 385420 If the common emitter current amplification factor of the transistor is β= IC / IB =100, the collector current IC= β*IB=10mA. There is a voltage drop VRC=10mA*500Ω=5V on the collector load resistor of 500Ω, and the voltage drop between the collector and emitter of the transistor is VCE=5V. If a small alternating current ib is superimposed in the base bias circuit, a corresponding alternating current ic will appear in the collector circuit, with c/ib=β, realizing the current amplification effect of the bipolar transistor.

The basic working principle of metal oxide semiconductor field effect transistor is to rely on the electric field effect on the surface of the semiconductor to induce a conductive channel in the semiconductor to work. When the gate voltage VG increases, the majority carriers, holes, on the surface of the p-type semiconductor gradually decrease and become exhausted, while electrons gradually accumulate to the inversion state. When the surface reaches inversion, the electron accumulation layer will form a conductive channel between the n+ source region S and the n+ drain region D. When VDS ≠ 0, a large current IDS flows between the source and drain electrodes. The gate-source voltage required to make the semiconductor surface reach strong inversion is called the threshold voltage VT. When VGS>VT and takes different values, the conductivity of the inversion layer will change, and different IDS will be generated under the same VDS.Realize the control of gate-source voltage VGS on source-drain current IDS .

2. Nomenclature of transistors

Transistors: The most commonly used are triodes and diodes. Triodes are represented by symbols BG (old) or (T ), and diodes are represented by D . According to the manufacturing materials, transistors can be divided into two types: germanium tubes and silicon tubes. According to polarity, transistors are divided into PNP and NPN, while diodes are divided into P and N. Most domestic tubes are represented by xxx, where each digit has a specific meaning: such as 3 AX 31, the first digit 3 represents the transistor, and 2 represents the diode. The second digit represents the material and polarity. A represents PNP type germanium material; B represents NPN type germanium material; C represents PNP type silicon material; D represents NPN type silicon material. The third digit indicates the purpose, where X represents a low-frequency, low-power tube; D represents a low-frequency, high-power tube; G represents a high-frequency, low-power tube; and A represents a high-frequency, high-power tube. The last number is the product serial number. Different serial numbers have slightly different indicators. Note that the second digits of diodes and triodes have basically the same meaning, but the third digits have different meanings. For diodes, the third digit P represents a detector tube; W represents a voltage regulator tube; and Z represents a rectifier tube. The example above is specifically a PNP germanium-based low-frequency, low-power tube. For imported transistors, they are different, so you should pay attention to accumulating information during actual use. Commonly used imported tubes include South Korea's 90xx and 80xx series, and Europe's 2Sx series. In this series, the third digit has the same meaning as the third digit of domestic tubes. 2. Commonly used small and medium-power transistor parameter table 385423 385424

philips_lu

This is not right, and the naming method is incomplete. Currently, the best way to check the parameters of the tube is to check the data sheet. For testing, a multimeter is generally sufficient, but for some special tubes, a transistor characteristic analyzer is still required. A solid theoretical foundation + data sheet is the best solution.