Transistor Basics

The bipolar junction transistor is equivalent to two back-to-back diode PN junctions. The forward-biased EB junction has holes 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-biased CB junction barrier electric field, forming the collector current IC. 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 the 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.

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, and c/ib = β, realizing the current amplification of the bipolar transistor.

金属氧化物半导体场效应三极管的基本工作原理是靠半导体表面的电场效应，在半导体中感生出导电沟道来进行工作的。当栅 G 电压 V _G 增大时， p 型半导体表面的多数载流子棗空穴逐渐减少、耗尽，而电子逐渐积累到反型。当表面达到反型时，电子积累层将在 n+ 源区 S 和 n+ 漏区 D 之间形成导电沟道。当 V _DS ≠ 0 时，源漏电极之间有较大的电流 I _DS 流过。使半导体表面达到强反型时所需加的栅源电压称为阈值电压 V _T 。当 V _GS >V _T 并取不同数值时，反型层的导电能力将改变，在相同的 V _DS 下也将产生不同的 I _DS , 实现栅源电压 V _GS 对源漏电流 I _DS 的控制。

2. Naming Method of Transistors
Transistors: The most commonly used are triodes and diodes. Triodes are represented by the symbol 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, triodes are divided into PNP and NPN, while diodes are divided into P type and N type. Most domestic tubes are represented by xxx, and each digit has a specific meaning: such as 3 AX 31, the first digit 3 represents triodes, and 2 represents diodes. 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 represents the purpose, where X represents low-frequency low-power tube; D represents low-frequency high-power tube; G represents high-frequency low-power tube; A represents high-frequency high-power tube.

The last number is the serial number of the product. Different serial numbers have slightly different indicators. Note that the second digit of diodes and transistors has basically the same meaning, but the third digit has a different meaning. 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-type germanium material low-frequency, low-power tube. For imported transistors, they are different, so 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 basically the same meaning as the third digit of domestic tubes.
3. Commonly used small and medium-power transistor parameter table, also provides: Commonly used transistor transistor information

4. Use a multimeter to test transistors
(1) Determine the base and the type of tube
Select the R*100 (or R*1K) range of the ohmmeter, first connect the red test lead to one pin and the black test lead to the other pin, and two resistance values ​​can be measured. Then connect the red test lead to the other pin and repeat the above steps to measure another set of resistance values. Do this 3 times. If there is a set of two very small resistance values, the red test lead corresponding to this set of values ​​is connected to the base, and the tube is a PNP type; conversely, if the black test lead is connected to one pin and the above steps are repeated, if both resistance values ​​are small, the black test lead is the base, and the tube is an NPN type.
(2) Determine the collector
Because when the emitter and collector of a transistor are correctly connected, β is large (the needle swings large), and when they are reversed, β is much smaller. Therefore, first assume a collector and connect it with the ohmmeter (for NPN type tubes, the emitter is connected to the black test lead and the collector is connected to the red test lead). When measuring, pinch the base and the assumed collector with your hands, and the two poles cannot touch each other. If the pointer swings greatly, and the pointer swings less after the two poles are swapped, it means that the assumption is correct, and the collector and emitter are determined.
(2) Estimation of the current amplification factor β
Select the R*100 (or R*1K) range of the ohmmeter. For NPN tubes, connect the red test lead to the emitter and the black test lead to the collector. When measuring, just compare the swing of the small pointer when pinching the base and collector with your hands (the two poles cannot touch each other) and when letting go. The larger the swing, the higher the β value.