TRANSISTOR

Crystal transistor, also known as bipolar transistor, abbreviated as transistor. The transistor has the function of current amplification and is the core device for signal amplification and processing, widely used in electronic products.

A transistor consists of two PN junctions (emitter junction and collector junction). It has three regions: emitter region, base region, and collector region, each leading to an electrode called emitter e (E), base b (B), and collector c (C).

1. Classification of transistor: (1) Classified according to the semiconductor types of the three internal regions, there are NPN and PNP types; (2) Classified by operating frequency, there are two types: low frequency (fa<3MHz) and high frequency (fa ≥ 3MHz); (3) Classified by power, there are two types: low power (Pc<0.1W) and high power (PC ≥ 1W); (4) Classified by purpose, there are ordinary transistors and switching transistors, etc; (5) Classified by semiconductor materials, there are germanium triodes and silicon triodes.

The appearance and circuit symbols of common transistors.

2. Main technical parameters of a transistor: 1) AC current amplification factor AC current amplification factor includes the common emitter current amplification factor p and the common base current amplification factor a, which are important parameters indicating the amplification capability of a transistor.

2) The maximum allowable collector current ICM refers to the collector current when the current amplification factor of the amplifier significantly decreases.

3) BVCEO refers to the maximum reverse voltage allowed to be applied between the collector and emitter of a transistor when the base of the transistor is open circuited.

4) The maximum allowable dissipated power of the collector (PCM) refers to the maximum dissipated power of the collector when the parameter change of the transistor does not exceed the specified allowable value.

3. Detection of transistor 1) Discrimination of transistor type and base: Place the pointer multimeter in RX100 or R × lk mode, touch one pole with the black probe, and touch the other two poles with the red probe. If the resistance measured twice is small (or large), the pin connected to the black probe (or red probe) is the base and NPN (or PNP) type.

2) If the discrimination between the emitter and collector electrodes has already determined the base and type, any other two electrodes can be set as e and c, and the discrimination between c and e can be performed. Taking PNP type as an example, assume that the red probe of the multimeter is connected to terminal C and the black probe is connected to terminal E. Use a damp finger to pinch the base b and the assumed collector c terminals, but the two poles cannot touch each other (the damp finger replaces the resistor lOOkfl in the figure).

Swap the assumed c and e electrodes, repeat the above steps, and compare the resistance values measured twice. The time when the resistance was measured to be low, the pin connected to the red probe was collector c, and the other end was emitter e