Identification and detection of transistor

By using a certain process to fabricate two PN junctions on a semiconductor substrate, a three-layer semiconductor is formed. A lead is drawn out from each of the three-layer semiconductors, which are the three electrodes of the transistor. The transistor is then packaged in a casing to make it.

The three electrodes of a transistor are called the emitter e, base b, and collector c. Each corresponding layer of semiconductor is called the emitter region, base region, and collector region. The PN junction where the emitter region and base region intersect is called the emitter junction, and the PN junction where the collector region and base region intersect is called the collector junction.

There are two types of transistors, NPN and PNP, which can be combined to form a transistor. The word symbol for a transistor is VT, and their basic structure. Common transistor shapes.

The main parameters of a transistor include performance parameters and limit parameters.

(1) Performance parameters.

① Current amplification factor.

a. The common emitter circuit's AC current amplification factor is commonly referred to as the current amplification factor port.

b. The DC current amplification factor FE of the common emitter circuit is usually taken as p-hFE for ease of use, and Lu is used as a constant.

② Reverse saturation current/CBO between collector and base. The reverse current when the collector is reverse biased. /The smaller the CBO, the better the unidirectional conductivity.

③ Reverse saturation current/CEO between collector and emitter. Its essence is the reverse current when a specified reverse voltage is applied between the collector and emitter, also known as the through current. /The smaller the CEO, the better the thermal stability of the transistor.

(2) Extreme parameters.

① Maximum allowable collector current/CM.

② Collector emitter reverse breakdown voltage U (BR) CEO.

③ The maximum allowable dissipated power of the collector is P [M.

2. Identification and testing of transistors (1) Identification of transistor type and base. A transistor can be seen as two diodes for easy discrimination. Using a multimeter with a resistance range of R × 100 or R × lkfl, connect the red probe to one of the pins and the black probe to the other two pins respectively. Measure the two resistance values. If both resistance values are small, the pin connected to the red probe is the base of the PNP transistor. If one of the two resistance values is large, you can change the red probe to the other pin and try again until the resistance measured by both pins is small.

A woman uses a black probe to connect to one pin and a red probe to connect to the other two pins. When both resistance values are measured to be low, the black probe is connected to the base of an NPN transistor.

(2) The method of identifying the collector electrode. The collector can be determined based on the principle that the forward current amplification factor of a transistor is greater than the reverse current amplification factor. Using a multimeter with a resistance range of R × 100 or R × lk, hold the probes tightly with both hands and connect the two probes to the other two pins of the tube. Use your tongue to contact the base of the tube and use human resistance to achieve bias. Observe the magnitude of the pointer deflection of the multimeter, then swap the two probes and measure the resistance value or pointer deflection amplitude in the same way. Compare the magnitude of two readings. For PNP type transistors, for the one with a smaller resistance value (larger deflection amplitude), the pin connected to the red probe is the collector. For NPN transistors with low resistance (large deflection), the pin connected to the black probe is the collector. After determining the base and collector, the remaining pin must be the emitter.

There is a simple method to distinguish the collector electrode, which is to place the multimeter in the R × lOk range after the base electrode is determined (NPN transistor), measure the other two electrodes except for the known base electrode, and observe the amplitude of the pointer swing. Then replace the probe and measure again, subject to the obvious swing of the probe. The electrode connected to the black probe is the emitter (PNP tube is the opposite). However, this method has certain limitations, which means that it is ineffective for some transistors.

In addition, the function of measuring the amplification factor port with a multimeter, i.e. hI; E range, can be used to distinguish between the collector electrode, base electrode, and emitter electrode, because when the electrode of the transistor is correctly inserted, its Lu value can be effectively displayed. Otherwise, it will display very small values or cannot be displayed normally. This can be read out according to the c, b, and e marked next to the socket.

The three electrodes of a transistor can be identified not only by a multimeter, but also by the shape of the pins.

(3) Penetrating current L.. The estimation. Measure the collector emitter reverse resistance using a multimeter with a resistance range of R × lk. The larger the measured resistance value, the greater the L.. The smaller, the better the stability of the transistor. Generally, silicon tubes have higher resistance values than germanium tubes, high-frequency tubes have higher resistance values than low-frequency tubes, and low-power tubes have higher resistance values than high-power tubes.

(4) Estimation of the common emitter current amplification factor Lu. If the multimeter has the function of measuring Lu, it can directly measure the reading; If there is no mouth measurement function, a lOOkQ resistor can be connected between the base and collector electrodes. At this time, the reverse resistance between the collector and emitter electrodes is small (i.e. the multimeter pointer has a large swing amplitude). The larger the pointer swing amplitude, the larger the value

(5) Stability performance discrimination of transistor. In judging L.. At the same time, hold the tube with your hand. Due to the influence of human body temperature, the reverse resistance between the collector and emitter of the tube will decrease. If the pointer swings significantly or the reverse resistance value rapidly decreases, the stability of the tube will be poor.