Transistor

 Semiconductor transistor consists of two PN junctions ( emitter junction and collector junction ), three electrode leads ( base ), the emitter and the collector and the outer shell package. In addition to the amplification, the transistor also plays the role of electronic switch, control, etc. It is the basic device widely used in electronic circuits and electronic equipment.

First, the classification of transistors

(1) materials can be divided into germanium transistors and silicon transistors.

(2) according to PN junction, it can be divided into NPN transistor and PNP transistor.

(3) according to structure, it can be divided into point contact type and surface combination type.

(4) according to the working frequency, it can be divided into high frequency tube (FR >3MHz) and low frequency tube (FR <3MHz).

(5) according to power division, it can be divided into high-power tube (P.>1W) and medium power tube (P). In 0.7~ 1W), small power pipe (P.<0.7W).

Second, the main parameters of the transistor

The main parameters of transistors reflect the various performance indicators of transistors, which are the basis for analyzing transistor circuits and selecting transistors.

1. Common emitter current amplification factor

(1) common emitter DC current amplification factor, which indicates that the ratio of Ic to Ip at a working point at a working point is expressed by means of beta.

(2) common emitter AC current amplification coefficient beta that indicates the ratio of the change of collector current AIc to the base current change OIp, that is, beta =Ic/Ib, when the common pole connection of the transistor is constant and Uc: is constant

When the beta value of the tube is too small, its amplification effect is poor, and its performance is unstable when the beta value is too large. Therefore, a tube with beta 30~80 is generally selected.

There are two ways to mark beta values: color and alphabet. The color code method was used earlier, usually painted on the top of the transistor, and the size of the tube was expressed in different colors.

2. Common base current amplification factor

Common base AC current amplification coefficient a, which represents the transistor as a common base connection, in the case of constant Ucb, Ie and Ig variation ratio.

3. Interpolar reverse current

(1). Set-base reverse saturation current IcBO IcB0 refers to the reverse current corresponding to the emitter open circuit when a certain reverse voltage is added between the collector and the base electrode.

At a certain temperature IcBo is a constant. With the increase of temperature, IcBo will increase, which is the main factor of unstable operation of transistors. At the same ambient temperature, the IcBo of the silicon tube is much smaller than that of the germanium tube IcBo.

(2). The penetration current IcEo IcEo refers to the collector current when the base is open and a certain reverse voltage is applied between the collector and the emitter. The current seems to be the same as the emitter through the collector, so it is known as the penetrating current. IcEo, like IcBo, is also an important parameter to measure the thermal stability of transistors.

4. Frequency parameter

The frequency parameter is a parameter that reflects the relationship between the transistor current amplification capability and the working frequency, and represents the frequency range of the transistor.

(1) The common emitter cut-off frequency f beta: the beta value of the transistor is a function of frequency, while the middle frontal beta = beta is almost independent of frequency, but with the increase of the leader, the beta value decreases. When the duty drops to 1 B of the intermediate frequency band, the corresponding frequency is called the common emitter cut-off frequency and is expressed by F beta.

(2) Characteristic frequency fT: when the transistor's beta value drops to =1, the corresponding frequency is called the characteristic frequency. In the range of F ~fT, the beta value is almost linear with the width. The higher the F is, the smaller the beta is. When the working frequency is f>f, the transistor will lose its magnifying power.

5. Limit parameters

(1) The maximum allowable collector dissipative power PcM Pcm is the maximum power of the collector dissipation when the transistor junction is heated and the transistor parameters change without more than the prescribed allowable values. When the actual power consumption is P. >Pcy not only changes the parameters of the pipe, but also burns the pipe.

(2) The maximum allowable collector current 1COM when the 1C is very large, the beta value gradually decreases. - the corresponding collector current is 1CW when the 2/3 (or 12) of the beta value drops to the rated value. When 1c>lcu, the beta value has been reduced to the unpractical degree and the possibility of burning down the tube.

(3) Reverse breakdown voltage BU and BUcao BUeco refer to the reverse breakdown voltage between collector and emitter when the base is open. BUcBo refers to the reverse breakdown voltage between the collector and the base when the emitter opens.

This article is from Allicdata Electronics Limited.