Triode, full name should be semiconductor triode, also known as bipolar transistor, crystal triode, is a kind of control current semiconductor device. Its function is to amplify the weak signal into a larger amplitude of the electrical signal, but also used as a contactless switch.

Triode is one of the basic components of semiconductor, which has current amplification function and is the core component of electronic circuit. The triode is made on a semiconductor substrate two PN junction is very close to each other, two PN junction the whole semiconductor is divided into three parts, the middle part is the base area, the two sides are the emitting area and collecting area, the arrangement has PNP and NPN two kinds, so there are PNP type triode and NPN type triode.

1. Triode classification

There are many kinds and classification methods of crystal triode. The following are classified by use, frequency, power, materials, etc.

(1) According to material and polarity, there are NPN and PNP triode of silicon material and NPN and PNP triode of germanium material.

(2) according to the purpose, there are high, medium frequency amplifier tube, low frequency amplifier tube, low noise amplifier tube, photocell, switching tube, high back pressure tube, Darlington tube, with damping triode, etc.

(3) According to the power points, there are small power triode, medium power triode, high power triode.

(4) According to the working frequency, there are low frequency triode, high frequency triode and ultra high frequency triode.

(5) According to the production process, there are plane triode, alloy triode, diffusion triode.

(6) According to the different types of packaging, there are metal encapsulated triode, glass encapsulated triode, ceramic encapsulated triode, plastic sealed half triode, etc.

(7) According to the working principle, there are bipolar junction triode and field-effect triode.


2. Main parameters of triode

The main parameters of triode are more than 10 items, such as collector – base reverse saturation current, collector – emitter reverse current, emitter – base reverse current, dc current exile large coefficient β, etc.

(1) collector – base reverse saturation current ICBO: when the emitter is open (IE=0), the reverse collector current between the base and the collector with the specified reverse voltage VCB, it is only related to temperature, is a constant at a certain temperature, so called collector – base reverse saturation current.

(2) Collector-emitter reverse current ICEO (through current) : when the base is open (IB=0), the collector current between the collector and emitter with the specified reverse voltage VCE. The smaller the value, the more stable the performance, germanium tube ICEO than silicon tube.

(3) Emitter – base reverse current ICBO: when the collector is open, the emitter current is when the specified reverse voltage is added between the emitter and the base, which is actually the reverse saturation current of the emitter.

(4) large coefficient β (or hEF) : this refers to the dish emission connection method, no AC signal input, the ratio of the dc output of the collector and the dc input of the base, that is, β=Ic/Ib

(5) cut-off frequency F β, F α : 0.707 times of frequency when β drops to low frequency, is the cut-off frequency fβ of common emitter; When α drops to low frequency 0.7.7 times of frequency, is the common base cutoff frequency fα β, F α is an important parameter to show the frequency characteristics of the tube, the relationship between them is: F β≈ (1-α) F α

(6) characteristic frequency fT: because the frequency f rises, the β will decrease, when the β drops to 1, the corresponding F is fT, fT is a comprehensive reflection of the transistor’s high frequency amplification performance of the theoretical parameters.

(7) the maximum allowable collector current ICM, when the collector current IC increases to a certain value, causing the β value to drop to 2/3 or 1/2 of the rated value, then the IC value is called ICM, so when THE IC exceeds ICM, although it does not cause damage to the pipe, but the β value significantly decreases, will affect the quality of amplification.

(8) Collector-base breakdown voltage BVCBO: when the emitter is open, the reverse breakdown voltage of the collector is called BVCBO.

(9) Emitter – base reverse breakdown voltage BVEBO: when the collector is open, the reverse breakdown voltage of the emitter is called BVEBO.

(10) Collector-emitter breakdown voltage BVCEO: when the base is open, the maximum allowable voltage added between the collector and emitter, if VCE>BVCEO, the tube will be broken down.

(11) Maximum allowable collector dissipation power PCM: when the collector flows through IC and the temperature rises, the maximum collector dissipation power is called PCM when the variation of parameters caused by heating of the pipe does not exceed the allowable value. The actual dissipated power of the pipe is equal to the product of the collector dc voltage and current, that is, PC=UCE×IC, and PC PCM is related to heat dissipation conditions, and adding heat sink can improve PCM.</pcm>

2.2.6 Triode measurement

The inside of a triode is like a combination of two diodes, with the base (b-pole) in the middle. First we need to find the base and determine whether it is PNP or NPN tube. The base of a PNP tube is the common ground of two negative poles, and the base of an NPN tube is the common ground of two positive poles.

First we can use digital multimeter diode block to measure and determine the base. See Figure 2-27, for THE PNP tube, when the black pen (even battery negative) in the base, the red pen to measure the other two poles is generally not much smaller reading (generally 0.5 ~ 0.8), such as the pen is connected in turn for a larger reading (generally 1). For NPN table is the red pen (connected to the table battery positive) connected to the base. The three NPN tube, the middle of the red pen pin for the base.

After finding the base and knowing what type of audion it is, you can judge the emitter and collector, and adjust the range of the multimeter to hFE block. Plug the triode into the socket of the corresponding NPN triode with the base corresponding to the B letter above. Read and record, insert its other two pins inversely, read and record again. The polarity with the highest reading corresponds to the letter on the chart, and the C and E poles of the triode are identified against the letter. Other triode judgment method is similar.

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