Basic transistor knowledge

I. Basic Concepts

Its main function isCurrent Amplification(Analog circuit) andSwitchFunction (digital circuit ).

A transistor is composed of two PN knots, and a shared electrode becomes the base pole of the transistor (represented by B ). The other two electrodes are the collector (in C) and the emission pole (in E ). Due to different combinations, a transistor is formed, which is a type of PNP and a type of PNP.

Transistor is mostly Plastic Encapsulation or metal encapsulation, the appearance of common transistor, there is an arrow of the electrode is the emission pole, the arrow toward the outside is the type of the, and the arrow toward the inside is the PNP type. In fact, the arrow points in the direction of current.

The first part of the symbol "3" indicates the transistor. The second part of the symbol represents the material and structure of the device: A--PNP type Ge material; B--NPN type Ge material; C--PNP type silicon material; D--NPN type silicon material. The third part of the symbol indicates the function: u -- optical tube; k -- switch tube; X -- Low Frequency small power tube; G -- high frequency small power tube; d -- low frequency high power tube; A -- high frequency high power tube. In addition, 3dj is a field effect tube, and Bt is a special semiconductor component. For example, 3dg12b and 3ax21.

The most basic function of a transistor is to zoom in.Weak electrical signalsChangeSignal of a certain intensityOf course, this conversion still follows the conservation of energy. It only converts the energy of the power source into the energy of the signal. One important parameter of the transistor is the current amplification factor B. When a tiny current is added to the base pole of the transistor, a current that is B times of the injected current can be obtained on the collector, that is, the collector current. The collector current changes with the change of the base current, and a small change of the base current can cause a great change of the collector current, which is the amplification of the transistor.
The transistor can also be used as an electronic switch, and can be used together with other components to form an oscillator.

Ii. Category of Transistor
1) The combination of PN knots can be classified into two types;
2) the materials can be divided into Ge transistor and silicon transistor;
3) high-frequency transistor (FA ≥ 3 MHz) and low-frequency transistor (FA <3 MHz) according to the operating frequency );
4) divided by power can be divided into large power tube (PC ≥ 1 W) and small power transistor (Pc <1 W)
5) courses can be divided into common transistor amplification and switch transistor.

 

Iii. Current amplification of the transistor
1) external conditions for Transistor amplification: the polarity of the power supply should make the emission junction in a positive bias state, while the collector junction in a reverse bias state.
2) Current Distribution LawIe = IC + IB
3) The essence of Transistor Current amplification is to control large changes in the collector current IC with minor changes of the base current IB.

Iv. Transistor output features

1) when the transistor is working in the saturation and cut-off areas, it has the "Switch" feature and can be applied to the pulse digital circuit;
2) When the transistor is working in a magnification area, it can be used in a analog circuit to play a amplification role;
3) The transistor has two functions: "Switch" and "zoom in.

V. Test the working status

Measure the ground-to-ground voltage of the transistor pin to determine the operating status of the pipe:
(1) An-VC> VB> ve,
PnP Manager -- VC <VB <ve. InZoom in status.
2) If the collector-to-ground voltage VC of the transistor is close to the power supply voltage VCC, it indicates that the pipe is inClosing status (switch disconnected).
3) if the collector-to-ground voltage VC of the transistor is close to zero (the silicon tube is less than 0.7 V, and the GE tube is less than 0.3 V), it indicates that the tube is inSaturation (Closed Switch).

Judgment steps and solutions:

1) First, generate the voltage of the Peer Points C, B, and E.

2) If UCE <UBESaturation status

(3) special-case-VC> VB> ve,
PnP Manager -- VC <VB <ve. InZoom in status.
4) otherwiseEnd status

Example: