The output characteristic curve of a transistor is usually divided into three regions. What are they?

are: 1. Cut-off area, which refers to the area under the curve corresponding to the transistor input current of 0 in the transistor output characteristic curve; 2. Amplification area, which refers to the approximately horizontal part of each curve in the transistor output characteristic curve. The area corresponding to the set; 3. The saturation area refers to the area where the collector junction and the emitter junction are both forward-biased and the collector current is not controlled by the base current.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

The transistor output characteristic curve mainly includes three areas: cut-off area, amplification area, and saturation area. The 3 areas represent different working states of the transistor. The output characteristics of the transistor are introduced below according to the three regions.

Cut-off area

The transistor cut-off area refers to the area below the curve corresponding to the transistor input current of 0 in the transistor output characteristic curve. For transistors with common emitter connection, the cut-off area refers to the area below the Ib=0 curve in the transistor output characteristic curve. Ib=0 is because Vbe

In the cut-off area, the base current Ib=0, the collector current Ic≤Icbo, almost equal to 0, only a very small reverse penetration current Iceo flows, and the Iceo of the silicon transistor is usually Below 1μA. In fact, the area where Ie=0, that is, Ic≤Icbo, should be called the cutoff area. At this time, both the collector junction and the emitter junction are in a reverse biased state.

Amplification area

The transistor amplification area refers to the area corresponding to the set of approximately horizontal parts of each curve in the transistor output characteristic curve. This shows that within a certain range of the collector-emitter voltage U(CE), the collector current I(C) has nothing to do with U(CE) and only depends on the value of I(B). According to this characteristic, the change of I(B) can be used to linearly control the change of I(C), thereby achieving linear amplification of the current, so the amplification area also becomes a linear area. At this time, the emitter junction is forward biased and the collector junction is reverse biased, I(C)=β·I(B), and △I(C) =β·△I(B).

Saturation area

The saturation area of ​​the transistor refers to the area where the collector junction and emitter junction are both forward biased and the collector current is not controlled by the base current, also called saturation work area. For common-emitter transistors, the saturation region is the region where I(B)>0 and U(CE)<0.7V.

When U(CE)<0.7V, U(CB)=U(CE)

In summary, the main characteristics of a transistor when operating in the saturation region are:

(1) Both the collector junction and the emitter junction are forward biased;

(2) I The value of (C) has a great relationship with U(CE), and I(C) increases with the increase of U(CE);

(3) The value of I(C) has a lot to do with I(B ) is not proportional and linear amplification cannot be achieved;

(4) The transistor has no amplification effect. The collector and emitter are equivalent to a short circuit and can be used in conjunction with the cutoff area for switching circuits.

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