Principle and characteristics of transistor 2

2、 Characteristic curve of transistor

1. The input characteristic diagram 2 (b) is the input characteristic curve of the transistor, which represents the relationship between Ib and Ube. Its characteristics are: 1) When Uce is in the range of 0-2 volts, the position and shape of the curve are related to Uce, but when Uce is higher than 2 volts, the curve Uce is basically independent. Usually, the input characteristic can be represented by two curves (I and II).

2) When Ube<UbeR, the segment of Ib ≈ O (0~UbeR) is called the "dead zone". When Ube>UbeR, Ib increases with the increase of Ube. When amplified, the transistor operates in a more straight segment.

3) The input resistance of a transistor is defined as: rbe=(△ Ube/△ Ib) Q point, and its estimated formula is: rbe=rb+(β+1) (26 millivolts/Ee millivolts). rb is the base resistance of the transistor, and for low-frequency low-power transistor , rb is about 300 ohms.

2. Output characteristics

The output characteristic represents the relationship between Ic and Uce (with Ib as the parameter). As shown in Figure 2 (C), the output characteristic is divided into three regions: cutoff region, amplification region, and saturation region. When Ube<0 in the cutoff region, Ib ≈ 0, and there are no electron injections into the base region in the emission region. However, due to the thermal motion of molecules, there is still a small amount of current passing through the collector, that is, Ic=Iceo, which is called the penetration current. At room temperature, Iceo is about a few microamperes, and germanium tubes are about tens of microamperes to hundreds of microamperes. Its relationship with the reverse current Icbo of the collector is: Icbo=(1+β) Icbo. At room temperature, the Icbo of silicon tubes is less than 1 microampere, and the Icbo of germanium tubes is about 10 microamperes. For germanium tubes, for every 12 ℃ increase in temperature, The Icbo value doubles, while for every 8 ℃ increase in the temperature of the silicon transistor, the Icbo value doubles. Although the Icbo value of the silicon transistor changes more dramatically with temperature, the germanium transistor is still heavily affected by temperature due to its larger Icbo value. In the amplification region, when the emitter junction of the transistor is in forward bias and the collector junction is in reverse bias operation, Ic changes approximately linearly with Ib, and the amplification region is the area where the transistor operates in an amplification state. When both the emitter and collector junctions are in a positive bias state in the saturation region, Ic basically does not change with Ib and loses its amplification function. Based on the bias of the emitter and collector junctions of the transistor, its working state may be determined.