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2、 Characteristic curve of transistor

1. Input characteristics

Figure 2 (b) shows 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:

The estimation formula for rbe=(△ Ube/△ Ib) Q point is:

Rbe=rb+(β+1) (26 millivolts/Ie millivolts)

Rb is the base resistance of a transistor, and for low-frequency low-power transistors, rb is approximately 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.transistor

When Ube<0 in the cutoff region, Ib ≈ 0, and there are no electrons injected into the base region in the emission region. However, due to the thermal motion of molecules, a small amount of current still passes through the collector, i.e. 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:transistor

Icbo=(1+β)Icbo

At room temperature, the Icbo of a silicon transistor is less than 1 microampere, while the Icbo of a germanium transistor is about 10 microamperes. For a germanium transistor, the Icbo value doubles for every 12 ℃ increase in temperature, while for a silicon transistor, it doubles for every 8 ℃ increase in temperature. Although the Icbo value of a silicon transistor changes more dramatically with temperature, due to the fact that the Icbo value of a germanium transistor itself is larger than that of a silicon transistor, it is still heavily affected by temperature. In the amplification region, when the emitter junction of a transistor is in forward bias and the collector junction is in reverse bias operation, Ic approximately changes linearly with Ib, and the amplification region is the area where the transistor operates in the amplification state.