Principle and characteristics of transistor 3

2. The input and output characteristics of a transistor

The cutoff region and saturation region are the areas where the transistor operates in a switching state. When the transistor is turned on, the operating point falls in the saturation region, and when the transistor is turned off, the operating point falls in the cutoff region.

3、 Main parameters of transistor

1. DC parameters

(1) The reverse saturation current Icbo between the collector and base, when the emitter is open (Ie=0) and a specified reverse voltage Vcb is applied between the base and collector, is only related to temperature and remains constant at a certain temperature. Therefore, it is called the reverse saturation current between the collector and base. A good transistor has a very small Icbo. The Icbo of a low-power germanium transistor is about 1-10 microamperes, while the Icbo of a high-power germanium transistor can reach several milliamps. The Icbo of a silicon transistor is very small, at the nanoampere level.

(2) When the collector emitter reverse current Iceo (penetration current) is open at the base (Ib=0), the collector current is determined by applying a specified reverse voltage Vce between the collector and emitter. Iceo is approximately β times that of Icbo, i.e. Iceo=(1+β). Icbo and Iceo are greatly affected by temperature and are important parameters for measuring the thermal stability of tubes. The smaller the value, the more stable the performance. The Iceo of low-power germanium tubes is larger than that of silicon tubes.transistor

(3) When the collector is open and a specified reverse voltage is applied between the emitter and base, the current at the emitter is actually the reverse saturation current at the emitter junction.transistor

(4) The DC current amplification factor β 1 (or hEF) refers to the ratio of the DC current output by the collector to the DC current input by the base when there is no AC signal input in the common emitter connection, that is: β 1=Ic/Ib

2. Communication parameters

(1) The AC current amplification factor β (or hfe) refers to the ratio of the change in collector output current △ Ic to the change in base input current △ Ib in a common emitter connection, that is, β=△ Ic/△ Ib. Generally, the β of a transistor is between 10-200. html "target=" -blank "title=" 10-200 ">10-200. If β is too small, the current amplification effect is poor. If β is too large, although the current amplification effect is large, the performance is often unstable.

(2) The common base AC amplification factor α (or hfb) refers to the ratio of the change in collector output current △ Ic to the change in emitter current △ Ie when connected in a common base configuration, i.e., α=△ Ic/△ Ie. Since △ Ic<△ Ie, α<1. If the alpha of a high-frequency transistor is greater than 0.90, the relationship between alpha and beta can be used: alpha=beta/(1+beta) beta=alpha/(1- alpha) ≈ 1/(1- alpha)transistor