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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. The situation may determine its working status. 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.transistor

(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