| 摘要 |
PURPOSE:To obtain the constant output current with the switching action by connecting two NPN transistors and one PNP transistor in a specified relationship. CONSTITUTION:Two NPN transistors and one PNP transistor are connected as illustrated. With the input terminal grounded, the NPN transistors Q1 and Q2 are turned off and no collector current flows in the transistor Q2. On the other hand, when the input terminal 1 is opened, the collector current of the PNP transistor Q3 mostly flows to the grounded terminal through the transistor Q1. At this point, current flows to the collector terminal at the level almost equal to multiplication of the collector current of the transistor Q1 by the emitter area ratio of the transistors Q1 and Q2. The collector current I3 of the transistor Q3 is as given by I3 (Vcc- VBE3)/R while the collector current I2 is as given by I2=A2(Vcc-VBE3)/A1.R (where, Vcc represents the external power source, VVE3 the voltage between the base and emitter terminals of the transistor Q3, R resistance and A1 and A2 the emitter area of the transistor Q1 and Q2). Accordingly, the resistance R can set the collector current I2 with the voltage Vcc being constant. |
