| 摘要 |
PURPOSE:To start a constant current circuit exactly and to generate a stable constant current output by turning on the 1st transistor (TR) at the time of power supply to make starting current inflow and turning on the 2nd TR to stop the operation of the 1st TR. CONSTITUTION:When electric power is supplied between a power supply terminal and an earth point, a base current flows into the base of a TR24 through a resistor 26, so that the TR24 is turned on simultaneously with the start of the power supply and the starting current is led from the base/collection side of a TR2 and discharged to the earth side. Consequently, the constant current circuit is started and current made flow into the TR2 by a current mirror circuit consisting of the TRs 2, 30 flows also into the TR30, which detects the starting of the constant current circuit. When the operating current of the TR30 is applied to the base of a TR28, the TR28 is turned on, the base/emitter of the TR24 is shorted and the TR24 is turned off, so that the operation of the constant current circuit is stopped and leading of the starting current is released. |
