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在某些应用电路里,要求发光二极管在宽的供电范围内能正常工作指示,图示的恒流发光电路即能满足要求。当电压在+3V 到+45V 的范围内变动时,LED 的亮度基本保持不变。图中,三极管T_1,T_2组成恒流电路,对发光二极管供电。当电压升高时,流过T_2的集电极电流和发射极电流增加,但因电阻R_2上的电压上升,T_1的基极电
In some application circuits, LEDs are required to function properly over a wide range of supply voltages. The illustrated constant current light-emitting circuit can meet the requirements. When the voltage changes in the range of +3 V to +45 V, the brightness of the LED remains unchanged. The figure, the transistor T_1, T_2 form a constant current circuit, the light-emitting diode power supply. When the voltage rises, the collector current and emitter current flowing through T_2 increase, but because the voltage on the resistor R_2 rises, the base current of T_1