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图1中的电路用三只NPN晶体管和三只PNP晶体管做了一个逻辑探头。两只晶体管作为驱动LED的开关;逻辑1是绿色LED,逻辑0是红色LED。Q_1和Q_2测试探头尖的逻辑1状况,Q_3和Q_4测试逻辑O的状况。Q_1在Q_2射极电路中用作齐纳二极管。R_(12)和R_(14)构成的分压
The circuit in Figure 1 uses a logic probe with three NPN transistors and three PNP transistors. Two transistors act as switches to drive LEDs; logic 1 is a green LED and logic 0 is a red LED. Q_1 and Q_2 test probe tip logic 1 conditions, Q_3 and Q_4 test logic O conditions. Q_1 is used as a Zener diode in the Q_2 emitter circuit. R_ (12) and R_ (14) constitute the partial pressure