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图示用双D触发器74HC74组成电压控制触发器,输出占空比为50%的矩形波,且工作电流很小.输入控制电压范围为5～12V,输出频率为20～70KHz。为说明电路的工作情况,先假定IC—A的初态为Q=0。D_1关闭,输入电压V_(in)通过R_1给C_1充电,C_1上的电压达到一定电平时,IC—A将翻转,使Q=1;C_1将通过二极管D_1放电.IC—A的CL端为低,又使Q=0,R_2与C_2的延迟时间将使IC—A恢复Q=0前C_1充分放
The figure shows that the 74HC74 dual voltage-controlled flip-flop is used to generate a rectangular wave with a duty cycle of 50% and a small operating current. The input voltage range is 5 ~ 12V and the output frequency is 20 ~ 70KHz. To illustrate the work of the circuit, first assume that the initial state of IC-A is Q = 0. D_1 is turned off, the input voltage V_ (in) charges C_1 through R_1, and when the voltage on C_1 reaches a certain level, IC_A flips to make Q = 1; C_1 discharges through diode D_1. CL terminal of IC_A is low , So that Q = 0, R_2 and C_2 delay time will make IC-A recovery Q = 0 before C_1 fully released