Duty cycle adjustable multivibrator circuit composed of MC14574

　　The Schmidt type comparator is formed by using the MC14574 voltage comparator. The inverting input plus the charge and discharge circuit constitutes a multivibrator, as shown in the figure below.
　　
　　The VT+ of the comparator = VCC. R5/(R3∥R4+R5)≈2/3Vcc. VT- =Vcc.R4∥R5/(R4∥R5+R3)≈1/3Vcc.
　　
　　At this time, the output of the voltage comparator is high level, and the potential of the comparator's in-phase input is 2/3Vcc. The high level output of the comparator charges the capacitor Cx through the diode D2 and the adjustable resistor Wl. When the potential on the capacitor Cx rises to 2/3Vce. The output of the voltage comparator changes from high level to low level. At this time, the potential of the comparator's in-phase input changes from the original 2/3Vce to 1/3Vce. At the same time, the voltage on capacitor Cx generates electricity to the output end of the comparator through diode D1 and another adjustable resistor W2. When the voltage on capacitor Cx drops, the output of the comparator changes from low level to high level, thus entering the charging process again and forming oscillation. It can be seen that the charging and discharging time is related to the two adjustable resistors. Changing their resistance values ​​can change the charging and discharging time. In this way, the duty cycle of the multivibrator output pulse can be adjusted. The
　　
　　charging and discharging time Tl and T2 of the multivibrator are:
　　
　　Tl=WICxln2≈0.693WICx, T2=W2Cxln2≈0.693W2Cx.
　　
　　F=l/(T1+T2)≈0.78RC.