A simple compound oscillator for generating a stable frequency while duty cycle is adjusted. Useful for driving brushed dc motor by PWM control.
The circuit as shown here is not tested yed but its simulation is coherent with the expectations.
The output of the seconf NE555 used as monostable is suitable for driving a power Mosfet like IRFZ44N thus it could be used for controlling a micro lathe DC motor speed aiming to keep its torque high enough even when rotation is set at low RPM.
To check how it works, start the simulation then edit the resistance value of monostable section.
It is easy to see that duty cycle variation is made possible within the imposed range.
I will probably upgrade this schematic with the power stage for those that would like to try for any purposes.
In case this circuitry is wanted to be a driver for a switching converter, I recomend to set the initial duty cycle at 65%. The maximum energy transferred from the switched inductor is achieved at 80% thus, 65% is the middle point for being sit on when you like to regulate the output voltage by a closed ring control.
Do not forget to connect filtering capacitors at NE555 control pins #5 if they are not used for other purposes.
