This simple power or speed control for DC Motors uses a Power MOSFET as driver stage and a 4093 IC as oscillator. The maximum current in the load depends only of the MOSFET used in the driver stage. This transistor, in a practical project, must be mounted on a heatsink. C1 and C2 can be changed to achieve the best performance. The motor can be powered from a different supply, above 15 V that is the limit for the oscillator. Figure bellow shows the simulation.
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The waveshape of the voltage applied to the motor is dispayed as Bellow in the virtual oscilloscope of the MultiSIM.
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To download the simulation files and Netlist - click here (ni0009.zip)