Pulse width modulation control circuit with a variable zero to one hundred percent duty cycle

摘要

This invention forms a basic circuit for the input to a voltage control device for an inductive load. It consists of a basic constant frequency oscillator comprising a Schmitt trigger and inverter having an input with a capacitor to ground and an output which feeds back to the input to one end of a potentiometer or feeds forward from the other end of that potentiometer to the output. A point in between the ends of the potentiometer is connected to the input to the Schmitt trigger. If the input potential of the Schmitt trigger is low its output will be high and vice versa. If its input is low, current flows from the output through a diode to the potentiometer and to the capacitor to ground and if it is high, current flows from the capacitor through the potentiometer and a diode to the output of the Schmitt trigger. Thus, a clean square wave pulse current is provided of variable width pulse ratio dependent upon the setting of the contact between the input to the Schmitt trigger and a point on the potentiometer. There is a second part which has to do with expanding the duty cycle of the pulse width modulation from zero to one hundred percent by passing the output of the Schmitt trigger and inverter to a low pass (high cut) filter and to a buffer and to an electronic switch means to control the current through the load.