US 4,636,711 A · Pulse width modulation control circuit with a variable zero to one hundred percent duty cycle

Abstract

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.

Claims12

Dependent claims

In an apparatus for controlling the average current through a load means by means of a pulse width modulated signal to an electronic switch means in series with said load means;

the improvement in constant period oscillator and pulse width modulator comprising:
(a) a source of selected voltage;
(b) Schmitt trigger and inverter (STAI) means;
(c) resistance means with a first of its two ends connected to the output of said STAI through a first diode, having its anode connected to said output;
the second of said two ends connected to said output through a second diode, having its cathode connected to said output;
(d) an intermediate point between said two ends connected to the input of said STAI;
and a first capacitor connected between said input and ground.

4 more elements

Apparatus for generating output pulses of variable width duty cycle comprising:

(a) a Schmidt trigger circuit having a sawtooth input and a inverted square wave output pulse with one-half becoming increasingly positive and one-half becoming increasingly less positive,
(b) a first variable time constant charging circuit coupling said increasingly positive one-half of said inverted output of said Schmidt trigger to said input for providing a linearly increasing input voltage whose slope varies with the time constant of said charging circuit, and
(c) a second variable time constant discharging circuit coupling the other one-half of said inverted output of said Schmidt trigger to said input for providing a linearly descreasing input voltage whose slope varies with the time constant of said discharging circuit thereby providing a square wave output pulse whose duty cycle varies with said first and second time constant circuits.

Dependencies are inferred from the claim text.

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

Life of this patent

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

Life of this patent

Abstract

Claims12