Method and apparatus for accurate pulse width modulation

A pulse width modulation (PWM) circuit having a PWM output signal featuring accurate timing in the face of an interference signal being imposed upon a control signal input thereto that is representative of the duty cycle of the desired PWM output, the circuit comprising:

• a first section having a comparator provided with at least first and second inputs and an output, one of inputs being a noninverting input and the other input being an inverting input, the output producing a PWM signal when proper signals are applied to the first and second inputs of the comparator;
• a second section having an operational amplifier provided with first and second inputs and an output, one of the inputs being a noninverting input and the other input being an inverting input, the output producing a substantially on-and-off signal, and the output of the operational amplifier being connected to one of the inputs of the comparators of a switching section,
• the second section having signal adding means for combining first and second input signals, and providing the summed signal to at least one of the inputs of the operational amplifier,
• the first input signal being connectable to a triangular wave source, and
• the second input signal being connectable to a control input signal whose value is generally proportional to the duty cycle of the PWM signal produced by the output of the comparator, and
• wherein the control signal is summed and amplified in combination with the first input from the triangular wave source by the operational amplifier, whereby the output signal from the output of the operational amplifier is a trapezoidal waveform, and that output signal is delivered to and is in communication with at least one input of the comparator of the first section.