The quad operational amplifier circuit yields full 0 to 100 percent pulse width control. The controller uses an LM3900 requires only a single supply voltage of 4-30 V. The pulse repetition frequency is set by a 1 kHz oscillator amplifier that integrates AI. The oscillator feeds the Az ramp generator, which generates a linear ramp voltage for each pulse oscillator. The ramp signal feeds the inverting input of comparator A3, the control voltage feeds speed non-inverting input. Thus, the output of the comparator is a 1 kHz pulse train, pulse width that changes linearly with control voltage.
The control voltage may be provided by a _ adjustable potentiometer or an external source of feedback as an engine speed detection circuit. Depending on the setting of control voltage, the pulse duration can be set at a value between zero (zero average dc voltage applied to the motor) to full repetition period of pulses (voltage applied to the motor equal to voltage DC power supply). An amplifier stage (A4) with a gain of 10 acts as a pulse squaring circuit. TIP-31 medium-power transistor is driven by the A4 and serves as a distinct stage of power amplifier.