Abstract: The output of a fuel pump of an internal combustion engine is controlled by the duty cycle of its power supply circuit, which is in turn controlled in accordance with engine and fuel conditions. Sensor signals indicative of the engine and fuel conditions are processed to derive a DC voltage level suitable to the conditions. The derived voltage and a triangular voltage signal of fixed frequency and amplitude are compared by a comparator which outputs a train of pulses. The frequency of the pulse train is that of the triangular wave and the duty cycle thereof is determined strictly by the derived voltage. The pulse train from the comparator is amplified to drive the fuel pump.There may be many different kinds and combinations of engine and/or fuel condition sensors. In addition, sensor signal processing to derive the DC voltage level may take a number of different forms and may include feedback from the fuel pump power supply circuit in order to suppress transient fluctuations.