An apparatus for and method of control of a switch (102) in an electrical power converter (100) using pulse width modulation to regulate output voltage (112) and current The method allows precise output voltage regulation to be achieved whilst accurately controlling the proportion of load-current supplied by multiple modules connected in parallel. A ramped waveform (408), consisting of a component representing the instantaneous current and a component representing the input voltage applied since the switch (102) switched on in the current PWM cycle, is compared with an error signal (406) to determine the width of each PWM pulse.