Abstract: A primary-side power modulator for an isolated switching-mode power supply operating under secondary-side control comprising a pulse width determining circuit for real-time primary-side adjustment of a PWM control signal received from a secondary-side PWM controller. While accepting pulse width commands from an isolated secondary-side PWM controller, the pulse width determining circuit has the ability to reduce the width of the switching pulse in response to primary-side information. The power modulator may further comprise a start-up circuit for ensuring that the primary-side supply voltage is above a minimum under-voltage lock out threshold, a soft start circuit for controlling the power switch at power-up, a pulse receiver for receiving the PWM control signal generated by the secondary-side PWM controller, and a drive circuit for driving an external solid-state power switch with the adjusted PWM control signal.

Abstract: A stepping motor generates first and second voltages each varying in accordance with a sinusoidal function having a period proportional to the period of rotation of the motor's rotor, the first and second voltages being in quadrature with each other. A control device generates from the first and second voltages a signal representative of a number that is proportional to the square root of the sum of the squares of the first and second voltages. This signal is used to modify the energizing current provided to the phase windings of the stator, in order to reduce fluctuations in torque and shaft angular velocity.