Patent ID: 6028760
Filing Date: 2000-02-22
Classification: G01V,H02M,Y02B

Abstract:
A pulse generator for energizing a coil with periodic bipolar current pulses having a generally square waveform comprising bipolar transition intervals defining successive edges of unipolar current pulse intervals of alternating frequency, the pulse generator comprising a resonant DC to AC converter circuit including a DC input and an output coupled to the coil, a control circuit for controlling the switching of the converter, a resonant capacitor connected in parallel across the DC input, and decoupling means for decoupling the resonant capacitor from the DC input when the voltage across the resonant capacitor exceeds that of the DC input, the converter circuit further including first and second resonant charging sub-circuits in which the capacitor is connected to resonate with the coil for allowing the amplitude of the coil current to increase, first and second resonant discharging sub-circuits in which the capacitor is connected to resonate with the coil for allowing the amplitude of the coil current to decrease, first and second freewheeling sub-circuits in which the resonant capacitor is effectively isolated from the coil and a short circuit current path is provided for allowing the amplitude of the coil current to gradually decrease, and an exponential charging circuit in which the DC input is electrically connected to the coil so as to allow for a rise in current through the coil, the control circuit being arranged to control the amplitude and frequency content of the generally square waveform by switching the converter circuit to operate between at least two of the above sub-circuit types in at least one controlled switching cycle during the unipolar current pulse intervals.