Switching ac voltage regulator

An ac voltage regulator for receiving an ac input signal having a voltage to be regulated and providing an ac output signal having a regulated voltage, the regulator comprising:

• a transformer having a plurality of windings;
• ac switching means, including four switching circuits, each containing a series-connected transistor and diode, for alternately connecting the transformer windings in a first switch configuration, in which the windings are connected such that the ac output signal is substantially the same as the ac input signal, and a second switch configuration, in which the windings are connected so as to transform the ac input signal and cause the ac output signal to have an instantaneous voltage that is a predetermined percentage of the instantaneous voltage of the ac input signal, the duty cycle of the alternate configuration providing a selected average voltage for the ac output signal;
• quadrant detection means for determining the instantaneous voltage polarity and current direction of the ac output signal and for producing a corresponding quadrant signal having four possible states;
• and
• control means, responsive to the quadrant signal, for controllably biasing selected transistors of the switching means so as to alternate between the first and second switch configurations at a predetermined modulation frequency substantially greater than the frequency of the ac input signal and at a prescribed duty cycle selected to provide a desired average voltage for the ac output signal;
• wherein, for each of the four possible states of the quadrant signal, the control means biases a predetermined first transistor on continuously and biases a predetermined second transistor alternately on and off at the predetermined modulation frequency, wherein each time the second transistor is biased on, the diode connected in series with the associated first transistor becomes reverse biased and electrical current is immediately diverted from the first transistor to the second transistor, without the need for any snubber circuit, and wherein each time the second transistor is biased off, electrical current is immediately diverted from the second transistor to the associated first transistor, without the need for any snubber circuit.