Voltage controlled preload

Claim 1

A converter comprising: an input means; a power transformer having a primary winding circuit arranged to receive an input from the input means, the primary winding circuit including a primary winding connected to a switching means for switching the input to the primary winding, and a controller means for controlling a duty cycle at which the switching device operates, and the power transformer also having at least two secondary windings respectively arranged in a main output circuit and an auxiliary output circuit for receiving a transformed input from the primary winding; a preload circuit including, a comparing means arranged with a first input for sensing an output value from the auxiliary output, a second input for sensing a preselected reference value, and an output for outputting a differential output based on the values sensed by the first and second inputs, and a preload means operatively connected to appear at the main output, and also arranged to receive the differential output of the comparing device, whereby linear variations in operation of the preload means due to the linearly varying output of the comparing means causes the preload means to appear at the main output as a linearly varying preload; and, a feedback circuit associated with an output terminal of the main output circuit and the controller means, for providing a feedback signal to the controller means to adjust the duty cycle of the switching means to compensate for the appearance of the linearly varying preload at the main output.

Claim 19

A method of applying a linearly varying preload at a main output of a converter having a primary winding circuit for receiving an input, and a secondary winding arrangement including a main winding in a main output circuit and an auxiliary winding in an auxiliary output circuit, the method comprising: applying the input to input terminals of the primary winding circuit; switching with a switching means the input to the primary winding which in turn transfers a transformed input to the secondary winding arrangement; controlling with a controlling means a duty cycle at which the switching device operates; supplying the controlling means with a feedback signal from a feedback circuit to determine the duty cycle of switching; comparing with a comparing means a preselected reference value with an auxiliary output value to produce a linearly varying differential output; supplying the linearly varying differential output to a preload means connected at the main output such that a gain of the preload means is dependent upon the differential output.

Claim 20

A method of applying a linearly varying preload at a main output of a converter having a primary winding circuit for receiving an input, and a secondary winding arrangement including a main winding in a main output circuit and an auxiliary winding in an auxiliary output circuit, the method comprising: applying the input to input terminals of the primary winding circuit; switching with a switching means the input to the primary winding which in turn transfers a transformed input to the secondary winding arrangement; controlling with a controlling means a duty cycle at which the switching device operates; supplying the controlling means with a feedback signal from a feedback circuit to determine the duty cycle of switching; comparing with a comparing means a preselected reference value with an auxiliary output value to produce a linearly varying differential output; supplying the linearly varying differential output to a preload means connected at the main output such that a gain of the preload means is dependent upon the differential output.