Control circuit for tap-switching power supplies and multi-tap transformers

A tap-switching circuit for use in conjunction with a multi-tap transformer which includes on its secondary side a center tap, a first tap having a first pair of windings and a first pair of rectifying diodes each of which is electrically coupled to one of the first pair of windings and a second tap having a second pair of windings and a second pair of rectifying diodes each of which is electrically coupled to one of the second pair of windings, said tap-switching circuit comprising:

• a capacitor having a first plate and a second plate, said first plate being electrically coupled to the first tap of the multi-tap transformer and said second plate being electrically coupled to the center tap of the multi-tap transformer;
• comparing means for sensing and comparing the voltage of said first plate of said capacitor to a reference voltage when the sensed voltage at said first plate of said capacitor goes below a predetermined voltage level as a result of either load increase or line decrease, said comparing means having an output, normally high, which goes low when the sensed voltage at said first plate of said capacitor goes below said predetermined voltage level;
• switching means connected to said comparing means for electrically coupling the second tap of the multi-tap transformer to said first plate of said capacitor, when said comparing means output goes low it turns on said switching means so that both the first and second pairs of windings are electrically coupled to said first plate of said capacitor.

A tap-switching circuit for use in conjunction with a multi-tap transformer which includes on its secondary side a center tap, a first tap having a pair of windings and a pair of rectifying diodes each of which is electrically coupled to one of the pair of windings and a plurality of multiple taps each of which has a pair of windings and a pair of rectifying diodes each of which is electrically coupled, respectively, to one of the pair of windings, said tap-switching circuit comprising:

• a capacitor having a first plate and a second plate, said first plate being electrically coupled to the first tap of the multi-tap transformer and said second plate being electrically coupled to the center tap of the transformer;
• a plurality of comparing means for sensing and comparing the voltage at said first plate of said capacitor to a reference voltage, to determine when the sensed voltage at said first plate of said capacitor goes below a predetermined voltage level as a result of either load increase and/or line decrease, each of said plurality of comparing means having an output, normally high, which goes low when the sensed voltage at said first plate of said capacitor goes below said predetermined voltage level;
• a first plurality of switching means for electrically coupling the plurality of multiple taps of the transformer to said first plate of said capacitor, said comparing means, when its output goes low, turning on said switching means so that both the first and subsequent pairs of windings are electrically coupled to said first plate of said capacitor.