Low loss DC voltage regulator - automatically switches to tappings on mains transformer used as drive to suit input voltage conditions

摘要

A mains transformer driven low-loss, direct voltage regulator automatically selects a set of transformer tappings from which to produce the regulated supply according to the mains input voltage amplitude. The circuit reduces the ohmic loss normally inherent in series regulator circuits. The mains transformer has three sets of symmetrical secondary windings which supply a series transistor regulating circuit via full wave rectifying diodes. The regulating circuit contains, two effectively parallel output transistors supplied from different tapping pairs and a Zener diode based switching circuit incorporating a switching transistor in the base of one output transistor. When the supply voltage is low, only one transistor supplies the regulated output. A system supply voltage brings both transistors into circuit, whilst an even higher one forces conduction in the Zener diode and switches resulsts in the conduction lining through the second regulating transistor.