DC Power Supply: SCR-Regulated, Voltage and Current Bridges with Automatic Cross-Over (Kupferberg & Ash, Forbro, US 3,305,763, 1967)

A variable DC supply regulated by controlled rectifiers instead of a series transistor. Two of the four rectifiers in the bridge are silicon controlled rectifiers; how late in each half-cycle they are fired sets the output. A voltage bridge and a current bridge each make an error signal, an analog OR gate passes whichever is larger, and the supply crosses over automatically between holding the voltage and holding the current. Result: a variable voltage / current regulated DC supply with automatic cross-over. Source: K. Kupferberg and J. Ash (Forbro Design), US 3,305,763 (1967), Fig. 1. Unknown: component values and the firing-angle circuit. Picture: the patent drawing.