AC line operation of monolithic power control circuits

The major difficulty encountered in the operation of a bipolar IC-directly from the ac line is the maintenance of back bias on the substrate isolation junction. The circuit power supply is derived by rectification of line voltage with diodes contained in the pellet. Because of the direct connection to the ac line no negative potential reference point exists and the substrate isolation junction becomes forward biased as the ac wave changes polarity. The flow of current through the substrate junction gives rise to deleterious parasitic currents, making the circuit inoperative. A technique was developed that reduced the current flow in the substrate junction to a negligible value with only a slight addition to circuit complexity. This technique prevents the substrate junction from becoming forward biased and establishes a negative potential reference during ac operation.