Patent ID: 7560871

Claim:
A ballast for powering a lamp load comprising at least one gas discharge lamp, the ballast comprising: an inverter, comprising first and second inverter input terminals, and an inverter output terminal; and an output circuit, comprising: a plurality of output connections adapted for coupling to the lamp load, the plurality of output connections including a first output connection and a return output connection; an output transformer, comprising a primary winding coupled to the inverter output terminal, and a secondary winding operably coupled to the first output connection and the return output connection, wherein the secondary winding includes a tap connection; and a voltage-limiting impedance coupled between the tap connection of the secondary winding and earth ground; wherein the tap connection of the secondary winding is positioned, and the voltage-limiting impedance is sized, such that when a voltage between the first output connection and the return output connection has a root-mean square value of about 650 volts, a voltage between earth ground and either one of the first output connection and the return output connection is limited to a root-mean-square value of less than about 430 volts.