Patent ID: 7276859

Claim:
A ballast for powering at least one gas discharge lamp, the ballast comprising: a rectifier circuit, comprising: first, second, and third input terminals; and first and second output terminals, wherein the second output terminal is coupled to circuit ground; a high frequency filter capacitor coupled between the first and second output terminals of the rectifier circuit; an inverter coupled to the first and second output terminals of the rectifier circuit, the inverter comprising a plurality of output connections adapted for connection to the at least one gas discharge lamp; and a three-phase electromagnetic interference (EMI) filter coupled between the rectifier circuit and a three-phase alternating current (AC) voltage source, the three-phase EMI filter comprising: a plurality of input connections, comprising: (i) a first input connection adapted to receive a first phase of the three-phase AC voltage source; (ii) a second input connection adapted to receive a second phase of the three-phase AC voltage source; (iii) a third input connection adapted to receive a third phase of the three-phase AC voltage source; and (iv) a fourth input connection adapted to receive a ground of the three-phase AC voltage source; a common-mode inductor assembly, comprising: a first inductor coupled between the first input connection and the first input terminal of the rectifier circuit; a second inductor coupled between the second input connection and the second input terminal of the rectifier circuit; and a third inductor coupled between the third input connection and the third input terminal of the rectifier circuit, wherein the first, second, and third inductors are magnetically coupled to each other; a Y-capacitor coupled between the fourth input connection and a reference node; a first X-capacitor coupled between the reference node and the first input terminal of the rectifier circuit; a second X-capacitor coupled between the reference node and the second input terminal of the rectifier circuit; and a third X-capacitor coupled between the reference node and the third input terminal of the rectifier circuit.