Ballast with socket-to-fixture voltage limiting

1. 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.

2. The ballast of claim 1 , wherein:

a first voltage exists between first output connection and earth ground;

a second voltage exists between the return output connection and earth ground; and

the first voltage and the second voltage are each limited to a root-mean-square value of no more than about 430 volts.

3. The ballast of claim 1 , wherein the voltage-limiting impedance has an impedance that is on the order of about two hundred thousand ohms.

4. The ballast of claim 1 , wherein the tap connection of the secondary winding is a center tap.

5. The ballast of claim 1 , wherein the voltage-limiting impedance comprises a resistance.

6. The ballast of claim 5 , wherein the resistance is on the order of about two hundred thousand ohms.

7. The ballast of claim 5 , wherein the tap connection of the secondary winding is positioned, and the resistance 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.

8. The ballast of claim 7 , wherein the tap connection of the secondary winding is a center tap.

9. The ballast of claim 8 , wherein the resistance is on the order of about two hundred thousand ohms.

10. The ballast of claim 1 , wherein the output circuit further comprises:

a resonant capacitor coupled in parallel with the primary winding of the output transformer;

a direct current (DC) blocking capacitor coupled between the resonant capacitor and circuit ground; and

a first ballasting capacitor coupled between the secondary winding of the output transformer and the first output connection.

11. The ballast of claim 1 , wherein the inverter is at least one of:

a half-bridge type inverter;

a self-oscillating type inverter; and

a current-fed type inverter.

12. The ballast of claim 1 , wherein the inverter is current-fed self-oscillating half-bridge type inverter.

13. A ballast for powering a lamp load comprising at least one gas discharge lamp, the ballast comprising:

inverter means for receiving a source of substantially direct current (DC) voltage and for providing an alternating current (AC) output voltage; and

output circuit means for receiving the AC output voltage of the inverter means and for providing a magnitude-limited current for operating the at least one gas discharge lamp, the output circuit means including:

a plurality of output connections adapted for connection to the at least one gas discharge lamp; and

a voltage-limiting impedance means for limiting a voltage between earth ground and each of the output connections to a root-mean-square value of less than about 430 volts;

wherein the output circuit means includes an output transformer comprising a primary winding and a secondary winding, wherein a tap connection means of the secondary winding is positioned, and the voltage-limiting impedance means is sized, such that when a voltage between a first output connection of the plurality of output connections and a second output connection of the plurality of output connections has a root-mean square value of about 650 volts, a voltage between earth ground and each output connection is limited to a root-mean-square value of less than about 430 volts.

14. The ballast of claim 13 , wherein:

the inverter means is a half-bridge type inverter, comprising:

first and second inverter input terminals adapted to receive the source of substantially DC voltage; and

an inverter output terminal at which the inverter provides the AC output voltage; and

the output circuit means is a parallel resonant type output circuit, comprising:

a first output connection and a return output connection, wherein the first output connection and the return output connection are adapting for coupling to the at least one gas discharge lamp;

an output transformer, comprising:

a primary winding coupled to the inverter output terminal; and

a secondary winding operably coupled between the first output connection and the return output connection, wherein the secondary winding includes a tap connection;

a resonant capacitor coupled in parallel with the primary winding of the output transformer;

a direct current (DC) blocking capacitor coupled between the resonant capacitor and circuit ground;

a first ballasting capacitor coupled between the secondary winding and the first output connection; and

wherein the voltage-limiting impedance means is coupled between the tap connection and earth ground.

15. The ballast of claim 14 , wherein the voltage-limiting impedance means has an impedance that is on the order about two hundred thousand ohms.

16. The ballast of claim 14 , wherein the tap connection of the secondary winding is a center tap.

17. The ballast of claim 16 , wherein the voltage-limiting impedance means comprises a resistance.

18. The ballast of claim 17 , wherein the resistance is on the order of about two hundred thousand ohms.

19. A ballast for powering a lamp load comprising at least one gas discharge lamp, the ballast comprising:

a current-fed half-bridge type inverter, comprising:

first and second inverter input terminals adapted to receive a source of substantially direct current (DC) voltage; and

an inverter output terminal; and

a parallel resonant type output circuit, comprising:

a first output connection and a return output connection, wherein the first output connection and the return output connection are adapting for coupling to the at least one gas discharge lamp;

an output transformer, comprising:

a primary winding coupled to the inverter output terminal; and

a secondary winding operably coupled between the first output connection and the return output connection, wherein the secondary winding includes a center tap connection;

a resonant capacitor coupled in parallel with the primary winding of the output transformer;

a direct current (DC) blocking capacitor coupled between the resonant capacitor and circuit ground;

a first ballasting capacitor coupled between the secondary winding and the first output connection; and

a voltage-limiting resistance coupled between earth ground and the center tap connection of the secondary winding of the output transformer, the voltage-limiting resistance having a resistance that is greater than about two hundred thousand ohms;

wherein the center tap connection of the secondary winding and the voltage-limiting resistance result in, 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 that is limited to a root-mean-square value of less than about 430 volts.