Ballast with protection circuit for quickly responding to electrical disturbances

A ballast for powering a gas discharge lamp load, comprising:

• an inverter operable to provide a high frequency voltage at an inverter output;
• an output circuit coupled to the inverter output and having output connections adapted for connection to the gas discharge lamp load;
• a protection circuit coupled to the inverter and the output circuit, wherein the protection circuit is operable to:
• (i) monitor a signal within the output circuit;
• and
• (ii) disable the inverter for at least a predetermined period of time in response to a disturbance wherein at least a portion of the signal exhibits a time-rate-of-change that substantially exceeds the time-rate-of-change of the signal during normal operation of the ballast and gas discharge lamp load, wherein:
• during normal operation of the ballast and gas discharge lamp load, the high frequency voltage at the inverter output is a substantially periodic signal having a period;
• and
• the protection circuit is operable, in response to a disturbance in the signal within the output circuit, to disable the inverter within a response time that is less than at least one of:
• twice the period of the high frequency voltage at the inverter output;
• and
• 100 microseconds.

An electronic ballast, comprising:

• an inverter having first and second output terminals, the second output terminal being coupled to circuit ground, the inverter being operable to provide a high frequency voltage between the first and second output terminals;
• an output circuit coupled to the output terminals of the inverter, the output circuit comprising:
• first and second output connections adapted for connection to a lamp load comprising at least one gas discharge lamp;
• a resonant inductor coupled between the first output terminal of the inverter and the first output connection;
• a resonant capacitor coupled between the first output connection and circuit ground;
• and
• a direct current blocking capacitor coupled between the second output connection and circuit ground;
• a protection circuit having an input coupled to the output circuit, and an output coupled to the inverter, the protection circuit being operable to monitor a signal within the output circuit and, in response to occurrence of a disturbance in the signal, to disable the inverter for a predetermined period of time, wherein a disturbance is deemed to have occurred when at least a portion of the signal has a time-rate-of-change that substantially exceeds the time-rate-of-change of the signal during normal operation of the ballast and lamp load, wherein the protection circuit further comprises:
• a latching device coupled between the output of the protection circuit and circuit ground, the latching device having a control terminal and being operable to:
• (i) turn on and couple the output of the protection circuit to circuit ground in response to a voltage at the control terminal reaching a predetermined triggering voltage;
• and
• (ii) remain on for as long as the amount of current flowing through the latching device from the output of the detection circuit to circuit ground exceeds a predetermined holding current;
• and
• a triggering circuit coupled to the input of the protection circuit, the control terminal of the latching device, and circuit ground, the triggering circuit being operable, in response to a disturbance, to provide sufficient voltage at the control terminal to turn on the latching device.

A ballast for powering at least one gas discharge lamp, comprising:

• an inverter having a pair of output terminals and operable to provide a high frequency voltage between the inverter output terminals;
• an output circuit coupled to the output terminals of the inverter, the output circuit comprising:
• output connections adapted for connection to the at least one gas discharge lamp;
• a resonant capacitor coupled between the inverter output terminals;
• and
• an output transformer, comprising:
• a primary winding coupled between the inverter output terminals;
• a secondary winding coupled to the output connections;
• and
• an auxiliary winding coupled to the inverter, the auxiliary winding having a first end and a second end;
• and
• a protection circuit coupled to the inverter and the auxiliary winding of the output transformer, the protection circuit being operable to monitor a voltage signal associated with the output transformer and, in response to occurrence of a disturbance in the voltage signal, to disable the inverter for a predetermined period of time, wherein a disturbance is deemed to have occurred when at least a portion of the voltage signal has a time-rate-of-change that substantially exceeds the time-rate-of-change of the signal during normal operation of the ballast and lamps, wherein the protection circuit includes:
• a first input coupled to the first end of the auxiliary winding;
• and
• a second input coupled to the second end of the auxiliary winding.