High frequency electronic ballast for multiple lamp independent operation

An electronic ballast for driving one or more gas discharge lamps in a set of discharge lamps, comprising:

• a voltage-fed half-bridge inverter having an input adapted to be coupled to a source of DC voltage, an output, and one or more switching devices which convert DC voltage at the input of the inverter to an AC voltage at the output of the inverter, each switching device having a control input;
• a tank circuit resonant at a given frequency coupled to the output of the inverter, the tank circuit providing a voltage at an output thereof to ignite operable lamps coupled to the ballast and maintain them lighted, the tank circuit including at least one resonant inductor and at least one resonant capacitor;
• a transformer having a primary coupled to the output of the tank circuit and a secondary;
• a ballast device coupled to each lamp;
• control and feedback circuitry including
• a controller having an output coupled to each control input and supplying control signals thereto to control switching of the switching devices and
• a feedback loop coupled from the tank circuit to the controller including a voltage feedback loop portion, a current feedback loop portion and a phase shift circuit which provides a phase shifted control signal to the controller in response to a signal related to the current in the tank circuit provided by the current feedback loop portion and a signal related to the voltage at the output of the tank circuit provided by the voltage feedback loop portion;
• the phase shift circuit tracking phase angle changes with one, some or all of the lamps of the set connected and during a transition when a lamp is extinguished, ignited, disconnected or connected, and the controller being so constructed and cooperating with the feedback loop to supply control signals to the inverter which cause the inverter to provide an AC output with substantially constant phase angle, whereby a substantially constant voltage output is supplied to the lamp or lamps.

A method of regulating an output of an electronic ballast to which a set of gas discharge lamps can be coupled, the ballast operating all, some or one of the lamps of the set coupled thereto, the ballast comprising a voltage-fed resonant inverter, a resonant tank circuit coupled thereto and a controller which operates the inverter;

• the method comprising the steps of:
• providing a first signal related to the current in the tank circuit;
• providing a second signal related to the voltage at an output of the tank circuit;
• providing a phase shift signal as a feedback correction signal to the controller which is the first signal phase shifted by the second signal which tracks phase angle changes with one, some or all of the lamps of the set connected and during a transition when a lamp is extinguished, ignited, disconnected or connected, whereby the controller causes the output of the electronic ballast to provide a substantially constant voltage output to the lamp or lamps.

An electronic ballast for driving at least one rapid start gas discharge lamp at a user selectable lighting level, comprising:

• a voltage-fed half-bridge inverter having an input adapted to be coupled to a source of DC voltage, an output, and one or more switching devices which convert DC voltage at the input of the inverter to an AC voltage at the output of the inverter, each switching device having a control input;
• a tank circuit resonant at a given frequency coupled to the output of the inverter, the tank circuit having a tank circuit current flowing therethrough and providing a voltage at an output thereof to ignite an operable lamp coupled to the ballast and maintain it lighted;
• a ballast device coupled to the at least one lamp;
• control and feedback circuitry including
• a controller having an output coupled to each control input and supplying control signals thereto to control switching of the switching devices;
• a command input for setting the lighting level of the at least one lamp;
• and
• a feedback loop coupled from the tank circuit to the controller;
• the control and feedback circuitry being so constructed as to supply control signals to the inverter which cause the inverter to provide an AC output voltage from the tank circuit with a substantially constant phase angle between said AC output voltage and the tank circuit current as set by a signal supplied to the command input, the feedback loop being operative to track phase angle changes and supply correction signals to the controller which in response supplies the control signals to the inverter, whereby a substantially constant output voltage can be supplied to the at least one lamp coupled to the ballast in response to the signal supplied to the command input.