High frequency electronic ballast for multiple lamp independent operation

• US 6,326,740 B1
• Filed: 12/22/1998
• Issued: 12/04/2001
• Est. Priority Date: 12/22/1998
• Status: Expired due to Fees

• Current Assignee: Philips Electronics North America Corporation (Koninklijke Philips N.V.)
• Original Assignee: Philips Electronics North America Corporation (Koninklijke Philips N.V.)
• Inventors: Chang, Chin, Bruning, Gert W.
• Primary Examiner(s): Philogene, Haissa
• Application Number:
  US09/218,556
• Time in Patent Office: 1,078 Days
• Field of Search: 315/194, 315/291, 315/209.R, 315/307, 315/224, 315/244, 315/221, 315/231, 315/94, 315/105-107, 315/DIG.4, 315/DIG.5, 315/DIG.7
• US Class Current: 315/291
• CPC Class Codes: H02M 7/53803 with automatic control of output voltage or current
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• CPC Class Codes: H05B 41/2986 against internal abnormal circuit conditions
• CPC Class Codes: H05B 41/3925 by frequency variation H05B41/3922 takes precedence
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
• CPC Class Codes: Y10S 315/07 Starting and control circuits for gas discharge lamp using transistors

Abstract

An electronic ballast with a voltage-fed, LC or LLC resonant inverter for multiple gas discharge lamp independent operation which maintains a substantially constant voltage to a lamp or lamps connected to the ballast even during a transition period when a lamp or lamps is ignited, extinguished, added or removed. The ballast includes a feedback loop that maintains a substantially constant phase angle between the voltage and the current in an LC or LLC tank circuit, which has the effect of the ballast providing the substantially constant voltage output. The feedback loop obtains a current feedback signal and a voltage feedback signal from the tank circuit, and provides a phase shifted signal as a feedback correction signal which is the current feedback signal phase shifted by the voltage feedback signal that tracks phase angle changes with one, some or all of the lamps of a set thereof connected to the ballast, and during the transition period. The feedback loop includes a phase-shift circuit which includes at least one differential amplifier stage that receives the current feedback signal at both inputs and the voltage feedback signal at one input so as to phase shift the current feedback signal at that one input. The ballast operates instant start or rapid start gas discharge lamps in various configurations, including dimming configurations.

Claims

1. 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 having a tank circuit current flowing therethrough and providing a voltage at an output thereof to ignite operable lamps coupled to the ballast and maintain them lighted;

a respective 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;

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 substantially constant phase angle between said AC output voltage and the tank circuit current, the feedback loop being operative to track 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 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 lamp or lamps coupled to the ballast.

2. The ballast as recited in claim 1 wherein the feedback loop includes a voltage feedback loop portion and 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.

3. The ballast as recited in claim 2 wherein the controller comprises a pulse width modulation control circuit, the phase-shifted control signal being supplied to the pulse width modulation control circuit.

4. The ballast as recited in claim 3 wherein the phase shift circuit comprises at least one phase-shift stage which includes a differential amplifier having inverting and non-inverting inputs, both of which are coupled to receive the signal related to the current in the tank circuit and one of which is coupled to receive the signal related to the voltage at the output of the tank circuit.

5. The ballast as recited in claim 1 wherein the ballast is adapted to operate instant start lamps and the ballast device comprises a ballast capacitor coupled in series with a respective lamp.

6. The ballast as recited in claim 1 wherein the ballast is adapted to operate rapid start lamps and includes means for heating the filaments of rapid start lamps coupled thereto.

7. The ballast as recited in claim 6 wherein the ballast device comprises a ballast capacitor coupled in series with a respective lamp.

8. The ballast as recited in claim 6 wherein the control and feedback circuitry is coupled to monitor current in the lamps, includes a command input for dimming operation and is responsive to a signal coupled to the command input to change the phase angle and thereby adjust the lighting level of the lamps.

9. The ballast as recited in claim 1 comprising a set of four instant start lamps coupled in parallel with each other and in series with a respective ballast device to the output of the tank circuit.

10. The ballast as recited in claim 1 comprising a set of four instant start lamps, a first pair of which is coupled in series with a ballast device and a second pair of which is coupled in series with another ballast device, the first and second pairs being coupled in parallel to the output of the tank circuit.

11. 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.

12. The ballast as recited in claim 11 wherein the controller comprises a pulse width modulation control circuit, the phase-shifted control signal being supplied to the pulse width modulation control circuit.

13. The ballast as recited in claim 12 wherein the phase shift circuit comprises at least one phase-shift stage which includes a differential amplifier having inverting and non-inverting inputs, both of which are coupled to receive the signal related to the current in the tank circuit and one of which is coupled to receive the signal related to the voltage at the output of the tank circuit.

14. The ballast as recited in claim 11 wherein the ballast is adapted to operate instant start lamps and the ballast device comprises a ballast capacitor coupled in series with a respective lamp.

15. The ballast as recited in claim 11 wherein the ballast is adapted to operate rapid start lamps and the transformer includes a secondary winding adapted to be coupled to a heater filament of each rapid start lamp coupled to the ballast, and wherein the ballast device comprises a ballast capacitor coupled in series with a respective lamp.

16. The ballast as recited in claim 15 wherein the control and feedback circuitry is coupled to monitor current in the lamps, includes a command input for dimming operation and is responsive to a signal coupled to the command input to change the phase angle and thereby adjust the lighting level of the lamps.

17. The ballast as recited in claim 15 wherein the resonant inductor has a set of secondary windings, each being coupled through a capacitor to a respective heater filament of a rapid start lamp coupled to the ballast.

18. 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.

19. The method as recited in claim 18 comprising the step of varying the phase shift signal in response to a level command input signal to vary the voltage output to the lamps and thereby provide for dimming operation of the lamps.

20. 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.