WO2002102114A2

WO2002102114A2 - Electronic lighting ballast

Info

Publication number: WO2002102114A2
Application number: PCT/US2002/017885
Authority: WO
Inventors: Joao Carlos Vecchio; Rick W. Kauffman
Original assignee: Acuity Brands, Inc.
Priority date: 2001-06-11
Filing date: 2002-06-07
Publication date: 2002-12-19

Abstract

A gas discharge lamp electronic ballast, comprises a rectifier for full wave rectifying alternating current line voltage, a converter for receiving an output of the rectifier and supplying a direct current voltage output, the converter operating in a discontinuous manner and including an inductor, a driver for energizing the gas discharge lamp, the driver receiving the direct voltage output of the converter and a controller for operating the converter in the discontinuous manner, the controller having as one of plural control signals input thereto a first control signal indicative of a state of the inductor.

Description

ELECTRONIC LIGHTING BALLAST

FIELD OF THE INVENTION

This invention relates generally to powering lamps of high discharge intensity and pertains more particularly to electronic lighting ballasts for powering gas lamps.

BACKGROUND OF THE INVENTION

A high discharge intensity lamp presents negative impedance when the contained gas is ionized. This characteristic prohibits connection of the lamp directly to power lines, i.e., the lamp would be destroyed by such connection.

There accordingly is need for interposing between the power lines and the lamp a device (ballast) which limits the circulating current in the lamp and consequently the power supplied thereto. Various electrical arrangements of devices allow such limiting, such as series resistance, capacitive reactance, inductive reactance and combinations thereof. The use of an inductor in series with the lamp is considered to be the most efficient arrangement in terms of cost and losses. However, the power regulation (power factor) is less than desired. Thus, a small variation in the power lines gives rise to great variation in the lamp, drastically reducing its useful lifetime. While auto regulated ballasts overcome this problem, they are very sensitive to the net frequency with high losses and are seen as resulting in an arrangement of low efficiency and high cost.

The prior art has addressed power factor correction in ballasts of the type including an inductor in series with the lamp. Power factor is defined as the ratio of power line wattage to lamp wattage and is desirably as close to unity (1.0) as possible.

U.S. Patent No. 5,969,484 discloses a "discontinuous conduction mode" (DCM) electronic ballast which drives the lamp with line frequency voltage and current, with its weight said to be substantially reduced due to operation at high switching frequency. The ballast is described as ensuring unity power factor at the input and stable lamp operation at the output.

In one circuit arrangement of the '484 patent, a diode bridge rectifies an input alternating current voltage, and a switching converter generates a square wave voltage at the switching frequency. A matching network is interposed between the switching converter output and the gas discharge lamp. This matching network is usually a high-frequency resonant filter (usually an L-C filter) tuned to a frequency equal to (or close to) the switching frequency. It attenuates all the harmonics of the square-wave voltage passing only the fundamental. Furthermore, the matching network is said to transform the switching converter output characteristic from a voltage source into a current source, thus said to ensure stable lamp operation. A high input power factor is said to be obtainable either by using a two-stage converter consisting of a unity-power-factor shaper followed by a high-frequency inverter or by using a single stage converter, which usually operates in discontinuous conduction mode at the input.

In a specific embodiment, shown in Fig. 12 of the '484 patent, a series circuit of a diode, a first inductor, a first capacitor and a second inductor is connected to ground by a storage capacitor. A single stage switch (transistor) connects the junction of the first inductor and first capacitor to ground. Control of the single stage switch is effected by a pulse width modulator which is in turn controlled by an integrator, the compared inputs to which are lamp current a fixed current reference value.

SUMMARY OF THE INVENTION The present invention has as its primary object an improved electronic lighting ballast having a controlled power-factor correction facility.

In obtaining the foregoing and other objects, the invention provides a gas discharge lamp electronic ballast, comprising: a) rectifying means for full wave rectifying alternating current line voltage; b) converter means for receiving an output of the rectifying means and supplying a direct current voltage output, the converter means operating in a discontinuous manner and including an inductor; c) driver means for energizing the gas discharge lamp, the driver means receiving the direct voltage output of the converter means; and d) control means for operating the converter means in the discontinuous manner, the control means having as one of plural control signals input thereto a first control signal indicative of a state of the inductor.

In a particularly preferred embodiment of the invention, further control signals input to the control means include a second control signal indicative of a level of the alternating current line voltage, a third control signal indicative of a level of the direct current voltage output of the converter means and a fourth control signal indicative of the manner of discontinuous operation of the converter means.

In a particular practice of the invention, steps of a method for controlling power supplied to a gas lamp, following ionization thereof, includes a step of measuring gas lamp consumption wattage, a step of determining whether the measured gas lamp wattage consumption is less than, equal to or greater than a preselected wattage. Where the wattage so determined is less than the preselected wattage, a discontinuous operation manner of the converter, e.g., a pulse width modulation therein, is reduced in value. Where the wattage so determined is greater than the preselected wattage, a discontinuous operation manner of the converter is increased in value. Where the wattage so determined is equal to the preselected wattage, a discontinuous operation manner of the converter is maintained unchanged.

The foregoing and other features of the invention will be further understood from consideration of the ensuing detailed description of embodiments and practices of the invention and of the drawings, in which like components are identified by like reference numerals throughout.

DESCRIPTION OF THE DRAWINGS

Figure 1 is a functional block diagram of the electronic ballast of the invention. Figure 2 is an electrical schematic of converter 20 of the Fig. 1 electronic ballast.

Figure 3 is flow chart setting forth certain operations effected by controller 30 of Fig. 1.

Figure 4, labeled P.F.C. (Power Factor Controller) is a detailed electrical schematic of a preferred electrical schematic of full-wave rectifier 16 and converter 20 of Figure 1. Figure 5, labeled "Control", is a preferred electrical schematic of controller 30 of

Figure 1.

Figure 6, labeled "Driver", is a preferred version of a driver 22 of Figure 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AND PRACTICES Referring to Fig. 1, electronic ballast 10 of the invention includes a-c power source 12 which furnishes line voltage over line 14 to full-wave rectifier 16. Rectifier 16 furnishes d-c voltage over line 18 to converter 20. Converter 20 furnishes its output to driver 22 over line 24 and driver 22 applies its output over line 26 to lamp 28.

Controller 30 has a plurality of control signals input thereto, respectively from a-c power source 12 over line 32 and from converter 20 over lines 34, 36 and 38. Controller 30 provides output signals over line 40 to converter 20 and over line 42 to driver 22.

Referring now to Fig. 2, converter 20 includes a series circuit having inductor 44 and diode 46. Capacitor 48 is connected between diode 46 and electrical ground. Three voltage dividers are incorporated in converter 20. A first voltage divider includes resistors 50 and 52 connected in series from inductor 44 to ground, with capacitor 54 connected in parallel with resistor 52. Converter output line 32 is connected to the junction of resistors 50 and 52 and hence provides indication of the voltage level of the output of a-c power source 12.

A second voltage divider includes resistors 56 and 58 connected in series from diode 46 to electrical ground. The junction of resistors 56 and 58 is connected to converter output line 34 and hence provides indication of the voltage level of the output converter 20.

A third voltage divider includes resistors 60 and 62 connected in series between line 36 and electrical ground. The junction of resistors 60 and 62 is connected to electronic switch 64, which is preferably a field-effect transistor (FET MOSFET), series connected between the junction of inductor 44 and diode 46 and resistor 62, which is connected to electrical ground. This voltage divider thus provides indication on line 36 of the current conducted through switch 64. The FET/MOSFET control electrode is connected through resistor 66 to output line 40 of controller 30.

Switch 64 is rendered conductive discontinuously by controller 30 by signals on line 40, i.e., thereby effecting variable pulse width modulation (PWM) in converter 20.

Converter 20 further includes inductor 68 magnetically coupled with inductor 44 and inductor 68 is series connected with resistor 70 between electrical ground and line 38, whereby line 38 informs controller 30 of the state of inductor 44.

Turning to Fig. 3, operations effected by controller are set forth in a flow chart. In step SI, POSITION PWM TO MAXIMUM OUTPUT, controller output line 40 is set to provide for switch 64 to effect maximum pulse width modulation. In step S2, TURN ON DRIVER, driver 22 is energized. In step S3, ? IS PWM LESS THAN 50%, inquiry is made as to whether the pulse width modulation occurring in switch 64 is less than a predetermined level. If the inquiry is answered in the negative (N), progress is to step S4, REDUCE PWM, where the line 40 output of controller 30 is set to reduce the pulse width modulation. If the inquiry is answered in the affirmative (Y), progress is to step S5, TURN OFF DRIVER, and then return is made to step SI. If the determination in step S3 is that pulse width modulation is equal to the predetermined level, progress is to step S6, ? IS THERE LAMP CURRENT, wherein inquiry is made as to whether the lamp gas has been ionized. If the inquiry is answered in the negative, progress is back to step S4. If the inquiry is answered in the affirmative, progress is to step S7, POSITION PWM TO MINIMUM OUTPUT, wherein the controller output line 40 is set such that switch 64 effects a predetermined minimum pulse width modulation. Progress is then to step S8, ? IS THERE LAMP VOLTAGE, controller 30 determines whether voltage is present at the output of converter 20 and hence at the output of driver 22. If this inquiry is answered in the negative, progress is to step S9, STOP MODE, wherein a reset occurs and the controller repeats its operations. If the inquiry is answered in the positive, progress is to step S10, MULTIPLY LAMP VOLTAGE BY LAMP CURRENT, wherein lamp wattage is consumption is determined. Progress is then to step SI 1, ? IS LAMP WATTAGE HIGHER THAN REFERENCE, wherein the wattage consumption determined in step S10 is compared with a preselected reference value. If the step 11 inquiry is answered in the negative, progress is to step S 12, REDUCE

PWM, wherein the controller operates switch 64 at a lower pulse width modulation value. If the step SI 1 inquiry is answered in the affirmative, progress is to step SI 3, INCREASE WPM, wherein the controller operates switch 64 at a higher pulse width modulation value. If the step SII inquiry determines that the wattage determined in step S 10 is equal to the preselected reference value, progress is to step S 14, WATTAGE EQUALS REFERENCE, and no change is made to the present pulse width modulation value.

As will be appreciated, the controller cycles among steps S 11, S 12, S 13 and S 14, whereby the lamp wattage is maintained at a constant value, providing for a system power factor quite closely approaching the desired unity value (1.0). Controller 30 operates driver 22 by control output signal on line 42 such that the driver oscillator begins its oscillations above the resonant frequency of an L-C circuit. This generates little tension. However, a ramp generated in the controller (PWM) makes the frequency to be gradually reduced and the tension in the capacitor of the L-C circuit increased, when passing by the resonant frequency the tension on the capacitor will be at its maximum and the lamp, connected in parallel with the capacitor, acts as a tension clamp. As will be understood from the foregoing, in case there is not ignition of the lamp, there will be a change in current in the bridge rectifier that will be detected by the controller, causing a reset. Upon such turn off, a temporizer (time counter) may be activated to restart the controller operations after the passage of a certain time period. However, if there is ignition of the lamp, an electric current will circulate through the lamp and is detected by the controller, whereupon the controller changes the frequency of the driver oscillator, taking the bridge to heating current and maintaining the lamp energized. Given the identification of component values and the identification of various integrated circuit components of Figures 4-6, e.g. IC LM317LZ (Figure 4), one skilled in the art will appreciate the totality of the preferred embodiment of the invention.

Various changes may be introduced in the disclosed preferred embodiments and practices without departing from the invention. Accordingly, it is to be appreciated that the true spirit and scope of the invention is set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A gas discharge lamp electronic ballast, comprising: a) rectifying means for full wave rectifying alternating current line voltage; b) converter means for receiving an output of said rectifying means and supplying a direct current voltage output, said converter means operating in a discontinuous manner and including an inductor; c) driver means for energizing said gas discharge lamp, said driver means receiving said direct voltage output of said converter means; and d) control means for operating said converter means in said discontinuous manner, said control means having as one of plural control signals input thereto a first control signal indicative of a state of said inductor.

2. The electronic ballast claimed in claim 1, wherein further control signals input to said control means include a second control signal indicative of a level of said alternating current line voltage, a third control signal indicative of a level of said direct current voltage output of said converter means and a fourth control signal indicative of said manner of discontinuous operation of said converter means.

3. The electronic ballast claimed in claim 1, wherein said converter means comprises a diode in series circuit connection with said inductor, a switch connected to a junction of said diode and said inductor, and a capacitor connected in parallel with said switch.

4. The electronic ballast claimed in claim 3, wherein an output of said control means controls the state of said switch to control said discontinuous operating manner of said converter means.

5. The electronic ballast claimed in claim 4, wherein said discontinuous operating manner of said converter means is a pulse width modulation effected by said control means in controlling the state of said switch.

6. The electronic ballast claimed in claim 1, wherein said control means includes first means for determining wattage consumption of said gas discharge lamp, second means for comparing said determined wattage consumption of said gas discharge lamp with a predetermined wattage level, and third means for varying said discontinuous manner of operation of said converter means correspondingly with the result of said second means comparison.

7. The electronic ballast claimed in claim 6, wherein said control means includes first means for determining wattage consumption of said gas discharge lamp, second means for comparing said determined wattage consumption of said gas discharge lamp with a predetermined wattage level, and third means for varying said pulse width modulation effected by said control means.

8. A method for controlling power supplied to a gas lamp, following ionization thereof, comprising the steps of: a) converting alternating current voltage into a direct current voltage for use in energizing said gas lamp; b) measuring gas lamp consumption wattage; c) determining whether the measured gas lamp wattage consumption is less than, equal to or greater than a preselected wattage; and d) controlling said converting step correspondingly with the determination made in said determining step.

9. A method for controlling power supplied to a gas lamp, following ionization thereof, comprising the steps of a) converting alternating current voltage by pulse width modulation into a direct current voltage for use in energizing said gas lamp ; b) measuring gas lamp consumption wattage; c) determining whether the measured gas lamp wattage consumption is less than, equal to or greater than a preselected wattage; and d) controlling said pulse width modulation in said converting step correspondingly with the determination made in said determining step.

10. The method claimed in claim 9, wherein said pulse width modulation is decreased where the determination made in said determining step is that the measured gas lamp wattage consumption is less than said preselected wattage.

1 1. The method claimed in claim 9, wherein said pulse width modulation is increased where the determination made in said determining step is that the measured gas lamp wattage consumption is greater than said preselected wattage.

12. The method claimed in claim 9, wherein said pulse width modulation is unchanged where the determination made in said determining step is that the measured gas lamp wattage consumption is equal to said preselected wattage.