Electronic ballast system

Details Electronic ballast system Electronic ballast system

2000-05-19

2001-07-17

Philogene, Haissa (Department: 2821)

Electric lamp and discharge devices: systems

Periodic switch in the supply circuit

Impedance or current regulator in the supply circuit

C315S2090SC, C315S307000, C315S291000, C315S308000

Reexamination Certificate

active

06262542

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to electronic ballast systems and, more particularly, the invention relates to an electronic ballast system that controls the duty cycle of a pulse-width modulated lamp drive signal based on a lamp current.
2. Description of Related Technology
Generally speaking, electronic ballast systems initiate a glow discharge within a gas-filled lamp, such as a conventional flourescent lamp, and thereafter maintain a stable supply of power to the lamp to sustain the discharge. As is well known, conventional electronic ballast systems typically include an inverter circuit that supplies alternating current (AC) power to the lamp and a lamp driver circuit, which uses a pulse-width modulated (PWM) control signal to vary the amount of power that the inverter supplies to the lamp.
As is also well known, the inverter circuit typically includes a power switch (e.g., a transistor) that is switched on and off at a frequency determined by the resonance of a timing capacitor and an inductor. In practice, the capacitance of the timing capacitor may deviate about five to ten percent from an ideal value. As a result, the frequency and duty cycle of the PWM control signal may also vary in proportion to the deviation of the capacitance value from the ideal value, thereby changing the amount of power which is delivered to the lamp. Additionally, the variation in the frequency and duty cycle of the PWM signal prevents precise zero voltage switching control of the power switch, which increases the operating temperature of the power switch and significantly reduces its expected operating life.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, an electronic ballast for use in illuminating a lamp includes a lamp driving circuit having a pulse-width modulated signal generator, a timing capacitor coupled to the lamp driving circuit, and a power controller. The power controller compares a signal associated with a current flowing through the lamp to a signal associated with a desired lamp current and, based on the comparison, provides a correction current to the timing capacitor to control a duty cycle of an output of the pulse-width modulated signal generator.
In accordance with another aspect of the invention, an electronic ballast system includes a voltage source for supplying power to the electric ballast system and a lamp driving circuit having a first, second and third terminals. The power of the voltage source is supplied through the first terminal to begin the driving of the electronic ballast system, and the lamp driving circuit outputs pulse-width modulated signals through the second and third terminals. The electronic ballast system may further include a half bridge converter having a first end that is connected to the second terminal of the lamp driving circuit and a second end that is connected to the third terminal of the lamp driving circuit. The half bridge converter receives input from the second and third terminals of the lamp driving circuit and outputs a current that changes flow directions according to the pulse-width modulated signals output by the lamp driving circuit. The electronic ballast system may additionally include a lamp portion having a first end connected to an output end of the half bridge converter such that the lamp portion operates according to the current output by the half bridge converter, and a power controller connected between the lamp driving circuit and a common terminal of the half bridge converter and the lamp portion. The power controller may detect an amount of current supplied to the lamp portion and may control a drive frequency of the lamp driving circuit based on the detected amount of current to thereby control an output power of the lamp portion.
The invention itself, together with further objectives and attendant advantages, will best be understood by reference to the following detailed description, taken in conjunction with the accompanying drawings and the appended claims.


REFERENCES:
patent: 4717863 (1988-01-01), Zeiler
patent: 5612597 (1997-03-01), Wood
patent: 5969482 (1999-10-01), Gradzki
patent: 5973437 (1999-10-01), Gradzki et al.
patent: 5973455 (1999-10-01), Mirskiy et al.
patent: 6137240 (2000-10-01), Bogdan

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