DIMMING ELECTRONIC BALLAST WITH PREHEAT CURRENT CONTROL

• US 20100109548A1
• Filed: 08/25/2009
• Published: 05/06/2010
• Est. Priority Date: 08/25/2008
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Matsuda, Kenji
• Granted Patent: US 8,294,384 B2
• Time in Patent Office: Days
• US Class Current: 315/279
• CPC Class Codes: H05B 41/295 with semiconductor devices and specially adapted for lamps with preheating electrodes, e.g. for fluorescent lamps
• CPC Class Codes: H05B 41/3925 by frequency variation H05B41/3922 takes precedence

Abstract

An electronic ballast is capable of realizing high frequency lighting of a discharge lamp and switching between at least two lighting modes with different light outputs. The ballast includes a preheating circuit having a winding component connected in parallel with a main resonant circuit with a lamp current flowing therein for the discharge lamp. A constant preheating current for the lamp filaments is supplied from a secondary winding of the winding component during lighting of the discharge lamp and a path of a current flowing on a primary winding side of the winding component is switched by a switch according to the lighting mode.

Claims

1. A electronic ballast for high frequency lighting of a discharge lamp having lamp filaments and operating in at least two different lighting modes comprising:

an inverter;

a main resonant circuit coupled to the inverter;

a preheating circuit having a winding component connected in parallel with the main resonant circuit, the winding component comprising a primary winding and a secondary winding, and a switch connected in series with the primary winding;

a path of a current flowing in the primary winding of the winding component is switched by the switch in accordance with the different lighting modes; and

wherein a constant preheating current for filaments in the lamp is supplied from the secondary winding of the winding component during lighting of the discharge lamp.

2. The electronic ballast according to claim 1, wherein the preheating circuit comprises a preheating resonant circuit including the primary winding of the winding component and a serially connected capacitance;

and

a resonant frequency in the electronic ballast during lighting is operated to be higher than a resonant frequency in the main resonant circuit with a lamp current flowing therein and lower than a resonant frequency in the preheating resonant circuit.

3. The electronic ballast according to either claim 1 or 2 having a first lighting mode with a nominal lamp output and a second lighting mode with a dimmed lamp output and wherein the ballast further comprises:

a switch control circuit;

in the first lighting mode, the switch control circuit causes the preheating circuit to disable the constant preheating current for the lamp filaments by turning off the switch arranged in the current path; and

in the second lighting mode, the switch control circuit causes the preheating circuit to supply the constant preheating current for the lamp filaments by turning on the switch arranged in the current path.

4. A lighting fixture comprising a electronic ballast according to any one of claims 1 to 3.