Fluorescent lamp power control
AssigneeMagneTek, Inc.
InventorsGeorge W. Mortimer, Robert V. Burke
Life of this patent
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Abstract
A fluorescent lamp power control having an input conditioning section, a lamp driver section, and a power command interface and control section to control power to fluorescent lamps. An external power command input is compared to an internally generated, computed power level and an electronic preregulator is controlled to regulate amp power. The preregulator output voltage and lamp driver current are multiplied to obtain a signal indicative of lamp power. A power command interface isolates the external power command input. Fluorescent lamp dimming is achieved by reducing the external power command input signal, reducing the power delivered to the fluorescent lamps.
Claims15
Apparatus for controlling a fluorescent lamp comprising:
- a) a discontinuous-mode flyback type preregulator receiving power from and providing power factor correction at an AC power line and providing a controllable DC electrical output;
- b) a lamp driver having a DC input connected to the DC output of the preregulator and having an output adapted to be connected to a fluorescent lamp such that the output power of lamp driver depends on the voltage level of said DC input;
- c) first means for providing an output representative of a voltage across the lamp;
- d) second means for providing an output representative of a current through the lamp;
- e) multiplier means for multiplying the outputs of the first and second means;
- and for providing a signal representative of lamp power;
- and
- f) power control means for controlling the output of the preregulator is response to the signal representative of lamp power to hold lamp power constant in the event of variations in the AC power line.
Apparatus for controlling a fluorescent lamp comprising:
- a) a discontinuous-mode flyback type preregulator operating from and providing power factor correction at an AC power line and providing a variable-output DC voltage at a power output thereof and having a signal input;
- b) a self-oscillating lamp ballast circuit having a DC input connected to the power output of the preregulator such that output power of lamp ballast depends on the voltage level of said DC input;
- c) power computing means for computing and providing at an output thereof a signal representative of output power delivered to a fluorescent lamp by the lamp ballast;
- d) a pulse-width modulator having:
- i) an input connected to the output of the power computing means, and
- ii) an output providing a pulse-width modulated signal to the signal input of the preregulator wherein the preregulator is controlled by the pulse-width modulator to maintain the output power constant.
A method of controlling a fluorescent lamp comprising the steps of:
- a) operating a discontinuous-mode flyback type preregulator from an AC power line supply voltage to provide a controllable DC voltage output and power factor correction at the AC power line;
- b) operating a lamp driver powered by the preregulator DC voltage output to provide a lamp voltage and a lamp current to power a fluorescent lamp;
- c) computing power supplied to the lamp by multiplying signals representative of lamp voltage and current;
- and
- d) controlling the preregulator output such that electrical power supplied to the lamp is regulated to a constant value as an RMS value of the AC power line supply voltage varies.
A method of controlling a fluorescent lamp comprising operating an electronic ballast having a discontinuous-mode flyback type preregulator with a controllable DC voltage output connected as an input to a self-oscillating lamp driver whose input voltage and current are proportional to fluorescent lamp voltage and current by computing lamp power as the product of the input voltage and current of the lamp driver and regulating the lamp driver to hold lamp power constant by adjusting the DC voltage level of the output from the preregulator and simultaneously making average current proportional to an AC line voltage at the input to the preregulator to provide power factor correction at the AC line.
Dependencies are inferred from the claim text.