Patent Number: 6,294,879

Title: Ballast for a discharge lamp

Abstract: A safety ballast for a discharge lamp capable of interrupting the supply of the electric power upon failure of starting the lamp. The ballast includes a converter providing a DC power voltage from a DC voltage source, a booster providing a boosted DC voltage to a starter which generates, based upon the boosted DC voltage, a starting voltage for starting the lamp, and an inverter receiving the DC power from the converter to provide an AC power for operating the lamp. The booster includes a capacitor which is charged by the DC power and accumulate the boosted voltage. A controller monitors a load condition of the lamp and issues a disable signal when a no-load condition continues over a predetermined starting period. The inverter includes a plurality of switching elements one of which is regulated to be turned on in response to the no-load signal for establishing a supply path of supplying the boosted voltage from the booster's capacitor through the switching element to the starter. The one switching element is also controlled to be turned off in response to the disable signal for interrupting the supply path. Thus, when the no-load condition continues over the predetermined starting period as indicative of the that the lamp has been removed or the lamp reaching its end of life, the booster's capacitor bearing the boosted voltage is disconnected from the starter, applying no voltage to the starter and therefore preventing the starter from being activated to generate unnecessary starting voltage.

Inventors: Nagase; Haruo (Kitakatsuragi-gun, JP), Satou; Noriyuki (Nishikanbara-gun, JP), Taga; Yoshitaka (Osaka, JP), Kataoka; Hisao (Nishikanbara-gun, JP), Ueno; Masatoshi (Nishikanbara-gun, JP)

Assignee: Matsushita Electric Works, Ltd.

International Classification: H02M 3/24 (20060101); H02M 3/335 (20060101); H02M 7/48 (20060101); H05B 41/28 (20060101); H05B 41/292 (20060101); H05B 037/02 ()

Expiration Date: 09/25/2018