Patent ID: 6140770
Filing Date: 2000-10-31
Classification: H05B,Y02B,Y10S

Abstract:
A ballast for a gas-discharge lamp, particularly for motor vehicles, comprising:switched dc/dc converter means which are intended to be connected to a direct-current voltage source such as the battery of a motor vehicle, and which can output a direct-current voltage higher than that supplied by the source,an H-shaped bridge switching circuit which is connected to the dc/dc converter means and in the central branch of which the discharge lamp and associated reactive starting means are disposed, andcontrol circuitry for driving the dc/dc converter means and the bridge switching circuit in a manner such that, each time the lamp is switched on, a very high voltage is applied initially, in particular in order to start the lamp, and subsequently a low voltage is applied, but with a high electrical power, in order to support the passage of a large current through the lamp during the heating (warming-up) of the lamp and during the subsequent steady operation of the lamp;the dc/dc converter means comprisinga switched dc/dc converter of the ""fly-back"" type and a second switched dc/dc converter of the ""feed-forward"" type,the control circuitry being arranged to drive the dc/dc converters in a manner such that, each time the lamp is switched on, first the ""fly-back"" converter is activated in order to generate the very high voltage and, subsequently, the ""feed-forward"" converter is activated in order to generate the low voltage with high electrical power.