Appeal No. 1997-1231
Application No. 08/308,985
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 the associated starting means are disposed.
A control circuitry is disposed in the ballast for driving the
DC/DC converter means and the bridge circuit to control the
voltage and the power to the gas-discharge lamp during its
operation. The invention is further illustrated by the
following claim.
1. 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,
and
control 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
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