Electric lamp and discharge devices: systems – Surge generator or inductance in the supply circuit
Reexamination Certificate
2000-05-17
2002-03-26
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Surge generator or inductance in the supply circuit
C315S290000, C315S219000, C315S276000
Reexamination Certificate
active
06362576
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a circuit arrangement for igniting a lamp, in particular a high-pressure discharge lamp, having an ignition transformer which has a primary side and a secondary side, the secondary side being connectable to the lamp which is to be ignited, and the primary side being connected to an ignition switch.
To illustrate the problem on which the invention is based,
FIG. 1
shows such a circuit arrangement, as is known from the prior art. A capacitor C
1
is charged from a DC voltage source U
G
via a resistor R
1
. The capacitor C
1
is then discharged, by shorting a spark gap FS, via the primary side L
1
of the ignition transformer TR, until it is empty. As an alternative to the spark gap, other self-triggering circuit breakers, for example SIDACs, or triggerable circuit breakers, for example thyristors or triacs, are also used in this case. The large current flowing through the primary L
1
of the ignition transformer TR is transferred to the secondary L
2
of the ignition transformer and causes the lamp LA to be ignited there. The capacitor CL shown in
FIG. 1
allows for the capacitance between the two lamp wires, which is usually between 20 and 200 pF, depending on the distance between the ignition circuit and the lamp LA. The field in which such circuit arrangements are used includes high-pressure discharge lamps, which, in respect of their diverse applications, can be regarded as a mass-produced product.
The object of the present invention is to refine a circuit arrangement of the type mentioned in the introduction such that production costs and complexity are lower than for the circuit arrangement known from the prior art.
SUMMARY OF THE INVENTION
To achieve this object, the present invention provides that the ignition switch can be controlled for actively disconnecting a current flowing through the primary side of the ignition transformer.
The solution according to the invention is based on the knowledge that, provided that the ignition switch can be controlled for actively disconnecting a current flowing through the primary side of the ignition transformer, the store used for the ignition energy can also be a charge store storing more charge than is necessary for the ignition process. In a particularly advantageous embodiment, to provide the ignition energy, the primary side of the ignition transformer is therefore connected to any desired DC voltage source, which is provided anyway in the circuit, for example to the intermediate circuit capacitor of the circuit arrangement for operating the lamp. This solution allows the components R
1
and C
1
shown in
FIG. 1
to be dispensed with. As a result of the charging time constant determined by R
1
and C
1
disappearing, the invention provides the option of producing, in principle, ignition pulses of the same amplitude which follow one another at any desired rate.
The variable turned-on duration of the ignition switch also permits the ignition pulse amplitude to be influenced. This effect can advantageously be used to compensate for component tolerances and, in particular, the influence of the output capacitance in such a way that the amplitude of the ignition voltage produced remains virtually constant. The result of this is very reliable lamp ignition.
In one advantageous implementation, the primary of the ignition transformer is arranged between the intermediate circuit capacitor and the ignition switch.
A component, particularly an inductor, which limits the rise in current and is arranged in the current path on the primary side and/or the secondary side of the ignition transformer is used to prevent an undesirably high current from flowing as soon as the ignition switch has been turned on. This component acts in addition to the leakage inductance of the ignition transformer, which is always present anyway, but allows other degrees of freedom when designing the ignition transformer.
However, the solution according to the invention also provides the basis for taking into account other demands on an ignition circuit: considering the basic circuit (shown in
FIG. 1
) for a circuit arrangement for igniting a lamp, this cannot, for many lamps, in particular high-pressure discharge lamps, always produce ignition pulses causing the lamps to be ignited reliably, even if the individual circuit parameters are optimized. The specification for an ignition pulse is frequently defined in standards, for example in the American standard ANSI M98, which defines the electrical data for operating a “70 W Single Ended HID Lamp”. For a load capacitance CL of 20 pF, the minimum ignition pulse level should be 3 kV, the maximum ignition pulse level should be 4 kV and the minimum pulse width should be 1 &mgr;s @ 2.7 kV. The minimum pulse repetition rate should be 240 Hz.
Using circuit arrangements based on the basic circuit shown in
FIG. 1
, an ignition pulse satisfying these ANSI M98 criteria could not be produced within the framework of a sensible physical size for the ignition transformer or without severely impairing the normal operation of the lamp, that is to say operation after ignition.
In this case, it should be taken into account that contradictory conditions arise when designing the ignition transformer, particularly the secondary side: first, for normal operation, that is to say after ignition of the lamp, L
2
needs to be proportioned such that the internal resistance is low, and, secondly, for ignition, L
2
needs to be proportioned such that it allows a wide ignition pulse to be produced. Whereas the first condition requires an L
2
with few windings, an L
2
with a large number of windings is necessary for the second condition. For these different demands, it is not possible to find a satisfactory solution on the basis of the basic circuit shown in FIG.
1
.
The situation is different with a particularly advantageous embodiment of the invention: if provision is made for a capacitor to act in parallel with the secondary of the ignition transformer, the capacitor and the secondary of the ignition transformer being able to form a resonant circuit having a predetermined resonant frequency and a predetermined maximum peak voltage, then a sinusoidal ignition pulse can be generated which can be used to satisfy the electrical demands on the ignition pulse, particularly in terms of its width. In this instance, L
2
can have few windings, for low resistance during operation of the lamp, that is to say after ignition. The load capacitance influences can also be drastically reduced as a result.
When implemented, the capacitor acting in parallel with the secondary can be a capacitor connected in parallel with the secondary of the ignition transformer, or a capacitor connected in parallel with the connection terminals of the lamp. The latter variant is suitable if there is an output filter capacitor at the output of the lamp current generator which is usually present. Since the capacitance value of the output filter capacitor is much higher than the capacitance value of the capacitor connected in parallel with the connection terminals of the lamp, a voltage change on the output filter capacitor during pulse generation remains small. The capacitor connected in parallel with the connection terminals of the lamp thus acts as if it were arranged in parallel with the secondary of the ignition transformer. The advantage of this implementation produces an additional filtering action on the current in normal operation and consequently results in more favorable RFI values. The ignition pulse remains largely unaffected by the arrangement of the capacitor acting in parallel with the secondary of the ignition transformer.
Whereas the circuit arrangement shown in
FIG. 1
can be used to produce only a cosinusoidal ignition pulse, the particularly preferred embodiment of the present invention can now be used to produce a sinusoidal ignition pulse, which can be used to satisfy the requirement regarding ignition pulse width, for example 1 &mgr;s @ 2.7 kV in accordance with ANSI M98, se
Huber Andreas
Limmer Walter
Niedermeier Peter
Bessone Carlo S.
Patent-Treuhand-Gesellschaft fuer elektrische Gluehlampen mbH
Philogene Haissa
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