Discharge lamp operating device

Details Discharge lamp operating device Discharge lamp operating device

2000-02-09

2001-01-30

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

Automatic regulation

C315S307000, C315S225000

Reexamination Certificate

active

06181087

ABSTRACT:

TECHNICAL FIELD
This invention relates to a discharge lamp lighting apparatus in which a lamp life ending detection is performed on a feedback loop with respect to a discharge lamp lighting apparatus of a method such that a consuming electric power of a discharge lamp (hereinbelow, abbreviated to a “lamp”) is fed back and the lamp is lit.
BACKGROUND ART
A conventional discharge lamp lighting apparatus will be described with reference to drawings.
FIG. 3
is a diagram showing a construction of a discharge lamp lighting apparatus of a lamp electric power feedback method which has conventionally been known.
In
FIG. 3
, reference numeral
1
denotes a DC source;
2
an inverting circuit having switching elements such as MOSFETs;
3
a driver;
4
a load circuit;
5
a
to
5
c
lamps;
6
a coupling capacitor;
7
a
to
7
c
ballast coils; and
8
a
to
8
c
starting capacitors.
In
FIG. 3
, reference numeral
9
denotes a load current detecting resistor;
10
an integrating circuit;
11
an operational amplifier;
11
a
a target value; further,
13
a control circuit;
14
a latch circuit;
19
a
to
19
c
lamp voltage detecting circuit;
20
an overvoltage detecting comparator; and
20
a
a threshold value.
The operation of the conventional discharge lamp lighting apparatus will be mentioned hereinafter.
The inverting circuit
2
is driven by the driver
3
and the DC source
1
is converted to a high frequency output. The high frequency output from the inverting circuit
2
lights the lamps
5
a
to
5
c
through the coupling capacitor
6
and ballast coils
7
a
to
7
c.
An active component (effective value) of the load current of the load circuit
4
is detected by integrating a voltage generated in the detecting resistor
9
by the integrating circuit
10
and set as a negative input of the operational amplifier
11
. The operational amplifier
11
sets the target value
11
a
as a positive input. An error-amplified output is outputted to the driver
3
. By the feedback of the operational amplifier
11
, the driver
3
controls a switching frequency of the inverting circuit
2
so as to hold the effective value of the load current of the load circuit
4
constant.
Thus, the consuming electric power of the lamp is held constant. Specifically speaking, as shown in
FIG. 4
, a feedback is performed so that an active component of drain currents of the switching elements constructing the inverting circuit
2
is constant and the frequency is controlled.
Since a lamp voltage increases and the feedback is performed in the direction where the lamp current is suppressed if the life of the lamp is shortened, the frequency beams high and the drain current waveform comes into what as shown in FIG.
5
.
In this case, the active component of the drain current is held constant due to the increase in frequency. However, a reactive current also increases simultaneously.
In the case where the life state of the lamp is further shortened and it becomes the life ending, if the frequency is high, the reactive current component further increases. When the reactive current exceeds a certain degree, the switching elements are heated, so that it causes a trouble.
Protecting means for the life ending lamp will be mentioned hereinbelow. The lamp voltage of the life ending lamp is higher than that of the normal lamp. As shown in
FIG. 3
, the lamp voltage is detected by lamp voltage detecting circuits
19
a,
19
b,
and
19
c.
The outputs of those detecting circuits are inputted to the comparator
20
. In the case where the detection value exceeds a predetermined threshold value
20
a,
the driver
3
is controlled by the operation of the control circuit
13
so that the inverting circuit
2
is protected. Such means has been known.
As for a protecting method, there are a method of stopping an oscillation of the driver
3
, a method of forcedly increasing an oscillation frequency of the driver
3
and decreasing both of an active component and a reactive component of the drain current (hereinafter, referred to as a “protection mode operation”) and the like. It is latched by the latch circuit
14
.
The operation of the lamp voltage detecting circuits
19
a
(similarly with regard to
19
b
and
19
c
) is performed in such a manner that the lamp voltage is divided by capacitors
21
and
22
, rectified by diodes
23
and
24
, and integrated by a resistor
25
and capacitor
26
, thereby obtaining a detection value.
As a result, if one lamp or more in the life ending state exist among the three lamps, the inverting circuit
2
is protected by the operation of the control circuit
13
.
However, in the foregoing conventional discharge lamp lighting apparatus, the lamp life ending detection has to be executed every lamp. Particularly, with regard to the apparatus having many lamps, it is a problem that the number of parts increases and costs increase.
In the case where a plurality of (for instance, three) lamps which are not detected in the life ending detection but the life state is slightly shortened (hereinbelow, referred to as a “half-life ending lamp”) are connected, a feedback is performed so that lamp currents are set to be constant in total. Consequently, the frequency is made high similar to the case where (for example, one) life ending lamp is mounted, and the burden of the inverting circuit is increased by the increase in the reactive current of the drain current, which causes another problem that the voltage that indicates life ending is not detected in any of the lamp voltage detecting circuit
19
a
to
19
c
to continue an ordinary operation despite of the operation state that is properly meant to be protected.
This invention is accomplished to solve the above mentioned problems. It is an object of the invention to provide a discharge lamp lighting apparatus in which the circuit can be protected from a life ending lamp without executing a life ending detection for each of lamps even if a plurality of lamps are mounted and the burden of the inverting circuit can certainly be detected and protected by detecting in total the states of lives of the plurality of lamps.
It is an object to provide a discharge lamp lighting apparatus in which in the case where the lamp is in the life ending state or the like, the protection mode operation can be performed with a simple construction.
DISCLOSURE OF INVENTION
A discharge lamp lighting apparatus according to this invention comprises: an inverting circuit for converting a DC input into a high frequency output; a load circuit which is connected to the inverting circuit and is constructed by a plurality of discharge lamps; a detecting resistor connected between a terminal of the inverting circuit and a ground; an integrating circuit for integrating a voltage generated in the detecting resistor; an operational amplifier which receives an output of the integrating circuit as a negative input, receives a predetermined target value as a positive input and performs an error amplification; a driver for controlling a switching frequency of the inverting circuit on the basis of an output of the operational amplifier; a frequency detecting comparator which inputs the output of the operational amplifier and whose output value is switched in the case where a frequency converted at an input value exceeds a predetermined value; a control circuit for switching an operating state of the driver depending on the output value of the frequency detecting comparator; and a latch circuit for holding the operating state switched by the control circuit in the case where the converted frequency exceeds the predetermined value.
In a discharge lamp lighting apparatus according to this invention, the control circuit has: an integrating circuit for a timer connected to an output terminal of the frequency detecting comparator; and a lighting sequence circuit connected between an output terminal of the integrating circuit for the timer and the driver, and when the output of the frequency detecting comparator is set to the low level, an output potential of the integrating circuit for t

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