Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2003-01-13
2004-08-24
Lee, Wilson (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S224000, C353S031000
Reexamination Certificate
active
06781328
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image display apparatus and a method for operating the same, and a lamp unit for an image display apparatus. In particular, the present invention relates to an image display apparatus, such as a liquid crystal projector, provided with a lamp unit including a high-pressure mercury lamp or a metal halide lamp and a discharge lamp ballast circuit for operating the lamp, and a method for operating the same.
Image display apparatuses such as liquid crystal projector devices are known as means for projecting magnified images of characters, graphics and the like and displaying them. Since such image display apparatuses (or image projection apparatuses) require a predetermined optical output, high-pressure mercury lamps with high brightness are, in general, used widely as light sources. Moreover, as projectors become widespread, there is a growing demand for a brighter and smaller projector.
FIG. 10
schematically shows a cross-sectional structure of a conventional lamp unit
1000
having a high-pressure discharge lamp
101
used for projectors.
The high-pressure discharge lamp
101
shown in
FIG. 10
is a high-pressure mercury lamp of alternating current operation type that operates with alternating current. A sealed portion of the lamp
101
is inserted into a neck
1011
a
of a reflecting mirror
1011
, where it is secured with cement and the like. This lamp
101
provided with the reflecting mirror
1011
is housed in a lamp housing
1013
, and thus the lamp unit
1000
is constituted.
A pin
311
that serves as a connector is provided in the lamp unit
1000
, and the lamp
101
is connected to this pin
311
via cables (leads)
321
.
FIG. 11A
is a perspective view schematically showing the lamp unit
1000
, and
FIG. 11B
is a partially cutaway perspective view schematically showing a projector main body
1100
in which the lamp unit
1000
is to be set.
The lamp unit
1000
can be detached from the projector main body
1100
, as shown in FIG.
11
B. To achieve such a removable structure, a plug
310
corresponding to the pin
311
provided in the lamp unit
1000
is provided in the main body
1100
, and the pin
311
is provided in the lamp unit
1000
. The plug
310
and the pin
311
are interchangeable, and the pin can be provided in the main body
1100
and the plug can be provided in the lamp unit
1000
.
When the lamp unit
1000
is set in the main body
1100
, the pin
311
is coupled to the plug
310
. The plug
310
is electrically connected to a ballast circuit (not shown) provided in the main body
1100
, and the ballast circuit starts and operates the lamp
101
in the lamp unit
1000
. When the lamp unit
1000
is set in the main body
1100
, a cooling fan
1104
is situated behind the lamp unit
1000
and a cover
1106
is mounted over the lamp unit
1000
. Moreover, an optical system using the lamp
101
as a light source and a system (main system) for controlling the optical system to display images are provided in the main body
1100
, and light emitted from the lamp
101
goes through the optical system and a projection lens
1105
to be projected on a screen, where an image is formed.
Next, the circuit structure of a ballast circuit
102
provided in the main body
1100
will be described with reference to
FIGS. 12 through 14
.
As shown in
FIG. 12
, the ballast circuit
102
for starting and operating the lamp
101
includes a direct current power
103
, a full-bridge inverter circuit
104
, which is an inverter circuit, and a start circuit
105
. As described above, the ballast circuit
102
is electrically connected to the plug
310
that is provided in the main body
1100
side, and the plug
310
is connected to the full-bridge inverter circuit
104
and the start circuit
105
with high withstand voltage cables
320
.
When the lamp unit
1000
is set, the pin
311
is inserted in the plug
310
, and the lamp
101
is connected to the pin
311
via the cables
321
. The lamp
101
is designed such that the lamp voltage during operation is lower than the maximum output voltage of the direct current power
103
. For example, in the case where the maximum output voltage of the direct current power
103
is about 370V, the maximum lamp voltage is about 50V to 250V.
The direct current power
103
is constituted by a step-down chopper circuit that outputs, for example, direct current of a maximum of about 370V in response to an input of direct current of about 370V. The step-down chopper circuit includes a control circuit
115
and a switching element (e.g., transistor, FET, or GTIB)
108
. The step-down chopper circuit detects an output voltage with resistors
112
and
113
and an output current with a resister
114
, calculates two detection signals with the control circuit
115
, and controls on-off of the switching element
108
by an output signal of the control circuit
115
such that the output power of the step-down chopper circuit becomes a predetermined value. Usually, an electrolytic capacitor
111
for smoothing voltage having a relatively large capacitance is connected in parallel to the output terminals of the direct current power
103
. In the case where alternating current is input, a rectifying and smoothing circuit for rectifying and smoothing the alternating current input and converting it to direct current is added in a previous stage of the step-down chopper circuit.
The full-bridge inverter circuit
104
is constituted by transistors
117
,
118
,
119
and
120
and a drive circuit
121
, as shown in FIG.
13
. In the full-bridge inverter circuit
104
, the transistors
117
and
120
and the transistors
118
and
119
are alternately turned on and off by output signals of the drive circuit
121
, and thus the output of the step-down chopper circuit is converted to alternating current.
One terminal A of the full-bridge inverter circuit
104
is connected to one terminal TB of a secondary coil (output side coil) constituting the transformer of the start circuit
105
(see
FIG. 14
) described below, whereas the other terminal B is connected to one end of the lamp via the plug
310
and the pin
311
. Moreover, a capacitor
300
is connected in parallel to the both output terminals of the inverter, and this capacitor
300
serves to bypass a high voltage pulse generated in the start circuit
105
.
The start circuit
105
is a circuit that generates a high voltage pulse for starting the high-pressure mercury lamp
101
. As shown in
FIG. 14
, the start circuit
105
includes a transformer
208
, a resistor
201
, a diode
205
, a capacitor
206
and a discharge gap
207
. Its input terminals are connected to the output terminals of the direct current power
103
, and one terminal Tb of the output terminals is connected to the output terminal A of the inverter, and the other terminal Ta is connected to one end of the lamp
101
via the plug
310
and the pin
311
, as described above.
The discharge gap
207
has the characteristics that it starts discharge at a voltage that is slightly lower than the output voltage of the direct current power
103
and is higher than the voltage of the lamp in operation (for example, about 350 V), and does not effect discharge (or stops discharge) at a voltage lower than that. Also, the discharge gap
207
has the characteristics that when a pulse voltage of about 350 V (peak value) is applied to a primary coil of the transformer
208
, it outputs the high pulse voltage having a peak value of about 10 kV to 15 kV across both the terminals Ta and The of the secondary coil. In such a transformer
208
for generating a high voltage, the primary coil and the secondary coil are wound around cores (e.g., ferrite cores) having a high magnetization capability (not shown).
In addition to this, a timer circuit (not shown) is incorporated in the ballast circuit
102
, and the timer circuit has the function of counting the time since the ballast circuit starts operating, and forcefully stopping the operation of the ballast circuit
102
when the lamp
Horiuchi Makoto
Ichibakase Tsuyoshi
Seki Tomoyuki
Alemu Ephrem
Lee Wilson
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