Electric lamp and discharge devices: systems – Current and/or voltage regulation – Automatic regulation
Reexamination Certificate
2003-05-23
2004-11-09
Tran, Thuy Vinh (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
Automatic regulation
C315S306000
Reexamination Certificate
active
06815911
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control method of a light source unit comprising a filament lamp, a light source control unit and a light source unit, and more particularly, to a control method of a light source unit comprising a filament lamp with a characteristic of having a light quantity changing almost in proportion to a control voltage, and a light source control unit, and a light source unit.
2. Description of the Related Art
As a light source unit where the illuminance of the filament lamp is changed, it is a commonly used method to employ a voltage stabilizer in the light source unit comprising a filament lamp.
FIG. 2
shows the simplest method in which a control voltage 15 Vc changes an applied voltage 7V of the lamp so that a luminous flux 10 Lm of the filament lamp is changed.
Continuing with
FIG. 2
, the voltage 7V applied to the lamp is proportionate to the voltage of the control voltage 15 Vc, and the voltage applied to the lamp at the maximum control voltage is set in such a manner that it becomes a rated voltage of the lamp. Although such a light source unit is priced moderately, it has a drawback in that an illuminance Lx of the lamp for the control voltage 15 Vc is nonlinear with the light quantity thereof changed exponentially as shown in the drawing, and a fine adjustment of setting it to a predetermined light quantity is difficult to perform.
On the other hand, in order to change the illuminance of this lamp in proportion to the control voltage, there are two methods conceivable. One method is to turn an inverse transformation corresponding to the nonlinearity of the light quantity for the control voltage into the control voltage. The other method is to feed back the light quantity and make a monitor light proportionate to the control voltage. These methods, however, make the units complicated, thereby making it difficult to manufacture the control units at a moderate price.
SUMMARY OF THE INVENTION
The present invention is to establish a power source control method of a light source in which the light quantity of the lamp is put into a proportional relationship with the control voltage, and to provide a light source control method particularly easy to adjust and available at a low price, and the control unit and light source unit thereof.
Shown in
FIG. 4
is a basic block diagram for explaining a basic principle of the present invention.
The diagram is constituted by a first control voltage 1V
1
, a square root circuit
2
for converting the first control voltage to a square root, a second control voltage 3V
2
which is an output voltage of the square root circuit, and a constant electric power source unit
16
which supplies an electric power proportionate to the second control voltage V
2
to a filament lamp
9
. By this constitution, it is possible to allow the luminous flux 10 Lm of the lamp to be proportionate to the first control voltage 1V
1
.
Assuming that the rated voltage, rated electric power and rated luminous flux of the lamp are generally taken as V
o
, W
o
, and Lm
o
, respectively, the power consumption W and the luminous flux Lm for the applied voltage V of the filament lamp are represented by:
W
W
o
=
[
V
V
o
]
1.54
,
L
m
L
m
o
=
[
V
V
o
]
3.19
(
1
)
When a voltage ratio of the lamp is deleted from both equations of the equation (1), the following equations are given:
L
m
L
m
o
=
[
W
W
o
]
2.07
(
2.
a
)
≈
[
W
W
o
]
2
(
2.
b
)
and a luminous flux ratio of the lamp for a rated value becomes a value close to the second power of an electric power ratio consumed by the lamp.
FIG. 5
shows a relationship of the square of the power consumption and an illuminance, and shows a measurement data by a halogen lamp having the electric power of a rated 150 W where the square of the power consumption of the lamp is shown in the axis of abscissas and the illuminance Lx of the lamp is shown in the axis of ordinate. A solid line denotes an actual measurement value, and a dotted line denotes a theoretical value of the equation (2.b). Continuing with
FIG. 5
, the closer an approximate equation of the equation (2.b) is to a straight line of the broken line, the more faithfully it reproduces an emission characteristic of the light of the lamp. It is conceivable from the graph of
FIG. 5
that even when the emission characteristic of the lamp is represented by the approximate equation of the dotted line of the equation (2.b), though there arise a few errors, it is still endurable for a practical use.
A basic principle and means capable of lightening the filament lamp in proportionate to the control voltage will be described with reference to
FIG. 4
by using the emission characteristic of the physical light of the filament lamp (the luminous flux is proportionate to the square of the power consumption) and an electronic circuit of the conventional art.
In the constant electric power source unit
16
shown in
FIG. 4
, the second control voltage 3V
2
corresponding to the rated electric power W
o
of the lamp is taken as V
2
f, and the power supply is taken as zero when the second control voltage 3V
2
is zero. This constant electric power source unit
16
is proportionate to the second control voltage 3V
2
and supplies the electric power to the lamp. Hence, when the equation (2.a) is represented by the second control voltage 3V
2
, the following equation is given:
L
m
=
L
m
o
×
[
V
2
V
2
f
]
2.07
≈
L
m
o
×
[
V
2
V
2
f
]
2
,
0
≤
V
2
≤
V
2
f
(
3
)
Continuing with
FIG. 4
, reference numeral
2
denotes a square root circuit, which takes the square root of the first control voltage 1V
1
and outputs it as V
2
. Here, assuming that the maximum value of the second control voltage 3V
2
is taken as V
2f
, when the first control voltage 1V
1
at that time is taken as V
1f
, the relationship thereof is established as follows:
V
2
=a·{square root over (V)}
1
, V
2f
=a·{square root over (V
1f
)}
(4)
Hence, when the equation (4) is substituted for the equation (3), and the equation (3) is represented by the first control voltage 1V
1
, the following equation is given:
L
m
=
L
m
o
×
[
V
1
V
1
f
]
1.035
≈
L
m
o
×
V
1
V
1
f
,
0
≤
V
1
≤
V
1
f
(
5
)
Hence, when the lamp is driven by the circuit constitution of the block diagram shown in
FIG. 4
, the luminous flux 10 Lm of the lamp is almost proportionate to the change in the first control voltage 1V
1
.
From the above explanation, it is apparent that by combining the square root circuit
2
and the constant electric power source unit
16
similarly to the block diagram shown in
FIG. 4
, the filament lamp can be lighted so that the luminous flux 10 Lm of the filament lamp is proportionate to the first control voltage 1V
1
because of physical properties of the light emission characteristic of the filament lamp.
In the filament lamp light quantity control method of controlling the light quantity of the filament lamp, the present invention is characterized by comprising a current detection sensor connected in series to the filament lamp having a characteristic in which a change in the light quantity of the lamp is almost proportionate to the square of the power consumption, a multiplication circuit for generating a voltage V
w
proportionate to the product of a terminal voltage of the filament lamp and an output voltage V
i
of the current detection sensor, a square root circuit for generating a voltage V
2
proportionate to the square root of the control voltage V
1
, an error amplifier circuit for controlling an error to the minimum by comparing the output voltage V
w
of the multiplication circuit and the output voltage V
2
of the square root circuit, and an constant voltage source unit for supplying an electric power to the filament lamp,
Knobbe Martens Olson & Bear LLP
Sumita Optical Glass Inc.
Tran Thuy Vinh
LandOfFree
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