Dimmer for vehicle use

Details Dimmer for vehicle use Dimmer for vehicle use

2003-03-25

2004-07-27

Le, Hoanganh (Department: 2821)

Electric lamp and discharge devices: systems

Special application

Vehicle

C315S080000, C315S178000

Reexamination Certificate

active

06768268

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dimmer for vehicle use that is used for controlling illumination of a display panel or an operation panel of a vehicle.
2. Background Art
Recently, a dimmer for vehicle use that adjusts brightness of instruments and switches of a vehicle so that a driver easily looks at them in the nighttime or during running through a tunnel becomes widespread. The instruments include a speed meter and the like disposed in an instrument panel, and the switches include an air conditioner switch and a hazard switch.
Such a conventional dimmer for vehicle use is described with reference to
FIG. 3
,
FIG. 4A
,
FIG. 4B
, and FIG.
4
C.
FIG. 3
is a circuit diagram of the conventional dimmer for vehicle use. In
FIG. 3
, conventional dimmer
16
includes the following elements:
oscillating circuit
1
for outputting voltage having a predetermined substantially triangular waveform,
comparing circuits
2
for outputting voltage having a predetermined substantially rectangular waveform based on the voltage having the substantially triangular waveform supplied from oscillating circuit
1
, and
driving circuits
3
for performing so-called duty controlling, namely controlling timing of turning on or off power supply to a light emitting part such as lamp
14
or light emitting diode
15
in response to the substantially rectangular voltage from respective comparing circuits
2
.
In oscillating circuit
1
, power supply terminal
4
is grounded through resistor
5
and resistor
6
in series, and junction point
5
A between resistor
5
and resistor
6
is coupled to non-inversion input part
7
A of amplifier
7
.
Output part
7
C of amplifier
7
is coupled to non-inversion input part
7
A through feedback resistor
8
and is grounded through resistor
9
and capacitor
10
in series.
Junction point
10
A between resistor
9
and capacitor
10
is coupled to inversion input part
7
B of amplifier
7
in oscillating circuit
1
, and is coupled to each comparing circuit
2
.
Junction point
10
A of oscillating circuit
1
is coupled to inversion input part
11
B of amplifier
11
of each comparing circuit
2
. In each comparing circuit
2
, an output terminal of variable resistor
12
coupled between power supply terminal
4
and the ground is coupled to non-inversion input part
11
A, and output part
11
C of amplifier
11
is coupled to each driving circuit
3
.
Lamp
14
or light emitting diode
15
coupled to power supply terminal
13
for a light emitting part is coupled to each driving circuit
3
including a transistor or the like (not shown). Dimmer
16
for vehicle use has a circuitry discussed above.
In dimmer
16
having the circuitry, for example, when a switch (not shown) for a headlight is turned on to supply power from power supply terminal
4
to non-inversion input part
7
A of amplifier
7
through resistor
5
, amplifier
7
comes into a high output state and outputs a voltage of, for example about 7V, from output part
7
C. Then, current flows to capacitor
10
through resistor
9
of amplifier
7
to charge capacitor
10
.
The voltage then rises from point A to point B in a substantially triangular waveform shown in the output waveform graph of
FIG. 4A
, and the rising voltage is supplied to inversion input part
7
B of amplifier
7
.
While, the current from output part
7
C of amplifier
7
flows through feedback resistor
8
and resistor
6
. The non-inversion input voltage of non-inversion input part
7
A reaches VH due to feedback resistor
8
, resistor
5
, and resistor
6
, based on the output voltage of power supply terminal
4
and the high output voltage of output part
7
C. Here, VH is indicated by an alternate long and short dash line in the top part of FIG.
4
A.
When the high output voltage of output part
7
C results in charging of capacitor
10
through resistor
9
and the voltage of inversion input part
7
B reaches point B of non-inversion input voltage VH, amplifier
7
is inverted to a low output state.
At this time, output part
7
C after the inversion to the low output state outputs a low voltage of about 0.6 V. Capacitor
10
thus discharges, current flows to output part
7
C of amplifier
7
through resistor
9
, and the output voltage decreases from point B to point C as shown in FIG.
4
A.
At this time, current flows also from power supply terminal
4
to output part
7
C of amplifier
7
through resistor
5
and feedback resistor
8
. The non-inversion input voltage of non-inversion input part
7
A reaches VL due to feedback resistor
8
, resistor
6
, and resistor
5
, based on the output voltage of power supply terminal
4
and the low output voltage of output part
7
C. Here, VL is indicated by an alternate long and short dash line in the bottom part of FIG.
4
A.
When the voltage of capacitor
10
fed into inversion input part
7
B decreases to voltage VL, amplifier
7
is inverted to the high output state and current flows from output part
7
C of amplifier
7
to capacitor
10
to charge capacitor
10
again. Voltage having the substantially triangular waveform is therefore generated repeatedly at the same cycle and supplied from oscillating circuit
1
to each comparing circuit
2
, as shown by the solid line of FIG.
4
A.
In each comparing circuit
2
, the voltage having the substantially triangular waveform fed into inversion input part
11
B of amplifier
11
is compared with a comparison voltage that is set by operation of variable resistor
12
and fed into non-inversion input part
11
A.
The set comparison voltage is assumed to be VS indicated by the solid line of
FIG. 4A
, for example. When the voltage having the substantially triangular waveform is higher than VS, output part
11
C of amplifier
11
outputs a low voltage for period T
1
as shown in FIG.
4
B. When the voltage having the substantially triangular waveform is lower than VS, output part
11
C outputs a high voltage for period T
2
. Voltage having a substantially rectangular waveform is supplied from each comparing circuit
2
in response to repeating of the voltage having the substantially triangular waveform as shown in FIG.
4
B.
The voltage having the substantially rectangular waveform supplied from each comparing circuit
2
is then fed into each driving circuit
3
, and power supply to lamp
14
or light emitting diode
15
is turned on or off in response to this voltage and timing.
For example, power is supplied at the duty ratio of OFF period T
1
to ON period T
2
to turn on lamp
14
or light emitting diode
15
.
When the comparison voltage supplied to non-inversion input part
11
A of amplifier
11
is changed by variable resistor
12
, the period ratio of the low voltage to high voltage of the substantially rectangular voltage supplied from output part
11
C of amplifier
11
changes in response to the set comparison voltage. The duty ratio in the power supply to lamp
14
or light emitting diode
15
therefore changes, so that brightness of lamp
14
or light emitting diode
15
changes to allow dimming.
When the comparison voltage is closed to non-inversion input voltage VH by variable resistor
12
in the conventional dimmer, the duty ratio of ON to OFF is increased to make lamp
14
or light emitting diode
15
bright. When the voltage is closed to voltage VL, the duty ratio of ON to OFF is decreased to make them dark.
In the conventional dimmer, amplifier
7
of oscillating circuit
1
is made of a semiconductor. The semiconductor generally has a negative temperature characteristic in which decreasing temperature promotes voltage drop, and thus the low output voltage of amplifier
7
rises at a low temperature, for example, in the winter season or when it is cold in the vehicle.
When the current flows to output part
7
C of amplifier
7
through feedback resistor
8
, the voltage variation of the low output also affects the non-inversion input voltage. For example, non-inversion input voltage VL rises to VL
1
as shown by the substantially triangular waveform indicated by t

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