JPH0225701Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an illuminance adjustment device for an illumination lamp provided in an automobile instrument panel.

(Prior art) Automobile instrument panels are equipped with lighting lamps, but if the light is too strong when the lamps are turned on, it becomes dazzling and makes it difficult to see the instrument panel. In some cases, the illuminance of the lamp can be adjusted. An example of such a device is an illuminance adjustment device for an interior lamp of an automobile, which is disclosed in Japanese Utility Model Application Publication No. 52-8848. This is possible by connecting a lamp via an output transistor as a switching element to a multivibrator circuit that repeatedly generates a rectangular wave signal, and by changing the resistance value of a variable resistor provided in the multivibrator circuit. The lamp's duty ratio, that is, the ratio of ON time in one cycle, can be changed, and with this, the illuminance of the lamp can be adjusted arbitrarily without generating heat in the device itself.

However, in the case of the above-mentioned illuminance control device, when the switch is turned on to light the lamp, a large current (rush current) momentarily flows through the circuit, and this current destroys the output transistor. There is a possibility that To solve this problem, for example, as shown in FIG.
There is a way to suppress the rush current that flows to the output transistor D when the switch C is turned on by preheating the filament and increasing its resistance value, but in this case, the current is constantly allowed to flow as described above. Therefore, power loss increases when the lamp is not lit, which may lead to battery drain or the like. Also, as shown in Fig. 5, a resistor G is inserted between the output transistor E and the lamp F...F, and this resistor G
It is conceivable to limit the lash current when the switch H is turned on, but this has the drawback that the voltage drop occurs due to the resistor G, and the lamps F...F become dark.

(Purpose of the invention) The present invention addresses the above-mentioned actual situation regarding the illuminance adjustment device of an automobile instrument panel. The object of the present invention is to prevent the switching element from being destroyed by the lash current without causing problems such as power loss.

(Structure of the invention) That is, the illuminance adjustment device according to the invention includes: an illumination adjustment circuit that is connected to a power source via a disconnect/disconnect switch to generate a rectangular wave signal and to vary the duty ratio of the rectangular wave; In a configuration including a switching element that receives a rectangular wave signal from an illumination adjustment circuit and supplies current to a light emitting element of an automobile instrument panel, a bypass circuit that bypasses the switching element is provided between the above-mentioned disconnection switch and the light emitting element. It is characterized by having been provided. This bypass circuit functions to bypass the switching element and supply power to the light emitting element when the above-mentioned disconnection switch is turned on, and also to supply power to the light emitting element via the switching element after a predetermined time has elapsed. This prevents a large lash current from temporarily flowing through the switching element when the disconnect/disconnect switch is turned on.

(Example) Examples of the present invention will be described below.

As shown in FIG. 1, an illumination adjustment device 1 for an automobile instrument panel includes an illumination adjustment circuit 4 connected to a power source 2 via a disconnection switch 3, and an illumination adjustment circuit 4 connected to the output side of this illumination adjustment circuit 4. It has an output transistor 6 as a switching element that receives a signal from the circuit 4 and supplies current to the lamps 5 . . . 5 of the instrument panel.

The illuminance adjustment circuit 4 includes a duty control section 4a.
The duty control section 4a includes a first amplifier 10 in which a variable resistor 7, a capacitor 8, and a first transistor 9 are combined, and a variable resistor 7 and a capacitor 11.
and the second transistor 12 are coupled to each other.
and an amplifier 13, and the respective output sides and input sides of both amplifiers 10 and 13 are connected to each other, forming an astable multivibrator circuit that generates a rectangular wave signal a as shown in FIG. . By changing the resistance value of the variable resistor 7, the duty ratio of the rectangular wave signal a, that is, with respect to the period _T1 , can be changed.
It is now possible to change the ratio of ON time _T2 . Further, the drive section 4b is equipped with a third transistor 15 connected to the output terminal 14 of the duty control section 4a, which receives the output signal a from the control section 4a and amplifies it. The output transistor 6 is driven by the amplified signal b. In that case, since the capacitor 16 is provided between the base and collector of the third transistor 15, the waveform of the signal b which is inverted from the signal a and input to the output transistor 6 as shown in FIG. In other words, the rising and falling parts of the signal b are slightly distorted to prevent noise from being generated in other electrical equipment such as a radio.

However, this illuminance adjustment device 1 is provided with a bypass circuit 17 that temporarily bypasses the output transistor 6 and supplies the current from the power source 2 to the lamps 5...5 when the disconnection switch 3 is turned on. . This bypass circuit 17 is connected to the disconnection switch 3
Diode 18 and resistor 1 provided in parallel on the side
9 and a capacitor 20 provided in series with these on the side of the lamps 5...5 is connected between the emitter and collector of the output transistor 6.

According to such a configuration, the disconnection switch 3
When turned on, first from power supply 2 to bypass circuit 17.
A current I ₁ flows through the lamps 5 . . . 5 through the diode 18 and capacitor 20 in the lamps 5 , . . . , so that the lamps ₅ . At this time, it is conceivable that a current _I2 flows through the output transistor 6, but since the capacitor 20 is in a discharged state before the switch 3 is turned on, the current supplied to the lamps 5...5 is Mainly only the current _I1 . This causes lamp 5
... 5 is turned on, a large rush current is prevented from momentarily flowing into the output transistor 6,
As a result, there is no possibility that the transistor 6 would be destroyed by the rush current.

Further, after the capacitor 20 in the bypass circuit 17 is sufficiently charged as described above, the current I ₁ for charging the capacitor 20 stops flowing, so that the current I 1 for charging the capacitor 20 stops flowing, and therefore the lamp 5... A current _I2 flows through the lamps 5, and the lamps 5...5 are lit by this current _I2 . In that case, the output transistor 6 is driven by the output signal b (see FIG. 2) from the illumination adjustment circuit 4 so that it is OFF when the signal is ON, and is ON when it is OFF, so that the output of the transistor 6 is As shown in FIG. 2, the voltage waveform of the signal c has a substantially rectangular waveform that is inverted and corresponds to the voltage waveform of the output signal b from the illuminance adjustment circuit 4. Therefore, by changing the resistance value of the variable resistor 7 in the duty control section 4a of the illuminance adjustment circuit 4, that is, the time constant of the multivibrator, and changing the duty ratio of the output signal a, the output signal a is transmitted through the output transistor 6 to the lamp 5. ...current supplied to 5 I ₂
Figure 3 shows the ON/OFF time ratio of (signal c)
The lamps 5...5 change accordingly.
The illuminance will also change. That is, in the case of FIG. 3, it is bright, and as shown in the same figure, it becomes darker.

The charge stored in the capacitor 20 of the bypass circuit 17 is discharged through the resistor 19 as shown by the current I ₃ when the disconnection switch 3 is turned off, and is stored in preparation for the next time the disconnection switch 3 is turned on. It will be done.

(Effects of the invention) As described above, according to the invention, the illuminance of the lamp for illuminating the instrument panel of an automobile can be arbitrarily adjusted, and the lamp is equipped with a switching element such as a transistor that supplies current to the lamp. In the illuminance adjustment device using the above-described method, when the switch is turned on, a large lash current is prevented from momentarily flowing to the switching element, and as a result, problems such as destruction of the switching element by the lash current are avoided. will be done.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the present invention, FIG. 1 is an electric circuit diagram showing the configuration of an illuminance adjustment device according to the embodiment, and FIGS. 2 to 3 show duty control in the illumination adjustment device. FIGS. 3A and 3B are waveform diagrams showing the waveforms of the output signals of the output transistor, the drive unit, and the output transistor, respectively. FIGS. Further, FIGS. 4 and 5 are schematic circuit diagrams showing known examples of the lash current prevention circuit, respectively. DESCRIPTION OF SYMBOLS 1... Illuminance adjustment device, 2... Power supply, 3... Disconnection switch, 4... Illuminance adjustment circuit, 5... Light emitting element (lamp), 6... Switching element (output transistor), 17... Bypass circuit .

Claims (1)

[Scope of utility model registration request] An illuminance control circuit that is connected to a power supply via a disconnect/disconnect switch to generate a square wave signal and to make the duty ratio of the rectangular wave variable; a switching element that supplies current to the light emitting element; and a bypass circuit that bypasses the switching element to light the light emitting element when the disconnection switch is turned on, and lights the light emitting element via the switching element after a predetermined period of time. An illuminance adjustment device for an automobile instrument panel, characterized in that it is equipped with the following.