JPH0148172B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to an indoor lighting device that blinks a room lamp, for example, a room lamp of an automobile, by a door switch. The present invention relates to a dimming-type indoor lighting device that gradually reduces the amount of light from a lamp and then turns off the lamp.

(Background of the Invention) In general, the interior lamp of a car is equipped with a door switch that turns on and off as the door opens and closes, so that the lamp is turned on when the door is opened and turned off when the door is closed. If you turn off the room lamp after a certain period of time rather than turning it off the moment the door closes, it would be convenient to prepare for exercise such as inserting the key and starting the engine. This may give the driver anxiety that the room lamp switch for turning on the room lamp may be left on (closed). A dimming room lamp, that is, a dimming type indoor lighting device, eliminates the above drawback by gradually dimming the room lamp after the door switch is turned off, and distinguishing it from lighting when the room lamp switch is turned on. .

By the way, as a conventional dimming type indoor lighting device,
A system has been put into practical use that blinks a room lamp at a frequency that does not cause flickering when the light is dimmed, and changes the duty ratio of this blinking so that the lighting period gradually becomes shorter. However, in this conventional example, an oscillation circuit for blinking and a circuit for changing the duty ratio are required, resulting in a complicated circuit configuration and an increase in the cost of the device. Other conventional examples include a room lamp, a door switch that turns on and off when the door is opened and closed, a CR time constant circuit that is reset when the door switch is on and operates when it is off, and an output of the CR time constant circuit. a drive circuit that drives the room lamp in response to the door switch, and lights the room lamp while the door switch is on;
It is also known that when the door switch is turned off, the current flowing through the room lamp is gradually reduced to gradually dim the room lamp and then turn it off (for example, Japanese Patent Laid-Open No. 57-167839). ).
However, in this conventional example, the drive circuit includes an inverting amplifier circuit that inverts the output of the CR time constant circuit, and a transistor that drives the room lamp according to the output of the inverting amplifier circuit. For this reason, the collector current of the transistor flows for a considerable time due to the CR charging characteristics, which not only makes the light from the room lamp dim and unsightly, but also increases the collector loss of the transistor, so a relatively large transistor must be used. However, this has the disadvantage of increasing costs.

(Object of the Invention) An object of the present invention is to provide a dimming indoor lighting device that has a simple circuit configuration and is inexpensive.

(Structure and Effects of the Invention) In order to achieve the above object, the present invention provides a CR time constant circuit that is reset when the door switch is turned on and operates when the door switch is turned off. The room lamp is driven by a switching circuit that gradually reduces the lamp current of this room lamp to dim the room lamp, and turns on when the lamp current falls below a predetermined current to form a positive feedback loop. It is characterized in that it is provided in the drive circuit, and when the lamp current becomes less than a predetermined current, the lamp current is quickly turned off by this positive feedback.

According to the present invention configured in this manner, a dimming lighting circuit having a relatively simple configuration consisting of a CR time constant circuit and a room lamp drive circuit is added to the conventional room lamp, and the current of the room lamp is further adjusted to a predetermined level. By simply adding a switching circuit that forms a positive feedback circuit including the room lamp drive circuit when the current becomes less than or equal to , an inexpensive dimming indoor lighting device can be provided. That is, according to the present invention, since an oscillation circuit and a circuit for changing the duty ratio are not required, the circuit configuration is simpler and cheaper than the first conventional example. Also, compared to the second conventional example, since the lamp current is turned off rapidly when it falls below a predetermined value, the amount of light is not only useless as it is too small, but it is even unsightly. This has the advantage that a certain weak lighting state is eliminated, the transistor can go through an operating region with large collector loss in a relatively short time, and a relatively small transistor can be used. Here, as shown in the embodiments described later, the switching circuit can have a simple configuration of, for example, one diode and one resistor.
By using small transistors, it is also possible to construct the device at a lower cost than the second conventional example.

(Description of Examples) Examples of the present invention will be described below with reference to the drawings.

FIG. 1 shows a circuit configuration of a dimming type indoor lighting device according to an embodiment of the present invention. In the figure, a door switch 1 is turned on (closed) and off (opened) as a door (not shown) opens and closes. The room lamp switch 2 consists of a 3-position switch, and when switched to the ON and OFF positions, the room lamp 3 turns on and off regardless of whether the door is opened or closed.
In the AUTO position, the light is turned on when the door is opened, that is, when the door switch 1 is turned on, and when the door is closed, the current flowing through the room lamp 3 is gradually reduced to gradually dim the room lamp 3, and then the light is turned off.

The door indicator 4 lights up when the door is opened, and notifies the driver that the door is open. Ignition switch 5
is a switch that closes when the ignition is turned on.
Reference numeral 6 designates a dimming circuit which is a feature of the present invention, and includes a time constant circuit 61 consisting of a resistor R3 and a capacitor C2, a drive circuit 62 including a transistor Q3 for driving the room lamp 3, and the like.

Next, the operation of the dimming indoor lighting device shown in FIG. 1 will be explained. In the following, it is assumed that the room lamp switch 2 is in the AUTO position.

When the door is opened, the door switch 1 closes, the door indicator 4 lights up, and the battery 7 switches the room lamp 3, the room lamp switch 2, and the resistor R.
1. A current flows through the diode D1 and the door switch 1, and the room lamp 3 is turned on. Further, the charge in the capacitor C2 of the time constant circuit 61 is discharged by the door switch 1 via the resistor R2 and the diode D3, and the time constant circuit 61 is reset.

Next, when the door is closed, voltage is applied from the battery 7 to the time constant circuit 61 and drive circuit 62 of the dimmer circuit 6 through the open door indicator 4 and the diode D2 of the dimmer circuit 6. Therefore, the capacitor C2 of the time constant circuit 61
is charged via resistor R3, and its terminal voltage V1
increases as shown in FIG. 2 with a time constant determined by the resistance value of resistor R3 and the capacitance of capacitor C2. The transistor Q1 and the resistor R5 constitute an emitter follower, and the output of the time constant circuit 61, that is, the terminal voltage V1 of the capacitor C2 (strictly speaking, higher than V1 by the emitter-base voltage V _BE of the transistor Q1) appears at the emitter of the transistor Q1. . At the moment the door closes, the voltage V1, that is, the transistor Q1
Since the emitter voltage of is approximately 0V, a base current is applied to transistor Q2 through resistors R7 and R6, and current flows from the collector of transistor Q2 to the base of transistor Q3 through resistor R9, turning on transistor Q3. Thus, the lighting state of the room lamp 3 is maintained. However, as voltage V1 increases, transistor Q
2 and Q3's base currents decrease. Therefore, the current flowing through the room lamp 3 through the collector of the transistor Q3 decreases, and the lamp 3 gradually becomes darker. Note that the collector voltage V2 of the transistor Q3 after the door is closed is shown in FIG. 2 together with the voltage V1.

FIG. 3 shows how the voltage of the room lamp 3 changes after the door is closed. Initially, the lamp voltage does not change because transistor Q3 is in a saturated state. If there is no diode D5, the lamp voltage will decrease as shown by the broken line, but if this continues, the voltage will decrease as in the case of the second conventional example.
Due to the charging characteristics of resistor R3 and capacitor C2, current flows through transistor Q3 for a fairly long time.
The room lamp 3 becomes a thin light that is unsightly, and the power loss of the transistor Q3 increases. Therefore, in this embodiment, the diode D
5 is provided, and the collector voltage V2 of the transistor Q3 is
When exceeds voltage V1, a positive feedback loop is formed that charges capacitor C2 from the collector of transistor Q3 via diode D5 and resistor R4,
Transistors Q1, Q2, and Q3 are turned off instantaneously. As a result, a lamp voltage, that is, a dimming curve as shown by the solid line in FIG. 3 can be obtained, which looks good and also reduces the loss of the transistor Q3.

The diode D4 is for immediately charging the capacitor C2 and turning off the room lamp 3 when the ignition switch 5 is turned on.

As described above, a dimming indoor lighting device can be realized with a relatively simple configuration. Furthermore, since all transistors Q1, Q2, and Q3 are turned off after the lamp is turned off, current consumption during parking can be extremely reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a dimming indoor lighting device according to an embodiment of the present invention, FIG. 2 is a graph showing the output voltage of the time constant circuit and the drive circuit with respect to the time after the door is closed, and FIG. FIG. 3 is a graph showing lamp voltage versus time after the door is closed. FIG. 1...Door switch, 3...Room lamp, 6
...Dimming circuit, 61...Time constant circuit, 62...Drive circuit, C2...Capacitor, Q1, Q2, Q3
...Transistor, D5...Diode.

Claims (1)

[Claims] 1. A room lamp, a door switch that turns on and off as the door opens and closes, a CR time constant circuit that is reset when the door switch is on and operates when the door switch is off, and a CR time constant circuit that operates according to the output of the CR time constant circuit. and a drive circuit for driving the room lamp, and lights the room lamp while the door switch is on, and gradually reduces the current flowing through the room lamp when the door switch is turned off. In a dimming indoor lighting device that gradually dims a room lamp and then turns it off, the driving circuit is turned on when the current flowing through the room lamp becomes less than a predetermined current, forming a positive feedback loop. A dimming indoor lighting device characterized by comprising a switching circuit that rapidly turns off the output of a drive circuit. 2. The drive circuit includes an inverting amplifier circuit that inverts the output of the CR time constant circuit, a transistor that drives the room lamp according to the output of the inverting amplifier circuit, and a collector-emitter voltage of the transistor that is set to a predetermined value. 2. The dimming type indoor lighting device according to claim 1, further comprising a diode as said switching circuit which is turned on when the voltage exceeds the threshold voltage, and feeds back the collector voltage of said transistor to the input side of said inverting amplifier circuit.