JPH0685358B2 - Lamp light intensity control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light amount adjusting device for adjusting the brightness of, for example, a lamp for an instrument panel lighting of an automobile.

(Prior Art) As a light amount adjusting device used for adjusting the light amount of a lamp for lighting an instrument panel of an automobile, a lamp driving circuit and a lamp driving circuit have recently been used instead of a device using a variable resistance for electric power. A pulse oscillator having a variable duty ratio for generating an input signal to the circuit is used, and this device adjusts the light quantity by changing the duty ratio of the pulse.

By the way, when an incandescent lamp is used as a lamp, a large inrush current flows immediately after lighting, for example, as indicated by the chain double-dashed line in FIG. In order to prevent the drive element from being destroyed, the capacity of the transistor etc.
It is often much larger than the required capacity during lighting.

(Problems to be Solved by the Invention) The method of increasing the capacitance of a driving element such as a transistor to prevent destruction due to an inrush current has a drawback that a required space becomes large and a cost increases.

The present invention aims to solve such problems.

(Means for Solving the Problems) A means for solving the above problems will be described with reference to the drawings corresponding to the embodiments. A light quantity adjusting device for a lamp according to the present invention includes a lamp driving circuit 1 and Variable duty ratio pulse generator 2 for generating input signal of lamp drive circuit 1
In the light quantity adjusting device, the pulse oscillator 2 is configured to supply power from the DC power supply 3 through the power cutoff circuit 6 controlled by charging / discharging the capacitor C1, and the power cutoff circuit 6 supplies the power to the capacitor C1. In the discharging state, it is turned off to cut off the current from the DC power supply 3, and in the charging state.
In addition to being turned on, the current is continuously controlled between ON and OFF.

In the above configuration, the power supply cutoff circuit 6 can be constructed by connecting the control capacitor C1 between the emitter and the base of the transistor Q4 that constitutes the base-grounded transistor switch circuit. Then, in parallel with the bias resistor R6 between the base of the transistor Q4 and the negative electrode side of the DC power source 3, a diode D having a reverse polarity with respect to the DC power source 3 is provided.
Can be provided.

(Operation) When the lighting operation switch 4 is turned ON in the above configuration,
A predetermined power supply voltage is applied to the lamp drive circuit 1 and the power cutoff circuit 6. Thus, when the power supply voltage is applied to the power cutoff circuit 6, the capacitor C1 is in a discharged state, so that the power cutoff circuit 6 maintains the OFF state and cuts off the current from the DC power supply 4. . Therefore, the power source voltage is not applied to the pulse oscillator 2. When the power supply voltage is applied to the power cutoff circuit 6, electric charge is gradually accumulated in the capacitor C1 and charging proceeds, so that the current flowing through the power cutoff circuit 6 gradually increases and the power supply voltage of the pulse oscillator 2 also gradually increases. To do. Therefore, the pulse output voltage of the pulse oscillator 2 and the input signal current of the lamp drive circuit 1 also gradually increase.

Therefore, the transistor Q1 or the like as the drive element of the lamp drive circuit 1 initially operates in the active region according to the input signal current to limit the output current, and subsequently the output current also rises as the input signal current rises. I will do it. For this reason,
The rush current flowing in the lamp 5 immediately after lighting can be suppressed as indicated by the solid line in FIG. 2, for example.

When the capacitor C1 reaches a predetermined charging state after a predetermined time elapses in this way, the power cutoff circuit 6 is turned on, and a predetermined power supply voltage is applied to the pulse oscillator 2, so that the pulse oscillator 2 operates in a predetermined state. The pulse output voltage is generated to bring the lamp drive circuit 1 into a normal operating state and the lamp 5 into a normal lighting state.

Next, when the lighting operation switch 4 is turned off and the supply of the power supply voltage is stopped, the electric charge accumulated in the capacitor C1 of the power cutoff circuit 6 is gradually discharged, and after a predetermined time elapses, a predetermined discharge state is established, To prepare for the lighting operation.

The power cutoff circuit 6 can be constructed by connecting a control capacitor C1 between the emitter and the base of the transistor Q4 that constitutes the base-grounded transistor switch circuit. If a diode D having a polarity opposite to that of the DC power supply 3 is provided in parallel with the bias resistor R6 between the base of the transistor Q4 and the negative side of the DC power supply 3, the above-mentioned capacitor C1 when the lamp 5 is turned off is provided. Can be discharged in a shorter time, and the above-described inrush current can be surely suppressed even when the time interval between the light-off operation and the lighting operation is relatively short.

(Example) Next, the Example of this invention is described about figures.

FIG. 1 is a circuit diagram showing an example of the overall configuration of the present invention. Reference numeral 1 is a lamp driving circuit, 2 is a pulse oscillator with a variable duty ratio for generating an input signal of the lamp driving circuit, 3 is a DC power supply, and 4 is a DC power source. Is a lighting operation switch, and 5 is a lamp of an incandescent bulb. Reference numeral 6 is a power cutoff circuit 6 which is controlled by charging and discharging the capacitor C1. The power cutoff circuit 6 is interposed between the DC power supply 3 and the pulse oscillator 2 to supply a power supply voltage to the pulse oscillator 2. I am trying. The power cutoff circuit 6 turns off in the discharging state of the capacitor C1, cuts off the current from the DC power supply 3, turns on in the charging state, and continuously controls the current between ON and OFF. It is configured to do.

In this embodiment, first, the lamp drive circuit 1 is configured as a grounded-emitter transistor switch circuit,
The base of the transistor Q1 is connected to the output section 7 of the pulse oscillator 2 via the current limiting resistor R1, and the lamp 5 is connected via the lighting operation switch 4 between the collector and the positive electrode side of the DC power supply 3. Are connected.

Further, the pulse oscillator 2 is configured by using an astable multivibrator whose duty ratio is adjustable. That is, the pulse oscillator 2 is configured by connecting a pair of transistor switch circuits to each other from the output side to the input side through a CR coupling circuit to form an astable multivibrator.
The resistance of the CR coupling circuit is such that the sliding variable resistance VR is connected between the bases of the respective transistors Q2 and Q3 of the pair of transistor switch circuits, and the slider 8 side is connected to the power source 3 via the resistance R2. It is connected to the negative electrode side. The output of the transistor switch circuit on the right side of the figure is the pulse oscillator 2
Of the lamp driving circuit 1 and is connected to the current limiting resistor R1 of the lamp driving circuit 1.

In the above configuration, when the transistors Q2 and Q3 are alternately turned on and off repeatedly, the transistor Q2 on the right side in the figure
At the time of N, the transistor Q1 of the lamp drive circuit 1 is turned on, and the drive current flows through the lamp 5.
The -OFF time ratio can be adjusted by moving the slider 8 of the variable resistance VR. That is, for example, if the slider 8 is moved to the left in the figure, the CR on the base side of the transistor Q2 on the right side in the figure is
At the same time as the time constant of the coupling circuit decreases, the time constant of the CR coupling circuit on the base side of the transistor Q3 on the left side in the figure increases, so the ON time of the transistor Q2 on the right side in the figure increases and the output section 7 The ON-OFF time ratio and the ON-OFF time ratio of the lamp drive circuit 1 are also increased, so that the effective current flowing through the lamp 5 is increased and the lamp 5 is adjusted in the bright direction. When the slider 8 is moved to the right in the figure contrary to the above, the effective current flowing through the lamp 5 is reduced by the operation opposite to that described above, and the lamp 5 is adjusted in the dark direction. Symbols R3 and R4 are load resistance, C
2 and C3 are capacitors that form the CR coupling circuit.

Next, the power cutoff circuit 6 is the emitter of the transistor Q4 that constitutes the base-grounded transistor switch circuit,
The capacitor C1 for control is connected between the bases. Reference numeral R5 is a current limiting resistor, and R6 is a bias resistor.

When a power supply voltage is applied to the power cutoff circuit 6 by turning on the lighting operation switch 4 in the above configuration, as will be described later, the charging current passing through the bias resistor R6 is applied to the capacitor C1 which has been in a discharging state until then. Flowing, the base voltage of the transistor Q4 rises up to almost the input power supply voltage through the current limiting resistor R5. For this reason, no current flows from the emitter of transistor Q4 to the base of transistor Q4.
Is in the OFF state, so that the current from the DC power supply 3 is not supplied to the pulse oscillator 2 and the power supply voltage is not applied. Therefore, the pulse oscillator 2 does not operate immediately, and therefore the lamp drive circuit 1 does not operate either.

On the other hand, as the charging of the capacitor C1 progresses, the transistor
The voltage on the base side of Q4 gradually decreases, so that the base current of the transistor Q4 gradually increases and the current flowing from the emitter to the collector gradually increases. Therefore, the power supply voltage supplied to the pulse oscillator 2 also gradually increases. Therefore, the pulse output voltage of the pulse oscillator 2 and the input signal current of the lamp driving circuit 1, that is, the current limiting resistor
The base current of the transistor Q1 via R1 will also gradually rise.

Therefore, the transistor Q1 of the lamp driving circuit 1 initially operates in the active region in accordance with the input signal current to limit the output current, that is, the current flowing through the lamp 5, and subsequently outputs the output signal as the input signal current increases. The current also rises. Therefore, the inrush current flowing through the lamp 5 immediately after lighting can be suppressed as indicated by the solid line in FIG. 2, for example.

When the capacitor C1 reaches a predetermined charge state after a predetermined time elapses in this way, the transistor Q4 operates in the saturation region, and thus a predetermined power supply voltage is applied to the pulse oscillator 2. Therefore, the pulse oscillator 2 generates a predetermined pulse output voltage, and the transistor Q1 of the lamp driving circuit 1 is turned on and off repeatedly in a saturated state. Thus, the lamp 5 is turned on in the normal state.

Next, when the lighting operation switch 4 is turned off and the supply of the power supply voltage to the power cutoff circuit 6 is stopped, the electric charge accumulated in the capacitor C1 is transmitted through the power cutoff circuit 6 and the bias resistor R6 to the pulse oscillator. 2. Discharged through the constituent elements of the lamp drive circuit 1, and after a predetermined time elapses, a predetermined discharge state is established to prepare for the next lighting operation. In this case, if a diode D having a polarity opposite to that of the DC power supply 3 is provided in parallel with the bias resistor R6, a discharge current easily flows through this diode D, and therefore, a discharge current flows more easily. Even when the predetermined discharge is completed in a short time and therefore the time interval between the turning-off and the lighting operation is relatively short, the above-mentioned inrush current can be surely suppressed.

In addition to the configurations of the embodiments described above, the specific configurations of the lamp drive circuit 1, the pulse oscillator 2, and the power cutoff circuit 6 are appropriate.

(Advantages of the Invention) As described above, the present invention provides a light quantity adjusting device that includes a lamp driving circuit and a duty ratio variable pulse oscillator that generates an input signal of the lamp driving circuit. By supplying power via the power cutoff circuit controlled by charging / discharging the capacitor, in the state where the resistance of the lamp is small immediately after the lighting operation, the transistor etc. as the drive element is changed according to the input signal current. Initially, it is operated in the active region to limit the output current, and then the output current is raised to the normal state as the input signal current rises, so the inrush current flowing to the lamp immediately after lighting is suppressed. Therefore, the space required can be reduced compared to the conventional method in which the capacity of the driving element is made sufficiently large to prevent damage due to inrush current. In addition to that, there is an effect that the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the overall configuration of the present invention,
Further, FIG. 2 is an explanatory view showing the operation of the present invention and the conventional one. Reference numeral 1 ... Lamp driving circuit, 2 ... Pulse oscillator, 3 ...
… DC power supply, 4 …… Lighting operation switch, 5 …… Lamp,
6 ... power cutoff circuit, 7 ... output section, 8 ... slider.

Continuation of the front page (56) Reference JP-A-63-6782 (JP, A) JP-A-60-59697 (JP, A) JP-A-62-256399 (JP, A) Actual development 61-73447 (JP , U) Actual Development Sho 59-170996 (JP, U) Special Public Examination Sho 58-18755 (JP, B2) Actual Public Sho 39-16625 (JP, Y1)

Claims (3)

[Claims] 1. A light quantity adjusting device comprising a lamp driving circuit and a pulse oscillator having a variable duty ratio for generating an input signal to the lamp driving circuit, wherein the pulse oscillator is controlled by charging and discharging a capacitor. The power is cut off from the DC power supply through the circuit, and the power cutoff circuit cuts off the current from the DC power supply when the capacitor is discharged and turns it on when the capacitor is charged.
Light intensity control device for lamps, characterized in that the current is continuously controlled between F 2. The light quantity adjusting device for a lamp according to claim 1, wherein the power cutoff circuit is configured by connecting a control capacitor between an emitter and a base of a transistor forming a base-grounded transistor switch circuit. 3. A light quantity adjusting lamp, wherein a diode having a polarity opposite to that of the DC power source is provided in parallel with a bias resistor between the base of the transistor and the negative electrode side of the DC power source. apparatus