JPH0685357B2 - 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 light bulb is used as a lamp, a large inrush current flows to the incandescent light bulb 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 configured by, the pulse oscillator 2 is configured to supply power from the DC power source 3 via the voltage adjusting resistor RO, and the power source short circuit 6 controlled by charging / discharging the capacitor C1 is connected in parallel. The power supply short circuit 6 is turned on when the capacitor C1 is discharged.
As a result, the power supply is short-circuited, the power is turned off in the charging state, and the current is continuously controlled between ON and OFF.

In the above configuration, the power supply short circuit 6 can be configured by connecting the control capacitor C1 between the collector and the base of the transistor Q4 of the grounded-emitter transistor switch circuit. Then, instead of the bias resistor R6 between the emitter and the base of the transistor Q4, a diode D having a reverse polarity with respect to the power supply can be provided.

(Operation) When the lighting operation switch 4 is turned ON in the above configuration,
A predetermined power supply voltage is instantaneously applied to the lamp drive circuit 1,
Further, a predetermined power supply voltage is also applied to the pulse oscillator 2 and the power supply short circuit 6 via the voltage adjusting resistor RO.

At the time when the power supply voltage is applied to the power supply short-circuit 6, the capacitor C1 is in a discharged state, so that the power supply short-circuit 6 immediately operates to turn on and short-circuit the power supply. Therefore, a short-circuit current flows through the voltage adjusting resistor RO, and the voltage on the load side, that is, the power supply voltage supplied to the pulse oscillator 2 and the power supply short circuit 6, immediately drops. With this operation, the electric charge is gradually accumulated in the capacitor C1 and the charging proceeds, so that the short-circuit current flowing through the power supply short-circuit 6 gradually decreases. Therefore, the voltage gradually increases on the load side of the voltage adjusting resistor R6. 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 inrush current flowing in the lamp 5 immediately after lighting can be suppressed as shown by the solid line in FIG. 3, for example.

When the capacitor C1 reaches the predetermined charging state after the predetermined time elapses in this way, the power supply short circuit 6 is turned off and the predetermined power supply voltage is applied to the pulse oscillator 2.
Therefore, the pulse oscillator 2 generates a predetermined pulse output voltage to bring the lamp driving 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 to stop the supply of the power supply voltage, the electric charge accumulated in the capacitor C1 of the power supply short circuit 6 is gradually discharged, and after a lapse of a predetermined time, a predetermined discharge state is established. To prepare for the lighting operation.

The power supply short circuit 6 can be configured by connecting a control capacitor C1 between the collector and base of the transistor Q4 of the grounded-emitter transistor switch circuit,
In such a configuration, when the transistor switch circuit is turned on, the voltage applied to the capacitor C1 is about the saturation voltage between the collector and emitter of the transistor Q4, so that a time constant of a predetermined length can be obtained with a small capacitance. . Further, in such a transistor switch circuit, if the diode D having a reverse polarity to the power source is provided instead of the bias resistor R6 between the emitter and the base, 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 symbol RO is a voltage adjusting resistor, and the pulse oscillator 2 is configured to supply power from the DC power supply 3 via the voltage adjusting resistor RO. A power supply short circuit 6 controlled by charging and discharging the capacitor C1 is connected in parallel to the pulse oscillator.

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 a sliding variable resistor VR is connected between the bases of the respective transistors Q2 and Q3 of the pair of transistor switch circuits, and this slider 8 side is connected to the power source 3 via the resistor 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
And is connected to the current limiting resistor R1 of the lamp drive 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 supply short circuit 6 is configured by connecting the above-mentioned control capacitor C1 between the collector and the base of the transistor Q4 that constitutes the grounded-emitter transistor switch circuit. Reference numeral R5 is a current limiting resistor, and R6 is a bias resistor.

In the above configuration, when the lighting operation switch 4 is turned ON, a predetermined power supply voltage is applied to the power supply short circuit 6 together with the pulse oscillator 2 through the voltage adjusting resistor RO, as described later, the discharge state is reached until then. A charging current flows through the existing capacitor C1, and this charging current flows into the base of the transistor Q4 via the current limiting resistor R5 and flows to the emitter. Therefore, the transistor Q4 is turned on in the saturated state, the power supply is short-circuited, and the short-circuit current flows from the collector to the emitter. Due to this short-circuit current, the voltage on the load side of the voltage adjustment resistor RO, that is, the power supply voltage supplied to the pulse oscillator 2 and the power supply short circuit 6, immediately drops to about the saturation voltage of the transistor Q4, for example, about 0.4 to 0.7V. To do. Therefore, the pulse oscillator 2 does not operate immediately. Meanwhile, the capacitor C1
The voltage applied to the battery also decreases, and charging proceeds due to such a low voltage. Since the capacitor C1 is charged with such a low voltage, a large time constant can be obtained even with a small capacitance.

In this way, when the charge is gradually accumulated in the capacitor C1 and the charging progresses, the voltage of the current limiting resistor R5 side of the capacitor C1 gradually decreases and the base current of the transistor Q4 decreases, so the short-circuit current also gradually decreases. Therefore, the voltage on the load side of the voltage adjusting resistor RO 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 shown by the solid line in FIG. 3, for example.

When the capacitor C1 reaches a predetermined charging state after a predetermined time elapses in this way, the transistor Q4 is turned off and the short-circuit current disappears, thus applying a predetermined power supply voltage 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.

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 supply short circuit 6 is a constituent element of the power supply short circuit 6, the pulse oscillator 2, and the lamp drive circuit 1. After a predetermined period of time has elapsed, the battery is discharged into a predetermined discharge state to prepare for the next lighting operation. In this case, in the transistor switching circuit, if a diode D having a polarity opposite to that of the power source is provided as shown in FIG. As a result, the discharge current easily flows, so that the predetermined discharge is completed in a shorter time, so that the above-mentioned inrush current can be surely suppressed even when the time interval between the turning-off and the lighting operation is relatively short.

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 supply short circuit 6 are appropriate.

(Advantages of the Invention) As described above, the present invention provides a light quantity adjusting device that includes a lamp drive circuit and a pulse oscillator with a variable duty ratio that generates an input signal of the lamp drive circuit. , By connecting a power supply short circuit controlled by charging / discharging a capacitor, when the resistance of the lamp is small immediately after the lighting operation, the transistor etc. as a driving element is initially activated according to the input signal current. In order to limit the output current and then to increase the output current to the normal state as the input signal current increases, it is possible to suppress the inrush current flowing to the lamp immediately after lighting, Therefore, the required space can be reduced as compared with the conventional method in which the capacity of the driving element is made sufficiently large to prevent the destruction due to the inrush current. 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,
Also, FIG. 2 is a circuit diagram showing another embodiment of the main part, and FIG. 3 is an explanatory diagram 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 supply short circuit, 7 ... Output part, 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 drive circuit and a pulse oscillator having a variable duty ratio for generating an input signal of the lamp drive circuit, wherein the pulse oscillator is a DC power source through a voltage adjusting resistor. The power supply short-circuit is controlled in parallel by charging and discharging the capacitor, and the power-supply short-circuit is turned on when the capacitor is discharged to short-circuit the power supply and charged. It is turned off and the current is controlled continuously between on and off. 2. The light quantity adjusting device for a lamp according to claim 1, wherein the power supply short-circuit circuit is configured by connecting a control capacitor between the collector and the base of a grounded-emitter transistor switch circuit. 3. A light quantity adjusting device for a lamp, wherein a diode having a polarity opposite to that of a power source is provided in place of the bias resistor between the emitter and the base of the transistor switch circuit according to claim 2.