JP2003109779A - Dimmer control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dimmer control circuit 1 which makes a plurality of elements share consumption power in a first resistor connected in series to a light-emitting diode D1, and can keep the brightness of the light-emitting diode D1 constant without depending on the battery 10 voltage through cost reduction by using a small capacity resistor of general use as the first resistor. SOLUTION: An emitter of a transistor Tr1 is structured to be connected to the ground through a resistor R2. With this, consumption power of the resistor R1 in a conventional dimmer control circuit 100 is shared by three resistors R1, R2 and the transistor Tr1, whereby the resistor R1 is made one of lower capacity at low cost, to reduce the cost of the dimmer control circuit 1. Also, the circuit is operated as an emitter follower by adding the resistor R2, and the brightness of the light-emitting diode D1 can be kept constant as electric current I flowing in the light-emitting diode D1 is made constant in a band where the voltage E of a battery 10 is not less than a given value.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to various warning displays,
Alternatively, for example, it relates to a dimming control circuit for controlling a lighting operation of a light emitting diode for illuminating an instrument panel mounted on a vehicle, and is suitable for use in an automobile or the like.

[0002]

2. Description of the Related Art Conventionally, as a dimming control circuit of this type, a light emitting diode D1 as shown in the circuit diagram of FIG. 6 has been used in which a controller 2 applies a pulse signal to a transistor Tr1 and controls its duty ratio. Accordingly, for example, a dimming control circuit is known in which a current flowing through a light emitting diode D1 as various warning lights is controlled to control (dimming) its lighting operation.

In the conventional dimming control circuit 100, as shown in FIG. 6, the collector of the transistor Tr1 is connected to the light emitting diode D1 and the light emitting diode D1 in series to limit the current flowing through the light emitting diode D1. Is connected to the + pole side of the battery 10 which is a power source via a resistor R1 which is a first resistor of the. On the other hand, the controller 2 uses the constant voltage circuit 4 which supplies 5V of power to the CPU.
3, the ignition switch 9 closing signal,
Alternatively, the detection signal from the liquid level sensor 8 is converted into the A / D converter 7
The duty ratio of the pulse signal applied to the base of the transistor Tr1 is controlled by the CPU 3 and the output circuit 6 on the basis of the A / D converted signal in (1) to control the lighting operation of the light emitting diode D1.

[0004]

By the way, in the controller 2, in order to reduce the size and reduce the manufacturing man-hours, surface mounting (SMD) of electronic parts is attempted, and the transistor Tr1 and the resistor R1 are also SMD type. It is used. Since the resistor R1 consumes a large amount of power, a resistor having a capacity of 1 W is used, for example. However, the 1 W SMD type resistor is large and has low versatility, and thus the cost is high. In recent years, the number of light-emitting diodes used per vehicle has been increasing, and the use of the 1 W resistor R1 has been a cause of increasing the cost of the dimming control circuit and inhibiting miniaturization.

Further, in the conventional dimming control circuit 100 as shown in FIG. 6, when the voltage of the battery 10 as the power source changes, the current value flowing through the light emitting diode D1 also changes,
The brightness of the light emitting diode D1 changes. This allows
There is a possibility that the brightness of various warning lights of a car may change subtly, giving the driver a feeling of strangeness.

The present invention has been made in view of the above points, and an object of the present invention is to connect a light emitting diode in series.
By providing a dimming control circuit that has a circuit configuration in which the power consumption of the resistor is shared by a plurality of elements and the first resistor is a highly versatile small-capacity resistor, the cost can be reduced. is there.

Another object of the present invention is to provide a dimming control circuit capable of maintaining the current value flowing through the light emitting diode substantially constant even if the battery voltage fluctuates.

[0008]

In order to achieve the above object, the present invention employs the following technical means.

In the dimming control circuit according to claim 1 of the present invention, the collector of the transistor is connected to one of the power source through the light emitting diode and the first resistor, and the base of the transistor is connected to the output side of the control means. The emitter of the transistor is connected to the other of the power supplies via the second resistor. Thus, the power consumption of the first resistor is shared by the first resistor, the second resistor, and the transistor, and the first resistor is replaced with a low-cost small-capacity resistor to reduce the cost of the dimming control circuit. It can be reduced.

Further, since the emitter follower is formed by adding the second resistor, the current value flowing through the light emitting diode can be maintained at a constant value in the region where the battery voltage is equal to or higher than the predetermined value.

In the dimming control circuit according to the second aspect of the present invention, the controller is configured to apply the pulse signal to the transistor and control the duty ratio thereof to control the lighting state of the light emitting diode. Thereby, the brightness of the light emitting diode can be easily controlled as needed.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A dimming control circuit according to an embodiment of the present invention is applied to a dimming control circuit for controlling a lighting operation of a light emitting diode as a brake abnormality warning light of an automobile as an example. It will be described based on. The brake abnormality warning light is lit when the liquid level of the brake fluid in the reservoir tank falls below a predetermined level, to alert the driver. Further, in each of the drawings, the same components are designated by the same reference numerals.

FIG. 1 is a block diagram of a dimming control circuit 1 according to an embodiment of the present invention.

The dimming control circuit 1 is mainly composed of a light emitting diode D1 which is a brake abnormality warning lamp and a light emitting diode based on a detection signal from the liquid level sensor 8 when the ignition switch 9 is turned on or a signal for turning on the ignition switch. The controller 2 controls the lighting operation of the light emitting diode D1 by always controlling the amount of current flowing through D1 by the duty operation of the transistor Tr1.

The anode side of the light emitting diode D1 has a first
It is connected to the + pole side of the battery 9 which is a power source through the resistor R1 which is the resistor and the diode D2. Here, the resistor R1 is for limiting the current flowing through the light emitting diode D1. The diode D2 is for protecting the light emitting diode D1 by blocking reverse current such as surge current. On the other hand, the light emitting diode D1
The cathode side of is connected to the collector side of a transistor Tr1 described later.

The controller 2 has a CPU 3 as a main part and a constant voltage circuit 4, a memory 5, an output circuit 6, an A / D converter 7, a transistor Tr1 and a resistor R2 which is a second resistor.

The constant voltage circuit 4 is connected to the battery 10 so that the voltage of the battery 10 (about 12 in the first embodiment).
V) is converted to 5V and supplied to the CPU 3. The constant voltage circuit 4 is always stable even if the voltage of the battery 10 fluctuates.
The voltage of V can be supplied to the CPU 3.

The CPU 3 is connected via an A / D converter 7 to an ignition switch 9 and a liquid level sensor 8 for detecting the brake liquid level in a reservoir tank (not shown). Further, the memory 5 stores, as table data, a duty ratio of an ignition switch closing signal, a detection signal from the liquid level sensor 8 and a pulse signal corresponding to them. Then, the CPU 3 determines the duty ratio of the pulse signal based on the detection signal from the liquid level sensor 8. In this example, the duty ratio is set to only one value, but a plurality of duty ratios are set so that the duty ratio becomes higher (that is, brighter) as the liquid level of the brake fluid decreases, so that the driver should be careful. You may set so that it may be called up step by step.

The output circuit 6 applies a pulse signal having a duty ratio determined by the CPU 3 to the base of the transistor Tr1.

The emitter of the transistor Tr1 is connected to the ground, that is, the negative pole side of the battery 10 via the resistor R2 which is the second resistor.

The specifications of the resistors R1 and R2 in the dimming control circuit 1 according to the embodiment of the present invention configured as described above and the specifications of the resistor R1 in the conventional dimming control circuit 1 are shown in the specification list of FIG. Shown in. FIG. 3 is a graph showing the relationship between the voltage E of the battery 10 and the current I flowing through the light emitting diode D1. In FIG. 3, the characteristic A shows the case of the dimming control circuit 1 according to the embodiment of the present invention, and the characteristic B shows the case of the conventional dimming control circuit 100.

A dimming control circuit 1 according to an embodiment of the present invention.
In, the resistor R2 is added between the emitter of the transistor Tr1 and the ground to operate the circuit as an emitter follower, and the current value flowing through the light emitting diode D1 is made constant when the voltage of the battery 10 is equal to or higher than a predetermined value. The brightness of the diode D1 is the battery 1
It can be maintained constant regardless of the zero voltage. That is, as shown in FIG. 3, in the conventional dimming control circuit 100, since the voltage E of the battery 10 and the current I of the light emitting diode D1 are in a substantially proportional relationship, the current I changes with the fluctuation of the voltage E. It fluctuates, that is, the brightness of the light emitting diode D1 changes. On the other hand, in the dimming control circuit 1 according to the embodiment of the present invention, the voltage E of the battery 10 is 11
In a region below V, as the voltage E increases, the current I flowing through the light emitting diode D1 also increases, and in a region where the voltage E is 11 V or higher, the current I has a constant value. Thereby, the brightness of the light emitting diode D1 can be kept constant. Normally, the battery 1
Since the voltage E of 0 is 12 V or more, the dimming control circuit 1 according to the embodiment of the present invention can always keep the brightness of the light emitting diode D1 constant during the operation of the vehicle. Further, the power consumption by the resistor R1 can be kept constant to save power.

Further, in the dimming control circuit 1 according to the embodiment of the present invention, the power consumption of the resistor R1 in the conventional dimming control circuit 100 is shared by the three elements of the resistor R1, the resistor R2 and the transistor Tr1. By letting
As shown in FIGS. 2 and 3, the capacitance of the resistor R1 can be reduced from the conventional 1 W to 1/8 W, and the cost of the dimming control circuit 1 can be reduced by adopting a versatile and low-cost resistor. it can. Also, the size of the resistor R1 is from 6.4 mm × 3.2 mm of the 1 W type to 2.0 of the 1/8 W type.
Since it is reduced to mm x 1.25 mm, the controller 2
It is possible to save the mounting space on the printed circuit board (not shown) and improve the degree of freedom in designing the circuit pattern.

Next, the operation of the dimming control circuit 1 according to the embodiment of the present invention will be briefly described.

(1) When the ignition switch 9 is turned on.

When the driver turns on the ignition switch 9 of the automobile, the CPU 3 detects that,
A pulse signal having a duty ratio determined by referring to the table data of the memory 5 is applied to the base of the transistor Tr1 for a predetermined time (for example, 1 second). Therefore, the light emitting diode D1 is turned on for a predetermined time and then turned off. As a result, the driver can operate the brake abnormality warning light normally,
Moreover, it is possible to know that the brake fluid level is at a normal level.

(2) When the liquid level of the brake fluid in the reserve tank falls below a predetermined level.

In this case, the CPU 3 detects the detection signal from the liquid level sensor 8 and applies a pulse signal having a duty ratio determined by referring to the table data of the memory 5 to the base of the transistor Tr1 to emit light. The diode D1 is turned on. In this case, the driver can be surely notified of the brake fluid level abnormality by causing the light emitting diode D1 to continuously light up or blink in a predetermined cycle.

In the dimming control circuit 1 according to the embodiment of the present invention described above, the emitter of the transistor Tr1 is connected to the ground via the resistor R2 which is the second resistor. Accordingly, the conventional dimming control circuit 100
It is possible to reduce the cost of the dimming control circuit 1 by sharing the power consumption of the resistor R1 in FIG. 3 with the resistor R1, the resistor R2, and the transistor Tr1 and replacing the resistor R1 with a low-cost small capacity resistor.

Further, by adding the resistor R2, the circuit is operated as an emitter follower, and the current I flowing through the light emitting diode D1 is made constant in a region where the voltage E of the battery 10 is a predetermined value or more, in other words, the light emitting diode D1. The brightness of can be maintained constant.

FIG. 4 is a block diagram of a modification of the dimming control circuit 1 according to the embodiment of the present invention. In the dimming control circuit 1 according to the embodiment of the present invention, the lighting operation of one light emitting diode D1 is controlled.
The lighting operation of each of the light emitting diodes D1 and D3 is independently controlled. That is, in addition to the light emitting diode D1 which is the brake abnormality warning lamp in the dimming control circuit 1 according to the embodiment of the present invention described above, the lighting operation of the light emitting diode D3 for illuminating the instrument panel (not shown) is controlled. There is. The CPU 3 applies the pulse signal of the duty ratio determined by referring to the table data of the memory 5 on the basis of the detection signal from the illuminance sensor 11 that detects the illuminance of the instrument panel to the base of the added transistor Tr2, and the light emitting diode. Turn on D3. That is, the CPU 3 changes the duty ratio of the pulse signal applied to the base of the transistor Tr2 in response to the change in the illuminance of the instrument panel, thereby maintaining the illuminance of the instrument panel at a brightness that is easily visible to the driver. is doing. Also in this modification, as shown in FIG. 4, the emitter of the transistor Tr2 is connected to the negative electrode side of the battery 10 via the resistor R3 which is the second resistor. Therefore, the same effect as that of the dimming control circuit 1 according to the embodiment of the present invention described above can be obtained.

In the modified example of the dimming control circuit 1 according to the embodiment of the present invention described above, the lighting operation of the two light emitting diodes is independently controlled. Alternatively, the lighting operation of each light emitting diode may be independently controlled.

In the dimming control circuit 1 according to the embodiment of the present invention described above, the transistor Tr1 is used.
Although the lighting operation of one light emitting diode D1 is controlled by the above, it may be two as in another modification of the dimming control circuit 1 according to the embodiment of the present invention shown in FIG. .

[Brief description of drawings]

FIG. 1 is a configuration diagram of a dimming control circuit 1 according to an embodiment of the present invention.

FIG. 2 shows resistors R1 and R2 of a dimming control circuit 1 according to an embodiment of the present invention, and a resistor R of a conventional dimming control circuit 100.
It is a specification list of No. 1.

FIG. 3 is a graph showing the relationship between the voltage E of the battery 10 and the current I flowing through the light emitting diode D1 in the dimming control circuit 1 according to the embodiment of the present invention.

FIG. 4 is a configuration diagram of a modified example of the dimming control circuit 1 according to the embodiment of the present invention.

FIG. 5 is a configuration diagram of another modification of the dimming control circuit 1 according to the embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional dimming control circuit 100.

[Explanation of symbols]

1 Dimming control circuit 2 controller 3 CPU D1, D3 light emitting diode D2 diode E voltage I current R1 resistance (first resistance) R2, R3 resistance (second resistance) Tr1 and Tr2 transistors

Continued front page    F term (reference) 3K073 AA54 AA63 AB01 AB04 CC12                       CG10 CG13 CJ17 CJ21                 5F041 AA09 BB05 BB06 BB13 BB22                       BB25 BB26 FF11

Claims (2)

[Claims] 1. A dimming control circuit comprising a light emitting diode, a transistor, and a controller, wherein the controller operates the transistor to control the lighting state of the light emitting diode, wherein the collector of the transistor is the light emitting diode and It is connected to one of the power supplies via a first resistor, the base of the transistor is connected to the output side of the control means, and the emitter of the transistor is connected to the other of the power supplies via the second resistor. A dimming control circuit characterized by. 2. The dimming control circuit according to claim 1, wherein the controller controls the lighting state of the light emitting diode by applying a pulse signal to the transistor and controlling the duty ratio thereof.