JPH1078765A - Led driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent rise of internal temperature, variation of luminance of light emission of a LED, and the like. SOLUTION: A power source from a power source supply terminal 1 and a power source from an incorporated battery 2 are used as a driving power source for an equipment by being selected by a switch 3. A power source from this switch 3 is connected to one end of a LED5 through a resistor 4, and the other end of this LED 5 is grounded through a transistor 6 for switching. Also, a power source from the switch 3 is connected to a stabilized power source circuit 7, and a power source from this power source circuit 7 is connected to a pulse oscillation circuit 8. And an output of this pulse oscillation circuit 8 and a power source supplied from the switch 3 through a resistor 9 are selected by a switch 10, and connected to a base of a transistor 6. Further, a detection signal that an external power source is connected to the supply terminal 1 is supplied to a detecting circuit 11 for the incorporated battery and the external power source. And, the above-mentioned switching by the switch 10 is performed by a signal from this detecting circuit 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LE which is suitable for use in a display unit of an audio-visual apparatus such as a VTR integrated with a camera and driven by a built-in battery and an external power supply.
It relates to a D drive circuit.

[0002]

2. Description of the Related Art For example, an audio-visual apparatus such as a camera-integrated VTR is driven by a built-in battery such as a rechargeable battery or by connecting an external power supply obtained by converting a commercial AC power supply or an automobile battery. In this case, two types of usage can be considered. In this case, for example, continuous driving with an internal battery is limited to at most several hours, while continuous driving with an external power supply can be performed indefinitely.

Therefore, when such an audio-visual apparatus is continuously driven by, for example, an external power supply, an increase in the internal temperature of the apparatus body has become a problem. Here, an increase in power consumption can be considered as a cause of such a rise in temperature. For example, the amount of drive current in a drive circuit of an LED for display is also cited as a factor.

Further, when the above-described audiovisual equipment is driven by, for example, a built-in battery, it is required to reduce power consumption in order to extend the use time of the battery. Also in this case, for example, a reduction in the amount of drive current in the LED drive circuit is a necessary condition.

Further, when the above-described audio-visual equipment is used by switching between a built-in battery and an external power supply, a change in the power supply voltage causes, for example, the light emission luminance of the LED to fluctuate. For this reason, there has been a problem that the user may be misunderstood as a failure or the like.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and a problem to be solved is to use an audio-visual apparatus by switching between an internal battery and an external power supply. In such a case, problems such as a rise in the internal temperature of the device body and a change in the light emission luminance of the display LED have occurred.

[0007]

According to the present invention, a plurality of driving means are selected according to the connection between a built-in battery and an external power supply. Problems such as an increase in the internal temperature of the LED and a change in the light emission luminance of the LED can be solved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS That is, in the present invention, a built-in battery and an external power supply are connected, and a plurality of driving means at least one of which is driven by a pulse are provided, and in accordance with the connection between the built-in battery and the external power supply. A plurality of driving means are selected.

Hereinafter, the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an example of an LED driving circuit to which the present invention is applied. First, FIG. 1 addresses the problem of the rise in the internal temperature of the audiovisual equipment when the audiovisual equipment is continuously driven by the external power supply, and the fluctuation of the light emission luminance of the LED when switching between the internal battery and the external power supply. It was done.

In FIG. 1, for example, a power supply line from a power supply device 100 to which a commercial AC power supply is connected is connected to an external power supply terminal 1. Then, the power supply from the power supply terminal 1 and the power supply from the built-in battery 2 are selected by the switch 3 and used as the drive power supply for the device. Here, this switch 3
For example, when a power supply line from the power supply device 100 is connected to the external power supply terminal 1, the switching is performed.

A power supply from the switch 3 is connected to one end of an LED 5 through a resistor 4, and the other end of the LED 5 is grounded through a switching transistor 6.
The power supply from the switch 3 is connected to the stabilized power supply circuit 7, and the power supply from the power supply circuit 7 is connected to the pulse oscillation circuit 8. The output of the pulse oscillation circuit 8 and the power supplied from the switch 3 through the resistor 9 are selected by the switch 10 and connected to the base of the transistor 6.

Further, for example, a detection signal indicating that the power supply line from the power supply device 100 is connected to the external power supply terminal 1 is supplied to the detection circuit 11 for the internal battery and the external power supply. The selection by the switch 10 is performed by the signal from the detection circuit 11.

That is, in this circuit, for example, when the power supply line from the power supply device 100 is connected to the external power supply terminal 1, the output of the pulse oscillation circuit 8 is selected by the switch 10, for example. Thereby, the transistor 6
Is controlled in accordance with the pulse signal, and the LED 5 is pulse-driven. By driving the LED 5 in a pulsed manner, the amount of drive current of the LED 5 is reduced, the power consumption is reduced, and the temperature rise inside the device body is suppressed.

For example, when the power supply line from the power supply device 100 is not connected to the external power supply terminal 1, for example, the power supplied through the resistor 9 is selected by the switch 10. As a result, the base of the transistor 6 is pulled up to the power supply through the resistor 9, the transistor 6 is continuously turned on, and the LED 5 is continuously driven.

Further, in this circuit, when an external power supply is selected by the switch 3, the voltage of, for example, 8.4 V is applied to the LED 5. On the other hand, when the built-in battery is selected by the switch 3, a voltage of, for example, 5.3 V is applied to the LED 5. Therefore this LE
When D5 emits light under the same condition, the emission luminance varies, and, for example, the display becomes bright when an external power supply is selected.

Therefore, in this circuit, when the external power supply is selected by the switch 3 as described above, the LED 5
Are pulsed. As a result, the light emission luminance of the LED 5 is reduced by pulse driving, and the light emission luminance when the external power supply is selected and when the internal battery is selected can be made equal.

Therefore, in this circuit, a plurality of driving means are selected according to the connection between the built-in battery and the external power supply.
Problems such as fluctuations in the light emission luminance of D can be solved.

That is, when a long-time continuous driving by an external power supply is conceivable, the driving current amount is reduced by pulsing the LED, the power consumption is reduced, and the temperature rise inside the device body is reduced. Can be suppressed. Also, L
The light emission luminance of the ED is reduced by pulse driving, so that the fluctuation of the light emission luminance between when the external power supply is selected and when the internal battery is selected can be eliminated.

FIG. 2 shows another embodiment of the present invention. The embodiment of FIG. 2 addresses the problem of fluctuations in the light emission brightness of the LED particularly when switching between the built-in battery and the external power supply.

In FIG. 2, for example, a power supply line from a power supply device 100 to which a commercial AC power supply is connected is connected to an external power supply terminal 1. Then, the power supply from the power supply terminal 1 and the power supply from the built-in battery 2 are selected by the switch 3 and used as the drive power supply for the device. Here, this switch 3
For example, when a power supply line from the power supply device 100 is connected to the external power supply terminal 1, the switching is performed.

The power from the switch 3 is connected to one end of the LED 5 through the resistor 4, and the other end of the LED 5 is grounded through the switching transistor 6.
The power supply from the switch 3 is connected to the stabilized power supply circuit 7, and the power supply from the power supply circuit 7 is connected to the pulse oscillation circuit 8. The output of the pulse oscillation circuit 8 is directly connected to the base of the transistor 6.

Further, for example, a power supply from the above-described switch 3 is connected to a power supply voltage detection circuit 12. The output of the detection circuit 12 is connected to the pulse oscillation circuit 8 described above. Thereby, for example, the duty of the output pulse from the pulse oscillation circuit 8 is controlled in accordance with the power supply voltage from the switch 3 as shown in FIG. 3, for example.

That is, in this circuit, for example, when the above-mentioned external power supply device 100 is selected and the power supply voltage from the switch 3 is as high as 8.4 V, for example, this voltage is detected by the detection circuit 12 and the pulse oscillation circuit 8 Is reduced to, for example, 20%. As a result, the conduction time of the transistor 6 is shortened, and LE
The driving time of D5 is shortened, and the light emission luminance is reduced.

When the internal battery 2 is selected and the power supply voltage from the switch 3 is as low as 5.3 V, for example, this voltage is detected by the detection circuit 12 and the output from the pulse oscillation circuit 8 is output. The duty of the pulse is increased to, for example, 80%. As a result, the conduction time of the transistor 6 is lengthened, the driving time of the LED 5 is lengthened, and the light emission luminance is increased.

Therefore, in this circuit, the duty of the output pulse from the pulse oscillation circuit 8 is changed in accordance with the connected power supply voltage, and the driving time of the LED 5 is controlled.
The light emission luminance can always be kept constant with respect to the fluctuation of the power supply voltage. Note that the duty of the output pulse can be changed linearly or non-linearly according to the connected power supply voltage.

Further, in the above-described circuit, if only the reduction of power consumption by the built-in battery is a problem, for example, FIG.
It is sufficient that the switch 10 can be switched in the reverse manner in the circuit described above. Thus, for example, when the built-in battery 2 is selected by the switch 3, the output of the pulse oscillation circuit 8 is selected, and the LED 5 is pulse-driven, so that the power consumption of the driving circuit of the LED 5 can be reduced.

In the circuit described above, the pulse oscillating circuit 8, the resistor 9, the switch 10, the built-in battery and the external power supply detecting circuit 11 of FIG. 1 and the pulse oscillating circuit 8 and the power supply voltage detecting circuit 12 of FIG. Each can be realized by a microcontroller, which allows these circuits to be implemented with a small number of components.

Thus, according to the above-described LED drive circuit,
A built-in battery and an external power supply are connected, and a plurality of driving means, at least one of which is pulsed, are provided, and a plurality of driving means are selected according to the connection between the built-in battery and the external power supply. In addition, it is possible to solve problems such as a rise in the internal temperature of the device body and a change in the light emission luminance of the LED.

[0029]

According to the present invention, a plurality of driving means are selected in accordance with the connection between the built-in battery and the external power supply, thereby increasing the internal temperature of the device body and changing the light emission luminance of the LED. And so on.

That is, according to the present invention, when long-term continuous driving by an external power supply is conceivable, the driving current is reduced and the power consumption is reduced by setting the LED to pulse driving to reduce the power consumption. It can suppress the temperature rise inside the main body.

According to the present invention, the light emission luminance of the LED is reduced by pulse driving to eliminate the fluctuation of the light emission luminance between when the external power supply is selected and when the internal battery is selected. Can be done.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of an LED drive circuit to which the present invention is applied.

FIG. 2 is a configuration diagram of another example of an LED drive circuit to which the present invention is applied.

FIG. 3 is a diagram for explaining the operation.

[Explanation of symbols]

Reference Signs List 100 power supply device, 1 external power supply terminal, 2 built-in battery, 3 switches, 4 resistors, 5 LEDs, 6 switching transistors, 7 stabilized power supply circuit, 8 pulse oscillation circuit, 9 resistors, 10 switches, 11 built-in Battery and external power supply detection circuit, 12 Power supply voltage detection circuit

Claims (4)

[Claims] An internal battery is connected to an external power supply, and a plurality of driving means are provided, at least one of which is pulse-driven. The plurality of driving means are selected according to the connection between the internal battery and the external power supply. LED drive circuit characterized by being performed. 2. The LED driving circuit according to claim 1, wherein the driving means of the pulse driving is selected at least when the external power supply is connected to prevent heat generation.
ED drive circuit. 3. The LED driving circuit according to claim 1, wherein the driving means for pulse driving is selected at least when the built-in battery is connected to reduce power consumption. 4. The LED driving circuit according to claim 1, wherein the plurality of driving means are selected in accordance with a connection between the internal battery and an external power supply, and a variation in light emission luminance due to a change in power supply voltage is corrected. Characteristic LED drive circuit.