JPH0713226A - Lamp driving device - Google Patents

Abstract

PURPOSE:To maintain the specified color temp. of a halogen lamp by detecting the voltage of a lithium ion battery, maintaining the voltage from this lithium ion battery in accordance with the detected output at a specified voltage and impressing this voltage to a lamp. CONSTITUTION:A switch 8 for lighting the lamp of the lamp driving device is operated to turn on. As a result, the voltage from the lithium ion battery pack 1 is impressed to a noise preventive capacitor 2 and is impressed to a voltage detecting circuit 3 and a pulse width modulating circuit 4. This voltage detecting circuit 3 detects the present voltage from the lithium ion battery pack 1 in accordance with the reference voltage impressed from a reference voltage circuit 7 and impresses this voltage to the pulse width modulating circuit 4. The pulse width modulating circuit 4 modulates the width of the impulsive pulses outputted according to the detected present voltage and supplies the modulated pulses to a semiconductor switch 5. This semiconductor switch 5 is controlled to turn on and the voltage from the noise preventive capacitor 2 is impressed to the halogen lamp 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lamp driving device using a lithium ion battery which is suitable for use in, for example, a lamp system of a portable video camera device.

[0002]

2. Description of the Related Art Today, portable video camera devices are becoming popular because they are lightweight, compact, and easy to carry. In this video camera device, image pickup light is received by a CCD image sensor to form an image pickup signal, and the image pickup signal is recorded on a video tape.

Since the video camera device uses the CCD image sensor, it is possible to obtain a clear image by receiving the brightest imaging light. For this reason, a lamp driving device that irradiates a subject with light is used for imaging in a place where there is insufficient light around the room.

A conventional lamp driving device is designed to drive a halogen lamp by using a rechargeable so-called nickel-cadmium battery pack (NiCd battery pack) as a power source. The NiCd battery pack has a voltage value of, for example, 1 with respect to the remaining amount of accumulated charge as shown by the dotted line in FIG.
Since it is approximately constant at about 1 V, a stable voltage can be applied to the halogen lamp and the color temperature of the lamp can be kept constant.

[0005]

However, the conventional lamp driving device has a problem that the device itself becomes large because the NiCd battery pack provided as a power source is large. Further, the NiCd battery pack has a problem in terms of life because it can be repeatedly charged and used about 300 times, for example.

Here, a lithium-ion battery pack has been attracting attention as a power source that replaces the NiCd battery pack. Since this lithium-ion battery pack can obtain a high voltage and has a large energy density, the pack itself can be extremely miniaturized, and the number of times it can be repeatedly charged and used is, for example, 1200 or more.
It has four times the life of iCd battery packs.

However, in the lithium ion battery pack, as shown by the solid line in FIG. 5, the voltage value changes drastically from 17 V to 11 V with respect to the remaining amount of accumulated charge. Also,
The color temperature of the halogen lamp provided in the lamp driving device is usually about 3000 K, but the color temperature largely depends on the terminal voltage of the halogen lamp.

Therefore, when the lithium ion battery pack is used in the lamp driving device, there arises a problem that the color temperature of the halogen lamp changes in accordance with the change in the remaining amount of accumulated charge. When the color temperature of the halogen lamp changes in this way, it becomes necessary to readjust the white balance of the video camera device many times. This white balance adjustment is impossible during continuous imaging.

Further, the lithium ion battery pack is
Since a very high voltage of 17V is applied when fully charged, if this voltage is applied to the halogen lamp as it is,
A voltage higher than the rated voltage of the halogen lamp is applied, which shortens the life of the halogen lamp.

For this reason, conventionally, as a lamp driving device for a video camera device, a lithium ion battery pack cannot be used as a power source, and a NiCd battery pack is used in consideration of a disadvantage such as an increase in size. I had no choice.

The present invention has been made in view of the above-mentioned problems, and it is possible to keep the color temperature of a halogen lamp constant even when a lithium ion battery pack is used as a power source, and a voltage higher than a rated voltage is applied. It is an object of the present invention to provide a lamp driving device capable of preventing a problem such as application to a halogen lamp and shortening the life of the halogen lamp.

[0012]

SUMMARY OF THE INVENTION A lamp driving device according to the present invention comprises a lithium ion battery for supplying power, a voltage detecting means for detecting the voltage of the lithium ion battery, and a lamp which is driven to light by applying a voltage. And the constant voltage means for applying the voltage from the lithium ion battery as a constant voltage to the lamp based on the detection output from the voltage detection means.

In the lamp driving device according to the present invention, the constant voltage means has a pulse width modulating means for forming a modulated pulse whose pulse width is modulated based on the detection output from the voltage detecting means, and the pulse width modulating means. The above-mentioned problems are solved by a switch means which is on / off controlled in accordance with the modulated pulse from and is applied with the voltage from the lithium ion battery to the lamp.

The lamp driving device according to the present invention has a control means for controlling the pulse width modulation means so that the voltage applied to the lamp gradually becomes the constant voltage at the start of lighting of the lamp. The above-mentioned problem is solved by the feature.

[0015]

In the lamp driving device according to the present invention, the voltage detecting means detects the voltage of the lithium ion battery and supplies the detection output to the constant voltage means. The constant voltage means applies the voltage from the lithium ion battery as a constant voltage to the lamp based on the detection output from the voltage detection means.

Specifically, the constant voltage means is composed of a pulse width modulation means and a switch means, and the pulse width modulation means modulates the pulse width based on the detection output from the voltage detection means. A modulated pulse is formed and applied to the switch means. The switch means is
On / off control is performed according to the modulation pulse from the pulse width modulation means, and the voltage from the lithium ion battery is applied to the lamp. Accordingly, the voltage applied to the lamp can be controlled to be turned on and off according to the pulse width of the modulation pulse, and the voltage applied to the lamp can be made constant.

At the start of lighting of the lamp, the control means controls the pulse width modulation means so that the voltage applied to the lamp gradually becomes the constant voltage.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a lamp driving device according to the present invention will be described below with reference to the drawings.

The lamp driving device according to this embodiment can be applied to, for example, a lamp system of a portable video camera device that irradiates a subject with light in order to obtain bright imaging light, and can be charged as shown in FIG. Based on a reference voltage from a reference voltage circuit 7, a lithium ion battery pack (lithium ion battery) 1 for supplying power, a noise prevention capacitor 2 for removing a noise component superimposed on the voltage from the lithium ion battery pack 1 And a voltage detection circuit (voltage detection means) 3 for detecting the current voltage from the lithium ion battery pack 1.

Further, the lamp driving device according to the present embodiment is
A pulse width modulation circuit (pulse width modulation means) 4 for performing pulse width modulation processing on the voltage from the lithium ion battery pack 1 based on the current voltage detected by the voltage detection circuit 3, and the pulse width modulation circuit. A semiconductor switch 5 which is on / off controlled by a modulation pulse from the switch 4, a halogen lamp (lamp) 6 which is driven to be turned on by a voltage through the noise prevention capacitor when the semiconductor switch 5 is on-controlled, and the halogen lamp. The lamp lighting switch 8 is turned on at the start of lighting of the lamp 6, and the pulse is applied so that the voltage applied to the halogen lamp 6 gradually becomes the constant voltage when the lamp lighting switch 8 is turned on. It has a soft start circuit (control means) 9 for controlling the width modulation circuit 4.

Next, the operation of the lamp driving device according to this embodiment having the above structure will be described. First, when a subject is imaged by a video camera device in a dark place such as a room, the lamp lighting switch 8 of the lamp driving device is turned on in order to obtain bright imaging light. This allows
The voltage from the lithium ion battery pack 1 is applied to the noise prevention capacitor 2 and the voltage detection circuit 3
And pulse width modulation circuit 4.

The noise prevention capacitor 2 suppresses an alternating current flowing between the lithium ion battery pack 1 and the circuit parts such as the voltage detection circuit 3 and the pulse width modulation circuit 4 and leaks magnetic flux generated from the connection line. It is provided to reduce noise caused by. The noise prevention capacitor 2 reduces the noise superimposed on the voltage from the lithium ion battery pack 1 and applies the noise to the semiconductor switch 5.

The voltage detection circuit 3 detects the current voltage from the lithium ion battery pack 1 based on the reference voltage applied from the reference voltage circuit 7, and applies it to the pulse width modulation circuit 4.

The pulse width modulation circuit 4 modulates the pulse width of the pulse to be output according to the current voltage detected by the voltage detection circuit 3, and supplies this modulated pulse to the semiconductor switch 5.

Specifically, the voltage of the lithium ion battery pack 1 changes to 17V to 11V depending on the remaining amount of accumulated charge as shown by the solid line in FIG. 5, for example. For this reason,
In the pulse width modulation circuit 4, the current voltage detected by the voltage detection circuit 3 is 17 as indicated by the hatched line in FIG.
If it is V, a modulated pulse having a pulse width of 50% of the normal pulse width is formed, and this is supplied to the semiconductor switch 5. If the current voltage detected by the voltage detection circuit 3 is 11 V as indicated by the diagonal line in FIG. 2, a modulated pulse having a pulse width of 80% of the normal pulse width is formed. The semiconductor switch 5
Supply to.

The semiconductor switch 5 is ON-controlled when a high level modulation pulse is supplied from the pulse width modulation circuit 4, and applies the voltage from the noise prevention capacitor 2 to the halogen lamp 6. That is, the application time of the voltage to the halogen lamp 6 is changed according to the pulse width of the modulation pulse.

As a result, the current flowing through the halogen lamp 6 can be varied according to the current voltage as shown in FIG. 3 (a), and the brightness (color temperature) of the halogen lamp 6 can be the same. As shown in FIG. 3B, the lithium-ion battery pack 1 can be controlled to be substantially constant regardless of the remaining charge.

Therefore, the lithium ion battery pack 1 described above
It is possible to irradiate the subject with light having a substantially constant color temperature irrespective of the remaining amount of the accumulated charge, and to prevent the inconvenience of re-adjusting the white balance of the video camera device during imaging.

Further, since the lithium ion battery pack 1 is used as the power source, the power source itself can be made smaller than when the NiCd battery is used as the power source. Therefore, the lamp driving device itself can be downsized, and the overall image pickup system of the video camera device and the lamp driving device can be downsized.

Further, since the lithium ion battery is used as the power source, the number of times of charging and repeated use can be made four times or more that of the NiCd battery (NiCd).
d battery: Approximately 300 times, lithium ion battery: 1200
(More than once), it is possible to extend the life of the lamp driving device.

Here, in the lamp driving device according to this embodiment, when the lamp lighting switch 8 is turned on,
The soft start circuit 9 detects this. When the soft start circuit 9 detects that the lamp lighting switch 8 has been turned on, the soft start circuit 9 gradually outputs a modulated pulse having a pulse width corresponding to the current voltage of the lithium ion battery pack 1 over a predetermined period. The pulse width modulation circuit 4 is controlled as described above.

As a result, the voltage applied to the halogen lamp 6 at the start of lighting can be gradually raised to the target voltage value over a predetermined period (Soft Start period in FIG. 4) as shown in FIG. Therefore, it is possible to prevent a voltage higher than the rated voltage from being applied to the lamp at the start of lighting. Therefore, the lamp can have a long life.

[0033]

As is apparent from the above description, the lamp driving device according to the present invention can drive the lamp for lighting at a constant voltage. Therefore, the color temperature of the lamp can be kept constant, and the inconvenience of re-adjusting the white balance of the video camera device during image pickup can be prevented.

Since the lithium ion battery is used as the power source, the power source itself can be made smaller than when the NiCd battery is used as the power source. Therefore, the lamp driving device itself can be downsized,
It is possible to reduce the size of the total imaging system of the video camera device and the lamp driving device.

Further, since the lithium ion battery is used as the power source, the number of times of charging and repeated use can be made four times or more that of the NiCd battery (NiCd battery).
d battery: Approximately 300 times, lithium ion battery: 1200
(More than once), it is possible to extend the life of the lamp driving device.

Further, in the lamp driving device according to the present invention, at the start of lighting of the lamp, the control means controls the pulse width modulating means so that the voltage applied to the lamp gradually becomes the constant voltage. By controlling, it is possible to prevent the voltage higher than the rated voltage from being applied to the lamp at the start of lighting of the lamp. Therefore, the lamp can have a long life.

[Brief description of drawings]

FIG. 1 is a block diagram of a lamp driving device according to an exemplary embodiment of the present invention.

FIG. 2 is a waveform diagram of pulses pulse-width modulated by the pulse modulation circuit provided in the lamp driving device according to the above-described embodiment according to the voltage of the lithium-ion battery pack.

FIG. 3 is a diagram showing a relationship between a pulse width-modulated pulse applied to a halogen lamp of the lamp driving device according to the above embodiment and a change in luminance of the halogen lamp.

FIG. 4 is a diagram showing a voltage applied to the halogen lamp at the start of lighting of the halogen lamp provided in the lamp driving device according to the embodiment.

FIG. 5 is a graph showing the relationship between changes in the remaining amount of accumulated charge and voltage of NiCd batteries and lithium-ion batteries.

[Explanation of symbols]

1 Lithium-ion battery pack 2 Noise suppression capacitor 3 Voltage Detection circuit 4 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Pulse width modulation circuit 5 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Semiconductor switch 6 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・Halogen lamp 7: Reference voltage circuit 8: Lamp lighting switch 9:・ Soft start circuit

Claims (3)

[Claims] 1. A lithium-ion battery for power supply, a voltage detection means for detecting the voltage of the lithium-ion battery, a lamp driven to be turned on by applying a voltage, and a detection output from the voltage detection means. A lamp driving device, comprising: a constant voltage means for applying a constant voltage to the lamp from the lithium-ion battery. 2. The constant voltage means responds to the pulse width modulation means for forming a modulated pulse whose pulse width is modulated based on the detection output from the voltage detection means, and the modulated pulse from the pulse width modulation means. 2. The lamp driving device according to claim 1, wherein the lamp driving device comprises an on / off controlled switch means for applying a voltage from the lithium ion battery to the lamp. 3. The control means for controlling the pulse width modulation means so that the voltage applied to the lamp gradually becomes the constant voltage at the start of lighting of the lamp. Lamp drive as described.