JPH09102399A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide good circuit efficiency and a wide dimming range in a dimming discharge lamp-lighting apparatus. SOLUTION: This lighting apparatus is a current feedback discharge lamp- lighting apparatus composed of a chopper circuit 2 and a discharge lamp-lighting circuit 3 containing a DC/AC converter part. Lighting is dimmed by a dimming system to control a lamp current from 40% to 100% by a dimming signal switching apparatus 11 and lighting is dimmed by repeating lighting and extinguishing operations of a discharge lamp 5 by a chopping dimming signals from 5% to 40%. Consequently, without lowering the circuit efficiency so much, the dimming can be carried out to 5%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device, and more particularly to a lighting device suitable for a dimming control system having a wide dimming range.

[0002]

2. Description of the Related Art A conventional discharge lamp lighting device is an actual open flat 5-8.
As described in Japanese Patent No. 0191, the current flowing through the discharge lamp detected by the tube current detection circuit is fed back to the voltage control means provided in the preceding stage of the lighting circuit, and the current flowing through the discharge lamp is kept constant. Voltage is supplied to the lighting circuit from the voltage control means. In general, the tube current detection circuit has a structure in which a tube current is passed through a resistor and a voltage generated across the resistor is output.

Such a discharge lamp lighting device is generally called a current feedback type, and a metal such as a liquid crystal backlight using a cold cathode type discharge lamp having a relatively high impedance and a small diameter as a light source is provided around the discharge lamp. There is a characteristic that the startability and the characteristics are stable because the problems that the startability is lowered and the characteristics are easily changed due to the influence of the stray capacitance generated due to the close proximity of the reflection film are stable.

[0004]

However, according to the above-mentioned prior art, when dimming is performed, a method of adjusting the voltage supplied to the lighting circuit and controlling the current flowing through the discharge lamp is generally used. Since the voltage supplied to the lighting circuit cannot be lower than the discharge lamp lighting maintenance voltage, the dimming degree is 100%.
There is a drawback that it is as narrow as 40%. Further, as another method of performing dimming, there is also a chopping dimming control method of intermittently stopping the voltage supplied to the lighting circuit and adjusting the stop period to control the brightness of the discharge lamp. Although the dimming degree can be widened from 100% to 5%, there is a drawback that the circuit efficiency during dimming is poor.

[0005]

The above-mentioned object is to adjust the voltage supplied to the lighting circuit to a certain degree by a dimming method for controlling the current flowing through the discharge lamp, and when dimming the dimming method. This is achieved by switching the method to the chopping dimming control method and dimming.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a block diagram of one embodiment of the present invention. In FIG. 1, 1 is a DC power supply, 2 is a chopper circuit, 3 is DC / s having at least one switch element.
A discharge lamp lighting circuit including an AC converter, 4 a ballast circuit,
Reference numeral 5 is a discharge lamp, 6 is a tube current detector having a function of converting a tube current into a voltage, 7 is an operation signal generator of a voltage control circuit composed of an error amplifier 12, a voltage comparator 13 and a reference triangular wave generator 14. , 8 is a reference voltage generator, 9 is a chopping dimming signal generator, 10 is a switch circuit operated by a chopping dimming signal, 11 is a dimming signal switching device, 1
Reference numeral 5 is a control signal line.

The chopper circuit 2 receives the supplied DC voltage Vi.
n is chopped according to the operation signal input from the operation signal generator 7 through the control signal line 15. These waveforms are shown in FIG. In FIG. 2, (1) shows the operation signal waveform input from the operation signal generator 7 through the control signal line 15, and (2) shows the waveform of the output voltage Vcont of the chopper circuit 2.

The discharge lamp lighting circuit 3 receives the input Vcont
Is smoothed, the voltage is converted into an AC voltage by the DC / AC converter, and the voltage is boosted and output. The high frequency high voltage output from the discharge lamp lighting circuit 3 is applied to the discharge lamp 5 via the ballast circuit 4 to light the discharge lamp 5. The tube current flowing through the discharge lamp 5 is converted into a DC voltage by the tube current detector 6,
It is input to the operation signal generator 7.

A voltage proportional to the difference voltage between the input DC voltage and the reference voltage Vref output from the reference voltage generator 8 is input from the error amplifier 12 to the voltage comparator 13.
The voltage comparator 13 receives the input voltage and the reference triangular wave generator 1
The output voltage of FIG. 4 is compared with the output voltage of FIG. In FIG. 2, (3) indicates the output waveform of the reference triangular wave generator 14 and the error amplifier 12 to the voltage comparator 13.
The waveform of the DC voltage input to is shown.

For example, when the tube current decreases for some reason, the DC voltage detected by the tube current detector 6 decreases,
The voltage input to the error amplifier 12 decreases. Since the error amplifier 12 is an inverting amplifier, when the voltage input to the error amplifier 12 decreases, the output voltage of the error amplifier 12 increases on the contrary. Therefore, the ON time of the waveform shown in FIG. 2 (1) increases, the ON time of the chopper circuit 2 also increases, the voltage applied to the lighting circuit 3 increases, and the tube current increases. Since the above feedback is applied so that the difference voltage between the voltage input to the error amplifier 12 and Vref becomes almost zero, the tube current is kept constant. The same applies when the tube current increases for some reason.

A discharge lamp 5 is provided in the current feedback type discharge lamp lighting device.
There is a method of changing Vref output from the reference voltage generator 8 when adding a dimming function for adjusting the brightness of the. For example, when Vref is reduced, the tube current detector 6
Since the DC voltage detected from the control is controlled to decrease, the tube current decreases. Therefore, dimming becomes possible. However, when this dimming method is used, when the maximum brightness is set to 100%, when the dimming is 40% or less, the voltage supplied from the voltage control means to the lighting circuit 3 decreases, and the lighting of the discharge lamp 5 is maintained. Since the lighting circuit 3 cannot output the voltage, the discharge lamp 5
Turns off. However, the circuit efficiency when dimming does not decrease so much.

On the other hand, as another dimming method, there is a chopping dimming method. The chopping dimming signal output from the chopping dimming signal generator 9 is input to a place where the tube current is kept constant and is stably lit by the action of the current feedback type discharge lamp lighting device. The switch circuit 10 operates by the chopping dimming signal, and the control signal line 15
The control signal flowing through is turned on and off at a constant cycle. As a result, the voltage waveform of Vcont also becomes 0V in a constant cycle. These waveforms are shown in FIG. In FIG. 3, (1)
Is intermittent due to chopping dimming signal Vcon
The voltage waveform of t, (2) shows the chopping dimming signal waveform. As shown in FIG. 3, the frequency of the chopping dimming signal is ½ or less of the operating signal. Therefore, the lighting circuit 3
Cannot smooth the period of 0V in the input Vcont due to the chopping dimming, and the discharge lamp 5 repeatedly turns on and off according to the chopping dimming signal.
When changing the brightness, it is realized by lengthening or shortening the lighting period by the chopping dimming signal. Further, since the frequency of the chopping dimming signal is slow during the period when the discharge lamp 5 is lit, it is the same as when the dimming light is not dimmed and is the same as when the chopping dimming signal is not applied.
cont is output.

Therefore, even when the period of lighting by the chopping dimming signal is set to 5% of the constant lighting, the same Vcont as that when the chopping dimming signal is not applied is output during the period of lighting. Lighting circuit 3
Outputs a voltage necessary for maintaining the lighting of the discharge lamp 5, and the lighting can be maintained. However, the circuit efficiency when dimming decreases in proportion to dimming.

Therefore, the dimming signal switch 11 is used to adjust the Vref by controlling the reference voltage generator 8 from 100% to 40% of the dimming signal input from the outside. Light is dimmed and chopping dimming is performed while maintaining Vref at a dimming voltage of 40% from dimming 40% to 5%, thereby dimming up to 5% while maintaining circuit efficiency during dimming. You can

[0015]

As described above, according to the present invention, it is possible to provide a discharge lamp lighting device capable of reducing dimming to 5% without significantly reducing circuit efficiency.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration diagram of an embodiment of a discharge lamp lighting device according to the present invention.

FIG. 2 is an operation explanatory view of one embodiment of the discharge lamp lighting device according to the present invention.

FIG. 3 is an operation explanatory view of one embodiment of the discharge lamp lighting device according to the present invention.

[Explanation of symbols]

1 ... DC power supply, 2 ... Chopper circuit, 3 ... Discharge lamp lighting circuit, 4 ... Ballast circuit, 5 ... Discharge lamp, 6 ... Tube current detector, 7 ... Operation signal generator, 8 ... Reference voltage generator, 9 ... Chopping dimming signal generator, 10 ... Switch circuit, 11
… Switch.

Front page continued (72) Inventor Takashi Okada 888 Fujihashi, Ome-shi, Tokyo Inside the heater lighting division, Hitachi, Ltd. (72) Kenji Kawabata 888 Fujibashi, Ome-shi, Tokyo Inside the heater lighting division, Hitachi, Ltd. (72) Inventor Ryuichi Ikeda, 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa, Ltd.Multimedia Systems Development Division, Hitachi, Ltd. (72) Inventor Motohiro Sugino 292, Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Mfg. Co., Ltd. Multimedia System Development Headquarters (72) Inventor, Kaei Watanabe 1623 Shimotsuruma, Yamato City, Kanagawa Prefecture 14 Yamato Works, IBM Japan, Ltd.

Claims (1)

[Claims] 1. A lighting circuit for supplying a current to a discharge lamp connected to an output to maintain lighting by using a DC power supply as a power source, and a current flowing through the discharge lamp flows through an impedance device,
A voltage control circuit that controls the voltage supplied to the lighting circuit so as to keep the current flowing through the impedance device constant, and the lighting circuit is intermittently stopped, and by adjusting the stop period, the discharge lamp In a discharge lamp lighting device provided with a chopping dimming control circuit for adjusting brightness, regarding a control method for adjusting the brightness of the discharge lamp, in the middle of dimming, dimming by the voltage control circuit and chopping dimming are performed. A discharge lamp lighting device characterized by switching a light control circuit.