JPH08222393A - Fluorescent lamp dimming circuit - Google Patents

Abstract

PURPOSE: To provide fluorescent lamp dimming circuits which perform a wide range of dimming from 1/1000 to 1/1 rated lighting without causing brightness unevenness by applying a high AC voltage with a small duty factor to a fluorescent lamp in a low brightness range, and applying a low AC voltage with a large duty factor to the fluorescent lamp in a high brightness range. CONSTITUTION: Two dimming circuits, i.e., a first dimming circuit consisting of a first pulse control circuit 101 and a first drive circuit 102, and a second dimming circuit consisting of a second pulse control circuit 107 and a second drive circuit 108, are provided. In a low brightness range, a high AC voltage with a small duty factor is applied to a fluorescent lamp 113 by means of an output of the first drive circuit 102 and an output of the second drive circuit 108, while in a high brightness range a low AC voltage with a large duty factor is applied to the fluorescent lamp 113.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent lamp dimming circuit, and more particularly to a dimming circuit for a liquid crystal backlight fluorescent lamp.

[0002]

2. Description of the Related Art A conventional example of a fluorescent lamp dimming circuit will be described with reference to FIG. In FIG. 7, 705 is a fluorescent lamp to be dimmed. Reference numeral 704 denotes a capacitor that is connected in series with the fluorescent lamp 705 and operates as a ballast. A transformer 703 introduces electric power to the fluorescent lamp 705, and its secondary winding is connected to the fluorescent lamp 705 and the capacitor 704 in series. 702 is a self-oscillation circuit, and the output thereof excites the primary winding of the transformer 703. A pulse width control circuit 701 and a dimming signal 700 are input to the pulse width control circuit 701.

Here, the primary winding of the transformer 703 is excited by the self-excited oscillation circuit 702, and 1000 V is applied to the secondary winding.
A continuous AC voltage of several tens of kHz is generated and this A
The C voltage is applied to the condenser 704 and the fluorescent lamp 705 which are ballasts connected in series, and the fluorescent lamp 705 is turned on. Then, the pulse width control circuit 701 supplies an output pulse of several 100 Hz to the self-excited oscillation circuit 702 according to the dimming signal, and intermittently generates an AC voltage as shown in FIG. 8 for dimming. is there.

[0004]

The conventional fluorescent lamp light control circuit described above is pulse width modulated by the pulse width modulation output of several 100 Hz which is the output generated by the pulse width control circuit 701 corresponding to the light control signal 700. The self-excited oscillation circuit 702 outputs the AC voltage of several tens of kHz to intermittently operate the fluorescent lamp 705. To make the fluorescent lamp emit light with low brightness by this dimming circuit, the OFF period of the AC voltage is lengthened. However, if the OFF period is dimmed for a long time so that it is ⅕ or less of the rated lighting, both ends of the fluorescent lamp are The surface brightness of the nearby area becomes darker than the surface brightness of the central area, or uneven brightness occurs or the light is turned off.

When a fluorescent lamp is used as a liquid crystal backlight, the uneven brightness on the surface of the fluorescent lamp causes uneven brightness on the liquid crystal surface, which causes a problem that the liquid crystal is not displayed because there is no backlight. This invention has a dimming ratio of 1 for rated lighting.
It is an object of the present invention to provide a fluorescent lamp dimming circuit which solves the above-described problem of causing the fluorescent lamp to uniformly emit light even when the light intensity is / 1000.

[0006]

A first pulse control circuit 10
The first dimming circuit including the first dimming circuit 1 and the first driving circuit 102, and the second dimming circuit including the second pulse control circuit 107 and the second driving circuit 108 are provided. An AC voltage having a high voltage and a small duty factor is applied to the fluorescent lamp 113 in the low luminance region by the output of the driving circuit 102 and an output of the second driving circuit 108, and an AC having a low voltage and a large duty factor is applied in the high luminance region. A fluorescent lamp dimming circuit for applying a voltage to the fluorescent lamp 113 was constructed.

Then, in response to the dimming signal that changes the fluorescent lamp 113 from the low luminance region to the high luminance region, the pulse width is fixed at several 100 nS and the repeating frequency is increased from about 100 Hz to several tens kHz. A first pulse control circuit 101 that outputs a pulse by frequency modulation and that outputs a pulse by pulse width modulation that extends the pulse width from several 100 nS to several tens of μS by fixing the repetition frequency when the repetition frequency is several tens kHz or more. In response to a dimming signal that changes from a low luminance region to a high luminance region, the frequency of about 100 Hz is synchronized with the repetition frequency in the first pulse control circuit 101.
To several tens of kHz, the pulse width is fixed to several 100 nS and the pulse is output by frequency modulation to increase the repetition frequency, and when the repetition frequency is several tens kHz or more, the repetition frequency is fixed and the pulse width is several hundreds.
A second pulse control circuit 107 that outputs a pulse by pulse width modulation that reduces from nS to 0 nS is provided. The output pulse of the first pulse control circuit 101 is input, and the primary pulse of the first transformer 106 is input by this input pulse. Is driven by push-pull, and the secondary winding of the first transformer 106 is driven by about several tens.
The first drive circuit 102 that outputs an AC voltage of 0 V is provided, and the output pulse of the second pulse control circuit 107 is input,
This input pulse push-pull-drives the primary winding of the second transformer 112, and includes a second drive circuit 108 that outputs an AC voltage of about 2000 to 3000 V from the secondary winding of the second transformer 112. A fluorescent lamp dimming circuit was configured by connecting the secondary winding of the first transformer 106 of the driving circuit 102, the secondary side wire of the second transformer 112 of the second driving circuit 108, and the fluorescent lamp 113 in series.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIG. The present invention provides a first dimming circuit including a first pulse control circuit 101 and a first driving circuit 102, and a second dimming circuit including a second pulse control circuit 107 and a second driving circuit 108. A dimming circuit is provided, and an AC voltage having a high voltage and a small duty factor is applied to the fluorescent lamp 113 in the low brightness region by the output of the first drive circuit 102 and the output of the second drive circuit 108, and in the high brightness region. AC voltage with low voltage and large duty factor
3 is a fluorescent lamp dimming circuit to be applied to 3.

More specifically, the first pulse control circuit 101, which constitutes the first dimming circuit, performs a modulation in which repetition frequency modulation and pulse width modulation are combined in proportion to the input dimming signal. It is a circuit that outputs the generated pulse. That is, the repetition frequency of the fluorescent lamp is about 100H in response to the dimming signal changing from the low brightness region to the high brightness region.
From z to several 10 kHz, the pulse width is fixed to several 100 nS and the pulse is output by frequency modulation to increase the repetition frequency, and when the repetition frequency is several 10 kHz or more, the repetition frequency is fixed and the pulse width is several 10 kHz.
A pulse is output by pulse width modulation that extends from 0 nS to 10s of microseconds.

As will be specifically described with reference also to FIG. 2, the first pulse control circuit 101 has 1/100 of the rated luminance.
In the low brightness region of 0 to 1 / several tens, the pulse width is fixed to several hundreds of nanoseconds, and only the repetition frequency changes continuously in the range of about 100Hz to several tens of kHz in proportion to the input dimming signal. Is generated and output. Then, the first pulse control circuit 101 operates in the high-luminance region of 1 / several tens to 1/1 of the rated luminance.
Referring to FIG. 3, the repetition frequency is fixed at several tens of kHz, and the pulse width is proportional to the input dimming signal.
It generates and outputs a pulse that continuously changes within the range of 0 nS to ten and several μS. As described above, the first pulse control circuit 101 generates and outputs a pulse having a small duty factor in the low luminance region, but generates a pulse having a large duty factor in the high luminance region.
Output.

The second pulse control circuit 107 constituting the second dimming circuit is a circuit for generating and outputting a pulse in which frequency modulation proportional to the dimming signal and pulse width modulation inversely proportional to the dimming signal are combined. That is, in response to the dimming signal changing from the low luminance region to the high luminance region, the frequency of about 1 is synchronized with the repetition frequency in the first pulse control circuit.
From 00Hz to several tens of kHz, the pulse width is several 100n
The pulse is output by the frequency modulation that is fixed to S and increases the repetition frequency, and the repetition frequency is several tens of kHz.
Above z, the pulse is output by pulse width modulation that fixes the repetition frequency and reduces the pulse width from several 100 nS to 0 nS.

The second pulse control circuit 107 will be described concretely. 1/1000 to 1 / several tens of the rated brightness
In the low brightness region of, the same pulse as the output pulse is generated in synchronization with the output pulse of the first pulse control circuit 101 and with respect to the repetition frequency and the pulse width.
Output. The second pulse control circuit 107 fixes the repetition frequency to several tens of kHz in a high luminance region of 1 / several tens to 1/1 of the rated luminance and is inversely proportional to the dimming signal, as shown in FIG. A pulse whose pulse width continuously changes within the range of several 100 nS to 0 nS is generated and output. As described above, the second pulse control circuit 107 generates and outputs a pulse having a small duty factor in the low luminance region, and finally generates and outputs a pulse having a smaller duty factor in the high luminance region.

Next, the first drive circuit 102 will be described. This is a circuit for lighting the fluorescent lamp 113 with high brightness. That is, input the output pulse of the first pulse control circuit,
With this input pulse, the primary winding of the first transformer is push-pull driven, and about 100
It is a circuit that outputs an AC voltage of V. The first drive circuit 102 will be described in detail with reference to FIG. 5, in which the output pulse of the first pulse control circuit 101 is input and the input pulse is changed by the toggle circuit 103 as shown in FIG. The signals are applied alternately to the transistors 104 and 105 while being alternately shifted in time, the transistors are alternately turned on, and the primary winding of the first transformer 106 is push-pull driven. In this way, an AC voltage having a voltage peak value of about several hundred volts and a repetition frequency and pulse width equal to the repetition frequency and pulse width of the output pulse of the first pulse control circuit 101 is applied to the secondary winding of the first transformer 106. appear. This AC voltage generated in the secondary winding of the first transformer 106 is applied to the secondary winding of the second transformer 112 in the secondary winding.
From the place where the next winding is connected in series, about 100-2
The voltage drops to 00V and is applied to the fluorescent lamp 113 to light it.

Here, in the low brightness region, the fluorescent lamp 113 is driven by setting the voltage of the supply pulse to a high voltage of about 2000 to 3000 V and reducing the duty factor. If this is not done, uneven brightness will occur or the light will turn off. Then, in the high brightness region, the voltage of the supply pulse is set to a low voltage of about 100 to 200 V, and the duty factor is increased to drive. If you don't do this
The deterioration of the fluorescent lamp progresses rapidly. Therefore, the first driving circuit 102 that generates and outputs a pulse having a low duty factor at a low voltage is a circuit that contributes to exciting the fluorescent lamp 113 in a high-luminance region.

The second drive circuit 108, which is a circuit for lighting the fluorescent lamp 113 at a low brightness, will be described. This is because the output pulse of the second pulse control circuit is input, the primary winding of the second transformer is push-pull driven by this input pulse, and an AC voltage of about 2000 to 3000 V is output from the secondary winding of the second transformer. This is the output circuit. To describe this second drive circuit 108 in detail, the output pulse of the second pulse control circuit 107 is input, and the input pulse is shifted by the toggle circuit 109 alternately in time as shown in FIG. The voltage is applied to the transistor 110 and the transistor 111, and these transistors are alternately turned on to make the second transformer 112
The primary winding is driven by push-pull. Thus, the secondary winding of the second transformer 112 has a voltage peak value of about 20.
An AC voltage having a repetition frequency and pulse width of 0 to 3000 V, which is equal to the repetition frequency and pulse width of the output pulse of the second pulse control circuit 107, is generated. This AC
The voltage is superimposed on the secondary side voltage of the first transformer 106 and applied to the fluorescent lamp 113 to light it. In this way, the output pulse of the second drive circuit 108 depends on the output of the second pulse control circuit 107, and in the low brightness region, A
The C voltage is output, but the AC voltage is hardly output in the high brightness region. This is because, as described above, the fluorescent lamp lights up evenly in the low brightness region without uneven brightness if the pulse voltage is about 2000 to 3000 V and the pulse has a small duty factor. It is necessary to avoid applying high voltage from the viewpoint of preventing deterioration and destruction. Therefore, the second drive circuit 108 that generates and outputs an AC voltage having a high voltage and a small duty factor is a circuit that contributes to exciting the fluorescent lamp 113 in the low luminance region. Here, in the high brightness region, the secondary winding of the second transformer 112 operates as a ballast because there is no input to the primary winding.

In the fluorescent lamp light control circuit of the present invention described above, in the low luminance region, both the first drive circuit 102 and the second drive circuit 108 have the first pulse control circuit 101 and the second pulse control circuit 101 shown in FIG. A with a high voltage and a small duty factor corresponding to the output pulse waveform of the pulse control circuit 107
The C voltage is generated, and the AC voltage that superimposes these is applied to the fluorescent lamp 1.
13 is applied. In the high brightness area, the first
The drive circuit 102 is the first pulse control circuit 1 shown in FIG.
An AC voltage having a low voltage and a large duty factor corresponding to the output pulse waveform of 01 is applied to the fluorescent lamp 113, while the second drive circuit 108 outputs the output pulse of the second pulse control circuit 107 shown in FIG. An AC voltage with a low voltage and a very small duty factor corresponding to the waveform is applied to the fluorescent lamp 11.
No. 3 is applied. After all, in the high-luminance region, the second driving circuit 108 hardly contributes to driving the fluorescent lamp 113, and the first driving circuit 102 exclusively uses the low voltage and the AC voltage having a large duty factor for the fluorescent lamp 113.
Will be driven.

[0017]

As described above, the fluorescent lamp dimming circuit of the present invention includes the first dimming circuit including the first pulse control circuit 101 and the first driving circuit 102, and the second pulse control circuit 107. The second dimming circuit including the second dimming circuit and the second driving circuit 108 is provided, and in the low brightness region, an AC voltage having a high voltage and a small duty factor is applied to the fluorescent lamp 11.
3 and simultaneously, in the high-luminance region, by applying an AC voltage having a low voltage and a large duty factor to the fluorescent lamp 113, deterioration and destruction of the fluorescent lamp is reduced, and there is no luminance unevenness from 1/1000 to 1/1. A wide range of dimming can be performed until the rated lighting is reached. The fluorescent lamp dimming circuit of the present invention is suitable as a dimming circuit for a liquid crystal backlight fluorescent lamp.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating an embodiment.

FIG. 2 is a diagram showing output pulse waveforms of a first pulse control circuit and a second pulse control circuit in a low luminance region.

FIG. 3 is a diagram showing an output pulse waveform of a first pulse control circuit in a high brightness region.

FIG. 4 is a diagram showing an output pulse waveform of a second pulse control circuit in a high brightness area.

FIG. 5 is a diagram showing input / output pulse waveforms of a toggle circuit.

FIG. 6 is a diagram showing input / output pulse waveforms of another toggle circuit.

FIG. 7 is a block diagram illustrating a conventional example.

FIG. 8 is a diagram showing an output waveform of a conventional example.

[Explanation of symbols]

 101 first pulse control circuit 102 first drive circuit 103 toggle circuit 104 transistor 105 transistor 106 first transformer 107 second pulse control circuit 108 second drive circuit 109 toggle circuit 110 transistor 111 transistor 112 second transformer 113 fluorescent lamp

Claims (2)

[Claims] 1. Two dimming circuits, a first dimming circuit including a first pulse control circuit and a first driving circuit, and a second dimming circuit including a second pulse control circuit and a second driving circuit. With the output of the first drive circuit and the output of the second drive circuit, an AC voltage with a high voltage and a small duty factor is applied to the fluorescent lamp in the low brightness region, and a duty factor with a low voltage is applied in the high brightness region. A fluorescent lamp dimming circuit, characterized in that an AC voltage having a large voltage is applied to the fluorescent lamp. 2. The repetition frequency of the fluorescent lamp is about 10 in response to a dimming signal that changes from a low brightness region to a high brightness region.
From 0Hz to several 10kHz, pulse width is several 100nS
The pulse is output by the frequency modulation that is fixed to and the repetition frequency rises, and the repetition frequency is several tens of kHz.
In the above, the first pulse control circuit that outputs a pulse by pulse width modulation that fixes the repetition frequency and expands the pulse width from several 100 nS to ten and several μS is provided, and the dimming that changes from the low brightness region to the high brightness region is provided. Corresponding to the signal, the pulse width is fixed to several 100 nS from a frequency of about 100 Hz to several tens of kHz in synchronization with the repetition frequency in the first pulse control circuit, and the pulse is output by frequency modulation to increase the repetition frequency. Is several tens of kHz or more, it has a second pulse control circuit that outputs a pulse by pulse width modulation that fixes the repetition frequency and reduces the pulse width from several 100 nS to 0 nS, and inputs the output pulse of the first pulse control circuit. , The primary winding of the first transformer is push-pull driven by this input pulse , A first drive circuit that outputs an AC voltage of about several hundreds of volts from the secondary winding of the first transformer, and receives the output pulse of the second pulse control circuit, and the input pulse causes the primary winding of the second transformer. Approximately 2000-3000 from the secondary winding of the second transformer by push-pull driving the wire.
A second drive circuit for outputting an AC voltage of V is provided, and the secondary winding of the first transformer of the first drive circuit, the secondary side wire of the second transformer of the second drive circuit, and the fluorescent lamp are connected in series. A fluorescent light dimming circuit characterized in that