JP2000357599A - Lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lighting device in which an adverse effect of an abrupt change in magnetic flux is improved. SOLUTION: A control circuit 14 controls an ON time width of a switching element 3 in response to a signal from a tube current detecting circuit 13 in such a manner as that a voltage to be supplied to an inverter circuit 1 becomes constant. A resistance element 17 is interposed between a duty cycle signal input and the tube current detecting circuit 13. Since this connection enables a high voltage signal produced from a duty cycle signal V2 to be transmitted to the tube current detecting circuit 13 even if a detection signal from a lighting tube 12 becomes zero at turn-off of a flashing operation, the control circuit 14 receives the signal as if there is flowing a tube current, shortens the turn-on time to the switching element 3, and then, stops supplying the voltage to the inverter circuit 1. In contrast, at the time of turn-on of the flashing operation, the control circuit 14 gradually raises a drive pulse in advance in the state in which the turn-on time of the switching element 3 is zero.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device for lighting a lighting tube used for a backlight of a liquid crystal panel, and more particularly to a lighting device for performing a wide range of brightness adjustment.

[0002]

2. Description of the Related Art In general, in order to obtain a wide light control range, there is a light control method in which a lighting tube is blinked (on / off) at a constant cycle to change a duty of a lighting period.

FIG. 5 is a block diagram showing an example of a lighting device using the prior art, FIG. 6 is a block diagram showing another example of a lighting device using the conventional technology, and FIGS. ), (C)
FIG. 7 is a diagram showing an example of the operation waveforms of FIGS. 5 and 6;

The lighting device shown in FIG. 5 includes an inverter circuit 1, an input power supply 2, switching elements 3 and 6, a rectifying element 4, an inductor 5, a lighting tube 12, a tube current detecting circuit 13,
A control circuit 14 and a resistance element 15 are provided.

[0005] The inverter circuit 1 includes a resistance element 7A,
7B, capacitors 8, 11, switching elements 9A, 9
B, and a drive transformer 10.

A circuit for generating a duty signal (PWM signal) V2 composed of a rectangular wave 16 may be provided inside the lighting device or may be provided on the peripheral device side. The symbol V1 in the inverter circuit 1 is
This is the collector voltage of the switching elements 9A and 9B.

In this configuration, the switching element 6 is driven by the duty signal (PWM signal) V2, and the base current to the switching elements 9A and 9B of the inverter circuit 1 is supplied at a constant cycle and with a certain duty to obtain intermittently. Ignition tube 1 by the voltage from the inverter circuit 1
2 flashes.

Similarly, the lighting device shown in FIG. 6 includes a synthesizing means 18 for combining the pulse signal from the control circuit 14 and the duty signal V2, and supplies a signal current to the switching element 3 at a constant cycle and with a certain duty. Thus, the voltage supply to the inverter circuit 1 is performed intermittently. With the output voltage from the inverter circuit 1 obtained by this,
The flashing of the lighting tube 12 is performed.

FIGS. 7 (a), 7 (b) and 7 (c) show a state where a high-frequency oscillation pulse train of the switching element 9A (or 9B) in the inverter circuit 1 is generated when the duty signal (PWM signal) V2 is high. It shows. According to this waveform observation, as shown in (b) and (c) of the figure, an overshoot occurs when blinking is turned on (or both when turned on and when turned off).

[0010]

The conventional duty dimming method by blinking is a method in which a voltage capable of securing a maximum luminance state is intermittently applied to a luminous tube in an audible frequency range to repeatedly turn on and off. When the lamp is turned off, the signal level from the tube current detection circuit becomes zero level. At the next lighting, the control circuit generates a signal that starts the tube current from the maximum level, as shown in FIG. Causes overshoot in the waveform.

For this reason, there is a disadvantage that the magnetic flux of the drive transformer greatly changes and the vibration sound (noise) of the step-up transformer is large over the entire dimming range. In addition, there is a disadvantage that line noise due to overshoot at the time of blinking (on / off) adversely affects peripheral circuits.

It is an object of the present invention to provide a lighting device in which a change in magnetic flux of a drive transformer in the audible region is suppressed as much as possible and an adverse effect caused by a sudden change in magnetic flux is improved.

[0013]

To achieve the above object, a first aspect of the present invention comprises an input power supply, a switching element, an inverter circuit, a lighting tube, a tube current detection circuit, and a control circuit, wherein a tube current detection circuit is provided. A lighting device that drives a switching element with a pulse signal from a control circuit based on a circuit signal and a duty dimming signal and blinks a lighting tube with a voltage from an inverter circuit obtained intermittently; A resistance element is connected between the optical signal input section and the tube current detection circuit.

In order to achieve the above object, a second aspect of the present invention comprises an input power source, a switching element, an inverter circuit, a lighting tube, a tube current detection circuit, and a control circuit, based on a signal from the tube current detection circuit. A pulse signal from the control circuit;
In a lighting device, which drives a switching element by a duty dimming signal and blinks a lighting tube by a voltage from an inverter circuit obtained intermittently, a rectifier is provided between the duty dimming signal input portion and a tube current detection circuit. It is characterized in that the elements are connected.

In the first aspect of the present invention, the duty dimming signal is injected into the tube current detection circuit via the resistance element, and the rising waveform and the falling waveform are inclined.
Vibration noise (noise) from the inverter drive transformer can be reduced.

In the second aspect of the present invention, the duty dimming signal is injected into the tube current detection circuit via the rectifying element, and the rising waveform and the falling waveform are inclined.
Vibration noise (noise) from the inverter drive transformer can be reduced.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of a lighting device according to an embodiment of the present invention, and FIG. 2 is an operation waveform diagram thereof.

The lighting device shown in FIG. 1 includes an inverter circuit 1, an input power supply 2, a switching element 3, a rectifying element 4, an inductor 5, a lighting tube 12, a tube current detecting circuit 13, and a control circuit 14. Further, a resistance element (or a rectifying element) 17 is provided between the input part of the duty signal (PWM signal) V <b> 2 and the tube current detection circuit 13.

The control circuit 14 receives the signal from the tube current detection circuit 13 and controls the ON time width of the switching element 3 so that the voltage supplied to the inverter circuit 1 becomes constant. Here, the frequency for driving the switching element 3 is several tens to several hundreds kHz, and the lighting frequency of the lighting tube 12 is several tens of kHz.
Hz and the frequency of the duty signal for blinking use a frequency band in the audible range that is sufficiently lower (several tens Hz to several kHz) than the lighting frequency.

Then, the resistance element 17 outputs the duty signal V
2 and the tube current detection circuit 13, even when the detection signal from the lighting tube 12 becomes zero when the flashing operation of the lighting tube 12 is turned off, the duty signal V2 High level voltage signal from the tube current detection circuit 1
3, the control circuit 14 receives the signal as if a tube current is flowing, narrows the ON time to the switching element 3, and stops the voltage supply to the inverter circuit 1.

When the flashing operation of the lighting tube 12 is turned on, the control circuit 14 gradually raises the driving pulse from the state where the on time of the switching element 3 is zero in advance, so that no overshoot occurs. .

FIG. 2A shows V1 when the duty is 100%.
(Collector voltage of switching elements 9A and 9B), V2
(B) shows the operation waveforms of V1 and V2 when the duty is 60%, and (c) shows the operation waveforms of V1 and V2 when the duty is 40%. According to No. 2, it is observed that no overshoot occurs when the flashing of the lighting tube 12 is on (or both on and off).

FIG. 3 is a block diagram showing a specific example of the lighting device shown in FIG. The tube current detection circuit 13 is configured by connecting resistors R1 and R4, a capacitor C1, and a diode D1 in parallel to the resistors R2 and R3 connected in series. Further, a rectifying element composed of a diode can be used instead of the resistance element 17 as shown by a dashed line.

FIG. 4 is a block diagram showing another example of the tube current detection circuit. The tube current detection circuit 13 shown in FIG.
1, R4, capacitor C1, and diode D1 are connected in parallel. Further, the tube current detection circuit 13 shown in (b) is configured to connect the resistors R1 and R4 and the capacitor C to the resistors R2 and R3 and the diode D2 connected in series.
1. The diode D1 is connected in parallel.

[0025]

According to the first aspect of the present invention,
By injecting the duty dimming signal into the tube current detection circuit via the resistance element and giving rise and fall waveforms to slopes, vibration noise (noise) from the inverter drive transformer can be reduced.

According to the second aspect of the present invention, the duty dimming signal is injected into the tube current detection circuit via the rectifying element, so that the rising waveform and the falling waveform have slopes, thereby providing an inverter. It has features such as the ability to reduce the vibration noise (noise) from the drive transformer.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing an example of an operation waveform of the lighting device.

FIG. 3 is a configuration diagram showing a specific example of the lighting device.

FIG. 4 is a configuration diagram showing another example of the tube current detection circuit.

FIG. 5 is a configuration diagram illustrating an example of a lighting device according to a conventional technique.

FIG. 6 is a configuration diagram showing another example of a lighting device according to the related art.

FIG. 7 is a diagram showing an example of an operation waveform showing the operation of FIGS. 5 and 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter circuit 2 Input power supply 3 Switching element 4 Rectifying element 5 Inductor 6 Switching element 7A Resistance element 7B Resistance element 8 Capacitor 9A Switching element 9B Switching element 10 Driving transformer 11 Capacitor 12 Lighting tube 13 Tube current detection circuit 14 Control circuit 15 Resistance Element 16 Rectangular wave 17 Resistance element 18 Synthesizing means V1 Collector voltage of switching element V2 Duty signal (PWM signal)

Claims (2)

[Claims] An input power supply, a switching element, an inverter circuit, a lighting tube, a tube current detection circuit, and a control circuit, wherein a pulse signal from a control circuit based on a signal of the tube current detection circuit and a duty dimming signal are used. In a lighting device that drives a switching element and blinks a lighting tube with a voltage from an inverter circuit obtained intermittently, a resistance element is connected between the duty dimming signal input unit and the tube current detection circuit. Characteristic lighting device. 2. An input power supply, a switching element, an inverter circuit, a lighting tube, a tube current detection circuit, and a control circuit, wherein a pulse signal from a control circuit based on a signal of the tube current detection circuit and a duty dimming signal are used. In a lighting device that drives a switching element and blinks a lighting tube with a voltage from an inverter circuit obtained intermittently, a rectifying element is connected between the duty dimming signal input unit and the tube current detection circuit. Characteristic lighting device.