JP2000268986A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent moving streaks of a modulated light based on a simple circuit configuration without using parts allowing high withstand pressure and high electric current. SOLUTION: In this lighting device provided with a push-pull circuit 1 connected between a dc electric power source 7 and a discharge lamp 3 and a control circuit 2 for controlling a pair of switching elements 11 and 12 of the push-pull circuit 1 to light the discharge lamp 3, input or output of one of switching elements 11 and 12 of the push-pull circuit 1 is fed back by impedance and the switching elements 11 and 12 are controlled to shift the timing to turn off. Thereby, a high frequency electric power supplied to the discharge lamp 3 is made to have an asymmetric waveform with respect to the positive and negative parts.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a discharge lamp lighting device for lighting a discharge lamp at a high frequency.

[0002]

2. Description of the Related Art In a discharge lamp lighting device, a high frequency lighting system using an inverter is used to increase the efficiency of the discharge lamp.

[0003] A discharge lamp lighting device of a high frequency lighting system is composed of a plurality of switching elements (transistors), and an inverter circuit connected between a DC power supply and the discharge lamp, and controls on / off of the switching elements. Control circuit, a DC blocking capacitor and an inductor connected in series between the discharge lamp and the switching element,
A resonance capacitor connected in parallel to the discharge lamp,
There is a lighting device having a structure in which a switching circuit of an inverter circuit is alternately turned on by a control circuit to convert an output voltage of a DC power supply into a high-frequency voltage and supply the high-frequency voltage to a discharge lamp.

[0004] By the way, when a discharge lamp is lit by a high-frequency lighting method, it is conventionally known that moving stripes are generated. In particular, moving fringes are likely to occur when the ambient temperature is low or when the current flowing through the discharge lamp is reduced.

As means for eliminating such moving fringes,
Conventionally, it has been known that the voltage of a discharge lamp is made asymmetrical between positive and negative, and some specific configurations have been proposed.

For example, Japanese Patent Application Laid-Open No. 9-7777 discloses an inverter for inputting a DC voltage and converting it to a high-frequency voltage, a control circuit for controlling the operating frequency of the inverter based on a dimming signal, and a connection to the output side of the inverter. Lamp dimming lighting device having a series circuit consisting of a coil, a discharge lamp, and a DC cut capacitor supplied to the discharge lamp by adding a series circuit consisting of a resistor and a rectifying element in parallel with the DC cut capacitor. There is disclosed a circuit configuration for asymmetrical AC power (positive / negative asymmetric waveform) to prevent moving fringes.

In Japanese Patent Application Laid-Open No. 6-104092, two sets of a series circuit of two switching elements are connected in parallel with a DC power supply (full bridge connection), and switching of each switching element of one of the series circuits is performed. By turning on and off alternately with different periods and alternately turning on and off each switching element of the other series circuit with the same switching cycle as one of the switching elements of one series circuit, LC resonance There is disclosed an apparatus for preventing moving fringes by making positive and negative power supplied to a circuit unbalanced (positive / negative asymmetric waveform).

[0008]

According to the circuit configuration disclosed in Japanese Patent Application Laid-Open No. 9-7777, among the above-mentioned prior arts, the means for changing the voltage of the discharge lamp into a positive / negative asymmetric waveform is provided by a switching element. Since it is provided on the load (discharge lamp) side, it is necessary to use a component that allows a high withstand voltage and a large current, and there are problems in terms of component reliability, cost, and power loss.

On the other hand, according to the device described in Japanese Patent Application Laid-Open No. 6-104092, since a positive / negative asymmetric waveform is created by the control of the control circuit, it is not necessary to use parts having a high withstand voltage and a large current. Is a full bridge circuit, so that there is a problem that the number of components such as switching elements increases.

The present invention has been made in view of such circumstances, and it is an object of the present invention to prevent light-adjusting moving fringes with a simple circuit configuration without using components that allow a high withstand voltage and a large current. It is an object of the present invention to provide a discharge lamp lighting device which can be used.

[0011]

To achieve the above object, a discharge lamp lighting device according to the present invention comprises a push-pull circuit (inverter circuit) connected between a DC power supply and a discharge lamp.
And a control circuit for controlling the on / off of the pair of switching elements of the push-pull circuit to turn on the discharge lamp, and the control circuit staggers the timing of turning off the pair of switching elements of the push-pull circuit. , Which are configured to create positive and negative asymmetric waveforms.

In the discharge lamp lighting device according to the present invention, as a specific configuration for producing a positive / negative asymmetric waveform, one of the input or output of a pair of switching elements of the push-pull circuit is fed back to the control circuit by impedance. Shift the timing to turn off the switching element,
Configuration.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of the present invention. The discharge lamp lighting device shown in FIG. 1 includes a pair of switching elements (transistors) 11 and 12, a push-pull circuit (inverter circuit) 1 connected between a DC power supply 7 and a discharge lamp 3, Control circuit 2 for controlling on / off of elements 11 and 12
A DC blocking capacitor 4 and an inductor 5 connected in series between the switching elements 11, 12 and the discharge lamp 3, and a resonance capacitor 6 connected in parallel to the discharge lamp 3. The control circuit 2 alternately turns on the switching elements 11 and 12 of the push-pull circuit 1 to convert the output voltage of the DC power supply 7 into a high-frequency voltage and supply it to the discharge lamp 3. .
Note that each switching element 11 of the push-pull circuit 1
12, the diodes 13 and 14 are built in parallel.

The present embodiment is characterized by the operation of the control circuit 2 for controlling the pair of switching elements 11 and 12. That is, as shown in the timing chart of FIG. 2, the pulse width of one of the drive signals V1 and V2 output from the control circuit 2 to the push-pull circuit 1 is reduced so that the pair of switching elements 11 and 12 are switched. The feature is that the off timing is shifted.

By performing such switching control, the high-frequency voltage supplied to the discharge lamp 3 has a positive / negative asymmetric waveform, whereby the current flowing through the discharge lamp 3 is reduced when the ambient temperature of the discharge lamp 3 is low. Even in this case, it is possible to prevent the occurrence of moving stripes.

In the above-described embodiment, the pulse width of the drive signal V2 supplied to the switching element 12 connected to the low voltage side of the pair of switching elements 11 and 12 of the push-pull circuit 1 is reduced to be positive-negative asymmetric. Although the waveform is generated, the reverse configuration, that is, a configuration in which the pulse width of the drive signal V1 supplied to the switching element 11 connected to the high voltage side is reduced as shown in the timing chart of FIG. Good.

FIG. 4 is a block diagram showing the configuration of the control circuit 2. Hereinafter, another embodiment of the present invention will be described with reference to FIG.

First, the control circuit 2 includes a triangular wave generation circuit 2
1, a comparator 22, a pulse distribution circuit 24, a pulse amplification circuit 25, and the like. The output signal A1 from the triangular wave generation circuit 21 is compared with a control signal (dimming signal) A2 by the comparator 22, and the drive signal Pout And a pulse is supplied to the push-pull circuit 1.

The embodiment is characterized in that a mixing circuit 23 is provided at the input of the control signal A2, and one output E2 of the push-pull circuit 1 is fed back to the control signal A2 by impedance. By applying such signal feedback, the high-frequency voltage supplied to the discharge lamp 3 has a positive / negative asymmetric waveform. The operation will be described below.

First, when no feedback is applied (in the case of a conventional circuit configuration), as shown in the timing chart of FIG.
A signal generated by the output signal (triangular wave) A1 of the triangular wave generating circuit 21 and the control signal (linear waveform) A2, that is, the comparator output Pout is a waveform signal having a constant pulse duty ratio, and the two outputs of the push-pull circuit 2 The pulse widths of E1 and E2 are the same.

On the other hand, as shown in FIG. 4, when the output E2 of the push-pull circuit 1 is fed back to the control signal A2 by impedance, as shown in the timing chart of FIG. 5, the comparator output Pout has a waveform as shown in FIG. 5, and the pulse width of one output E1 of the push-pull circuit 1 changes. The timing for turning off the element 11 or 12 can be shifted, and a high-frequency voltage having a positive / negative asymmetric waveform can be supplied to the discharge lamp 3.

In the example shown in FIG. 4, the output E2 of the push-pull circuit 1 is fed back to the control signal A2 by impedance. However, the output E1 of the push-pull circuit 1 is fed back to the control signal A2 by impedance. You may. In this case, the control signal A2 changes according to the output E1 of the push-pull circuit 1, and the pulse width of one output E2 of the push-pull circuit 1 changes.

Here, the present invention can be applied to a discharge lamp lighting device using a switching regulator (TL494) 8 based on a pulse width control method as shown in FIG. 7 as a push-pull circuit. In this case, one of the outputs E1 and E2 of the switching regulator (TL494) 8 is fed back to Rt or Ct by impedance, so that the pulse width of one output E1 or E2 can be changed.

[0025]

As described above, according to the discharge lamp lighting device of the present invention, the timing of turning off the pair of switching elements of the push-pull circuit is shifted by the control of the control circuit, so that the high frequency applied to the discharge lamp is controlled. Since the voltage is asymmetrical in waveform to prevent moving fringes, it is not necessary to use components having a high withstand voltage and a large current, thereby increasing the reliability of each component and reducing power loss. Moreover, since a push-pull circuit (half-bridge circuit) is employed as the inverter, the number of components can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a timing chart showing the operation of the embodiment of FIG.

FIG. 3 is a timing chart showing another example of the operation of the embodiment of FIG. 1;

FIG. 4 is a main configuration (control circuit) of another embodiment of the present invention.
FIG.

FIG. 5 is a timing chart showing the operation of the embodiment of FIG.

FIG. 6 is a timing chart showing an operation of a control circuit of a conventional discharge lamp lighting device.

FIG. 7 is a block diagram showing a configuration of a switching regulator (TL494).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 push-pull circuit 11, 12 switching element 13, 14 diode 2 control circuit 21 triangular wave generating circuit 21 a comparator 21 b integrator 22 comparator 23 mixing circuit 3 discharge lamp 4 capacitor (for blocking DC current) 5 inductor (for blocking DC current) 6 Resonant capacitor 7 DC power supply 8 Switching regulator (TL494)

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 3K072 AA02 BA03 BC01 BC03 CA02 DB03 DD04 GA03 GB12 GC04 HA10 HB03 3K098 CC44 CC62 DD22 DD37 EE14 EE32 GG02 5H007 BB03 CA02 CB06 DB01 DC05 EA08 5H730 AA15 AS11 BB11 BB62 FF62

Claims (2)

[Claims] 1. A push-pull circuit connected between a DC power supply and a discharge lamp, and a control circuit for controlling on / off of a pair of switching elements of the push-pull circuit to turn on the discharge lamp, A discharge lamp lighting device, wherein the control circuit is configured to generate a positive / negative asymmetric waveform by shifting a timing of turning off a pair of switching elements of a push-pull circuit. 2. The push-pull circuit is characterized in that an input or an output of one of a pair of switching elements of the push-pull circuit is fed back to a control circuit by impedance to shift a timing of turning off the switching element. The discharge lamp lighting device according to claim 1.