JPH01163999A - Lighting circuit for electric discharge lamp - Google Patents

Abstract

PURPOSE:To make sure the longer lifetime of an electric discharge lamp and the smooth dimmering thereof by applying the filament of the electric discharge lamp with alternated voltage from a d.c. power supply via a waveform conversion device for heating, and enabling the variable control of a discharge current value. CONSTITUTION:When one pair of switching elements S1 and S3 are in a continuity mode and the other pair of switching elements S2 and S4 are in an interrupted mode respectively on a certain timing, the forward direction of a d.c. power supply is from a point (a) to another point (d) via the switching element S1, the terminals (b) and (c) of a filament 16 and a switching element S3, respectively in turn. When the switching elements S1 and S3 are in an interrupted mode and the switching elements S2 and S4 are in a continuity mode on the next timing, the forward direction of the power supply 13 is from the point (a) to the point (d) via the element S4, the terminals (c) and (b) of the filament 16 and the element S2 respectively in turn. An electric current if, therefore, alternately flows between the terminals (b) and (c) of the filament 16, thereby heating the filament 16 and averaging the potential gradient nearly to a constant value across the terminals (b) and (c). In addition, a discharge current value can be variably controlled.

Description

TECHNICAL FIELD The present invention relates to a lighting circuit for a discharge lamp, and more particularly to a lighting circuit for a discharge lamp that is suitably implemented in a display device or the like composed of a large number of hot cathode discharge lamps.

Background technology A hot cathode discharge lamp heats a filament, which is a cathode, applies a voltage between an anode and a cathode, and uses the light emitted from a positive column inside the tube due to arc discharge between both electrodes as a light source. Fluorescent lamps have the characteristics of low power consumption, high efficiency, and high color rendering, and recently the hot cathode discharge lamps (
2. Description of the Related Art A large display device called a so-called jump screen, in which a large number of pixels (hereinafter abbreviated as discharge lamps) are arranged as pixels to form a large display screen, has been realized and is in use.

The lighting circuit for the discharge lamp that forms such a display device includes:
A dimming method using a DC power supply was adopted for ease of control.
The filament is preheated to maintain a weak discharge during dimming.

FIG. 3 is an electrical circuit diagram of a discharge lamp lighting circuit according to the prior art. The anode 5 of the discharge lamp 1 has a first terminal voltage v1.
The anode of the DC power supply 2 is connected via a current limiting resistor 4,
The voltage v2 of the second DC power source 3 is connected between the terminals 7 and 8 of the Hiramentoro, which are cathodes, with the terminal 701 of the Hiramentoro connected to the negative terminal and the terminal 8 side connected to the negative electrode, and the first il! [Flow power source 2
and the negative electrodes of the second DC power supply 3 are commonly connected to the line IO. The discharge lamp 1 is dimmed by varying the current limiting resistor 4 and adjusting the discharge current i.

However, in the lighting circuit shown in FIG. 3, since a potential gradient equal to the voltage v2 is generated across the Hiramentoro, discharge occurs between the anode 5 and the low potential side of the Hiramentoro, that is, the terminal 8 side, and therefore the Hiramentoro The wear and tear of the emission film on the surface is concentrated in one place, resulting in a shortened lifespan of the discharge lamp 1, and in a display device consisting of a large number of discharge lamps, maintenance problems such as replacement of discharge lamps may occur. There were also spots.

In order to eliminate such problems, a lighting circuit shown in FIG. 4 has been proposed. Figure 4 is similar to Figure 3;
In the lighting circuit shown in FIG. 4, in which corresponding parts are given the same reference numerals, the secondary voltage V3 of the transformer T connected to the AC power supply AC is applied to the filament terminal of the discharge lamp 1, and the first DC power supply 2 One side is the midpoint C of the secondary winding of the transformer T.
It is connected to the. This averages out the surface potential of Hiramentoro and eliminates the aforementioned problems.

However, in the lighting circuit shown in Figure 4, a transformer T is required to obtain the voltage 3 suitable for Hiramentoro, and although this is fine when a small number of discharge lamps are used, in the above-mentioned display device, a large number of discharge lamps are used. As a result, the weight and dimensions of the transformer become enormous, creating problems such as transportation and installation, and replacing defective discharge lamps requires a great deal of time and effort. There were also points.

Purpose The present invention has been made in view of the above-mentioned problems, and its purpose is to provide a compact and lightweight discharge lamp that can be suitably implemented for lighting and dimming a large number of discharge lamps. An object of the present invention is to provide a lighting circuit.

Embodiment FIG. 1 is an electrical circuit diagram of a lighting circuit for a discharge lamp according to an embodiment of the present invention. The first DC power supply 12 for applying the voltage Vll necessary for discharging the discharge lamp 11 between the anode 15 and the filament 16 which is the cathode has its anode connected to the anode 15 via the current limiting resistor 14, and the filament 16 which is the cathode. A second DC power supply 13 that supplies power for heating is connected to a switching inverter circuit 17 as a waveform conversion means that converts its terminal voltage V12 into an alternating voltage V13 with a predetermined cycle. The negative electrodes of the first DC power source 12 and the second DC power source 13 are commonly connected to the line 11.

As will be described later, the alternating voltage V13 outputted after waveform conversion by the switching inverter circuit 17 is applied between the terminals b and c of the filament 16, and
Heat 6. In addition, the resistance value of the current limiting resistor 14 interposed between the first DC power source 12 and the anode 15 is varied so that the discharge current i
a to perform a dimming operation.

The switching inverter circuit 17 is realized by connecting semiconductor switching elements 81 to S4, such as a plurality of transistors or thyristors, in a bridge circuit, and one of the pair of switching elements Sl and S3
When the other switching element 82 . is in a conductive state, the other switching element 82 . S4
The switching mode in which the switch is in a cut-off state is reversed at a predetermined period under control from a control circuit (not shown).

In FIG. 1, for example, if one pair of switching elements SL and S3 are in a conductive state and the other pair of switching elements S2 and S4 are in a cutoff state at a certain timing, the second DC current at this time The forward direction of the power supply 13 is as follows: reference symbol a → switching element S1 → filament 16
Terminal b → same terminal C → switching element S3 → reference mark d
If the switching mode is reversed at the zero-order timing along the path, and the switching elements Sl and S3 are in the cutoff state and the other pair of switching elements S2 and 34 are in the conduction state, the second DC power supply 13 at this time The forward direction is as follows: reference mark a→switching element S4→terminal C of filament 16→
The switching element S2 from the same terminal b follows the path indicated by reference numeral d.

Therefore, an alternating voltage V13 according to the above-mentioned timing is derived between the terminals b and c of the filament 16, and as a result, the current if flows in the filament 16 in alternating directions as shown by the solid line and the broken line, and the filament 16
, while the potential gradient between terminals b and c of the filament 16 is averaged almost constant across it due to the alternating voltage V13. This prevents problems such as concentration of discharge on low-potential locations on the filament 16 as described in the background art section, and extends the life of the discharge lamp 11. Further, in this embodiment, as a means for obtaining the alternating voltage V13, a waveform converting means is formed by a semiconductor switching element without using a transformer, thereby achieving a reduction in size and weight.

FIG. 2 is a timing chart illustrating the operation of the lighting circuit of this embodiment. Hereinafter, with reference to FIG. 1, a description will be given assuming that conduction is ON and interruption is OFF.

FIG. 2 (1) shows the switching mode of the switching element s1. The switching element 81 is OF at time t1.
F, the operation of turning on at time t8, turning off at time t9, and so on is repeated.

FIG. 2 (2) shows the switching mode of the switching element s2. The switching element s2 is turned on at time t2, which is delayed by a time ΔT from the above-mentioned time t1, and turned OFF at a time t7, which is delayed by a time ΔT from the above-mentioned time t8. Above time t9
The operation of turning on, . . . is repeated at time tlo, which is delayed by a time ΔT.

FIG. 2(3) shows a switching mode of the switching element S3. The switching element S3 forms a pair with the switching element S1, and is turned off at time t3, which is delayed by a time corresponding to time 2ΔT from the time t1. Time t
Turns ON at time t6, which is a time corresponding to time 2ΔT from 8, and is turned on at time t6, which is delayed by time 2ΔT from time t9.
Turn on with l, repeat the operation.

FIG. 2 (4) shows the switching mode of the switching element S4. The switching element S4 forms a pair with the switching element S2, and is turned on at 'jAt4 when delayed by a time corresponding to the time 3ΔT from the time t1. A time t5 that has advanced by a time corresponding to time 3ΔT from the time t8
ON, time t delayed by time 3ΔT from the time t9
Turn on at 12, repeat the operation.

Due to the above timing, switching elements S2 and S4
The period in which the terminals are simultaneously turned on is, for example, a period T1 between times t4 and t5, and during this period T1, the current if flows in the direction shown by the broken line in FIG. 1 (direction from terminal C→b).

Next, the period in which the switching elements Sl and S3 are simultaneously turned on is, for example, a period T2 between times t8 and t9, and during this period T2, the current if is directed in the opposite direction as shown by the solid line in FIG. 1- Flows in (direction).

As is clear from FIG. 2, the times Tl and T2 are equal;
Moreover, the switching elements SL, S2, and the switching element S3. With S4, both are not turned on at the same time,
Therefore, since there is always an OFF period TO corresponding to 2Δt when viewed from the second DC power supply 13, short-circuiting of the second DC power supply 13 is prevented, and furthermore, switching elements S2 and 8
3 share an ON period corresponding to the time 2ΔT, the path of the discharge current ia is not cut off as seen from the first DC power supply 12, and therefore the discharge lamp 11 continues safe and stable discharge.

In the above-described embodiment, the first DC power supply 12 and the second DC power supply 13 are separated, but they may be formed by − number of DC power supplies, and the voltage may be divided midway to obtain the voltage V12. Furthermore, the above DC power supply can be realized by a small and highly efficient so-called switching power supply, and as a result, the structure and connection of the entire lighting circuit can be made smaller and simpler, and the weight can be significantly reduced.

Effects As described above, the lighting circuit for a discharge lamp according to the present invention uses a DC power supply, and for heating the filament of the discharge lamp, alternating voltage is applied from the DC power supply to the filament via a waveform conversion means. As a result, the potential gradient of the filament is averaged, concentration of discharge due to the potential gradient and damage to the filament due to this is prevented, and the life of the discharge lamp is extended.

In addition, since the discharge current value can be variably controlled, the dimming of the discharge lamp can be smoothly performed.6 The lighting power source is DC, so
It becomes possible to use small, highly efficient so-called switching power supplies instead of heavy items such as transformers, and the overall lighting circuit configuration and connections are made smaller and simpler, and the weight is also significantly reduced. As a result, a discharge lamp lighting circuit suitable for a large display device constituted by a large number of discharge lamps is realized.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram of a lighting circuit for a hot cathode discharge lamp according to an embodiment of the present invention, FIG. 2 is a time chart showing its operation, and FIG. 3 is an electric circuit diagram of a lighting circuit according to the prior art. 4
The figure is an electrical circuit diagram of another prior art lighting circuit. 11... Hot cathode discharge lamp, 12... First DC power supply,
13... Second DC power supply, 14... Current limiting resistor, 1
5...Anode, 16...Cathode (Hilament), 81~
S4...Switching element agent Patent attorney Number of strokes Keiichi Figure 1 Figure N2

Claims (1)

[Scope of Claims] A first DC power supply for applying voltage necessary for discharge between the anode and cathode of the discharge lamp, and a second DC power supply for supplying power for heating the cathode of the discharge lamp.
A lighting circuit for a discharge lamp, comprising: a DC power supply; and a waveform conversion means for converting the DC voltage of the second DC power supply into an alternating voltage with a predetermined cycle.