JPH0322040B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a discharge lamp lighting device that lights a discharge lamp with direct current and bypasses the lamp current to a switch element to dim the discharge lamp. This discharge lamp lighting device is particularly suitable for use as a device for controlling the light of a plurality of discharge lamps individually, such as a display device.

[Background of the Invention] Conventionally, incandescent lamps, fluorescent lamps,
It is known that a display surface is constructed by arranging a large number of picture elements, each consisting of a light source such as a light-emitting CRT, in a matrix.

When using discharge lamps (lamps) as picture elements in such display devices, it is necessary to perform dimming lighting based on video signals, but for this purpose it is easy to use switch elements such as transistors for each lamp. It is desirable to use direct current for lighting.

However, if an attempt is made to directly light a discharge lamp with a DC power source, a negative resistance must be used as a current-limiting element of the discharge lamp, resulting in a large loss. When using a bulk power supply that is equipped with a high-frequency generator such as an inverter and generates high-frequency output from a DC power supply, this high-frequency output is limited by an inductor, and the discharge lamp is lit with the output that is full-wave rectified by a diode bridge. , the current limiting element becomes an inductor, which solves the above problem of loss, but when using multiple such lighting circuits, a common potential point cannot be obtained between each lighting circuit, and the power supply for filament preheating and dimming It is necessary to provide a DC power supply for the control circuit for each lighting circuit, or to use a transformer to connect the dimming switch element and the dimming control circuit, which leads to problems such as a complicated circuit configuration and an increase in the size of the circuit. It was hot. Furthermore, according to a lighting circuit that lights a discharge lamp with a current that is current-limited and half-wave rectified from the high-frequency output from the bulk power supply using a series circuit of an inductor and a diode, the above-mentioned problems of loss and common potential point can be solved. Although the problem was solved, there was a problem that the power transformer and the current limiting inductor became biased and magnetized, resulting in an increase in size.

FIG. 1 shows the circuit configuration of a discharge lamp lighting device previously filed by the present applicant as Japanese Patent Application No. 109390/1983. In the figure, reference numeral 1 denotes a bulk AC power supply such as a high frequency generator, to which the primary winding 2p of a power transformer 2 having a secondary winding 2s with a center tap is connected, and the secondary winding 2s has one end a connected to the winding start end of the first winding 31 of the ballast yoke 3, and the other end b connected to the winding end of the second winding 32 of the ballast yoke 3. Also, ballast yoke 3
The winding end of the first winding 31 and the second winding 32 of
The starting ends of the windings are connected to the anodes of diodes 4 and 5, respectively, and the cathodes of diodes 4 and 5 are both connected to the positive electrode of a discharge lamp (lamp) 6,
The negative pole of this lamp 6, that is, one end of the filament is connected to the center tap (neutral wire) c of the secondary winding 2s of the power transformer 2. Here, the ballast chain yoke 3 and diodes 4 and 5 connected to the secondary winding 2s of the power transformer 2 constitute a center tap type full-wave rectifier circuit, and the common cathode of the diodes 4 and 5 A full-wave rectified output is generated between the center tap c of the secondary winding 2s of the power transformer 2 and the center tap c of the secondary winding 2s of the power transformer 2. Reference numeral 7 designates a switch, such as a transistor, which dims the lamp 6 by short-circuiting and opening both ends of the lamp 6.

Next, the operation of this discharge lamp lighting device will be explained.

When the AC power supply 1 is turned on, the output voltage at both ends a and b of the secondary winding 2s of the power transformer 2 is 180° different from the neutral wire c as shown in FIG. Equal two-phase AC outputs are generated. Diodes 4 and 5 rectify this two-phase AC output to generate a full-wave rectified output. When the transistor 7 is off, this full-wave rectified output is supplied to the discharge lamp 6 to light the discharge lamp 6, and on the other hand, when the transistor 7 is on, it is bypassed by the transistor 7 and the discharge lamp 6 is turned on. does not light up. That is, discharge lamp 6
The light is dimmed according to whether the transistor 7 is turned on or off. FIG. 2 shows the output voltage a of the AC power supply 1 and the current waveform b of the transistor 7 in the device of FIG.

When dimming multiple discharge lamps individually, this discharge lamp lighting device uses a power source for preheating the filament of the discharge lamp and a power source for the dimming control circuit because the neutral wire becomes the common potential of each discharge lamp 6 and switch 7. can be common to all discharge lamps, and since the currents of the power transformer 2 and ballast yoke 3 are alternated to prevent unbalanced magnetization, the AC power supply, power transformer, and ballast yoke are This is suitable because it can be made smaller.

By the way, in the device shown in FIG. 1, if there is even a slight imbalance in the power transformer 2 or the ballast chain 3, when the transistor 7 is turned on, as shown in FIG. There is an unbalance in each half cycle of 1, and the effective current flowing through the circuit increases, resulting in the inconvenience that components with high ratings must be used for the power transformer 2, ballast switch 3, switch 7, etc.

In other words, if there is an imbalance in the secondary induced voltage of the power transformer 2, even if it is only 1.4V (just under 1%), the voltage distribution of each part will be as shown in Figure 3, and the diode 5 that should be cut off will be placed in the order of 0.7V. As a bias, both diodes 4 and 5 become conductive. For this reason,
The magnetic flux of the two windings of the ballast yoke 3 cancel each other out, and it no longer exhibits a current limiting effect. Therefore, the switch 7 receives the unbalanced voltage and the resistance of the circuit (the windings of the power transformer 2 and the ballast yoke 3). A problem occurred in that an overcurrent (Fig. 2c) determined by the resistance (resistance, etc.) flows.

[Object of the Invention] In view of the above-mentioned problems with the conventional type, the object of the present invention is to provide a DC lighting type discharge lamp lighting device that lights a discharge lamp with an output obtained by full-wave rectification of a two-phase AC power source. Prevents overcurrent due to unbalance of secondary induced output of components, especially power transformers,
The aim is to reduce the ratings of each component.

[Structure of the Invention] In order to achieve the above object, the present invention has a neutral wire and two output wires, and a two-phase wire having a phase difference of 180° with respect to the neutral wire and an approximately equal output voltage. Two diodes that generate a full-wave rectified output between an AC power source that generates an output and a neutral line from the two-phase AC output, and connected in series with each of the diodes and with opposite polarity to each other. A discharge lamp comprising a ballast yoke having two windings, a discharge lamp connected between the rectified output terminal of the diode and the neutral wire, and a switch element connected in parallel with the discharge lamp. The lighting device is characterized in that the number of turns of the two windings of the ballast yoke is made different to compensate for an unbalance between the two output voltages of the AC power source.

[Description of Examples] Examples of the present invention will be described below with reference to the drawings.

In the device shown in FIG. 1, the present invention compensates for the unbalance between the two induced outputs of the power transformer secondary winding 2s by making the numbers of turns of the two windings 31 and 32 of the ballast yoke 3 different. The circuit configuration is no different from that shown in FIG. In other words, the same voltage is ideally generated at the output terminals a and b of the secondary winding of the power transformer 2 in opposite phases to the center tap c, but in reality, the arrangement of the windings and the lead wires are different. Some imbalance occurs in the output voltage due to structural factors such as position. For example, the inductance and induced voltage are different between the inner winding and the outer winding. In addition, a difference in the number of turns of less than one turn occurs depending on the position of the lead wire, but in particular, in large transformers, the specific voltage (voltage per turn) is several volts or more, and a difference in the number of turns of a fraction of a turn occurs. However, an output voltage difference of about 1V will occur. Here, by creating a slight difference in the number of turns between the two windings 31 and 32 of the ballast yoke 3, the imbalance in the output voltage is canceled out, and the operation when the lamp is turned off is normalized.

When the present invention is applied to the device shown in FIG. 1, the secondary winding 2s of the power transformer 2 is
The windings between them are the same, and the number of turns of the windings 31 and 32 of the ballast yoke 3 is N ₁ > N ₂ (however, N ₁ is the number of turns of the inner winding 31, and N ₂ is the number of turns of the outer winding 32). ). In addition, the inner winding (terminal a) of power transformer 2
and the inner winding 31 of the ballast yoke 3 are connected, and the outer winding (terminal b) of the power transformer 2 and the outer winding 32 of the ballast yoke 3 are connected.

By compensating in this way, the induced voltage in the winding 32 in FIG.
Diode 5 if you can make it less than 149.3V
is cut off, the current flowing through the switch 7 has an ideal waveform as shown in FIG. 2b, and the effective value also decreases. In addition, each winding 31, 3 of the ballast yoke 3
2, the induced voltage ratio is the two (induced output - forward voltage drop of diodes 4 and 5) of power transformer 2.
It is preferable to set the ratio to be closest to the ratio of .

[Effects of the Invention] As described above, according to the present invention, the imbalance of the two-phase AC output is canceled out by making a difference in the number of turns of the ballast yoke.
Without adding any components, the effective current of the circuit can be reduced and smaller rated windings (power transformers, ballast chains) and semiconductors (switches) can be used.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a discharge lamp lighting device to which the present invention is applied, Figure 2 is a voltage and current waveform diagram of the device in Figure 1, and Figure 3 shows that the induced output of the power transformer in Figure 1 is unbalanced. FIG. 3 is a diagram showing voltages at various parts when 1... AC power supply, 2... Power transformer, 3...
Ballast switch, 4, 5...Diode, 6...
...Discharge lamp, 7...Switch, 8...Resistor.

Claims (1)

[Claims] 1. An AC power source that has a neutral wire and two output wires, and generates two-phase output with a phase difference of 180 degrees from the neutral wire and approximately equal output voltage, and a ballast yoke having two diodes that generate a full-wave rectified output between the diodes and a neutral wire, two windings connected in series with each of the diodes and having opposite polarities; In a discharge lamp lighting device comprising a discharge lamp connected between a rectified output terminal and the neutral wire, and a switch element connected in parallel with the discharge lamp, two windings of the ballast yoke are connected. A discharge lamp lighting device characterized in that the unbalance between the two output voltages of the AC power source is compensated for by varying the number of turns.