JPH0325898A - Discharge lamp lighting circuit - Google Patents

Abstract

PURPOSE:To provide a discharge lamp lighting circuit capable of starting a discharge lamp at a low voltage by providing a second voltage generating circuit for outputting a voltage for starting discharge between auxiliary electrodes. CONSTITUTION:When a discharge lamp 3 is started, a voltage is first outputted between auxiliary electrodes 6, 7 by a second voltage generating circuit 2 to start discharge between the both electrodes, whereby a number of electrons are emitted from the auxiliary electrodes 6, 7. These electrons facilitate discharge between main electrodes 4, 5, and by applying a voltage lower than the starting voltage of the case where no auxiliary electrode 6, 7 is provided between the main electrodes 4, 5 from a first voltage generating circuit 2, discharge can be started between the main electrodes. As the first voltage generating circuit 1 is separated from the second voltage generating circuit 2, power supply is never prevented by the circuit for starting at the time of steady lighting, and further, voltage resistant circuit elements suitable to the voltages added to the respective circuits can be used.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a voltage generating circuit that outputs a voltage for starting a discharge between the auxiliary electrodes of a discharge lamp or between the auxiliary electrode and one of the main electrodes, and This is to cause discharge to occur between the auxiliary electrode and the main electrode. This makes it possible to lower the discharge starting voltage between the main electrodes. [Industrial Application Field] The present invention relates to a lighting circuit for high-pressure discharge lamps such as high-pressure sodium lamps and metal halide lamps.

[Conventional technology]

High-pressure discharge lamps such as mercury lamps, high-pressure sodium lamps, and metal halide lamps are known as high-brightness, high-efficiency lamps. When starting or relighting these discharge lamps, it is necessary to apply a higher voltage than during steady lighting.
Some are equipped with a starting voltage generation circuit for this purpose.

FIG. 4 is a circuit diagram of a conventional lighting circuit that is driven by a rectangular wave AC voltage. The transistors 11 and 12 are alternately turned on and off by a signal from the drive circuit 13, and the power supply voltages of the two power supplies 14 and 15 are alternately applied to the discharge lamp 16. In addition, the discharge lamp 16
A winding l7 is connected in series to the winding 17, and a pulse generating circuit 18 is connected to the secondary side of this winding 17, and these circuits constitute a starting voltage generating circuit l9.

This starting voltage generating circuit 19 causes the winding 17 to
A high voltage sufficient for the discharge lamp 16 to start discharging is output between both ends of the discharge lamp 16, and the discharge lamp 16 is started.

[Problem to be solved by the invention]

However, in the lighting circuit described above, the switching element (
In order to prevent the transistors (for example, transistors l1, 12, etc.) from being destroyed by the high voltage pulse from the starting voltage generating circuit 19, there is a problem in that switching elements and the like must be of high voltage resistance.

Furthermore, when the starting voltage generating circuit 19 is connected in series with the discharge lamp l6, during steady lighting, for example, the winding 17 of the starting voltage generating circuit l6 acts as a load on the lighting circuit and obstructs the power supply to the discharge lamp. There was a problem. An object of the present invention is to provide a discharge lamp lighting circuit that can start a discharge lamp with a low voltage.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention.

In the figure, a first voltage generating circuit 1 is connected to main electrodes 4 and 5 of a discharge lamp 3, and outputs a voltage that starts a discharge between these main electrodes.

The second voltage generating circuit 2 is connected to, for example, the auxiliary electrodes 6 and 7, and outputs a voltage that starts a discharge between the auxiliary electrodes.

[For production]

In the above-described discharge lamp lighting circuit, when starting the discharge lamp 3, the second voltage generating circuit 2 first outputs a voltage between the auxiliary electrode 6 and the auxiliary electrode 7, and discharges between the two electrodes. start.

As a result, a large number of electrons are emitted from the auxiliary electrodes 6 and 7. These electrons tend to cause discharge between the main electrodes 4 and 5, and a voltage lower than the starting voltage in the absence of the auxiliary electrodes 6 and 7 is applied between the main electrodes 4 and 5 from the first voltage generating circuit l. By applying this voltage, discharge can be started between the main electrodes.

In addition, since the first voltage generating circuit 1 and the second voltage generating circuit 2 are separated, the power supply is not obstructed by the starting circuit during steady lighting, and moreover, the power supply is not interrupted by the starting circuit during steady lighting. It is possible to use circuit elements with a withstand voltage that matches the voltage. [Examples] Examples of the present invention will be described below with reference to the drawings. FIG. 2 is a circuit diagram of a lighting circuit for a metal halide lamp according to an embodiment of the present invention.

In the figure, a coil Ll is connected to the positive electrode side of the DC power supply 21.
One end of the coil Ll is connected, and the other end of the coil Ll is connected to a capacitor CI, a cathode of a diode Di, and a transistor TR.
The collector of I and one end of capacitor CI are connected.

The other end of the capacitor CI is connected to the primary winding L of the transformer 22.
2 are connected. The other end of the capacitor Ci, the anode of the diode D1, the emitter of the transistor TRI, and the other end of the winding L2 are connected to the negative electrode side of the DC power supply 2l.

These coil LL, transistor TRI, capacitor 0
1 constitutes a circuit that converts the voltage applied to the winding L2 of the transformer 22 into rectangular wave alternating current.

A drive signal of several tens of KHz is applied to the base of the transistor TRI from a control circuit (not shown), and the transistor TRI is repeatedly turned on and off according to this drive signal. As a result, a voltage generated by converting the voltage of the DC power supply 2l into a rectangular wave AC voltage is generated between the winding L2.

Further, the diode D1 is a diode that bypasses the reverse voltage applied between the collector and emitter of the transistor TR. The capacitor C8 is a capacitor for absorbing the surge voltage generated between the collector and emitter when the transistor TRI is turned off.

Both ends of a secondary winding L3 having n times as many turns as the primary winding L2 of the transformer 22 are connected to the main electrode 24 of the metal halide lamp 23, respectively.

The metal halide lamp 23 has a pair of main electrodes 24.
and a pair of auxiliary electrodes 25 are provided, and the auxiliary electrodes 25 are
It is arranged in a direction perpendicular to the main electrode 24.

Further, a secondary winding L4 of a transformer 26 is connected between both poles of the auxiliary electrode 25 of the metal halide lamp 23. A pulse generation circuit 27 is connected between both ends of the primary winding L5 of the transformer 26. This pulse generating circuit 27
A pulse voltage is output at the time of starting, and the pulse voltage is multiplied by m by the transformer 26 and applied between the auxiliary electrodes 25.

Next, the operation of the embodiment of the above structure will be explained.

At the time of starting, the pulse generating circuit 27 operates first, and a predetermined pulse voltage is output between both ends of the winding L5. Winding L
5 is multiplied by m by the transformer 26 and applied between the auxiliary electrodes 25 of the metal halide lamp 23. As shown in FIG. 2, the distance between the auxiliary electrodes 25 is much shorter than the distance between the main electrodes 24, so a voltage much lower than that required to start a discharge between the main electrodes 24 is applied to the auxiliary electrodes. By applying the voltage between the auxiliary electrodes 25, discharge can be started between the auxiliary electrodes 25.

On the other hand, in a circuit consisting of a coil L1, a transistor TRI, etc. that supplies voltage for starting and stable lighting to the main electrode 24 of the metal halide lamp 24, an on signal is applied to the base of the transistor TRI at the time of starting, and the transistor TR is turned on. Then, the energy supplied from the DC power supply 2l is stored in the coil Ll. The energy stored in this coil Ll is output to the primary winding L2 of the transformer 22 via the capacitor Cl when the transistor TRI is off, and a voltage boosted from the output voltage of the DC power supply 22 is applied across the winding L2. ．． This voltage is multiplied by n in the transformer 22 and applied between the main electrodes 24 of the metal halide lamp 23 as a starting voltage.

At this time, the voltage that needs to be applied between the main electrodes 24 to start discharging the metal halide lamp 23 is much lower than when the auxiliary electrodes 25 are not present.

That is, due to the voltage applied between the auxiliary electrodes 25, partial arc discharge is started between the auxiliary electrodes 25, and a large number of thermoelectrons are emitted from the auxiliary electrodes 25. As a result, there are many thermoelectrons in the central part of the lamp 23, and these thermoelectrons act as a trigger to turn the partial discharge caused by the voltage applied between the main electrodes 24 into a stable arc discharge. Easier to transition. As a result, the discharge opening voltage between the main electrodes 24 becomes low.

Therefore, the voltage that needs to be applied to the main electrode 24 to start the metal halide lamp 23 is much lower than that without the auxiliary electrode 25, and the conventional starting voltage generation circuit is connected to the main electrode 24 side. There is no need to provide the same, the circuit becomes simple, and the power supply by the starting voltage circuit is not obstructed.

Furthermore, since the electrode distance between the auxiliary electrodes is set short, compared to the conventional case where voltage is applied only between the main electrodes of the meral halide lamp 23 for starting, the distance between the auxiliary electrodes for starting is shorter. The voltage that needs to be applied to can also be a low voltage.

Therefore, the voltage rating of the transformer 26 connected to the auxiliary electrode side can be lowered, and the specifications of the transformer can be simplified.

In addition, since the circuit on the auxiliary electrode side for starting the lamp 23 and the circuit on the main electrode side for mainly maintaining stable lighting can be completely separated, it is necessary to make all circuit elements high voltage resistant. This eliminates the problem, and the lighting circuit can be made lower in cost and smaller in size.

Next, FIG. 3 is a circuit diagram of another embodiment in which one auxiliary electrode is provided in the center of the main electrode.

In the figure, circuit components that are the same as those in the circuit in Figure 2 are given the same reference numerals and their explanations will be omitted. The metal halide lamp 26 of this embodiment includes a pair of main electrodes 27a and 27b,
One auxiliary electrode 28 is provided, and the auxiliary electrode 28 is arranged approximately at the center of the main electrodes 27a, 27b. One end of the main wire L4 of the transformer 26 is connected to the auxiliary/auxiliary electrode 28, and the other end of the winding L4 is connected to one end of the winding L3 of the transformer 22 and the main electrode 27b.

During starting, the voltage generated across winding L4 is applied to auxiliary electrode 28.
and the main electrode 27b, and discharge is started between the auxiliary electrode 28 and the main electrode 27b. When the discharge starts, a large number of thermoelectrons are emitted around the auxiliary electrode 28 and the main electrode 27b. These thermoelectrons cause the main electrodes 27a, 27
Discharge between electrodes b becomes more likely to occur, and the discharge starting voltage between the main electrodes decreases.

That is, main electrodes 27a, 27b and one auxiliary electrode 2
By providing 8, the voltage required to be applied between the main electrodes for starting the lamp 26 can be reduced.

Furthermore, in this embodiment, the electrode structure of the metal halide lamp 26 can be made simpler than in the previously described embodiment. In the above-described embodiment, the auxiliary electrode is arranged approximately in the center between the main electrodes, but it may be arranged at a position biased to one side of the main electrodes.

Furthermore, the present invention is not limited to the lighting circuit that boosts the power supply voltage using the transformer described in the embodiments, but can be applied to various lighting circuits, for example, to lighting circuits configured with L and C resonant circuits.

Furthermore, the invention is not limited to the metal halide lamp described above, but can also be applied to other discharge lamps such as mercury lamps and high-pressure sodium lamps.

〔Effect of the invention〕

According to the present invention, the voltage applied to the discharge lamp for lighting the discharge lamp can be lower than that of the conventional lamp, and the lighting circuit can be simplified and the circuit elements used can have a lower withstand voltage.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the principle of the present invention, FIG. 2 is a circuit configuration diagram of a lighting circuit according to an embodiment of the present invention; FIG. 3 is a circuit diagram of another embodiment, FIG. 4 is a circuit diagram of a conventional lighting circuit. 1... first (7) voltage generation circuit, 2... second voltage generation circuit, 3...discharge lamp, 4, 5... Main electrode, 6, 7... Auxiliary electrode.

Claims (1)

[Scope of Claims] A first voltage generating circuit that is connected between the main electrodes of a discharge lamp and outputs a voltage that starts a discharge between the main electrodes; one end of which is connected to an auxiliary electrode of the discharge lamp, and the other end of which is is connected to another auxiliary electrode or one of the main electrodes, and a second voltage generating circuit outputs a voltage that starts discharge between the auxiliary electrodes or between the auxiliary electrode and one of the main electrodes. A discharge lamp lighting circuit featuring: