JPH10162986A - Discharge lamp lighting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a cata-pholysis phenomenon by proving means for superimposing a DC voltage to a discharge lamp and superimposing a positive DC voltage to a high-pressure side of a discharge lamp. SOLUTION: When a discharge lamp is lit by only a high-frequency power source, a mercury ion in the discharge lamp is one-sided to a highpressure side of the discharge lamp. A DC power source 11 is connected to the high- pressure side of a discharge lamp La so that a positive DC voltage is superimposed. Thereby, a mercury ion likely to one-side to the high-pressure side of the discharge lamp is returned back to a low-pressure side by a DC power source 11, a cata-pholysis phenomenon can be prevented. A polar inverting part is provided between a high-frequency power source 10 and the discharge lamp La, and a voltage is applied to the discharge lamp La, such that high- pressure and low-pressure sides of the discharge lamp La is periodically switched. Thereby, a period for inverting polarity of the highpressure and low- pressure sides is shortened than time of which a mercury ion in the discharge lamp is one-sided to the high-pressure side, thus preventing such cata-pholysis phenomenon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 Conventionally, when a discharge lamp such as a fluorescent lamp is lit by a DC power supply, mercury ions in the discharge lamp collect on the cathode side and the brightness of the anode side discharge lamp is reduced (electrophoretic phenomenon or electrophoresis phenomenon). The cataphoresis phenomenon (hereinafter referred to as cataphoresis phenomenon) was known (FIG. 13). In that case, alternating current lighting has been considered as an effective means for preventing the occurrence of the cataphoresis phenomenon. Further, a discharge lamp lighting device has been proposed in which a discharge lamp such as a fluorescent lamp is turned on at a high frequency to reduce the size and weight of the lighting device and improve the luminous efficiency of the discharge lamp.

FIG. 14 shows a conventional high-frequency discharge lamp lighting device. DC power is supplied from an AC power supply AC to an inverter unit 2 by a chopper unit 1 including a switching element Q1, an inductor L1, a diode D1, and a capacitor C1 via a diode bridge DB1. Switching element Q
2, Q3 is a half-bridge inverter and discharge lamp L through inductor L2 and capacitors C2 and C3 of resonance section 3.
a is supplied with high-frequency power.

[0004]

However, when the discharge lamp is lit at a high frequency, a cataphoresis phenomenon occurs, which is particularly promoted when the discharge lamp is lit at a low temperature. The cause will be described below. The inner wall of the discharge lamp is usually negatively charged. This is due to the asymmetry that the movement of electrons is faster than the movement of mercury ions. It is negatively charged for the same reason that the high frequency flows through the discharge lamp tube wall. Since the current flowing through the tube wall is generated between the ground and the ground, the larger the voltage between the ground and the ground, the greater the negative charge. If the voltage to ground differs in the length direction of the discharge lamp, a negative potential gradient is generated on the inner wall of the discharge lamp. Due to this gradient, the mercury ions are biased on the side where the negative charge is large, and the brightness is reduced (cataphoresis) on the other side (FIG. 15). In the following, the higher voltage to ground is referred to as the high voltage side, and the lower voltage to the low voltage side.

[0005] The occurrence of the cataphoresis phenomenon varies greatly depending on the shape of the lighting equipment and the strength of the wind around the discharge lamp. When the reflector of the lighting apparatus has a reflector close to the discharge lamp, the leakage current from the high-pressure side of the discharge lamp to the reflector increases, and the cataphoresis phenomenon easily occurs. Further, when wind is applied to the discharge lamp, there is a problem that the temperature of the tube wall of the discharge lamp decreases, the diffusion effect of mercury ions in the tube decreases, and the cataphoresis phenomenon easily occurs.

An object of the present invention is to provide a discharge lamp lighting device which can suppress the cataphoresis phenomenon and is suitable for reducing the size and weight of the device by lighting the discharge lamp at a high frequency.

[0007]

When the discharge lamp is turned on only by a high frequency power supply, mercury ions in the discharge lamp are biased toward the high pressure side of the discharge lamp as described above. Therefore, as shown in FIG. 1, the DC power supply 11 is connected so that a positive DC voltage is superimposed on the high voltage side of the discharge lamp La. As a result, mercury ions tending to lean to the high pressure side of the discharge lamp are drawn back to the low pressure side by the DC power supply 11, so that the cataphoresis phenomenon can be prevented. This is the first means, and will be described later as Examples 1 to 5.

[0010] As shown in FIG.
A polarity reversing unit 12 is provided between the discharge lamp La and the discharge lamp La, and a voltage as shown in FIG. 3 is applied to the discharge lamp so that the high-pressure side and the low-pressure side of the discharge lamp are switched periodically. Thus, the cataphoresis phenomenon is prevented by setting the cycle for inverting the polarity of the high-pressure side and the low-pressure side shorter than the time during which mercury ions in the discharge lamp are biased toward the high-pressure side. This is the second means, which will be described later as a sixth embodiment.

[0009]

FIG. 4 shows a first embodiment of the present invention. The high-frequency power supply 10 of FIG. 1 includes a commercial power supply AC, a diode bridge DB1, a chopper unit 1, an inverter unit 2, a resonance unit 3, and a control circuit 4. This circuit is the same as the conventional high-frequency lighting device of FIG. in this case,
The high pressure side of the discharge lamp La is the filament f1 in the figure. Therefore, as shown in FIG. 4, the output voltage (DC voltage) of the chopper unit 1 is supplied to the discharge lamp La via the diode D2 and the resistor R to configure the DC voltage superimposing unit 5. The DC voltage superimposed on the discharge lamp La can be changed according to the value of the resistor R. Since the positive DC voltage is superimposed on the high voltage side of the discharge lamp La, the cataphoresis phenomenon can be prevented with a simple circuit configuration by setting the value of the resistor R so that the cataphoresis phenomenon does not occur.

Here, the configuration of the chopper section 1 in FIG. 4 uses a step-up type chopper circuit, but other configurations such as a step-down type or a step-up / step-down type may be used. Further, a configuration may be adopted in which only a rectifying / smoothing circuit such as a complete smoothing system or a partial smoothing system is used without using a chopper circuit. In addition, although the configuration of the inverter unit 2 uses a half-bridge type inverter circuit, other configurations such as a push-pull type, a single-stone type, and a full-bridge type may be used. Further, a configuration in which the functions of the inverter unit 1 and the chopper unit 2 are also used, such as a chopper / inverter system, may be used.

FIG. 5 shows a second embodiment of the present invention. The chopper section 1 may be the same as in the first embodiment. As shown in FIG. 5, a resistor R is connected in parallel to a DC cut capacitor C3.
In the figure, the capacitor C3 is connected between the discharge lamp La and the source terminal of the switching element Q3. However, the operation is the same as that of the first embodiment, and the capacitor C3 and the resistor R are connected to the source terminal of the switching element Q2. It may be connected in between. Also in this case, the filament f1 of the discharge lamp La is on the high voltage side. Since a DC voltage is applied to the capacitor C3 in the direction of the arrow in the figure, a DC current flows in the direction of the filament f1 to f2 in the discharge lamp by connecting the resistor R, and the DC current is applied to the discharge lamp as in the first embodiment. The voltage is superimposed.
If the value of the resistor R changes, the DC current superimposed on the discharge lamp also changes, so that the cataphoresis phenomenon does not occur.
Should be set. In the present embodiment, similar effects can be obtained with a simpler circuit configuration than the case of the first embodiment.
A similar effect can be obtained with the circuit as shown in FIG.

FIG. 7 shows a third embodiment of the present invention. In the present embodiment, the resistor R of the DC voltage superimposing unit of the second embodiment is constituted by a variable resistor VR so that the DC voltage superimposed on the discharge lamp La can be changed. The degree of the cataphoresis phenomenon is greatly affected by the shape of the lighting equipment. This is because the distance between the discharge lamp and the reflector of the fixture differs depending on the lighting equipment.The closer the distance between the discharge lamp and the reflector, the greater the leakage current from the high-pressure side of the discharge lamp to the reflector, causing the cataphoresis phenomenon. It will be easier. Therefore, the value of the variable resistor VR is adjusted to a value at which the cataphoresis phenomenon does not occur in accordance with the device on which the lighting device is mounted. This makes it possible to realize a lighting device that can prevent a cataphoresis phenomenon that can handle a plurality of lighting fixtures with one type of lighting device. Here, the resistor R of the second embodiment is replaced with the variable resistor VR, but the same effect can be obtained with the circuit of the first embodiment.

FIG. 8 shows a fourth embodiment of the present invention. In the present embodiment, the resistor R of the DC voltage superimposing unit of the second embodiment is constituted by a positive temperature coefficient thermistor PTC so that the DC voltage superimposed on the discharge lamp La can be changed according to the ambient temperature. The degree of the cataphoresis phenomenon is greatly affected by the ambient temperature. This is due to the diffusion action of mercury ions in the discharge lamp. The diffusion action decreases as the temperature decreases, and the cataphoresis phenomenon is more likely to occur as the mercury ions move toward the high pressure side. By using the positive temperature coefficient thermistor PTC as in the present embodiment, the DC voltage superimposed on the discharge lamp is increased at low temperatures to prevent the cataphoresis phenomenon by utilizing the fact that the resistance value of PTC becomes small at low temperatures. Since the cataphoresis phenomenon does not easily occur at high temperatures, the DC voltage superimposed on the discharge lamp may be small, and the power consumed by the positive temperature coefficient thermistor PTC can be reduced by increasing the resistance value of the positive temperature coefficient thermistor PTC. Therefore, unnecessary power consumption can be cut.

FIG. 9 shows a fifth embodiment of the present invention. The occurrence of the cataphoresis phenomenon varies greatly depending on the wind intensity around the discharge lamp. This is because the wind on the discharge lamp lowers the wall temperature of the discharge lamp and reduces the diffusion of mercury ions in the tube. The stronger the wind, the more likely the cataphoresis phenomenon to occur. In this embodiment, as shown in FIG. 9, an air flow sensor 6 is provided near the discharge lamp La so that the DC voltage superimposed on the discharge lamp can be changed depending on the intensity of wind around the discharge lamp. When the wind hitting the discharge lamp is strong, the DC voltage superimposed on the discharge lamp is increased to prevent the occurrence of the cataphoresis phenomenon, and when the wind is weak, the DC voltage is reduced to cut excess power consumption.

FIG. 10 shows an example of a specific circuit configuration of the DC voltage superposition section 5 of the present embodiment. Coupling capacitor C
The DC voltage is superimposed on the discharge lamp by the resistors R1 to R4 connected in parallel with the discharge lamp 3. When the output of the air flow sensor 6 increases (wind increases), the base current of the transistor Q6 increases, and the current flowing through the resistors R3 and R4 increases, thereby increasing the DC voltage superimposed on the discharge lamp. it can. The same effect can be obtained by using a temperature sensor instead of the air flow sensor to detect the tube wall temperature of the discharge lamp and increasing the DC superimposed voltage superimposed on the discharge lamp when the tube wall temperature is low. Is obtained. Each of the above embodiments relates to the means 1, and the following embodiments relate to the means 2.

FIG. 11 is a circuit diagram of a sixth embodiment of the present invention.
FIG. 12 shows operation waveforms of the respective parts. In the present embodiment, the switching elements Q2 to Q5 composed of MOSFETs
And a full-bridge circuit configuration. As with the switching elements Q2 and Q3 of the inverter section 2, another output section of the switching element Q is connected to the output terminal of the chopper section 1.
4, Q5 are connected in series to form the polarity inverting unit 12.
The resonance unit 3 and the discharge lamp La are connected between the source terminal (referred to as point A) of the switching element Q2 and the source terminal (referred to as point B) of the switching element Q4. The resonance section 3 includes an inductor L2 and a capacitor C2.

Voltages as shown in FIGS. 12 (a) and 12 (b) are applied between the gate and source of the switching elements Q2 and Q3, respectively.
Q3 is alternately turned on and off at a high frequency. On the other hand, the switching elements Q4 and Q5 are shown in FIG.
Applying a voltage as shown in (d) between the gate and source,
The switching elements are turned on and off alternately at a lower frequency than the switching elements Q2 and Q3. Thereby, between point A and point B, FIG.
2 (e) is applied, and V.sub.V is turned on and off at the timing of switching elements Q4 and Q5.
The polarity of a-Vb is inverted. Therefore, the voltage Vla applied to both ends of the discharge lamp has a waveform as shown in FIG. 12 (f), and the high voltage side and the low voltage side of the discharge lamp can be switched periodically. By setting the on time of the switching elements Q4 and Q5 to be shorter than the time required for the mercury ions in the discharge lamp to shift to the high pressure side, the occurrence of the cataphoresis phenomenon can be prevented with a relatively simple circuit configuration.

[0018]

According to the present invention, there is provided a discharge lamp lighting device for lighting a discharge lamp by supplying high frequency power to the discharge lamp.
A means for superimposing a DC voltage on the discharge lamp is provided, and a positive DC voltage is superimposed on the high voltage side of the discharge lamp, or a polarity inversion means capable of periodically switching between the high voltage side and the low voltage side of the discharge lamp is provided. Since the polarity inverting means switches between the high pressure side and the low pressure side of the discharge lamp before the mercury ions in the discharge lamp are biased toward the high pressure side, the cataphoresis phenomenon can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing the configuration of the first embodiment of the present invention.

FIG. 2 is a block circuit diagram showing a configuration of the invention according to claim 5;

FIG. 3 is a waveform chart showing the operation of the invention of claim 5;

FIG. 4 is a circuit diagram of a first embodiment of the present invention.

FIG. 5 is a circuit diagram of a second embodiment of the present invention.

FIG. 6 is a circuit diagram of a modification of the second embodiment of the present invention.

FIG. 7 is a circuit diagram of a third embodiment of the present invention.

FIG. 8 is a circuit diagram of a fourth embodiment of the present invention.

FIG. 9 is a circuit diagram of a fifth embodiment of the present invention.

FIG. 10 is a circuit diagram of a DC voltage superposition unit used in a fifth embodiment of the present invention.

FIG. 11 is a circuit diagram of a sixth embodiment of the present invention.

FIG. 12 is a waveform chart showing the operation of the sixth embodiment of the present invention.

FIG. 13 is an explanatory diagram for explaining a conventional cataphoresis phenomenon at the time of DC lighting.

FIG. 14 is a circuit diagram of a conventional high frequency discharge lamp lighting device.

FIG. 15 is an explanatory diagram for explaining a conventional cataphoresis phenomenon at the time of high-frequency lighting.

[Explanation of symbols]

 10 High frequency power supply 11 DC power supply La Discharge lamp

Claims (5)

[Claims] 1. A discharge lamp lighting apparatus for lighting a discharge lamp by supplying high-frequency power to the discharge lamp, comprising means for superimposing a DC voltage on the discharge lamp, and superimposing a positive DC voltage on a high voltage side of the discharge lamp. A discharge lamp lighting device characterized by suppressing the cataphoresis phenomenon. 2. The discharge lamp lighting device according to claim 1, wherein said DC voltage superimposing means changes a DC voltage according to a lighting fixture. 3. The discharge lamp lighting device according to claim 1, wherein said DC voltage superimposing means changes a DC voltage according to an ambient temperature. 4. The discharge lamp lighting device according to claim 1, wherein the DC voltage superimposing means changes the DC voltage according to the strength of wind around the discharge lamp. 5. A discharge lamp lighting apparatus for lighting a discharge lamp by supplying high-frequency power to the discharge lamp, comprising: a polarity inversion means capable of periodically switching between a high pressure side and a low pressure side of the discharge lamp; A discharge lamp lighting device characterized in that the polarity reversing means switches between the high pressure side and the low pressure side of the discharge lamp before the mercury ions are biased toward the high pressure side, thereby suppressing the cataphoresis phenomenon.