JPH0366800B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a discharge lamp lighting device for lighting a high-intensity discharge lamp at high frequency.

Generally, while a high-intensity discharge lamp is lit, the coldest point temperature increases due to blackening of the inner wall of the arc tube due to evaporation of the electrodes, and as a result, the lamp voltage increases as the vapor pressure of the arc tube increases. Furthermore, due to deterioration of the electrodes, the discharge distance becomes longer and the lamp voltage increases, and changes in the contents in the arc tube cause the lamp voltage to increase. Then, when the voltage becomes higher than the voltage applied to the lamp, the lamp goes out, and this ends the lamp life.
In high-intensity discharge lamps, turning off due to this increase in lamp voltage is a major cause of lamp life.

FIG. 1 is a block circuit diagram of a conventional discharge lamp lighting device, in which 1 is a commercial power supply, 2 is a high frequency lighting device, 3 is a discharge lamp, and the discharge lamp 3 is a high intensity discharge lamp. The output characteristics (also called ballast droop characteristics) of the high frequency lighting device 2 are as shown in FIG. In Figure 2,
When discharge lamp 3 is not connected, I=0, V
= _V2 , and when the secondary side of the high-frequency lighting device 2 is short-circuited, I=Is and V=0, and when the discharge lamp 3 is steadily lit, I=Il and V=Vl. Here, V ₂ is the secondary voltage of the high-frequency lighting device, Xl is the lamp voltage when the discharge lamp 3 is steadily lit, and Il is the lamp current at that time. Further, in the case of the high frequency lighting device 2 which is IsIl and whose ballast has constant current characteristics, when the lamp voltage increases, it has the following drawbacks. Note that this will be explained in comparison with a general Chiyoke coil type, which is a commercial lighting device.

First, the fading and fading of the lamp voltage waveform will be explained. Figure 3a shows the lamp voltage Vl and 2 during commercial lighting.
Figure 3b shows the waveform of the secondary voltage _V2 of the lamp voltage Vl during high frequency lighting, and the broken lines in _both cases show the waveform when the lamp voltage Vl increases. There is. In the case of commercial lighting, when the lamp voltage Vl increases, the restriking voltage changes from Vp ₁ to
When the voltage rises to Vp ₁ ' and its instantaneous value becomes higher than the secondary voltage V ₂ , the discharge lamp goes out and becomes a malfunction. In the case of high frequency lighting, the lamp voltage Vl has a waveform as shown in Figure 3b, and as the lamp voltage Vl rises, Vp ₂ rises to Vp ₂ ', but as can be seen from the waveform, unless there is a large rise. There will be no disappearance. Note that the lamp voltage waveform in Figure 3b is due to high frequency lighting when the commercial power supply 1 is completely smoothed, but if the power supply is 1/2 smoothed or 1/3 smoothed, the restriking voltage will be slightly higher. but,
Very low compared to commercial lighting.

Next, lamp voltage and lamp power will be explained. During high-frequency lighting, even if the lamp voltage increases, it is difficult for the lamp to turn off, so it seems that it has a positive effect on the lamp life, but as the lamp voltage increases, the lamp power increases, causing a load on the wall of the arc tube. rises, and before it goes out, the arc tube becomes overloaded, causing damage or explosion, which is very dangerous from a safety standpoint. For example, when the lamp voltage Vl reaches Vl' shown in FIG. 2, the lamp power increases because Vl'×Il'>Vl×Il, and there is a risk that the arc tube will be overloaded. In order to make the turning-off of high-frequency lighting similar to that of a general chiyoke coil, it is possible to lower the secondary voltage V ₂ , but if the secondary voltage V ₂ is lowered, the discharge lamp 3 will not start, and the secondary voltage V ₂ will be lowered. There are limits.

As described above, when lighting high-intensity discharge lamps at high frequencies and making the ballast compact and lightweight, the high-frequency lighting device 2
If the output characteristics of the lamp are as shown in Figure 2, in other words, in a constant current type, the lamp voltage increases due to an increase in the coldest spot temperature, which is characteristic of high-intensity discharge lamps, and Vl′ in Figure 2, The problem is that the arc tube may break or explode before the lamp power increases and the lamp goes out.

The present invention has been made in view of the above, and its purpose is to prevent damage to the arc tube, explosion, etc. due to overloading of the arc tube at the end of the life of the high-intensity discharge lamp. , will be explained in detail below with reference to Examples.

In Fig. 4, 1 is a commercial power supply, 2 is a high-frequency lighting device, and 3 is a discharge lamp.The high-frequency lighting device 2 has a nearly constant current property, in other words, the lamp power always increases as the lamp voltage increases. The discharge lamp 3 is a high-intensity discharge lamp. 4 is a lamp voltage detection circuit section, and a discharge lamp abnormality detection circuit section 5
When the lamp voltage rises, this lamp voltage detection circuit section 4 detects it and feeds it back to the high frequency lighting device 2 to reduce the power in the lamp to prevent damage to the arc tube. be. Methods for reducing the lamp power include stopping the oscillation circuit of the high-frequency lighting device 2, changing the impedance, changing the frequency, or lowering the secondary voltage. It's good to wear.

FIG. 5 shows another embodiment of the present invention, in which a switch 7 is turned on by a switch drive circuit (not shown) provided in the high frequency lighting device 2 when the lamp voltage reaches a certain level according to the output of the lamp voltage detection circuit section 4. Both ends of the discharge lamp 3 are short-circuited to cause the lamp to go out. In order to turn off the discharge lamp 3, in addition to short-circuiting the discharge lamp 3 as described above, it is also possible to temporarily provide a pause period in the lamp current and turn it off using the restriking voltage. As described above, the present invention includes a discharge lamp abnormality detection circuit section that detects when the lamp voltage reaches a predetermined level higher than the rated voltage. It is possible to detect an abnormality before it occurs, and at this time, the output of the discharge lamp abnormality detection circuit section reduces the output of the high-frequency lighting device or turns off the luminous intensity discharge lamp, thereby extending the life of the luminous intensity discharge lamp. This has the effect of preventing the arc tube from being overloaded in the final stages, thereby preventing damage to the arc tube, explosion, etc.

[Brief explanation of drawings]

Figure 1 is a block circuit diagram of a conventional discharge lamp lighting device, Figure 2 is a characteristic diagram of the same as above, Figures 3a and b are voltage waveform diagrams during commercial lighting and high frequency lighting of the discharge lamp, and Figure 4 is FIG. 5 is a block circuit diagram of one embodiment of the present invention. FIG. 5 is a block circuit diagram of another embodiment of the present invention. 2... High frequency lighting device, 3... Discharge lamp, 5...
Discharge lamp abnormality detection circuit.

Claims (1)

[Claims] 1. In a discharge lamp lighting device that lights a high-intensity discharge lamp using a high-frequency lighting device with constant current property, high-frequency lighting is performed by the output of a discharge lamp abnormality detection circuit that detects when the lamp voltage has reached a predetermined level higher than the rated voltage. A discharge lamp lighting device characterized by reducing the output of the device or turning off a high-intensity discharge lamp.