JPH04277495A - Lighting device of electric discharge lamp - Google Patents

Abstract

PURPOSE:To provide a discharge lamp lighting device generating high-voltage pulses using a pulse transformer and perform lighting-up as starting, with which discharge lamp is prevented from acoustic resonance phenomenon likely to occur when the impedance of the discharge lamp remains low after it is started. CONSTITUTION:The output of a pulse transformer 6 is superimposed on the output of an inverter circuit connected with a DC power supply 1, and the result is impressed on a discharge lamp 3. If a lamp current sensing circuit 9, lamp voltage sensing circuit 10, and divider circuit 11 sense that the impedance of the discharge lamp after it is started is lower than the specified level, a control circuit 12 puts on a switch 8 to shortcircuit the primary side of the pulse transformer 6 and to lessen the inductance of the secondary side. This lessens the amplitude of the natural frequency oscillating current in an LCR series circuitry composed of secondary winding of pulse transformer, a capacitor 7, and discharge lamp 3, and high-frequency oscillating components will diminish in the lamp current. As a result, the discharge lamp is prevented from occurrence of acoustic resonance phenomenon, which permits achievement of stable lighting without stall or flicker.

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 controlling the lighting of a discharge lamp such as a metal halide lamp.

0002

2. Description of the Related Art In general, high-intensity discharge lamps such as high-pressure mercury lamps are extremely difficult to turn on once they have been turned off and then turned on again when the discharge lamp is in a high temperature state. Generally, high voltage pulses are applied. This conventional discharge lamp lighting device generally has a configuration as shown in Japanese Patent Publication No. 175597/1983. The configuration will be described below with reference to FIG. As shown in FIG. 6, its components include a commercial frequency AC power supply 18, an inverter circuit 19, and a current limiting element 20 that limits the lamp current.
21, 24, 27 are capacitors, 22 is a switch, 23
is a step-up transformer, 25 and 26 are diodes, 28 is a discharge gap which is a switch element, 29 is a pulse transformer,
30 is a high-pressure pulse generating circuit, and 31 is a discharge lamp as a load.

Next, the mutually related operations of the above-mentioned components will be explained. The inverter circuit 19 is supplied with power from the AC power supply 18 and generates a high frequency voltage. Inverter circuit 1
The high frequency output of 9 is input to the high voltage pulse generation circuit 30 via the switch 22. As will be described later, while the switch 22 is on, a high voltage pulse is generated on the secondary side of the pulse transformer 29, and this high voltage pulse is applied to the discharge lamp 31 via the bypass capacitor 21.

At the same time, the high frequency output of the inverter circuit 19 is supplied to the discharge lamp 31 via the current limiting element 20, and when the dielectric breakdown occurs between the main electrodes of the discharge lamp 31 due to the previous high voltage pulse, the current limiting element 20 The main current limited to an appropriate value is supplied to the discharge lamp 31, and the discharge lamp 31 is lit. When the switch 22 is turned off after the discharge lamp 31 is lit, the generation of high voltage pulses is stopped.

The operation of the high voltage pulse generating circuit 30 is as follows. When the switch 22 is on, the output voltage of the inverter circuit 19 is applied to the primary side of the step-up transformer 23 and output to the secondary side. When the anode side of the diode 25 is positive, the capacitor 24 is charged through the diode 25 to the peak value of the secondary side voltage of the step-up transformer 23 . Next, when the anode side of the diode 25 becomes negative,
The capacitor 27 is charged through the diode 26 to a maximum of twice the peak voltage value generated on the secondary side of the step-up transformer 23. If the breakdown voltage of the discharge gap 28 is set below this value, when the voltage of the capacitor 27 reaches the breakdown voltage of the discharge gap 28, the discharge gap 28 will break down and the capacitor 2
7 is discharged through the discharge gap 28 and the primary side of the pulse transformer 29, a pulse-like voltage is induced on the primary side of the pulse transformer 29, and this voltage is boosted and generated on the secondary side of the pulse transformer 29.

[0006]

[Problems to be Solved by the Invention] In such a conventional discharge lamp lighting device, after the discharge lamp starts, the inductance is mainly connected to the secondary side of the pulse transformer, and the inductance is connected in parallel to the series circuit of the discharge lamp and the pulse transformer. An LCR series circuit is formed between the capacitance of the connected capacitor and the lamp impedance, and a natural oscillating current flows within this closed circuit. The frequency of this natural oscillation is higher than the lighting frequency of the discharge lamp, and this natural oscillation current is superimposed on the lamp current. In order to improve the starting performance of discharge lamps, a method is used to increase the energy of high-voltage pulses by increasing the inductance of the pulse transformer, but the greater the inductance on the secondary side of the pulse transformer, the greater the amplitude of this natural oscillating current. . Furthermore, the lower the lamp impedance, the smaller the effect of suppressing and damping this natural oscillation current, and therefore the amplitude of the natural oscillation becomes larger. In other words, in reality, the influence of natural oscillation is strong immediately after starting the discharge lamp, and the high-frequency oscillating current, which is the natural oscillating current, is superimposed on the lamp current at the lighting frequency limited by the current limiting element as shown in Figure 7. , an acoustic resonance phenomenon occurs in the discharge lamp, causing the discharge lamp to flicker or go out.

The present invention solves the above problems, and aims to provide a discharge lamp lighting device that stably lights a discharge lamp without causing an acoustic resonance phenomenon by reducing the amplitude of the natural vibration. .

[0008]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a DC power source, a current reversing means connected to the output end of the DC power source, and a discharge lamp as a load of the current reversing means. , a pulse transformer having a secondary winding connected in series to a discharge lamp, and a capacitor connected in parallel to the series circuit of the discharge lamp and the secondary winding of the pulse transformer;
An impedance control means is provided for controlling the impedance on the secondary side of the pulse transformer according to a predetermined value of the lamp impedance of the discharge lamp.

Further, as a means for detecting the impedance of a discharge lamp, an impedance detection means for determining the impedance from a current value or a voltage value, a timer means for determining the impedance from the elapsed time from the start of the discharge lamp, or a frequency component flowing in the discharge lamp. It consists of a frequency discriminator that determines the frequency.

0010

[Operation] The discharge lamp lighting device of the present invention having the above structure is provided with means for detecting the impedance of the discharge lamp, thereby detecting when the lamp impedance of the discharge lamp is lower than a predetermined value, and detecting the natural vibration flowing through the discharge lamp. It suppresses the current. In other words, when the impedance of the discharge lamp is low, the loss in the circuit consisting of the discharge lamp, the secondary inductance of the pulse transformer for starting the discharge lamp, and the capacitor for bypassing the high-voltage pulse voltage decreases, and the natural vibration By controlling the impedance of the pulse transformer, the circulating current that tends to flow due to the number of pulse transformers is suppressed. By controlling the impedance of the pulse transformer, the natural oscillation frequency shifts and the Q of the circuit changes, so the amount of circulating current can be controlled. This prevents the discharge lamp from causing an acoustic resonance phenomenon and prevents the discharge lamp from flickering or going out.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the accompanying drawings. As shown in FIG. 1, its components include a DC power supply 1, an inverter circuit 2 connected to the output of the DC power supply and serving as a current reversal means for supplying AC to the load;
3 is a discharge lamp that is the load of the inverter circuit; 4 is a choke coil that is a current limiting element that limits the lamp current;
5 is a pulse generation circuit; 6 is a pulse transformer that generates a high-voltage pulse to start the discharge lamp; 7 is a capacitor for bypassing the high-voltage pulse; 8 is a switch connected between the primary windings of the pulse transformer 6; 9 is a lamp current detection circuit, 10 is a lamp voltage detection circuit, and 11 is a division circuit, which includes lamp current detection circuit 9 and lamp voltage detection circuit 1.
0 and the division circuit 11 constitute impedance detection means for detecting the state of the discharge lamp. Further, 12 is a control circuit that turns on and off the switch 8 according to the output signal of the division circuit 11, and together with the switch 8 constitutes impedance control means.

The related operations of the above components will now be described. First, when the discharge lamp is started, the switch 8 is open, and a pulse voltage is applied from the pulse generating circuit 5 to the primary winding of the pulse transformer 6. When a pulse voltage is applied to the primary winding of the pulse transformer 6, a high voltage pulse voltage necessary for starting the discharge lamp 3 is generated in the secondary winding of the pulse transformer 6, and the discharge lamp is activated via the bypass capacitor 7. 3 is applied.

At the same time, the high frequency output of the inverter circuit 2 is supplied to the discharge lamp 3 via the choke coil 4, and the previous high voltage pulse causes dielectric breakdown between the electrodes of the discharge lamp 3, causing the discharge lamp 3 to start. It lights up and continues to light up.

The discharge lamp 3 is detected by the lamp current detection circuit 9.
Starting of the discharge lamp 3 is determined by detecting the current. Also, when the discharge lamp 3 starts, the discharge lamp 3
An alternating current with a lighting frequency limited by the choke coil 4 flows through the lamp, and natural vibrations with a frequency higher than the lighting frequency occur between the inductance on the secondary side of the pulse transformer 6, the capacitor 7, and the discharge lamp 3. The lamp current has a waveform in which the lighting frequency component current and the natural vibration frequency component are superimposed. The amplitude of the natural oscillating current becomes large when the lamp impedance is low, and when the amplitude of the natural oscillating current is large, the discharge lamp 3 causes an acoustic resonance phenomenon. Therefore, the lamp impedance of the discharge lamp 3 is detected by inputting the output signal of the lamp voltage detection circuit 10 and the output signal of the lamp current detection circuit 9 to the division circuit 11. The lamp impedance generally has its minimum value immediately after the discharge lamp 3 is started, is high during steady lighting, and is infinite when the lamp is turned off. The control circuit 12 outputs a signal to turn off the switch 8 when the output signal voltage of the divider circuit 11 is above a predetermined value, that is, when the lamp impedance is above a predetermined value, and conversely, when the output signal voltage of the divider circuit 11 is When the lamp impedance is lower than a predetermined value, that is, when the lamp impedance is lower than a predetermined value, a signal that turns on the switch 8 is output. Here, the predetermined value of the lamp impedance is the minimum lamp impedance value at which the discharge lamp 3 does not cause an acoustic resonance phenomenon due to the natural oscillating current.

As described above, according to the first embodiment of the present invention, by short-circuiting the primary winding of the pulse transformer 6 when the lamp impedance is low after starting the discharge lamp 3,
The inductance on the secondary side is also almost equivalent to being short-circuited, and the inductance on the secondary side of the pulse transformer 6 is only the leakage inductance, so the Q of the resonant circuit decreases or the resonant frequency changes. Therefore, the amplitude of the high-frequency oscillating current that is superimposed on the lamp current during lighting becomes smaller in the lamp current waveform as shown in Fig. 2, which makes it possible to prevent the acoustic resonance phenomenon and prevent the discharge lamp 3 from flickering or turning off. It can be prevented. In addition, by opening the switch 8 connected to the primary side of the pulse transformer 6 during steady lighting and using the inductance on the secondary side, continuity can be made to the current when the polarity of the lamp current changes, and the restriking voltage can be increased. This does not occur, and the discharge lamp 3 can be stably lit. Further, since the lamp current has continuity, the current waveform does not have steep rises or falls, so radiation noise from the discharge lamp lighting device can be reduced.

Next, a second embodiment of the present invention will be explained based on the attached drawings. FIG. 3 is a block diagram of a discharge lamp lighting device according to a second embodiment. The difference in configuration from the first embodiment is that the lamp voltage detection circuit 10 and division circuit 11 of FIG. 1 are not provided, and a timer circuit 13 is connected between the lamp current detection circuit 9 and the control circuit 12A. The related operations of the above components will now be described. When the lamp current detection circuit 9 detects the start of the discharge lamp 3, a signal is input from the timer circuit 13 to the control circuit 12A for a predetermined period,
Continue to turn on switch 8. During this time, the inductance on the secondary side of the pulse transformer 6 becomes small. After a predetermined period of time has elapsed, the signal from the timer circuit 13 disappears, and the switch 8 is opened. Here, the predetermined period is
This refers to the time required for the lamp impedance to rise to a value at which the acoustic resonance phenomenon does not occur in the discharge lamp 3 even with the natural oscillating current, that is, for the impedance to rise sufficiently in a steady lighting state.

According to the second embodiment of the present invention, as in the first embodiment, when the lamp impedance of the discharge lamp 3 is low, the acoustic resonance phenomenon is prevented, and the discharge lamp 3 is prevented from flickering or turning off. You can prevent this from happening. Further, as in the first embodiment, no restriking voltage is generated during steady lighting, and radiation noise from the discharge lamp lighting device can be reduced. In this embodiment, the period during which the switch 8 is turned on is set to a predetermined period, but it may be set every one period of the lighting period or every several periods.

Next, a third embodiment of the present invention will be explained based on the accompanying drawings. FIG. 4 is a block diagram of a discharge lamp lighting device according to a third embodiment. The difference in configuration from the first embodiment is the lamp voltage detection circuit 10 and division circuit 11 in FIG.
A high-pass filter 14 is connected between the lamp current detection circuit 9 and the control circuit 12B as a frequency discrimination means that passes the lighting frequency component but not the high frequency vibration component of the lamp current detection signal.

The operation of the third embodiment with the above configuration will now be described. When the discharge lamp 3 starts, the lamp current detection circuit 9 detects both the lighting frequency component and the natural oscillation frequency component of the lamp current. By inputting the detection signal to a high-pass filter 14 that passes only the natural vibration frequency component, only the current detection signal of the natural vibration frequency component appears in the control circuit 12B. If this signal is larger than a predetermined value, the control circuit 12B turns on the switch 8 to reduce the inductance on the secondary side of the pulse transformer 6 for a predetermined period. After a predetermined period of time has elapsed, the switch 8 is opened and the natural vibration frequency component is detected again. At this time, if the natural vibration frequency component is below a predetermined value, the switch 8 is left open,
If it is larger than a predetermined value, switch 8 is turned on again for a predetermined period. In this way, the natural vibration frequency component is made below a predetermined value. Here, the predetermined value of the natural vibration frequency component refers to the value of the maximum natural vibration frequency component at which the discharge lamp 3 does not cause an acoustic resonance phenomenon.

As described above, according to the third embodiment of the present invention, the acoustic resonance phenomenon is prevented when the lamp impedance of the discharge lamp 3 is low, as in the first embodiment, and the discharge lamp 3 is prevented from flickering or turning off. You can prevent this from happening. Further, as in the first embodiment, no restriking voltage is generated during steady lighting, and radiation noise from the discharge lamp lighting device can be reduced.

Next, a fourth embodiment of the present invention will be explained based on the accompanying drawings. FIG. 5 is a block diagram of a discharge lamp lighting device according to a fourth embodiment. The difference in configuration from the third embodiment is that the frequency discrimination means has a low-pass filter 15 that passes the lighting frequency component and a high-pass filter 16 that passes the natural vibration frequency component, which are connected in parallel after the current detection circuit 9. The output terminal of the division circuit 17 is connected to the division circuit 17, and the output terminal of the division circuit 17 is connected to the control circuit 12C. The related operations of the above components will now be described. When the discharge lamp 3 starts, the lamp current detection circuit 9 detects the sum of the lighting frequency component and the natural vibration frequency component of the lamp current. The signal detected by the lamp current detection circuit 9 is divided into a lighting frequency component and a natural vibration frequency component by using a low-pass filter 15 and a high-pass filter 16. By inputting the divided signals to the division circuit 17, the ratio of the natural vibration frequency component to the lighting frequency component is detected. If this ratio is larger than a predetermined value, the control circuit 12C causes the switch 8 to
is input to reduce the inductance on the secondary side for a predetermined period. After a predetermined period of time has elapsed, the switch 8 is opened and the ratio of the natural vibration frequency component to the lighting frequency component is detected again. At this time, if the ratio of the natural vibration frequency component to the lighting frequency component is less than or equal to a predetermined value, the switch 8 is left open, and if it is greater than the predetermined value, the switch 8 is closed again for a predetermined period. In this way, the ratio of the natural vibration frequency component to the lighting frequency component is made equal to or less than a predetermined value. Here, the predetermined value of the ratio of the natural vibration frequency component to the lighting frequency component refers to the maximum ratio value at which the discharge lamp 3 does not cause an acoustic resonance phenomenon.

According to the fourth embodiment of the present invention, as in the first embodiment, when the lamp impedance of the discharge lamp 3 is low, the acoustic resonance phenomenon is prevented, and the discharge lamp 3 is prevented from flickering or turning off. You can prevent this from happening. Further, as in the first embodiment, no restriking voltage is generated during steady lighting, and radiation noise from the discharge lamp lighting device can be reduced.

In the first to fourth embodiments, all of the primary windings of the pulse transformer 6 are short-circuited, but a part of the primary windings may be short-circuited as long as an acoustic resonance phenomenon does not occur. You can also do this. Further, in the first to fourth embodiments, the primary winding of the pulse transformer 6 was short-circuited, but if a high-voltage switch is used, a configuration in which part or all of the secondary winding is short-circuited may be used. . Also, the first
In the fourth embodiment, the switch 8 that short-circuits the primary winding of the pulse transformer 6 may be a semiconductor switch such as a transistor or triac, or may be a relay, as long as it has a control terminal. It doesn't matter if it's something else. In addition, in the third and fourth embodiments, one switch was used, but by connecting two or more switches, the inductance of the secondary winding of the pulse transformer 6 can be switched in stages, and each switch has a unique Vibration frequency components may also be detected.

Further, in the first to fourth embodiments, the lamp current is detected to detect the state of the discharge lamp 3, that is, to determine whether it has started, but this determining means may also be by detecting the lamp voltage. , detection of lamp light, or detection of other lamp characteristics.

Although the first to fourth embodiments use the DC power source 1, the DC power source 1 may be a rectified alternating current, or may be a rectified and smoothed one. Also, DC/
It may be a DC converter or another one.
Further, in the first to fourth embodiments, the DC power supply 1 and the inverter circuit 2 are used in combination, but this part may be an AC power supply or an AC/AC converter.

Further, in the first to fourth embodiments, the choke coil 4 was used as a current limiting element for limiting the lamp current, but a series circuit of a choke coil and a capacitor or only a capacitor may be used. Also, other configurations may be used.

Further, the configuration of the pulse generating circuit 5 may be the same as that of the conventional example, or may have a different configuration.

[0028] Further, the short-circuit may be left at a selected point that does not cause an acoustic resonance phenomenon at the time of starting and improves the continuity of the current at the time of lighting. Further, if the configuration is such that the starting current flows depending on the lamp impedance, the switch may be turned on or off depending on the current value or voltage value.

[0029]

As is clear from the above description, the discharge lamp lighting device of the present invention is provided with a means for detecting the state of the discharge lamp, and the impedance control means for controlling the impedance of the pulse transformer based on the output of the means detects the state of the discharge lamp. By reducing the inductance of the secondary winding of the pulse transformer when the lamp impedance after startup is lower than a predetermined value, it is possible to prevent the acoustic resonance phenomenon and prevent the discharge lamp from flickering or going out.

Furthermore, by improving the continuity of the current when the lamp impedance is above a predetermined value, it is possible to compensate for the restriking voltage during steady lighting and to reduce radiation noise from the discharge lamp lighting device. can.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a discharge lamp lighting device according to a first embodiment of the present invention.

[Figure 2] Current waveform diagram of the discharge lamp of the same example

[Figure 3]
Block diagram of a discharge lamp lighting device according to a second embodiment of the present invention

FIG. 4 is a block diagram of a discharge lamp lighting device according to a third embodiment of the present invention.

FIG. 5 is a block diagram of a discharge lamp lighting device according to a fourth embodiment of the present invention.

[Figure 6] Block diagram of a conventional discharge lamp lighting device

[Figure 7]
Current waveform diagram of the conventional discharge lamp

[Explanation of symbols]

1 DC power supply 2 Inverter circuit 3 Discharge lamp 4 Choke coil 5 Pulse generation circuit 6 Pulse transformer 7 Capacitor 8 Switch 9 Lamp current detection circuit 10 Lamp voltage detection circuit 11 Division circuit 12 Control circuit

Claims (5)

[Claims] 1. A DC power source that generates a DC voltage; a current inverter connected to an output end of the DC power source and inverts a load output current every certain period; and a current inverter connected to the load output of the current inverter. a pulse transformer having a secondary winding connected in series to the discharge lamp; a capacitor connected in parallel to a series circuit of the discharge lamp and the secondary winding of the pulse transformer; A discharge lamp lighting device comprising impedance detection means for detecting impedance, and impedance control means for controlling impedance on the secondary side of the pulse transformer according to an output of the impedance detection means. 2. A DC power source that generates a DC voltage; a current inverter connected to the output end of the DC power source and inverts a load output current every certain period; and a current inverter connected to the load output of the current inverter. a pulse transformer having a secondary winding connected in series to the discharge lamp; a capacitor connected in parallel to a series circuit of the discharge lamp and the secondary winding of the pulse transformer; A discharge lamp lighting device comprising: timer means for detecting a later time, and impedance control means for controlling impedance on the secondary side of the pulse transformer according to an output of the timer means. 3. A DC power source that generates a DC voltage; a current inverter connected to the output end of the DC power source and inverts a load output current every certain period; and a current inverter connected to the load output of the current inverter. a pulse transformer having a secondary winding connected in series to the discharge lamp; a capacitor connected in parallel to a series circuit of the discharge lamp and the secondary winding of the pulse transformer; A frequency determining means is inserted into a closed circuit composed of a secondary winding, the capacitor, and the discharge lamp, and detects a frequency component higher than the lighting frequency of the discharge lamp, and A discharge lamp lighting device comprising control means for controlling impedance of a secondary winding of the pulse transformer. 4. The discharge lamp lighting device according to claim 3, wherein the frequency determining means includes means for outputting a component ratio between a lighting frequency component of the discharge lamp and a frequency component higher than the lighting frequency. 5. The discharge lamp lighting device according to claim 1, wherein the impedance control means comprises a switch means for shorting or opening the primary winding of the pulse transformer.