JP2007287488A - Discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a voltage required in startup, and to allow control in preheating. <P>SOLUTION: This discharge lamp lighting device is provided with: a first series circuit part composed by serially connecting a primary-side coil to a capacitor; a second series circuit part composed by serially connecting a secondary-side coil constituting a transformer along with the primary-side coil and having a winding number more than that of the primary-side coil to a discharge lamp; and a bridge type D.C.-A.C. conversion circuit having four transistors for converting a D.C. voltage from a power source part to an A.C. voltage to supply the A.C. voltage between both ends of the first and second series circuit parts connected in parallel to each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a discharge lamp lighting device.

  Conventionally, HID (High Intensity Discharge) lamps such as metal halide lamps have high efficiency and high brightness, so that they can be used for outdoor lighting such as road lighting, DLP (Digital Light Processing), liquid crystal projectors, etc. It has come to be used as a light source for a projection device.

  As a conventional discharge lamp lighting device for lighting such an HID lamp, for example, there is one that employs a starter disclosed in Patent Document 1.

The apparatus of Patent Document 1 supplies a square wave supply voltage having a relatively low amplitude and a relatively low frequency such that arc discharge continuously occurs in the lamp to the lamp, and the coil and the capacitor are electrically connected at start-up. A relatively high frequency supply voltage that resonates with the lamp is supplied to the lamp. In the apparatus of Patent Document 1, a relatively high voltage at the time of starting can be supplied to the lamp, and a voltage for maintaining the lamp normally lit can be supplied to the lamp.
JP 2005-507553 A

  By the way, in order to increase the voltage across the capacitor of a general series resonance circuit, conditions of large inductance, small capacitance, and small parasitic resistance are required. In the device of Patent Document 1, a bridge driving condition at a higher frequency is also imposed, and a sufficient voltage cannot be obtained as a voltage at the start. For this reason, in the apparatus of Patent Document 1, it may take a long time to relight, or a circuit for generating a higher voltage for starting needs to be prepared separately.

  It is an object of the present invention to provide a discharge lamp lighting device that can generate a relatively high voltage at the time of starting a lamp with a simple circuit and can perform preheating control.

  A discharge lamp lighting device according to the present invention comprises a first series circuit unit configured by connecting a primary side coil and a capacitor in series, and a transformer together with the primary side coil. A second series circuit unit configured by connecting a secondary coil having a large number of turns and a discharge lamp in series, four transistors, and converting a DC voltage from a power supply unit into an AC voltage in parallel And a bridge-type DC-AC conversion circuit that supplies an AC voltage to both ends of the connected first and second series circuit units.

  In the present invention, when the discharge lamp is started, a voltage generated in the primary side coil of the first series circuit is induced in the secondary side coil. Depending on the turns ratio, a sufficiently high voltage required for starting the discharge lamp is generated in the secondary coil, and this voltage is supplied to the discharge lamp to start the discharge lamp.

  According to the present invention, a relatively low input voltage can be used to supply a relatively low voltage during normal lighting and a relatively high voltage during start-up, and further, preheating control can be performed. Have.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a discharge lamp lighting device according to a first embodiment of the present invention.

  The power supply unit 11 generates a DC voltage. The power supply unit 11 generates constant power. In an actual circuit, for example, the power supply unit 11 can be configured by an output smoothing capacitor of a constant power control chopper circuit.

  The positive output terminal of the power supply unit 11 is connected to the drains of the transistors Q1 and Q3 via a power supply line. The negative output terminal of the power supply unit 11 is connected to the sources of the transistors Q2 and Q4 via a reference potential line. The source of the transistor Q1 and the drain of the transistor Q2 are connected to each other. Further, the source of the transistor Q3 and the drain of the transistor Q4 are connected to each other.

  These transistors Q <b> 1 to Q <b> 4 constitute a bridge-type DC / AC conversion circuit that converts a DC voltage from the power supply unit 11 into an AC voltage.

  A connection point (hereinafter referred to as a first connection point) between the source of the transistor Q1 and the drain of the transistor Q2 is connected to the source of the transistor Q3 and the drain of the transistor Q4 via the first series circuit of the coil L1 and the capacitor C. To the connection point (hereinafter referred to as the second connection point). Further, a second series circuit of the coil L2 and the lamp 12 is connected between the first connection point and the second connection point. As the lamp 12, an HID lamp is employed.

  The capacitor C is provided for vibration waveform formation and current limitation. Further, a transformer T is constituted by the coils L1 and L2. The coil L1 is the primary side of the transformer T, and the coil L2 is the secondary side of the transformer T. In the present embodiment, the number of turns of the coil L2 is set to n times the number of turns of the coil L1 (n is a positive number). For example, a value of several times to several hundred times is set as the turn ratio n.

  The control unit 13 generates a control signal for driving the transistors Q1 to Q4. Control unit 13 turns on transistors Q1 and Q4 and turns off transistors Q2 and Q3. Control unit 13 turns off transistors Q1 and Q4 and turns on transistors Q2 and Q3. The control unit 13 changes the switching frequency (driving frequency) of the transistors Q1 to Q4 according to each phase when the lamp 12 is turned on.

That is, in the present embodiment, the control unit 13 drives the transistors Q1 to Q4 at a relatively high frequency during start-up and preheating, and drives the transistors Q1 to Q4 at a relatively low frequency during normal lighting. It is supposed to be. ,
Next, the operation of the embodiment configured as described above will be described with reference to FIGS. FIG. 2 is a flowchart for explaining the operation of the embodiment.

<At start-up>
The power supply unit 11 supplies a positive output to the power supply line and supplies a negative output to the reference potential line. The DC voltage applied between the power supply line and the reference potential line is supplied to the transistors Q1 to Q4 constituting the bridge type DC / AC conversion circuit.

  At the start of lighting of the lamp 12, the process proceeds from step S1 to step S2 in FIG. 2, and the control unit 13 sets the first high frequency as the drive frequency of the transistors Q1 to Q4. The control unit 13 supplies a first high-frequency control signal to the transistors Q1 to Q4 to turn it on and off (step S3).

  That is, the transistors Q1 and Q4 constituting the bridge circuit are simultaneously turned on and off, and the transistors Q2 and Q3 are also simultaneously turned on and off. When the transistors Q1 and Q4 are on, the transistors Q2 and Q3 are off, and when the transistors Q1 and Q4 are off, the transistors Q2 and Q3 are on. In order to prevent a short circuit, the transistors Q1 to Q4 are all turned off for a short time.

  When the transistors Q1 and Q4 are on, current flows from the positive output terminal of the power supply unit 11 to the negative output terminal via the transistor Q1, the coil L1, the capacitor C, and the transistor Q4. On the other hand, when the transistors Q2 and Q3 are on, a current flows from the positive output terminal of the power supply unit 11 to the negative output terminal via the transistor Q3, the capacitor C, the coil L1, and the transistor Q2.

  When the transistors Q1 and Q4 are on, the capacitor C is charged through the coil L1, and the terminal voltage of the capacitor C rises to approximately the voltage Vin of the power supply unit 11. Next, due to the back electromotive force generated in the coil L1, the voltage VL generated in the coil L1 is added to the terminal voltage of the capacitor C, and rises to Vin + VL. Next, free vibration occurs between the coil L1 and the capacitor C, and the terminal voltage of the capacitor C converges to a predetermined value while changing the polarity. Even when the transistors Q2 and Q3 are on, the same operation as when the transistors Q1 and Q4 are on is performed.

  In the present embodiment, a high voltage corresponding to the turn ratio is generated in the coil L2 by the voltage generated in the coil L1. The voltage generated in the coil L2 has substantially the same waveform as the voltage generated in the coil L1 and the capacitor C, and the amplitude becomes a sufficiently large value according to the turn ratio. A voltage generated in the coil L2 is applied to the lamp 12.

  FIG. 3 is a waveform diagram showing the voltage across the lamp 12 at the time of starting (no-load starting voltage) with time on the horizontal axis and voltage on the vertical axis. FIG. 4 is a waveform diagram showing the time axis of FIG. In FIG. 3, a period T1 is a period in which the transistors Q1 and Q4 are on, and a period T2 is a period in which the transistors Q2 and Q3 are on.

  As shown in FIG. 3, extremely high voltages are generated at both ends of the lamp 12 when the transistors Q1 and Q4 are turned on and when the transistors Q2 and Q3 are turned on. In the example of FIG. 3, when Vin is 220 V, L1 is 2.1 μH for 7 turns, L2 is 1.3 mH for 200 turns, and C is 0.01 μF, the driving frequency of transistors Q1 to Q4 is set to 17 kHz. The case characteristics are shown. In the example of FIG. 3, the maximum value of the voltage across the lamp 12 is about 6640V, and the minimum value is about −4800V. This high voltage is applied to the lamp 12 every time the polarity of the full bridge drive is reversed. In addition, as a drive frequency at the time of starting, several hundred Hz-several hundred kHz can be used.

  Thus, by driving the transistors Q1 and Q4 and the transistors Q2 and Q3 on and off at the first high frequency, a high oscillating voltage can be applied to the lamp 12.

  Further, as shown in FIG. 4, it can be seen that the voltage waveform applied to the lamp 12 is a damped oscillation waveform with relatively little distortion.

  Thus, at the time of starting, free vibration occurs in the coil L1 and the capacitor C when the polarity of the full bridge is reversed. And at the time of this free vibration, the voltage applied to the coil L1 is induced to the coil L2 according to the turn ratio of the coil L1 and the coil L2. As described above, the free vibration of the first series circuit converges until the next polarity inversion, and the current becomes substantially zero.

<When preheating>
When a large voltage generated in the coil L2 is applied to the lamp 12, the lamp 12 causes dielectric breakdown. If the dielectric breakdown of the lamp 12 is caused by the control of the starting period, the process proceeds to the preheating period (step S4). The preheating period is a period for shifting from an unstable discharge state immediately after the start of discharge to a stable discharge state.

  As a result of the dielectric breakdown, the lamp 12 shifts to glow discharge, and further shifts to arc discharge to be in a normal lighting state. In the present embodiment, the lamp 12 is turned on by the energy from the power supply unit 11 during the entire starting period, preheating period, and normal lighting period.

  During preheating, a stable discharge state can be obtained in a shorter time when a larger amount of lamp current is passed through the lamp 12. However, when the lamp current is large, the electrode of the lamp 12 is damaged. For this reason, it is desirable that the lamp current can be controlled during preheating. In the present embodiment, preheating control is performed by controlling the driving frequency of the transistors Q1 to Q4.

  FIG. 5 is a waveform diagram showing changes in lamp current during preheating, with time on the horizontal axis and current on the vertical axis. FIG. 5 (a) shows the characteristics when the driving frequency (preheating frequency) of the transistors Q1 to Q4 during preheating is set to 10 KHz under the same conditions as in the example of FIG. 3, and FIG. 5 (b) is set to 12 KHz. The characteristics are shown. The example of FIG. 5 is an example in which the drive frequencies of the transistors Q1 to Q4 are set to be the same during start-up and during preheating. Note that the characteristics of the lamp current during preheating are affected by the ambient environmental temperature and the like, and FIG. 5 is an example under specific conditions.

  In any of the examples of FIGS. 5A and 5B, and in any of the examples from 8 KHz to 15 KHz (not shown), the lamp current does not become alternating but pulsating immediately after the start of preheating. Become. This polarity is reversed when the terminals of the lamp 12 are connected in reverse. Moreover, the pulsating flow immediately after the start of preheating changes to alternating current with the passage of time. Further, the lamp current value during preheating decreases as the preheating frequency increases from 8 KHz to 15 KHz. Further, as the preheating frequency is increased from 8 KHz to 15 KHz, the time required to change from pulsating flow to alternating current becomes longer. That is, if the preheating current is reduced, the time until the current changes to alternating current becomes longer.

  From the above, it is considered that the unstable discharge is stable with time and changes to alternating current immediately after the start of discharge (start of preheating). In the preheating period, as the flowing lamp current increases, the temperature of the internal gas or the electrode rises faster, and the state quickly shifts to a stable discharge state. This lamp current can be controlled by changing the preheating frequency.

  FIG. 6 is a waveform diagram showing the time axis of FIG. 5 in an enlarged manner. 6 shows an example in which the preheating frequency is 12 KHz, FIG. 6A shows the pulsating flow section of FIG. 5, and FIG. 6B shows the AC section of FIG.

  As shown in FIG. 6, the lamp current changes in a sawtooth waveform. The current changes in a sawtooth shape depending on the inductance of the coil. The peak of the current value is determined by the driving frequency of the transistors Q1 to Q4. In the pulsating section of FIG. 6 (a), the lamp current is slightly saturated, whereas in the alternating section, a ramp current having a sawtooth waveform with little distortion is obtained as shown in FIG. 6 (b). Has been obtained. Since the current peak value in the same direction is smaller in the AC section than in the pulsating section, saturation is less likely.

  In the example of FIG. 5, if a frequency slightly higher than 10 KHz is adopted as the preheating frequency, it is considered that the peak value of the preheating current is low and the preheating time is relatively long. Thus, preheating is possible without damaging the lamp electrode or the like by appropriately controlling the preheating frequency.

<Normal lighting period>
Next, preheating is terminated and the normal lighting period starts. In this case, the control unit 13 shifts the processing from step S6 to step S7, and sets the driving frequency of the transistors Q1 to Q4 to a frequency lower than the driving frequency at the time of starting and preheating. The example of FIG. 5 shows an example in which the drive frequency is set to 100 Hz during the normal lighting period.

  During normal lighting, current flows mainly through the coil L2 and the lamp 12 based on the rectangular wave voltage generated by the DC / AC conversion circuit including the transistors Q1 to Q4. Even when the drive frequency is lowered, the capacitor C is connected in series on the coil L1 side, so that no current continues to flow. Further, during normal lighting, the voltage Vin of the power supply unit 11 also has a low voltage value, so that the current of the coil L1 during polarity reversal is greatly reduced. During the normal lighting period, the lamp 12 shifts to a stable arc discharge, and a stable lamp current is obtained.

As described above, in the present embodiment, the first series circuit including the primary side coil and the capacitor that freely vibrate and the second series circuit including the secondary side coil and the lamp are connected in parallel to each other. A rectangular wave voltage is supplied to both ends of the series circuit by a bridge type DC / AC converter circuit using four transistors. A large voltage can be generated in the secondary coil according to the turns ratio of the primary coil and the secondary coil,
Furthermore, when the starting period ends and the preheating period starts, the driving frequency of the transistor can be controlled to shift to a stable discharge state without damaging the lamp electrode or the like. For example, in the conventional high-voltage pulse starting method, an uncontrollable lamp rush current flows from the power source, but in the present embodiment, preheating can be performed while sufficiently suppressing the lamp rush current. Thereby, the lifetime of the lamp can be extended.

  As described above, the high-pressure discharge lamp can be lit from the start to the normal lighting with a circuit having a relatively simple configuration, and only one stage of the starting circuit is required, which is advantageous for downsizing and cost reduction.

  Note that the control unit 13 may control switching of the start period, the preheating period, and the normal lighting period, for example, according to the time from the start of driving.

  FIG. 7 is a circuit diagram showing a modification of the first embodiment. In FIG. 7, the same components as those in FIG.

  In the example of FIG. 7, the capacitor C disposed on one end side of the coil L1 in FIG. 1 is disposed on the other end side of the coil L1. Even in this case, the first series circuit including the capacitor C and the coil L1 exhibits the same operation as the capacitor C and the coil L1 of FIG.

  Other configurations and operations are the same as those of the embodiment of FIG.

  FIG. 8 is a circuit diagram showing a second embodiment of the present invention. In FIG. 8, the same components as those in FIG.

  In the present embodiment, the secondary coil L2 of the coils L1 and L2 constituting the transformer T in FIG. 1 is divided into coils L21 and L22 and arranged at both ends of the lamp 12 in the first embodiment. Different from form.

  In the present embodiment, the terminal voltage of each coil L21, L22 can be set to a sufficiently high voltage by appropriately setting the ratio between the number of turns of coil L1 and the sum of the number of turns of coils L21, L22. Thereby, also in the present embodiment, a sufficiently high voltage necessary for starting the lamp 12 can be obtained as in the first embodiment.

  In the present embodiment, the voltage required for starting the lamp 12 may be divided by the coils L21 and L22 to generate different voltages, and the voltage generated in one coil is half. That is, the ground voltage of each coil can be reduced, and adverse effects on the peripheral elements can be further reduced.

  FIG. 9 is a circuit diagram showing a modification of the second embodiment. In FIG. 2, the same components as those of FIG.

  In the example of FIG. 9, the capacitor C arranged on one end side of the coil L1 in FIG. 8 is arranged on the other end side of the coil L1. Even in this case, the first series circuit including the capacitor C and the coil L1 exhibits the same operation as that of the capacitor C and the coil L1 in FIG.

  Other configurations and operations are the same as those of the embodiment of FIG.

  FIG. 10 is a circuit diagram showing a third embodiment of the present invention. In FIG. 10, the same components as those in FIG.

  This embodiment is different from the first embodiment in that a coil L3 is employed instead of the transformer T. One end of the capacitor C is connected to the second connection point of the second series circuit, and the other end is connected to the middle point of the coil L3.

  The winding ratio n2 / n1 between the winding point n2 of the coil portion L32 on the lamp 12 side from the middle point of the coil L3 and the winding number n1 of the coil portion L31 on the first connection point side from the middle point of the coil L3 is larger than 1. Is set to be

  Between the first connection point and the second connection point, the coil portion L31 of the coil L3 and the capacitor C are connected in series to form a first series circuit. Therefore, at the start, the voltage across the capacitor C changes in the same manner as the capacitor C of the first embodiment. Further, since a voltage corresponding to the turn ratio is induced in the coil portion L32, a voltage similar to that in FIG.

  Other operations are the same as those in the first embodiment.

  Thus, also in this embodiment, the same effect as that of the first embodiment can be obtained.

  FIG. 11 is a circuit diagram showing a modification of the third embodiment. In FIG. 11, the same components as those of FIG.

  In the example of FIG. 11, the lamp 12 and the capacitor C are disposed on the first connection point side in FIG. 10, and the coil L3 is disposed on the second connection point side.

  Other configurations and operations are the same as those of the embodiment of FIG.

1 is a circuit diagram showing a discharge lamp lighting device according to a first embodiment of the present invention. 6 is a flowchart for explaining the operation of the embodiment. FIG. 6 is a waveform diagram showing the voltage across the lamp 12 at the time of starting (no-load starting voltage) with time on the horizontal axis and voltage on the vertical axis. The wave form diagram which expands and shows the time axis of FIG. 3 10 times. The waveform diagram which shows the change of the lamp current at the time of preheating, with time on the horizontal axis and current on the vertical axis. The wave form diagram which expands and shows the time axis of FIG. The circuit diagram which shows the modification of 1st Embodiment. The circuit diagram which shows the 2nd Embodiment of this invention. The circuit diagram which shows the modification of 2nd Embodiment. The circuit diagram which shows the 3rd Embodiment of this invention. The circuit diagram which shows the modification of 3rd Embodiment.

Explanation of symbols

    DESCRIPTION OF SYMBOLS 11 ... Power supply part, Q1-Q4 ... Transistor, L1, L2 ... Coil, T ... Transformer, C ... Capacitor, 12 ... Lamp, 13 ... Control part.

Claims (4)

A first series circuit unit configured by connecting a primary coil and a capacitor in series;
A second series circuit unit configured by connecting a secondary coil having a number of turns larger than that of the primary coil and a discharge lamp in series with the primary coil;
A bridge-type DC-AC converter circuit that has four transistors, converts a DC voltage from a power supply unit into an AC voltage, and supplies the AC voltage to both ends of the first and second series circuit units connected in parallel. When,
A discharge lamp lighting device comprising:   2. The discharge lamp lighting device according to claim 1, wherein the second series circuit unit is configured by dividing the secondary coil at both ends of the discharge lamp. 3. A series circuit unit configured by connecting a coil and a discharge lamp in series;
A capacitor connected in parallel to the discharge lamp between one end of the series circuit portion and a midpoint of the coil;
A bridge type DC / AC converter circuit that has four transistors, converts a DC voltage from a power supply unit to an AC voltage, and supplies an AC voltage to both ends of the series circuit unit;
The midpoint is set to a point where the number of turns on one end side of the series circuit portion of the coil is larger than the number of other turns.   The DC / AC converter circuit is controlled to drive the four transistors at the first frequency at the start, and to set the four transistors to the same or different from the first frequency at the time of preheating after the start. The control means for driving the four transistors at a third frequency lower than the first and second frequencies during normal lighting after the preheating is provided. The discharge lamp lighting device according to any one of 3.

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