JP2008147004A - Discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device having a simple and easy configuration, and furthermore, enabling downsizing. <P>SOLUTION: This charging means 136 is equipped with a booster circuit, a charging diode 176, and a charging resistor 178. Then, in the booster circuit, a series circuit of a booster capacitor 170 and a booster diode 174 is connected in parallel with a discharge lamp 130 so that the booster diode 174 is on a secondary main power line side 128. Moreover, the charging diode 176 and the charging resistor 178 are arranged between a junction of the booster capacitor 170 and the booster diode 174 and a junction of a discharge gap 140 and a charging capacitor 137. Then, an electric charge is accumulated in the booster capacitor 170 by the booster diode 174 at one polarity of resonant power, and the charge in the booster capacitor 170 is charged into the charging capacitor 137 via the charging diode 176 and the charging resistor 178 at the other polarity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a discharge lamp lighting device, and more particularly to an improvement of its igniter mechanism.

In general, in order to light a high-pressure discharge lamp, it is necessary to break down the interior of the lamp by applying a high-voltage starting pulse such as several kV to sometimes 20 kV. For this reason, the discharge lamp lighting device includes a pulse transformer for generating the high-voltage start pulse.
As is well known, a pulse transformer is wound with a secondary winding connected in series with a lamp and inducing a high voltage pulse voltage, and a primary winding magnetically coupled to the secondary winding.
The primary winding is connected in series with a discharge gap that breaks (conducts) at a constant voltage, and a charging capacitor is connected in parallel to the series circuit of the discharge gap and the primary winding. And the discharge lamp lighting device constitutes a circuit for charging inside thereof, and charges the charging capacitor. The discharge gap breaks when the charging voltage of the charging capacitor reaches a constant voltage, and discharges the charge charged in the charging capacitor to generate a voltage in the primary winding of the pulse transformer. As a result, a voltage of n times is induced in the secondary winding having n times the number of turns of the primary winding, and a high voltage pulse voltage is output.

  Although the lighting device outputs a high voltage pulse by such an operation, there are many kinds of discharge gaps used in this circuit up to those having a breakover voltage of about several hundred V to 3000 V. . However, due to recent demands for light source device downsizing and cost reduction, pulse voltage values, and the size of pulse transformers, the discharge gap used is about 800V. For this reason, in order to break over the discharge gap, the charging circuit for charging the charge capacitor connected to the series circuit of the discharge gap and the primary winding of the pulse transformer has the ability to charge a voltage of 800 V or more. There must be.

By the way, in the case of a lighting device having an LC resonance circuit in the output of a full bridge circuit that uses the output of a DC-DC converter as a power source, when the resonance operation is performed in a no-load state, The no-load voltage output to the capacitor end is a high-frequency voltage having an effective value of about 300 to 400 V, and the peak value is also about 600 to 700 V.
Therefore, even if the no-load voltage is rectified and used as it is, the discharge gap having a breakover voltage of 800 V cannot be conducted. As a countermeasure, in order to further increase the no-load voltage, the operating frequency at this time may be a frequency close to the natural resonance frequency determined by the inductance of the choke coil of the resonance circuit and the capacitor capacity of the resonance circuit. Since the resonance current increases and the loss of the switching element used in the full bridge circuit increases, the possibility of a circuit failure increases, which is not practical.
For this reason, conventionally, various charging circuits as shown below are employed.

FIG. 3 shows a conventional method, which includes a full bridge circuit 18 including switching elements 10, 12, 14, and 16, and a resonance circuit 24 including a choke coil 20 and a resonance capacitor 22, and a desired no-load resonance voltage. Is supplied to the discharge lamp 30 via the first main power line 26 and the second main power line 28.
For starting the discharge lamp 30, a pulse transformer 32, a discharging unit 34, and a charging unit 36 are used.
That is, the secondary winding N2 of the pulse transformer 32 is connected in series to the first main power line 26. In FIG. 3, the secondary winding N2 is connected in series to the first main power line 26, but may be connected in series to the second main power line 28, and the divided winding N2 may be connected to the power line. 26 and 28 may be connected in series.

The discharging means 34 includes a first charging capacitor 37, a second charging capacitor 38, and a discharging gap 40. The first charging capacitor 37—the primary winding N1 of the pulse transformer 32—the discharging gap 40—the second charging capacitor 38. Are connected in parallel with the second main power line 28.
Further, the charging means 36 includes a first charging diode 44 and a second charging diode 46, and resistors 48 and 50. The anode of the first charging diode is connected to the first main power line 26, and the cathode is connected to the connection point of the first charging capacitor 37 and the pulse transformer 32 via a resistor 48. The cathode of the second charging diode 46 is connected to the first main power line 26, and the anode is connected to a connection point between the second charging capacitor 38 and the discharge gap 40 via a resistor 50.

In this configuration, the voltage applied to the series circuit of the discharge gap 40 and the primary winding N1 of the pulse transformer 32 is a value obtained by adding the both-ends voltage of the second charging capacitor 38 to the both-ends voltage of the first charging capacitor 37. Become.
At this time, the charging capacitors 37 and 38 are charged to a voltage obtained by half-wave rectifying the high-frequency no-load voltage, respectively, and can be charged up to 600 to 700 V, which is the peak value of the high-frequency no-load voltage. . In other words, it is possible to apply 1200 to 1400 V including the voltage across the first and second charging capacitors 37 and 38 to the series circuit of the discharge gap 40 and the primary winding of the pulse transformer 32, resulting in a breakover. It becomes possible to conduct a discharge gap having a voltage of about 800V.

  However, in the conventional example shown in FIG. 3, two charging capacitors used for the discharge means 34 of the igniter are required, and these two capacitors have a high withstand voltage, but the pulse is generated when the discharge gap 40 is broken over. It must have enough capacity to send the necessary energy to the primary winding of the transformer 32. Further, since the two charging capacitors 37 and 38 are connected in series, if each of them has the same capacity, the combined capacity becomes one half of the capacity of each capacitor. Therefore, the capacity of the charging capacitor is twice the required capacity, resulting in an increase in the size of the capacitor and the use of two more capacitors, leading to a problem of increased cost and increased size of the lighting device.

FIG. 4 shows another example of the prior art, which is an example of an igniter in a lighting device that does not use a choke coil and capacitor resonance circuit (see Patent Document 1). Note that portions corresponding to those in FIG. 3 are denoted by the same reference numerals, and description thereof is omitted.
The conventional igniter includes a step-up transformer 60 and a constant voltage semiconductor switch 62. When charge is accumulated in the capacitor 64 to a certain voltage, the constant voltage semiconductor switch 62 is turned on, and a current is supplied to the primary winding side of the step-up transformer 60. The charging capacitor 37 is charged with a high voltage generated on the secondary winding side of the step-up transformer 60. By repeating this operation, the voltage across the charging capacitor 37 rises, and when the breakover voltage of the discharge gap 40 is reached, the discharge gap 40 becomes conductive and an igniter operation is performed.

However, the conventional example shown in FIG. 4 requires the use of the step-up transformer 60, the preceding stage capacitor 64, the rectifier diode 44, and the constant voltage semiconductor switch 62 in the charging circuit of the charging capacitor 37. This leads to an increase in the size of the device.
JP 2003-36992 A

  The present invention has been made in view of the prior art, and a problem to be solved is to provide a discharge lamp lighting device having a simple configuration and capable of being downsized.

In order to solve the above problems, a lighting device according to the present invention includes:
A pulse transformer in which the secondary winding is connected in series with the discharge lamp;
A discharge means including a discharge gap and a charge capacitor, and connected in parallel to the second main power line, a discharge circuit connected to be a primary winding of the charge capacitor-discharge gap-pulse transformer;
Charging means for charging the charge capacitor up to a breakover voltage of a discharge gap,
The charging means includes a boost capacitor and a boost diode, and a boost circuit connected in parallel with the discharge lamp so as to be a second main power line-boost diode-boost capacitor-first main power line;
A connection point between the boost capacitor and the boost diode, and a charging diode and a charging resistor installed between the discharge gap and the connection point of the charging capacitor;
Charges are accumulated in the boost capacitor via a boost diode when the AC power has one polarity, and charges of the boost capacitor are charged to the charge capacitor via a charging diode and a charge resistor when the polarity is other.

In the lighting device, a choke coil is connected in series with the discharge lamp, a resonance capacitor is connected in parallel, and the resonance power of the choke coil and the resonance capacitor oscillated by supplying AC power is supplied to the first and second It is preferable to supply the main power line.
Further, in the lighting device, the boost diode of the charging means has its anode connected to the second main power line, its cathode connected to the boost capacitor via a resistor, and the other end of the boost capacitor connected to the first main power line. Is preferred.
As described above, according to the present invention, the charge is accumulated in the boost capacitor when the second main power line is positive (or negative) polarity, and the charge accumulated in the boost capacitor when the second main power line is negative (or positive) polarity is transferred to the charging capacitor. In this case, since the second power line has a negative (or positive) polarity, the charging voltage from the boosting capacitor is superimposed on the charging voltage of the charging capacitor itself, and a high voltage can be obtained.

  According to the present invention, the charging capacitor is charged with a high voltage by the boosting diode and the boosting capacitor, and this high voltage is applied to the discharge gap. Therefore, a plurality of charging capacitors having a large capacity and a high withstand voltage, or a dedicated capacitor An igniter can be configured without using a step-up transformer.

Preferred embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the configuration of a discharge lamp lighting device 100 according to an embodiment of the present invention. The parts corresponding to those in FIG.
The lighting device 100 shown in the figure has a choke coil as an output of a full bridge circuit 118 composed of four switching elements (MOSFETs) 110, 112, 114, 116 using the output of the DC-DC converter 102 as a power source. 120 and a resonance circuit 124 in which a resonance capacitor 122 is connected in series, and a high-pressure discharge lamp 130 serving as a load is provided in parallel with the resonance capacitor 122.

The igniter that is characteristic in the present embodiment includes a pulse transformer 132, a discharging unit 134, and a charging unit 136.
The pulse transformer 132 has a secondary winding N2 connected in series with the discharge lamp 130.
The discharge means 134 includes a discharge gap 140 and a charging capacitor 137 so that the second main power line 128 -the charging capacitor 137 -the discharge gap 140 -the primary winding N1 -the second main power line 128 of the pulse transformer 132 is provided. It has a connected discharge circuit.

The charging unit 136 includes a booster circuit, a charging diode, and a charging resistor.
The booster circuit includes a booster capacitor 170, a resistor 172, and a booster diode 174, and the discharge lamp 130 and the second main power line 128—the booster diode 174—the resistor 172—the booster capacitor 170—the first main power line 126. Connected in parallel.
The charging diode 176 is installed between the connection point between the boost capacitor 170 and the resistor 172 and the connection point between the discharge gap 140 and the charging capacitor 137, and is connected to the charging capacitor 137 via the charging resistor 178. Charge the battery.

Then, the charge is accumulated in the boost capacitor 170 by the boost diode 174 when the resonance power is in one polarity, and the charge capacitor 137 is charged through the charging diode 176 and the charge resistor 178 in the other polarity. .
Next, the operation of the lighting device according to the present invention will be described.
As is well known, the direct-current power adjusted by the DC-DC converter 102 is converted into an alternating current by a full bridge circuit 118 and further adjusted to a resonance frequency by which a desired no-load resonance voltage is output by a resonance circuit 124 to be discharged lamp. The lamp 130 is turned on.

  On the other hand, in order to cause dielectric breakdown of the lamp 130 at the start, a no-load high-frequency voltage is output by a resonance circuit 124 including a choke coil 120 and a capacitor 122. That is, the full bridge circuit 118 performs switching of several tens of kHz and performs polarity inversion operation. Here, when the anode side of the boost diode 174 has a positive polarity, the boost capacitor 170 is charged with a charge through the diode 174 and the resistor 172. The amount of charge once charged does not decrease until the polarity is reversed by the action of the diode 174, and remains charged in the boost capacitor 170. Next, when the polarity of the voltage output across the resonant capacitor 122 is reversed in this state, the charge capacitor 137 is charged with charge through the boost capacitor 170, the charge diode 176, and the charge resistor 178. At this time, the charge capacitor 137 is also charged together with the charge charged in the boost capacitor 170 in the previous cycle.

That is, the charge capacitor 137 can be charged with a charge amount twice as much as the charge amount originally charged in one charge cycle. Therefore, by repeating this cycle, the voltage at the end of the charging capacitor 137 can be increased to approximately twice the maximum value that can be increased.
The maximum value that can be raised is the peak value of the high-frequency no-load voltage, and the value is about 600 to 700V. Therefore, the voltage at the capacitor 137 end can be raised to 1200V to 1400V.
As a result, it becomes possible to conduct the discharge gap 140 having a breakover voltage of about 800 V, and the igniter operation is performed.

  More specifically, the resistor 172 is about 10 kΩ, the charging resistor 178 is about 50 kΩ, and the boost capacitor 170 is about 10000 pF. As the 10000 pF boost capacitor 170, a chip capacitor having a withstand voltage of about 630V can be used. The diodes 174 and 176 each have a withstand voltage of about 1600 V, and the discharge gap 140 is 800 V as described above. The charging capacitor 137 for supplying a voltage for breaking the discharge gap 140 is a film capacitor having a withstand voltage of 800 V or more and capable of withstanding a large current charge / discharge, and has a capacity of about 3000 to 5000 pF. However, as shown in FIG. 3, the number of film capacitors used is one compared to the conventional example in which two film capacitors are used, which contributes to the miniaturization of the apparatus.

With this configuration, the full bridge circuit 118 is switched at several tens of kHz to generate a no-load resonance voltage in the resonance circuit 124. At this time, the no-load resonance voltage output to the capacitor 122 end of the resonance circuit 124 is a high-frequency voltage having an effective value of 300 to 400 V and a peak value of 600 to 700 V as described above.
Upon receiving this no-load resonance voltage, the igniter charging circuit of the present invention starts the igniter operation. That is, the capacitor 170 charges and discharges the amount of charge determined by the resistance value of the resistor 172 and the time constant of the capacitance of the capacitor 170 for each inversion cycle of the resonance voltage. In a cycle in which the charge is discharged from the capacitor 170, the capacitor 137 is charged by the inverted resonance voltage, and in addition, the charge discharged from the capacitor 170 is charged to the capacitor 137. By repeating this, the voltage of the capacitor 137 increases, the voltage of the capacitor 137 reaches 800 V in several hundred cycles, and the discharge gap 140 breaks over. As a result, a high voltage pulse voltage is output from the lighting device. If the constants of the capacitors 137 and 170 and the resistors 172 and 178 described above are used, the resonance frequency is about 40 kHz, and the voltage of the charging capacitor 137 reaches 800 V every about 800 cycles, and the lighting device outputs a high voltage pulse. In other words, about 50 pulses can be output per second. The number of pulses output can be adjusted by the time constant of the charging circuit of the present invention.

FIG. 2 is a voltage waveform at the end of the capacitor 137 due to charging and discharging of the capacitor 137 according to the circuit of the present invention, and it can be confirmed that the voltage is repeatedly increased and decreased every time the voltage reaches 800V.
As described above, according to the present invention, there is no need to use a step-up transformer other than a pulse transformer, and accompanying semiconductor switches, diodes, and capacitors, and use a plurality of film capacitors used as charging capacitors for a charging circuit. Thus, a small and inexpensive igniter charging circuit can be configured.

It is a circuit block diagram of the discharge lamp lighting device concerning one Embodiment of this invention. FIG. 2 is a voltage waveform diagram at a charging capacitor 137 end of the device shown in FIG. 1. It is a circuit block diagram of the conventional discharge lamp lighting device. It is another circuit block diagram of the conventional discharge lamp lighting device.

Explanation of symbols

30, 130 Discharge lamp 32, 132 Pulse transformer 34, 134 Discharge means 36, 136 Charging means 37, 137 Charging capacitor 40, 140 Discharge gap 170 Boost capacitor 174 Boost diode 176 Charging diode 178 Charging resistance

Claims (3)

In the lighting device that supplies AC power via the first main power line and the second main power line and lights the discharge lamp,
A pulse transformer in which the secondary winding is connected in series with the discharge lamp;
A discharge means including a discharge gap and a charge capacitor, and connected in parallel to the second main power line, a discharge circuit connected to be a primary winding of the charge capacitor-discharge gap-pulse transformer;
Charging means for charging the charge capacitor up to a breakover voltage of a discharge gap,
The charging means includes a boost capacitor and a boost diode, and a boost circuit connected in parallel with the discharge lamp so as to be a second main power line-boost diode-boost capacitor-first main power line;
A connection point between the boost capacitor and the boost diode, and a charging diode and a charging resistor installed between the discharge gap and the connection point of the charging capacitor;
Charge is accumulated in the boost capacitor via the boost diode when the AC power is in one polarity, and the charge capacitor is charged via the charge diode and a charging resistor in the other polarity. Electric light lighting device.   2. The apparatus according to claim 1, wherein a choke coil is connected in series with the discharge lamp, a resonance capacitor is connected in parallel, and the resonance power of the choke coil and the resonance capacitor oscillated by supplying AC power is supplied to the first and the second. A discharge lamp lighting device characterized by being supplied to a two main power line. 3. The apparatus according to claim 1, wherein the boosting diode of the charging means has an anode connected to the second type power line, a cathode connected to the boosting capacitor via a resistor, and the other end of the boosting capacitor connected to the first main power line. A discharge lamp lighting device characterized by being connected.

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