Patent Grant
7511432
The present invention relates to a discharge lamp lighting device, which lights a high pressure discharge lamp for use as a light source of a liquid crystal projector and the like, an illumination device and a projector.
There has recently been proposed a use of a high pressure discharge lamp as a light source of a liquid crystal projector, an automobile headlight or the like. As shown in
The chopper circuit 1 has a serial circuit of a switching element Q1 made of a metal-oxide semiconductor field-effect transistor (MOSFET) and an inductor L1, which have been inserted between the direct current power source E and the smoothing capacitor C1, and a diode D1 is connected in parallel with the serial circuit of the inductor L1 and the smoothing capacitor C1. The polarity of the diode D1 is determined such that energy which is stored in the inductor L1 when the switching element Q1 is ON is then discharged as a regeneration current through the smoothing capacitor C1 when the switching element Q1 is OFF. Further, in the illustrated example, a resistor R1 for detecting a current is inserted between the negative electrode of the direct current power source E and the anode of the diode D1. The terminal voltage of the smoothing capacitor C1 is parted by a voltage detecting circuit 3 consisting of a serial circuit of two resistors R2 and R3, and a voltage across the resistor R3 is outputted, as a voltage proportional to the terminal voltage of the smoothing capacitor C1, from the voltage detecting circuit 3.
A polarity inversion circuit 2 is a circuit where four switching elements Q2 to Q5 each made of a MOSET are bridge-connected, and a serial circuit of the switching elements Q2 and Q3 and a serial circuit of the switching elements Q4 and Q5 are each connected as an arm of the bridge circuit between each terminal of the smoothing capacitor C1. A load circuit is connected between a connection point of the switching elements Q2 and Q3 and a connection point of the switching elements Q4 and Q5. That is, a state where the switching elements Q2 and Q5 are on while the switching elements Q3 and Q4 are off and a state where the switching elements Q2 and Q5 are off while the switching elements Q3 and Q4 are on are controlled so as to be alternately repeated, whereby an alternating voltage is applied to the load circuit. Since the load circuit includes the serial circuit of the capacitor C2 and the inductor L2, and a voltage across the capacitor C2 is applied to the high pressure discharge lamp La, the lamp current of the high pressure discharge lamp La can be changed by changing a frequency (hereinafter referred to as “inversion frequency”) for on/off of the switching elements Q2 to Q5.
The on/off of the switching elements Q1 to Q5 included in the chopper circuit 1 and the polarity inversion circuit 2 are controlled by a control circuit 4. The control circuit 4 starts controlling the switching elements Q1 to Q5 in the chopper circuit 1 and the polarity inversion circuit 2 when a lightning signal is inputted from an exterior portion, and the control circuit 4 changes an output power of the chopper circuit 1 when an electric power switching signal S2 is inputted from an external portion. Further, the control circuit 4 monitors, with a voltage across the resistor R1, a current corresponding to the lamp current of the high pressure discharge lamp La, and also monitors an output voltage of the voltage detecting circuit 3, to perform pulse-width-modulation (PWM) control of the switching element Q1 of the chopper circuit 1 so as to maintain electric power instructed by the electric power switching signal S2. Moreover, the control circuit 4 outputs a control signal for turning the switching elements Q2 to Q5 on and off, and the control signal is provided to the switching elements Q2 to Q5 through drivers 2a and 2b. An on/off duty ratio of the switching elements Q2 to Q5 is here set to 50% so as to equally wear out two electrodes disposed in the high pressure discharge lamp La.
Incidentally, the high pressure discharge lamp La for use as a liquid crystal projector or an automobile headlight has electrodes dose to one another and can thus be used as a point source, and it is known that, in this kind of high pressure discharge lamp La, a phenomenon occurs where a luminescent spot on the electrode, i.e. a radiant point of an electron current when the electrode is on the cathode side, is not stabilized in a fixed position and moves disorderly. This phenomenon is called an arc jump, and when the arc jump occurs in a light source for a liquid crystal projector, a luminescent spot is displaced with respect to an optical system to be used along with the light source, causing a problem of variations in light amount on a screen. That is, a change in electric power to be charged during lightening of the high pressure discharge lamp La leads to variations in temperature of or distance between the electrodes, and further when a fan for air cooling is built in a housing like a liquid crystal projector, a change in condition for air cooling leads to variations in temperature of or distance between the electrodes. As thus described, when the state of the electrodes varies, a voltage across the electrodes varies, resulting in occurrence of an arc jump. Especially when the illuminating time of the high pressure discharge lamp La becomes longer, the voltage across the electrodes increases, and also when supply power to the high pressure discharge lamp La is switched in the lower electric power direction, the lamp current decreases to cause lowering of the electrode temperature, thereby making the arc jump tend to occur.
In a state where the high pressure discharge lamp La is stably on, the lamp current varies as the voltage across the smoothing capacitor C1 is changed by PWM controlling the switching element Q1 of the chopper circuit 1. That is, the lamp current varies by changing either the on/off duty ratio of the switching element Q1 of the chopper circuit 1 or the inversion frequency of the switching elements Q2 to Q5 of the polarity inversion circuit 2. However, a knowledge has been obtained that there exists a relation for stabilizing the state of the electrodes of the high pressure discharge lamp La, between the voltage across the smoothing capacitor C1 (which corresponds to the lamp voltage, as described later) and the frequency of the alternating voltage to be applied to the high pressure discharge lamp La. In other words, it has been found that there exists an optimum value of the inversion frequency according to the lamp voltage (the voltage across the smoothing capacitor C1) to the polarity inversion circuit 2, as a condition for reducing variations in temperature of or distance between the electrodes to keep the electrodes in a stable state. Therefore, if the inversion frequency and the lamp voltage of the polarity inversion circuit 2 in combination are optimum values, the occurrence of the arc jump is suppressed to reduce the wearing out of the electrodes, thereby extending the life of the high pressure discharge lamp La.
In the following, the relation between the lamp voltage and the inversion frequency in the polarity inversion circuit 1 is considered. Firstly considered is the case where the inversion frequency is controlled so as to be kept constant irrespective of the lamp voltage. The optimum value of the inversion frequency is here set to f1 in the range of lamp voltages from V1 to V2. When the inversion frequency is controlled so as to be kept at f1 irrespective of the lamp voltage as shown by A in
Next, considered is the case where the electric power switching signal S2 instructs switching of the electric power and the inversion frequency of the polarity inversion circuit 2 is controlled so as to be kept constant irrespective of the instructed electric power. As shown by A in
As another example for the control, as shown in
In order to solve this kind of problem, a constitution has been proposed where information corresponding to the distance between the electrodes is monitored by the lamp voltage, the inversion frequency is made switchable in two stages, a width of increase/decrease of the lamp voltage from an initial value is detected, and the inversion frequency is increased when the lamp voltage is on the decrease and the increase/decrease width is larger than a prescribed threshold, while the inversion frequency is decreased when the lamp voltage stops increasing/decreasing (see e.g. Patent Document 1: Japanese Patent No. 3327895, p 10-11, FIG. 7)
In a technique described in Patent Document 1, the lamp voltage is monitored for obtaining information corresponding to the distance between the electrodes, and an inversion frequency is controlled so as to keep the distance between the electrodes almost constant for inhibiting an arc jump. However, the technique described in Patent Document 1 has difficulty in certainly detecting variations in state of the electrodes due to variations in temperature of the electrodes or condition for air cooling, thus having a problem of being unable to inhibit the occurrence of the arc jump by this kind of cause.
The present invention was made in view of the above described matters, and has an object to set an inversion frequency corresponding to an electric power applied to a high pressure discharge lamp in each range of lamp voltages, to provide a discharge lamp lighting device capable of inhibiting occurrence of an arc jump caused by variations in temperature of the electrodes or condition for air cooling, and further provide an illumination device and a projector.
The invention of claim 1 comprises: a direct current power source; a chopper circuit capable of controlling output power by performing DC-DC conversion with the direct current power source as a power source; a smoothing capacitor connected between the output terminals of the chopper circuit; a polarity inversion circuit for performing DC-AC conversion with a voltage across the smoothing capacitor as a power source; a high pressure discharge lamp to which an alternating voltage is applied by the polarity inversion circuit; a control circuit for controlling an output of the polarity inversion circuit as well as output power of the chopper circuit; and a voltage detecting circuit for detecting a voltage corresponding to a lamp voltage of a high pressure discharge lamp, characterized in that a switch voltage for defining a range of voltages detected by the voltage detecting circuit is set in the control circuit, and the control circuit has a function of controlling the polarity inversion circuit such that an inversion frequency, at which the polarity of the lamp current of the high pressure discharge lamp is inverted according to the magnitude relation between the detected voltage and the switch voltage, is changed in plural stages.
The invention of claim 2 is characterized in that, in the invention of claim 1, the control circuit is capable of selecting an output of the chopper circuit from several stages, and has a function of changing the inversion frequency corresponding to selectable electric power.
The present invention of claim 3 is characterized in that, in the invention of claim 2, the switch voltage is regularly set regardless of the selectable electric power.
The invention of claim 4 is characterized in that, in the invention of claim 2, at least one of the switch voltages is set to a different value with respect to different electric power.
The invention of the claim 5 is characterized in that, in the invention of any one of claims 2 to 4, an equal inversion frequency is applied immediately after lightening of the high pressure discharge lamp until a voltage detected by the voltage detecting circuit reaches a prescribed voltage, irrespective of the selectable electric power.
The invention of claim 6 is characterized in that, in the invention of anyone of claims 2 to 4, an equal inversion frequency is applied immediately after lightening of the high pressure discharge lamp until reaching a prescribed switch time, irrespective of the selectable electric power.
The invention of claim 7 is characterized in that, in the invention of any one of claims 1 to 4, hysteresis is added to the switch voltage.
The invention of claim 8 is characterized in that, in the invention of any one of claims 1 to 4, the control circuit determines whether or not to change the inversion frequency once every prescribed number of polarity inversions of the lamp current of the high pressure discharge lamp.
The invention of claim 9 is characterized in that, in the invention of any one of claims 1 to 4, the control circuit determines whether or not to change the inversion frequency upon at least every lapse of a prescribed fixed time.
The invention of claim 10 is characterized in that, in the invention of any one of claims 1 to 4, the control circuit determines the magnitude relation between the voltage detected by the voltage detecting circuit and the switch voltage at fixed time intervals so as to determine, once every prescribed times of determinations, whether or not to change the inversion frequency according to whether the number of determinations satisfying a prescribed magnitude relation is not less than or less than a prescribed number.
The invention of claim 11 is characterized in that, in the invention of any one of claims 1 to 4, the control circuit takes a voltage detected by the voltage detecting circuit every time the polarity of the lamp current of the high pressure discharge lamp inverts.
The invention of claim 12 is characterized in that, in the invention of claim 11, the control circuit takes a voltage detected by the voltage detecting circuit after the lapse of a prescribed time from the polarity inversion of the lamp current of the high pressure discharge lamp.
The invention of claim 13 is characterized in that, in the invention of claim 1, in the control circuit, the inversion frequency is changed at a timing when the polarity of the lamp current of the high pressure discharge lamp has inverted even times.
The invention of claim 14 is an illumination device, comprising the discharge lamp lighting device according to claim 1.
The invention of claim 15 is a projector, comprising the discharge lamp lighting device according to claim 1.
The invention of claim 16 is a projector, comprising: a discharge lamp lighting device; a fan for air-cooling a high pressure discharge lamp; and a projector control device which receives a lamp voltage detected by the discharge lamp lighting device and is capable of instructing, to the discharge lamp lighting device, an inversion frequency at which the polarity of the lamp current of the high pressure discharge lamp is inverted, characterized in that, the projector control device sets a control condition for air-cooling by the fan according to the lamp voltage received from the high pressure discharge lamp and instructs, to the discharge lamp lighting device, an inversion frequency corresponding to the control condition.
The invention of claim 17, in the invention of claim 1, comprises an arc jump detecting means for detecting an arc jump which occurs in the high pressure discharge lamp, characterized in that, in the control circuit, a duty ratio of a lamp current waveform of the high pressure discharge lamp is set to a different value from 50% when the arc jump is detected by the arc jump detecting means.
The invention of claim 18 is characterized in that, in the invention of claim 17, the number of polarity inversions of the lamp current is defined to such a degree of number as to eliminate the arc jump during a period when the duty ratio of the lamp current waveform has been set to a different value from 50%.
The invention of claim 19 is characterized in that, in the invention of claim 17, a period when the duty ratio of the lamp current waveform has been set to a different value from 50% is defined as a period when a value detected by the arc jump detecting means, with which the arc jump was detected, is changed by a variation thereof for returning to the original value.
The invention of claim 20 is characterized in that, in the invention of claim 18 or 19, the duty ratio of the lamp current waveform is changed with time during a period when the duty ratio has been set to a different value from 50%.
A discharge lamp lighting device to be described in the following embodiment basically has the constitution shown in
A microcomputer “M37450”, manufactured by Mitsubishi Electric Corporation, can for example be used as the microcomputer 10, and a driver “IR2111”, manufactured by International Rectifier Corporation, can for example be used as the drivers 2a and 2b. The microcomputer 10 has a function of operating and stopping the PWM control circuit 11 and the full bridge control circuit 12 with the lightning signal S1 provided from the external portion, and houses an A/D conversion circuit for converting a voltage (voltage proportional to the terminal voltage of the smoothing capacitor C1) detected by the voltage detection circuit 4 into a digital value. Further, upon receiving the electric power switching signal S2, the microcomputer 10 can switch a supply power to the high pressure discharge lamp La in two or more stages, and the electric power instruction value S5 is then determined by electric power selected by the electric power switching signal S2 and a voltage obtained from the voltage detecting circuit 3. That is, selectable electric power is previously stored in the microcomputer 10, and each electric power is alternatively selected every time the electric power switching signal S2 is inputted. The microcomputer 10 is also provided with a function of dividing the selected electric power by the detected voltage for determining a current value, and then providing this current value as the electric power instruction value S5 to the PWM control circuit 11. As apparent from this operation, when electric power to be supplied to the high pressure discharge lamp La is selected in the microcomputer 10, the relation between the terminal voltage of the smoothing capacitor C1 and the current detected by the resistor R1 is controlled such that the electric power is set to the selected electric power value, and the terminal voltage of the smoothing capacitor C1 corresponds to the lamp voltage while the current detected by the resistor R1 corresponds to the lamp current.
On the other hand, in the present embodiment, the inversion frequency of the control signal to be provided to the full bridge control circuit 12 is defined with the range of voltages detected in the voltage detecting circuit 3 as a parameter. That is, using a ROM [EEPROM] built in the microcomputer 10, the lamp voltage (i.e. the voltage detected in the voltage detecting circuit 3) is sectioned into plural ranges, in each of which a V/F conversion table corresponding to an inversion frequency is set, and the inversion frequency is determined by checking the voltage detected in the voltage detecting circuit 3 with reference to the V/F conversion table. At least one switch voltage, at which the inversion frequency is switched, is set, thus making the inversion frequency switchable in two or more stages. In the V/F conversion table, as shown in
It is to be noted that the relation of the polarity inversion frequencies is not restricted to the example of
An external control signal S3 for determining the on/off of the switching elements Q2 to Q5 of the polarity inversion circuit 2 can also be inputted in the microcomputer 10, and when the external control signal S3 is inputted, a rectangular wave signal inputted as the external control signal S3 is applied to the full bridge control circuit 12 irrespective of the inversion frequency having been determined in the V/F conversion table. That is, when the external control signal S3 is inputted, the on/off frequency and duty ratio) of the switching elements Q2 to Q5 of the polarity inversion circuit 2 is determined by the external control signal S3.
Moreover, upon receiving the lightening signal S1, the microcomputer 10 is activated, and during lightning of the high pressure discharge lamp La, a rectangular wave signal for determining a duty ratio according to the voltage of the smoothing capacitor C1 (which corresponds to the lamp voltage) is outputted as a voltage information signal S4 from the microcomputer 10. For example, when the terminal voltage of the smoothing capacitor C1 varies from 0 V to 255 V, the voltage information signal S4 is a rectangular wave signal corresponding 0 to 255 V to duty ratios of 0 to 100%.
Accordingly, the inversion frequency is set to a relatively low frequency f1 in the range of lamp voltages, detected as terminal voltages of the smoothing capacitor C1, lower than V1, and as in the conventional constitution, the lamp current decreases when the lamp voltage becomes higher than V1 with the inversion frequency kept fixed to f1, leading to lower temperatures of the electrodes of the high pressure discharge lamp La than in the case where the lamp voltage is below V1, which makes the arc jump tend to occur. As opposed to this, in the constitution of the present embodiment, the inversion frequency varies to f2, which is higher than f1, when the lamp voltage becomes higher than V1, allowing inhibition of a decrease in temperature of the electrodes of the high pressure discharge lamp La, and thereby it is possible to prevent the occurrence of the arc jump. Further, the occurrence of the arc jump can further be inhibited with greater certainty when two switch voltages are set rather than one switch voltage is set.
Embodiment 1 represents the constitution where the inversion frequency is determined using the lamp voltage alone as a parameter, whereas in the present embodiment, the electric power selected by the electric power switching signal S2 is also used as a parameter for determining the inversion frequency, along with the lamp voltage. That is, as the supply power to the high pressure discharge lamp La becomes smaller, the lamp current decreases to lower the temperatures of the electrodes of the high pressure discharge lamp La, and hence the inversion frequency is controlled so as to become higher as the supply power becomes smaller. In order to achieve this constitution, a V/F conversion table is set with respect to each electric power selected by the electric power switching signal S2, and when one switch voltage, V1, is for example used, as in
In the present embodiment, it is possible to correspond not only to the case where the temperatures of the electrodes of the high pressure discharge lamp La decrease due to the variations in lamp voltage, but to the case where the temperatures of the electrodes decrease according to the selected supply power, allowing significant suppression of the occurrence of the arc jump. Other constitutions and functions are the same as those of Embodiment 1.
In Embodiment 2, the switch voltage V1 (V2) is fixed irrespective of the electric power selected by the electric power switching signal S2, whereas in the present embodiment, the switch voltage is changed with respect to the selected electric power. That is, when the supply power is selected from the two stages and one switch voltage is set with respect to each stage of the electric power, as shown in
When the supply power is selected from the three stages of P1 to P3 (P1>P2>P3) and two switch voltages are set with respect to each stage of the electric power, the inversion frequencies may be respectively set to characters like (f1, f2, f3), (f1′, f2′, f3′) and (f1″, f2″, f3″) with respect to the electric power P1 to P3, as shown by A1 to A3 (corresponding to the electric power P1), B1 to B3 (corresponding to the electric power P2), and C1 to C3 (corresponding to the electric power P3) in
In the constitution of the present embodiment, since not only the inversion frequency is changed but the switch voltage is also changed according to the supply power, it is possible to make a setting with which the occurrence of the arc jump is further prevented. It is to be noted that, although every switch voltage is changed with respect to each stage of the electric power in the foregoing example as shown in
In the present embodiment, the inversion frequencies are equalized in the range of low lamp voltages irrespective of the selected electric power as in Embodiment 1 and, out of the inversion frequency and the switch voltage, at least the inversion frequency is changed with respect to each stage of the electric power in the range of relatively high lamp voltages as in Embodiment 2 or 3. That is, as shown in
As shown in
a) represents an example in which the electric power is made selectable from two stages and two switch voltages are set with respect to the small electric power, while in the case where the electric power is made selectable from three stages, two switch voltages are set with respect to the large electric power and three switch voltages are set with respect to each of the other electric power, the example shown in
In Embodiment 4, the inversion frequencies are equally set in the range of lamp voltages lower than the switch voltage V0 even with respect to different stages of the electric power selected by the electric power switching signal S2, whereas in the present embodiment, the inversion frequencies are equally set irrespective of the electric power selected by the electric power switching signal S2 until the time for lightning the high pressure discharge lamp La reaches a prescribed switch time, and the inversion frequencies are changed according to the selected electric power when the illuminating time passes the switch time. That is, the inversion frequencies are equalized irrespective of the electric power selected by the electric power switching signal S2 as in
Although the example is represented above in which the electric power is made selectable from two stages and only one switch voltage is set, the number of switch voltages can be further increased, and the electric power may be made selectable from three or more stages. Other constitutions and operations are the same as those of Embodiment 1.
Since each of the foregoing embodiments represents the constitution where the inversion frequencies are switched across the switch voltage, when the lamp voltage varies in the vicinity of the switch voltage, the inversion frequency may unstably vary to cause an unstable operation. In the present embodiment, therefore, hysteresis is added to the relation between the lamp voltage and the inversion frequency. Namely, as shown in
In Embodiment 6, the hysteresis is added to the relation between the lamp voltage and the inversion frequency to stabilize the operation at the time of switching the inversion frequency, whereas in the present embodiment, time intervals, at which whether or not to switch the inversion frequency is determined, are set to be relatively large so as to stabilize the operation at the time of switching the inversion frequency. Namely, the time intervals at which the lamp voltage is detected for determining the inversion frequency are defined by the number of polarity inversions of the lamp current, and for example, the lamp voltage is detected once every eight times of polarity inversions of the lamp current as shown in
In the illustrated example, the case is assumed where the inversion frequency is switchable in two stages, f1 and f2, with only one switch voltage set, and as shown in
As thus described, since the lamp voltage for use in determining whether or not to switch the inversion frequency is detected every time the number of polarity inversions of the lamp current reaches a prescribed number, the time intervals at which the lamp voltage is detected become relatively long, thereby enabling prevention of unstable switching of the inversion frequency Although the case of setting the inversion frequency in two stages is described as an example in the present embodiment, the same technique is applicable to the case where the inversion frequency is selectable from three or more stages. Moreover, although the lamp voltage is determined for determining whether or not to change the inversion frequency once every eight times of polarity inversions of the lamp current, the number of inversions is not particularly limited, and can be appropriately set so long as being such a degree that the time elapsed for the inversions is relatively short and the inversion frequency is not switched unstably. Other constitutions and operations are the same as those of Embodiment 1.
In Embodiment 7, the lamp voltage is detected for determining whether or not to change the inversion frequency once every prescribed number of polarity inversions of the lamp current, and thus the time intervals at which the lamp voltage is detected vary depending upon the selected inversion frequency. The present embodiment represents a constitution where the variations in time intervals are reduced more than the case of Embodiment 7 while the time intervals at which the lamp voltage is detected are made relatively long, in the same manner as in Embodiment 7.
Namely, in the present embodiment, at the time point when a prescribed fixed time T has elapsed after the detection of the lamp voltage and the lamp current polarity varies in a specific direction, the subsequent detection of the lamp voltage is performed. In the example shown in
As thus described, since the lamp voltage for use in determining whether or not to switch the inversion frequency is detected at the timing when the lamp current polarity inverts after the lapse of the fixed time T, the time intervals at which the lamp voltage is detected become relatively long, thereby enabling prevention of unstable switching of the inversion frequency. Further, although the case of setting the inversion frequency in two stages is described as an example in the present embodiment, the same technique is applicable to the case where the inversion frequency is selectable from three or more stages. Other constitutions and operations are the same as those of Embodiment 1.
In the present embodiment, the lamp voltage is detected at prescribed time intervals, as well as the magnitude relation between the lamp voltage and the switch voltage being determined, and at the time point when the lamp voltage has been detected the prescribed number of times, based upon the magnitude relation between the lamp voltage and the switch voltage in each of the determinations, a majority decision is made to adopt the magnitude relations the number of which is larger so as to determine the inversion frequency, and if the inversion frequency needs to be changed, the change is made at the subsequent timing of the polarity inversion of the lamp current.
Here described as an example is the case where one switch voltage, V1, is used while the inversion frequency is changed in two stages, f1 and f2(>f1), and the inversion frequency is determined once every five times of determinations of the magnitude relation between the lamp voltage and switch voltage. Namely, as shown in
As thus described, in the present embodiment, since the magnitude relation between the lamp voltage and the switch voltage is regularly determined so as to determine, by the majority decision at prescribed time intervals, whether or not to switch the inversion frequency, the time intervals at which the lamp voltage is detected become relatively long, thereby enabling prevention of unstable switching of the inversion frequency. Although, here, the number of times of determinations, based upon which the majority decision is made, is set to five, it is not particularly limited. However, it is preferable to set the number of times of determinations, based upon which the majority decision is made, to an odd number when the inversion frequency is selected from the two stages, and in this case, the inversion frequency can be prevented from becoming indeterminate. Further, whether or not to switch the inversion frequency may be determined not necessarily by the majority decision but by whether the number of determinations satisfying either condition for the magnitude relation out of the prescribed number of determinations is not less than or less than a prescribed number. Moreover, although the case of setting the inversion frequency in two stages is described as an example in the present embodiment, the same technique is applicable to the case where the inversion frequency is selectable from three or more stages. Other constitutions and operations are the same as those of Embodiment 1.
In Embodiment 9, the magnitude relation between the lamp voltage and the switch voltage is determined at fixed time intervals, whereas in the present embodiment, as shown in
In foregoing Embodiments 7 to 10, the comparison between the lamp voltage and the switch voltage is required. Here, as shown in
Moreover, in each of Embodiments 7 to 10, the number of polarity inversions at each inversion frequency is controlled so as to be an even number. This is for equalizing the wearing out of the electrodes of the high pressure discharge lamp La so as to extend the life of the high pressure discharge lamp La.
The discharge lamp lighting device of each of foregoing Embodiments 1 to 10 is usable for a variety of lightening devices using the high pressure discharge lamp La as a light source, and is used for a variety of projectors using the high pressure discharge lamp La as a light source, such as a liquid crystal projector.
As shown in
The lamp voltage is information which reflects the temperature of the high pressure discharge lamp La, and in the projector control circuit 22, a control condition for a fan 23 for cooling the high pressure discharge lamp La is determined based upon the voltage information signal S4, and the optimum inversion frequency is determined according to the control condition for the fan 23. In the projector control circuit 22, the external control signal S3 corresponding to the determined inversion frequency is provided to the discharge lamp lighting device 20, and upon receiving the external control signal S3, the discharge lamp lighting device 20 controls the polarity inversion circuit 2.
Namely, with the constitution of the present embodiment adopted, it is possible not only to adjust the inversion frequency but to control the fan 23 for cooling the high pressure discharge lamp La. Other constitutions and operations are the same as those of Embodiment 1.
In each of the foregoing embodiments, in order to prevent one electrode of the high pressure discharge lamp La from being worn out more than the other electrode, the polarity inversion circuit 2 is driven so as to set the duty ratio to 50%. As opposed to this, in the present embodiment, the arc jump is detected, and the duty ratio of the lamp current waveform is shifted from 50% when the arc jump is detected. For the detection of the arc jump, an arc jump determining means can be constituted, for example, such that the lamp current is monitored and the occurrence of the arc jump is determined when the average value of the lamp currents decreases. For example, as shown in
With this technique adopted, it is possible to control the temperature of the electrode in which the arc jump has occurred, so as to be raised at the time of the occurrence of the arc jump, thereby resulting in reduction in occurrence of the arc jump.
Moreover, when the arc jump is detected and the duty ratio is then changed to Dv, as shown in
With this technique, it is possible to control the temperature of the electrode of the high pressure discharge lamp La so as to be further raised even when the arc jump, having occurred due to variations in electrode temperature, is eliminated by the change in duty ratio, thereby permitting inhibition of the occurrence of another arc jump. The other constitutions and operations are the same as those of Embodiment 1.
In Embodiment 12, the duty ratio is controlled so as to be returned to the original value after the polarity of the lamp current has been inverted several times after the detection of the elimination of the arc jump, whereas in the present embodiment, as shown in
Although in each of Embodiments 12 and 13, the duty ratio is kept constant during a period when the duty ratio of the lamp current waveform has been changed due to the detection of the arc jump, the duty ratio may be changed with time during the period when the duty ratio has been changed to Dv, as shown in
As thus described, according to the constitution of the present invention, the relation between the lamp voltage and the inversion frequency can be kept appropriate according to the state of electrodes of the high pressure discharge lamp, consequently allowing inhibition of the occurrence of the arc jump in the high pressure discharge lamp.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-010411 | Jan 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2004/000285 | 1/16/2004 | WO | 00 | 7/15/2005 |
| Publishing Document | Publishing Date | Country | Kind |
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| WO2004/066687 | 8/5/2004 | WO | A |
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