HK1069707B - Discharge lamp lighting apparatus - Google Patents

Description

Discharge lamp lighting device

Technical Field

The present invention relates to a discharge lamp lighting device for converting a direct current into a rectangular wave alternating current to supply the rectangular wave alternating current to a discharge lamp. More particularly, the present invention relates to a discharge lamp lighting device for lighting a high-pressure discharge lamp such as a high-pressure mercury lamp or an extra-high pressure mercury lamp with a rectangular wave ac.

Background

It is known that a high-pressure discharge lamp can be efficiently lighted when the high-pressure discharge lamp is lighted by supplying a low-frequency rectangular wave ac of about 50 to 500Hz, for example.

The discharge lamp lighting device that lights with rectangular wave alternating current adopts the following mode: a general commercial alternating current is rectified into a direct current, and then power control is performed by a converter including a step-down chopper circuit or the like, and further, a current and a voltage of a low-frequency rectangular wave alternating current are converted by an inverter including a bridge circuit or the like in which two or four semiconductor switching elements are incorporated, and supplied to a discharge lamp.

Japanese patent laying-open No. 3-116693 discloses a discharge lamp lighting device that lights with such a rectangular wave alternating current. The discharge lamp lighting device disclosed in this patent document is connected to a dc power supply, and includes: the discharge lamp driving circuit includes a chopper circuit that operates at a high frequency, a bridge inverter circuit connected to the chopper circuit and including switching elements that operate at a low frequency, and a load circuit including a discharge lamp connected to an output side of the bridge inverter circuit via a pulse transformer. In order to reduce leakage magnetic flux, the pulse transformer can adopt a closed magnetic circuit. When the pulse transformer is provided as a closed magnetic circuit, there is a problem that magnetic energy generated in the iron core of the pulse transformer changes rapidly when a rectangular wave current flowing through a series circuit of the primary coil between the discharge lamp and the pulse transformer is inverted, and squealing occurs from a joint portion of the iron core.

Therefore, the discharge lamp lighting device disclosed in the conventional technical document controls the current supplied from the chopper circuit to be reduced in synchronization with the switching timing of ON (ON) and OFF (OFF) of the switching elements of the bridge inverter circuit, thereby reducing the howling generated in the pulse transformer.

However, in addition to the howling problem, there are cases where a discharge lamp lighting device that lights with a rectangular wave ac power: according to the impedance characteristics of the circuit of the discharge lamp lighting device and the impedance characteristics of the lamp itself, an overshoot (over shoot) occurs due to oscillation when the rectangular wave ac voltage and current are inverted. The occurrence of overshoot brings about various disadvantages to the discharge lamp.

The state of occurrence of overshoot is described below with reference to the drawings. Fig. 13 is a waveform diagram of each part of the discharge lamp lighting device that lights with a rectangular wave ac, showing the output voltage of the converter, the output current of the inverter, and the bridge signal of the inverter. Fig. 14 is a partially enlarged view of the waveform shown in fig. 13.

The output voltage/current of the converter is a controlled dc voltage/current, and is converted into an ac rectangular wave by a bridge inverter connected to a subsequent stage.

As shown in fig. 13, the output voltage of the converter and the output current of the inverter are controlled to be the voltage/current required by each lamp load before the timing of polarity inversion at which the on/off of the bridge signals 1 and 2 are switched, but oscillation occurs with the polarity inversion.

That is, the inverter is constituted by a bridge circuit using a normal semiconductor switching element. In order to prevent short circuit caused by simultaneous conduction, a dead time (dead time) is set at the time of polarity inversion to control on/off of the semiconductor switching elements of the bridge circuit.

As shown in fig. 14, since all the semiconductor switching elements are turned off during the idle time td, the energy transmitted from the inverter cannot reach the lamp as a load, and the output voltage of the inverter is increased. Further, since the commutation of the current occurs due to an inductance component existing in the circuit of the discharge lamp lighting device, and the current is regenerated from the discharge lamp located on the load side of the discharge lamp lighting device and flows to the inverter, the output voltage of the inverter is also increased by the component.

When the period of the dead time td ends, the semiconductor switching elements of the bridge circuit are turned on, and the output voltage of the inverter is applied to the discharge lamp side. At this time, the output voltage of the inverter rises, and the voltage/current supplied to the discharge lamp becomes a value larger than that before the polarity inversion, thereby causing oscillation and overshoot.

When the overshoot occurs, the current/voltage supplied to the discharge lamp becomes an overcurrent/overvoltage with respect to the discharge lamp. When such an overcurrent/overvoltage condition occurs every time the polarity of the rectangular wave ac voltage/current is inverted, the electrodes of the discharge lamp themselves are damaged every time, and when the damage to the electrodes is accumulated, the life of the discharge lamp itself is reduced.

In addition, although the overshoot can be reduced by increasing the capacity of the output capacitor of the converter, the oscillation period is extended while suppressing the rise of the output voltage of the converter, and therefore the oscillation adjustment time is also increased. If there is a residual oscillation in the voltage/current supplied to the discharge lamp, the oscillation appears on the light output of the discharge lamp or flickers, or the discharge lamp is extinguished, and there is a problem that the rush current (short-circuit current) to the discharge lamp when the polarity of the rectangular wave ac voltage/current is inverted becomes large.

When the rush current (short-circuit current) to the discharge lamp when the polarity of the rectangular wave ac voltage/current is inverted becomes large, the electrode of the discharge lamp is worn, and the life of the discharge lamp is reduced.

Therefore, in order to properly place the discharge lamp, it is necessary to adjust the voltage/current waveform supplied to the discharge lamp when the polarity of the rectangular wave ac voltage/current is inverted, thereby suppressing the occurrence of overshoot. The overshoot becomes larger when the current supplied to the discharge lamp is large, becomes smaller when the current supplied to the discharge lamp is small, and also changes with the cumulative lighting time of each discharge lamp, and therefore a discharge lamp lighting device capable of controlling the reduction amount of the overshoot is required.

Disclosure of Invention

One subject of the present invention is: provided is a discharge lamp lighting device which suppresses overshoot of voltage/current when the polarity of a rectangular wave AC voltage/current is reversed, and which achieves a long life of a discharge lamp.

Another object of the present invention is to: provided is a discharge lamp lighting device which suppresses oscillation of voltage/current at the time of polarity inversion of rectangular wave AC voltage/current and does not cause flickering or self-extinguishing of a discharge lamp.

Another object of the present invention is to: provided is a discharge lamp lighting device which controls the amount of suppression of voltage/current overshoot when the polarity of a rectangular wave AC voltage/current is reversed, and can stably light up regardless of the cumulative lighting time of a discharge lamp.

In order to solve the above problem, a discharge lamp lighting device according to the present invention includes a converter, an inverter, and a control unit.

The converter switches input power, converts alternating output into direct current, and outputs the direct current.

The inverter converts the direct current supplied from the converter into a rectangular wave alternating current to output the rectangular wave alternating current.

The control unit includes: the power control apparatus includes a power calculation unit, a control target value setting unit, a correction signal generation unit, an inverter control signal generation unit, and a pulse width control unit.

The power calculation unit calculates power using the voltage detection signal and the current detection signal detected on the output side of the converter, and generates a power detection signal.

The control target value setting unit outputs an output power command value for controlling the direct current as a target value.

The correction signal generation unit generates a correction signal for correcting the output power command value in accordance with the power detection signal, and outputs the correction signal in synchronization with the polarity inversion of the rectangular wave ac power.

The converter control signal generating unit is supplied with the output power command value, the correction signal, and the power detection signal, and outputs a signal corresponding to an error of the power detection signal with respect to the output power command value corrected by the correction signal.

The pulse width control unit controls the pulse width of the inverter based on the signal supplied from the inverter control signal generation unit.

In the discharge lamp lighting device of the present invention, the converter switches input power, converts an alternating output into a direct current and outputs the direct current, and the inverter converts the direct current supplied from the converter into an alternating rectangular wave power and outputs the alternating rectangular wave power, whereby the discharge lamp is driven by a rectangular wave alternating current.

The power calculation unit calculates power from the voltage detection signal and the current detection signal detected on the output side of the converter, and generates a power detection signal. The control target value setting unit outputs an output power command value for controlling the direct current as a target value. The correction signal generating unit generates a correction signal for correcting the output power command value in accordance with the power detection signal, and outputs the correction signal in synchronization with the polarity inversion of the rectangular wave ac power. The converter control signal generating unit is supplied with the output power command value, the correction signal, and the power detection signal, and outputs a signal corresponding to an error of the power detection signal with respect to the output power command value. The pulse width control unit controls the pulse width of the inverter based on the signal supplied from the inverter control signal generation unit.

Therefore, the inverter output is controlled to the power required by the discharge lamp and at the same time to the output power corrected by the correction signal when the polarity of the rectangular wave ac is reversed. Therefore, in the discharge lamp lighting device of the present invention, the overshoot and oscillation of the voltage/current at the time of the polarity inversion of the rectangular wave ac voltage/current are suppressed, and the suppression amount is controlled, thereby reducing the damage to the electrode of the discharge lamp and extending the life of the discharge lamp.

Further, it is possible to provide a discharge lamp lighting device which stably lights a discharge lamp regardless of the accumulated lighting time of the discharge lamp without flickering or self-extinguishing of the discharge lamp.

The discharge lamp lighting device of the present invention may be any one of voltage control, current control, and power control, but if the control target value is the current value of the direct current, it becomes current control, which is suitable for lighting a discharge lamp.

The control unit may be configured by at least a microcomputer to include the power calculation unit and the correction signal generation unit. If these two parts are constituted by a microcomputer, various control methods can be easily adopted: such as time control for controlling the generation period of the correction signal, level control for controlling the magnitude of the correction signal, waveform control for storing the correction signal waveform in a memory section of a microcomputer and selecting the stored waveform; also, zero correction control without suppressing overshoot is easily obtained.

Other objects, structures and advantages of the present invention will be described in more detail below with reference to the accompanying drawings. The examples given in the figures are only examples.

Drawings

Fig. 1 is a block diagram showing an embodiment of a discharge lamp lighting device of the present invention.

Fig. 2 is a flowchart showing a first control method of the embodiment shown in fig. 1.

Fig. 3 is a timing chart showing the first control method of the embodiment shown in fig. 1 in detail.

Fig. 4 is a flowchart showing a second control method of the embodiment shown in fig. 1.

Fig. 5 is a timing chart showing the second control method of the embodiment shown in fig. 1 in detail.

Fig. 6 is a flowchart showing a third control method of the embodiment shown in fig. 1.

Fig. 7 is a diagram of a correction signal and a load current waveform when the discharge lamp lighting device shown in fig. 1 is controlled by the second control method.

Fig. 8 is a graph of a correction signal and a load current waveform when control is performed with a correction signal that does not depend on a fixed correction amount according to the present invention, for comparison with fig. 7.

Fig. 9 is a diagram of waveforms of a correction signal and a load current when the discharge lamp lighting device shown in fig. 1 is controlled by the second control method.

Fig. 10 is a graph of a correction signal and a load current waveform when control is performed with a correction signal that does not depend on a fixed correction amount according to the present invention, for comparison with fig. 9.

Fig. 11 is a diagram of waveforms of a correction signal and a load current when the discharge lamp lighting device shown in fig. 1 is controlled by the second control method.

Fig. 12 is a graph of a correction signal and a load current waveform when control is performed with a correction signal that does not depend on a fixed correction amount according to the present invention, for comparison with fig. 11.

Fig. 13 is a waveform diagram of each part of a conventional discharge lamp lighting device that is lit with a rectangular wave ac.

Fig. 14 is a partially enlarged view of the waveform shown in fig. 13.

[ description of symbols ]

11 converter

12 inverter

2 control part

20 power calculation unit

21 signal generating part

22 control target value setting unit

23 pulse width control part

25 correction signal generating part

Detailed Description

Fig. 1 is a block diagram showing an embodiment of a discharge lamp lighting device of the present invention. The discharge lamp lighting device includes: converter 11, inverter 12, high voltage generator 13, and control unit 2.

The inverter 11 switches the input dc power Pin supplied to the input terminals T11 and T12, and converts the alternating output into a dc power output. The switching frequency of the inverter 11 can be set to a value of, for example, 10 to 500 kHz.

The inverter 12 converts the dc power output from the converter 11 into ac power and outputs the ac power. The inverter 12 is a rectangular wave generating circuit, which is configured by a bridge circuit or the like composed of two or four semiconductor switching elements, and outputs rectangular wave ac power. The inverter 12 is driven by the driving pulse signals S10 and S01 supplied from the inverter driving circuit 24. The drive pulse signal S10 is obtained by inverting the drive pulse signal S01, and therefore becomes low (logic value 0) when the drive pulse signal S01 is high (logic value 1), and becomes high (logic value 1) when the drive pulse signal S01 is low (logic value 0). The driving pulse signals S01 and S10 are set to a period in which all the semiconductor switching elements are turned off during the idle time and are at the high level in common during the switching. Instead of the high-level period, the driving pulse signals S01 and S10 may be set to the low-level period in common at the time of switching.

The switching frequency of the inverter 12 determined from the drive pulse signals S10, S01 is selected to be a lower value than the converter 11. For example, the switching frequency of the converter 11 is selected to be 10 to 500kHz, and the switching frequency of the inverter 12 is selected to be 50 to 500 Hz.

In the embodiment, a high voltage generator 13 is further included in the subsequent stage of the inverter 12. The high voltage generator 13 generates a high voltage necessary for starting the discharge lamp 3 and supplies the generated high voltage to the output terminals T21 and T22.

The discharge lamp 3 has both ends connected to output terminals T21 and T22, and is supplied with a start pulse of a high voltage from the high voltage generator 13 at the time of start and supplied with a rectangular wave ac power of the inverter 12 at the time of steady state via the output terminals T21 and T22. The control unit 2 includes: a power calculation unit 20, a converter control signal generation unit 21, a control target value setting unit 22, a pulse width control unit 23, an inverter drive circuit 24, and a correction signal generation unit 25. The power calculation unit 20 calculates power from the voltage detection signal s (v) and the current detection signal s (i) to generate a power detection signal s (iv).

The voltage detection signal s (v) is obtained by detecting the voltage on the output side of the inverter 11 by the voltage detection circuit 14. The output voltage of the inverter 11 is a dc voltage, but includes voltage information of the ac pulse voltage Vo supplied to the discharge lamp 3. Therefore, the voltage detection signal s (v) can be used as the output voltage information.

The current detection signal s (i) is obtained by a current detection circuit 15 that detects a current flowing through the power transmission line. The current flowing through the power line is substantially equivalent to the alternating pulse current Io flowing through the discharge lamp 3. Therefore, the current detection signal s (i) can be used as information of the ac pulse current Io.

The control target value setting unit 22 outputs an output power command value S1, and controls the dc power output from the inverter 11 so as to be suitable for the target value to be supplied to the discharge lamp.

The correction signal generator 25 is supplied with the power detection signal S (iv) from the power calculation unit 20, and also supplied with the polarity inversion signal S00 synchronized with the drive pulse signals S10 and S01 from the inverter drive circuit 24. Then, a correction signal S2 for lowering the output power command value S1 is generated in accordance with the power detection signal S (iv), and is output in synchronization with the polarity inversion of the rectangular wave ac power output from the inverter 12.

The converter control signal generator 21 is supplied with the output power command value S1, the correction signal S2 for correcting the output power command value S1, and the power detection signal S (iv) from the control target value setting unit 22, the correction signal generator 25, and the power calculation unit 20, respectively. Then, a signal Δ Po corresponding to an error between the output power command value S1 corrected by the correction signal S2 and the power detection signal S (iv) is output.

The pulse width control unit 23 performs pulse width control of the inverter 11 based on the signal Δ Po supplied from the inverter control signal generation unit 21. More specifically, the pulse width control unit 23 is provided with a triangular wave oscillation circuit 26, generates a signal having a pulse width based on the signal Δ Po from a triangular wave signal supplied from the triangular wave oscillation circuit 26 and the signal Δ Po supplied from the inverter control signal generation unit 21, supplies the signal to the inverter 11, and controls the switching operation.

When the inverter 11 is switched under the above-described pulse width control, the voltage and current on the output side of the inverter 11 are detected by the voltage detection unit 14 and the current detection unit 15. Then, the voltage detection signal s (v) and the current detection signal s (i) are supplied to the power calculation unit 20, and the power detection signal s (iv) is supplied from the power calculation unit 20 to the inverter control signal generation unit 21. The power detection signal S (iv) is compared with the output power command value S1 in the signal generation circuit 21, and a signal Δ Po corresponding to the error is generated. Then, the pulse width control unit 23 applies pulse width control according to the signal Δ Po to the inverter 11.

Here, the correction signal generating unit 25 generates the correction signal S2 for lowering the output power command value S1 in accordance with the power detection signal S (iv), and outputs the correction signal in synchronization with the polarity inversion of the rectangular wave ac power. Therefore, when the polarity of the rectangular wave ac power is reversed, the output power command value S1 is lowered, and the pulse width control is applied in the direction in which the output power of the inverter 11 is lowered, in comparison with the power detection signal S (iv). As a result, the overshoot and oscillation of the voltage/current at the time of the polarity inversion of the rectangular wave ac voltage/current are suppressed. Since the correction signal generation unit 25 generates the correction signal S2 for lowering the output power command value S1 in accordance with the power detection signal S (iv), the amount of suppression of overshoot and oscillation can be appropriately controlled.

The power operation unit 20, the correction signal generation unit 25, and the drive signal generation unit in the inverter drive circuit 24 constituting the control unit 2 are each constituted by a microcomputer 3. Thus, the microcomputer 3 can simplify the structure of the control unit 2 and perform high-level control.

Hereinafter, various control methods of the present embodiment will be described with reference to flowcharts and timing charts on the assumption that the control unit 2 includes the microcomputer 3.

Fig. 2 is a flowchart showing a first control method of an embodiment of the discharge lamp lighting device according to the present invention, and fig. 3 is a timing chart thereof. In the figure, td represents the idle time of the switching elements constituting the inverter 12, and an arrow Δ S represents the variable amount of the correction signal.

As indicated by an arrow Δ S in the figure, the present control method is a method of performing control by changing the level of the correction signal. In the present control method, when the sequence is started, the correction level is determined based on the power detection signal s (iv) supplied from the power calculation unit 20, and a correction signal is set. Next, the drive signal of the inverter 12 is switched, and the inverter 12 enters the idle time td. The period of the idle time td is a predetermined period determined in advance. After the idle time td elapses, the drive signal of the inverter 12 is switched, and the polarity of the ac rectangular wave output from the inverter 12 is inverted. After that, the correction signal is reset, and a series of processing is ended.

During this period, the correction signal generation unit 25 supplies the correction signal S2 for lowering the output power command value to the inverter control signal generation unit 21. Therefore, the overshoot and oscillation of the voltage/current at the time of the polarity inversion of the rectangular wave ac voltage/current are suppressed. Further, since the correction signal level is controlled in accordance with the power detection signal s (iv), the amount of suppression of overshoot and oscillation can be appropriately controlled.

Fig. 4 is a flowchart showing a second control method of the discharge lamp lighting device according to the embodiment of the present invention shown in fig. 2, and fig. 5 is a timing chart thereof. In the figure, t1 represents a correction signal generation period before the idle time of the switching elements constituting the inverter 12; t2 denotes idle time; t3 represents the correction signal generation period after the idle time; the arrow Δ S represents the variable amount of the correction signal.

As indicated by an arrow Δ S in the figure, the present control method is a method of performing control by changing the generation period of the correction signal. In the present control method, when the sequence is started, the period t1, the idle time t2, and the period t3, which are the generation periods of the correction signal S2, are determined based on the power detection signal S (iv) supplied from the power calculation unit 20, and the correction signal is set.

Next, the correction signal generation period t1 before the idle time elapses, the drive signal of the inverter 12 is switched, and the inverter 12 enters the idle time t 2. The period of the idle time t2 may be a predetermined period determined in advance, but in the present control method, it is determined based on the power detection signal s (iv) supplied from the power calculation unit 20. After the idle time t2 elapses, the drive signal of the inverter 12 is switched, and the polarity of the ac rectangular wave output from the inverter 12 is inverted. After that, the correction signal S2 is reset after the elapse of the correction signal generation period t3 after the elapse of the idle time, and a series of processing is ended.

During this period, the correction signal generation section 25 supplies the correction signal S2 for lowering the output power command value S1 to the inverter control signal generation section 21. Therefore, the overshoot and oscillation of the voltage/current at the time of the polarity inversion of the rectangular wave ac voltage/current are suppressed. Since the generation period of the correction signal S2 is controlled in accordance with the power detection signal S (iv), the amount of suppression of overshoot and oscillation can be appropriately controlled.

The first control method for controlling the level of the correction signal S2 and the second control method for controlling the generation period of the correction signal S2 have been described above, but a combination of these control methods can achieve a higher degree of control.

Fig. 6 is a flowchart showing a third control method for the discharge lamp lighting device shown in fig. 1. The graph shows an output waveform a, an output waveform B, and an output waveform C, which are timing charts showing the relationship between an example of a correction signal waveform stored in a memory unit of a microcomputer and an inverter drive signal.

The control method is a method of selecting one correction signal waveform from a plurality of correction signal waveforms stored in a memory of the microcomputer 3 according to the power detection signal s (iv) and outputting the selected correction signal waveform. The correction signal waveform may be prepared in plural according to the characteristic of the discharge lamp, the characteristic change due to the cumulative lighting time of the discharge lamp, or the like, in addition to the plural according to the power range to be supplied to the discharge lamp.

In the present control method, when the sequence is started, a correction signal pattern to be output is determined based on the power detection signal s (iv) supplied from the power calculation unit 20, for example, any one of the correction signal patterns shown in the output pattern a and the output pattern B. The correction signal waveform is output at a timing determined simultaneously with the drive signal of the inverter 12 and ends the processing.

Here, the output waveforms illustrated in the drawings will be described. The correction signal shown in the output waveform a includes correction signal generation periods t1, t3 at time (τ d/2) and a correction signal generation period t2 at time τ d, which are waveforms selected when the supply power to the discharge lamp is large.

The correction signal shown in the output waveform B occurs at time τ d only during period t 2. The correction signal shown in the output waveform C is only after the period t2, and a correction signal generation period having a time (τ d/2) is the waveform selected when the supply power to the discharge lamp is small.

Although the correction signal waveform in which only the generation period of the correction signal is changed has been described above, it is possible to set an infinite number of correction signal waveforms by using a correction signal waveform in which the correction level is changed or a combination waveform thereof, and including a waveform without a correction signal.

Fig. 7 to 12 are comparative diagrams of the correction signal and the load current waveform of the discharge lamp lighting device shown in fig. 2, and fig. 7, 9 and 11 are diagrams of the correction signal and the load current waveform when the control is performed in the second control method of the present invention; fig. 8, 10, and 12 are graphs of a correction signal and a load current waveform when the control is performed by the correction signal of the fixed correction amount not according to the present invention.

Fig. 7 and 8 show examples of lighting the discharge lamp at the maximum value of the allowable load current of the discharge lamp. Since the control is performed in the second control method of the present invention in fig. 7, the generation time of the correction signal is extended, and the overshoot is suppressed to 114% as appropriate. On the other hand, since the control is performed with the correction signal not in accordance with the fixed correction amount of the present invention in fig. 8, the correction amount for the load current is small and the overshoot increase is 184%.

Fig. 9 and 10 show examples of lighting the discharge lamp at an intermediate value of the allowable load current of the discharge lamp. The occurrence times of the correction signals are substantially equal in fig. 9 and 10, and the overshoot is suppressed appropriately in both fig. 9 and 10, i.e., 114% and 115%.

Fig. 11 and 12 show examples of lighting the discharge lamp at the minimum value of the allowable load current of the discharge lamp. Since the control is performed in the second control method of the present invention in fig. 11, the generation time of the correction signal is shortened, and the overshoot is appropriately suppressed to 132%. On the other hand, since the control is performed with the correction signal not having the fixed correction amount according to the present invention in fig. 12, the correction amount with respect to the load current becomes large, waveform distortion occurs, and the overshoot increases to 195%.

It can be seen that, according to the control method control of the present invention, overshoot can be suppressed in a wide range of allowable load current of the discharge lamp, but overshoot can be suppressed only in a specific load current range when the control is performed with the correction signal of the fixed correction amount not in accordance with the present invention.

The present invention has been described in detail with reference to the preferred embodiments, but it is to be understood that the present invention is not limited thereto, and various modifications of the present invention can be conceived by those skilled in the art based on the basic technical idea thereof.

Effects of the invention

As described above, according to the present invention, the following effects can be obtained.

(A) A discharge lamp lighting device capable of suppressing voltage/current overshoot at the time of polarity inversion of a rectangular wave AC voltage/current and prolonging the life of a discharge lamp.

(B) A discharge lamp lighting device capable of suppressing voltage/current oscillation at the time of polarity inversion of a rectangular wave AC voltage/current without flickering or self-extinguishing of a discharge lamp.

(C) A discharge lamp lighting device capable of controlling the amount of suppression of voltage/current overshoot at the time of polarity inversion of a rectangular wave AC voltage/current and stably lighting regardless of the cumulative lighting time of a discharge lamp.

Claims (6)

1. A discharge lamp lighting device comprising a converter, an inverter, and a control unit, wherein:

the converter switches input power, converts alternating output into direct current and outputs the direct current;

the inverter converts the direct current supplied from the converter into a rectangular wave alternating current to output the rectangular wave alternating current;

the control part comprises a power calculation part, a control target value setting part, a correction signal generation part, an inverter control signal generation part and a pulse width control part;

the power calculation unit calculates power using a voltage detection signal and a current detection signal detected on an output side of the converter, and generates a power detection signal;

the control target value setting unit outputs an output power command value controlled with the direct current as a target value;

the correction signal generation unit generates a correction signal for lowering the output power command value in accordance with the power detection signal, and outputs the correction signal during a period from the start of polarity inversion of the rectangular wave ac power to the end of the polarity inversion;

the converter control signal generating unit is supplied with the output power command value, the correction signal, and the power detection signal, and outputs a signal corresponding to an error of the power detection signal with respect to the output power command value corrected by the correction signal;

the pulse width control unit controls the pulse width of the inverter based on the signal supplied from the inverter control signal generation unit.

2. The discharge lamp lighting device recited in claim 1, wherein:

the control target value setting unit sets the current value of the direct current to a target value and performs current control.

3. The discharge lamp lighting device recited in claim 1, wherein:

the control unit includes at least a power calculation unit and a correction signal generation unit, which are configured by a microcomputer.

4. The discharge lamp lighting device as set forth in claim 3, wherein:

the correction signal generation unit controls the level of the correction signal in accordance with the power detection signal.

5. The discharge lamp lighting device as set forth in claim 3, wherein:

the correction signal generation unit controls a generation period of the correction signal in accordance with the power detection signal.

6. The discharge lamp lighting device as set forth in claim 3, wherein:

the microcomputer includes a storage section storing a plurality of correction signal waveforms;

the correction signal generation unit selects and outputs the correction signal waveform according to the power detection signal.