JP2010015735A - Lighting device for discharge lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain improvement in flicker and improve possible short lifetime of a lamp caused by this improvement measure. <P>SOLUTION: The DC voltage input from a power supply 11 is stepped down by a converter 12 and supplied to an inverter 15. The inverter 15 converts the DC power input into an AC power, and by generating a high-voltage voltage by a lamp starting circuit, supplies it to a high pressure discharge lamp 17 to light it. The lamp voltage at the time of lighting is detected by a lamp voltage detection part 13 and the detection result is supplied to a control part 18. The control part 18, when it determines that it is a prescribed voltage or more, outputs an output pulse d with widened duty width by output from a PWM control part 19 and increases the DC voltage output from the converter 12 and increases the power to be supplied to the discharge lamp 17. By detecting the increase in the lamp voltage and increasing the power to be supplied to the discharge lamp 17 when it increases, flickering can be reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention particularly relates to a discharge lamp lighting device for lighting a high-pressure discharge lamp used for an automobile headlamp.

A conventional discharge lamp lighting device for lighting a high-pressure discharge lamp with an alternating current variably controls the power supplied to the high-pressure discharge lamp with an arbitrary voltage, and a plurality of steps after the current value of the alternating current is commutated into a rectangular wave. A waveform that increases to a predetermined current value with a wave, and then increases until before commutation with multiple staircase waves, so that the amplitude of the multiple staircase waves is changed by an arbitrary voltage so that the power of the high-pressure discharge lamp becomes constant In addition, by controlling the average current of the alternating current, the luminance can be changed smoothly and a flicker reduction effect is obtained. (For example, Patent Document 1)
JP 2005-327661 A

  In the technique disclosed in Patent Document 1, the lamp voltage increases as the distance between the electrodes becomes longer due to the exhaustion of the lamp electrodes at the end of the lamp life, so that the lamp current decreases and the discharge is difficult to maintain. Cause flicker. There has been a problem that it is impossible to secure a stable view necessary for driving due to the occurrence of flicker.

  An object of the present invention is to provide a discharge lamp lighting device capable of improving flicker.

  In order to solve the above-described problems, a discharge lamp lighting device of the present invention boosts or steps down an input DC voltage, converts the DC voltage into a desired DC voltage, and converts the DC voltage into AC power. An inverter to be inserted into the high-pressure discharge lamp, a high-pressure pulse generation unit that applies a high voltage to the discharge lamp at the start, and a control unit that controls the lighting state of the discharge lamp based on the DC voltage, The control unit is in a state where the discharge lamp is controlled to be in a normal lighting state, detects a lamp voltage from the converter, and determines that the lamp voltage during a predetermined period in the normal lighting state is higher than a voltage outside the predetermined period. In some cases, the discharge lamp is lit with higher power than normal power.

  According to the present invention, the flicker can be improved and the shortening of the lamp life caused by this improvement measure can be improved.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  1 and 2 are diagrams for explaining the first embodiment of the discharge lamp lighting device according to the present invention. FIG. 1 is a circuit configuration diagram, and FIG. 2 is an explanatory diagram for explaining the lighting operation of FIG. It is.

  In FIG. 1, reference numeral 11 denotes a DC power supply, which supplies a DC voltage of the power supply 11 to a converter 12 that boosts the voltage. The converter 12 is connected to the cathode of the diode D whose ground is connected to one end of the choke coil L from the positive electrode of the power source 11 via, for example, a switch element SW formed of a MOS FET transistor. The other end of the coil L is grounded via the smoothing capacitor C <b> 1 and grounded via the lamp voltage detector 13. A lamp current detector 14 is interposed between the ground side of the lamp voltage detector 13 and the ground side of the capacitor C1.

  The output of the converter 12 constitutes an inverter 15 that converts the DC voltage output from the converter 12 into AC power, for example, full-bridge switch elements SW1 and SW4 that combine switch elements SW1 to SW4 using MOS type FET transistors, respectively. Connecting. The switch element SW1 is grounded via the switch element SW3, and the switch element SW4 is grounded via the switch element SW2. Between the connection point of the switch elements SW1 and SW3 and the connection point of the switch elements SW3 and SW2, a capacitor C2 for vibration waveform formation and current limitation is inserted and connected. The switch elements SW1 and SW2 are turned on / off at the same time, and the switch elements SW3 and SW4 are turned on / off at the same time.

  Both ends of the capacitor C2 are connected to a lamp starting unit 16 that generates a high voltage pulse voltage when the lamp is lit, and the output of the lamp starting unit 16 is supplied to a discharge lamp 17 having a rated voltage of, for example, 30V.

  Reference numeral 18 denotes a control unit. The control unit 18 generates a control signal b for turning on / off the PWM control unit 19 and a duty control signal c for controlling the duty of the PWM control unit 19 based on the start signal a supplied to the start terminal St. Output.

  The PWM control unit 19 outputs an output pulse d that drives the converter 12 with a duty based on the duty control signal c. The control unit 18 is supplied with the voltage detection signal e of the lamp voltage detection unit 13 of the converter 12 and the current detection signal f of the lamp current detection unit 14 respectively.

  Further, the control unit 18 supplies a control signal to the full bridge driver 20 and alternately turns on and off the switch elements SW1, SW2, SW3, and SW4 of the inverter 15 from the full bridge driver 20 and generates an AC voltage from the output of the inverter 15. A drive pulse signal g for output is output. The drive pulse signal g is generated after a time when the output of the converter 12 driven based on the output pulse d becomes a desired value.

  Next, the lighting operation of the discharge lamp in the circuit configuration of FIG. 1 will be described with reference to the timing chart of FIG.

  First, the control unit 18 to which the start signal St shown in FIG. 2A is supplied to the start terminal St in order to turn on the discharge lamp 17 sends the control signal b shown in FIG. 2B to the PWM control unit 19. A duty control signal c shown in FIG. 2C is supplied for supplying and controlling the on-state and for controlling the duty of the signal output from the PWM control unit 19. The start duty control signal c is generated based on the table information stored in advance in the control unit 18 and the driving information of the discharge lamp 17.

  As shown in FIG. 2 (d), an output pulse d having a duty based on the control signal c is generated from the output of the PWM control unit 19, and this output pulse d is supplied to the switch element SW of the converter 12.

  In the converter 12, the switch element SW is turned on / off based on the output pulse d to switch the DC voltage of the power source 11, and the switching output is converted into a predetermined DC voltage and output. This DC voltage controls the switching elements SW <b> 1 to SW <b> 4 of the inverter 15 with the drive pulse signal g shown in FIG. For example, the switch elements SW1 and SW2 are turned on when the drive pulse signal g is at the Hi level, and turned off when the drive pulse signal g is at the Lo level. The switch elements SW3 and SW4 are turned on when the drive pulse signal g is at the Lo level. To turn off. The frequency of the drive pulse signal g is selected to be lower than that of the converter 12.

  The driving pulse signal g at the start of lighting and preheating is such that the switch elements SW1 to SW4 are driven at a relatively high frequency Hf of, for example, about 17 kHz after the start signal a is supplied, for example, as shown in FIG. An AC voltage h of about 400 to 450V is output. In some cases, only the switch elements SW1 and SW2 are at the Hi level and output a DC voltage. Thereafter, the drive pulse signal g during normal lighting is configured to drive the switch elements SW1 to SW4 at a relatively low frequency Lf of, for example, about 300 to 500 Hz.

  The lamp starting unit 16 during a period in which the switch elements SW1, SW2 and SW3, SW4 are alternately turned on and off at a high frequency Hf causes the discharge lamp 17 to generate a lamp voltage VL of a high-voltage pulse of about 25 kV shown in FIG. In the discharge lamp 17, lighting is started when the insulation between the electrodes constituting the discharge lamp 17 is broken by the lamp voltage VL due to the high voltage pulse.

  By the way, as shown in FIG. 2 (i), when the discharge lamp 17 is broken down by the lamp voltage VL of the high-pressure pulse during the start-up / preheating period, the lamp voltage VL decreases and the voltage of the discharge lamp 17 during the normal lighting period is reduced. Turn on with. Since the control unit 18 tries to control the lamp power to be constant, it tends to flow a large amount of lamp current at the boundary between the periods f1 and f2 in FIG. The subsequent lamp current gradually decreases and settles to the rated current as the lamp voltage increases as shown in the period f2 in FIG.

  An increase in lamp current immediately after lighting causes an increase in switching loss and deteriorates circuit efficiency. This is a burden on the lighting device, and in the worst case, the circuit may be damaged.

  In the converter 12, the switch element SW is turned on / off based on the output pulse d to switch the DC voltage of the power source 11, and the switching output is converted into a predetermined DC voltage and output. This DC voltage controls the switching elements SW <b> 1 to SW <b> 4 of the inverter 15 with the drive pulse signal g shown in FIG. For example, the switch elements SW1 and SW2 are turned on when the drive pulse signal g is at the Hi level, and turned off when the drive pulse signal g is at the Lo level. The switch elements SW3 and SW4 are turned on when the drive pulse signal g is at the Lo level. To turn off. The frequency of the drive pulse signal g is selected to be lower than that of the converter 12.

  With reference to FIGS. 3 and 4, flicker reduction by the configuration of FIG. 1 will be described. FIG. 3 is a flowchart for explaining a part of the operation of the control unit, and FIG. 4 is an explanatory diagram for enlarging and explaining a part of the waveforms of the input / output signals of the control unit in FIG. Hereinafter, FIGS. 3 and 4 will be described with reference to FIGS.

  Steps S1 to S6 in FIG. 3 show a processing routine up to (i) in FIG. 2 in which the start signal a is supplied to the control unit 18 and the discharge lamp 17 is normally lit.

  by the way. The control unit 18 during normal lighting obtains lamp voltage information from the lamp voltage detection unit 13. When flicker occurs, the fluctuation rate of the lamp voltage per cycle increases. When the variation rate of the lamp voltage increases, the control unit 18 is programmed in advance so that the input power is higher than that of the normal lighting. The detection of the fluctuation rate is, for example, about 1 to 20 cycles of the lamp voltage VL during normal lighting in FIG.

  Therefore, when detecting that the fluctuation rate of the lamp voltage has increased (S7), the control unit 18 generates the output pulse d corresponding to the fluctuation rate of the duty of the converter 12 (S8), and increases the output voltage of the converter 12. Let

  As shown in FIG. 4, when the lamp voltage is VL1 higher than the normal lighting period, an output pulse d1 having a wider duty than the normal lighting period is used. When the lamp voltage is VL2 lower than the VL1 and higher than the normal lighting period, The output pulse d2 whose duty is narrower than the output pulse d1 and wider than normal lighting is output.

  Then, the lamp starting unit 16 increases the power supplied from the lamp starting unit 16 to the discharge lamp 17 based on the output of the converter 12 having an output voltage higher than that during normal lighting based on the output pulse d1 or d2 (S9). .

  By performing such control, when flicker occurs, the lamp power can be increased to increase the lamp current, and the amount of electrons emitted from the electrode can be increased to reduce flicker.

  Increasing the power when flicker occurs raises the concern that the power during normal lighting will increase and the life of the lamp will be shortened, but it is possible to minimize the shortening of the life by reducing the input power at the beginning of lighting. it can. As an improvement in flicker, the input power during normal lighting is suitably within about 25%.

  In this embodiment, when flicker occurs, flicker can be improved by increasing the lighting power. In addition, although the lamp life tends to be shortened by increasing the input power, the shortening of the life is improved by reducing the input power at the beginning of lighting.

  FIG. 5 is an explanatory diagram for explaining another embodiment relating to the discharge lamp lighting device of the present invention.

  The power control in the above-described embodiment is performed with the characteristic of I in FIG. 5 that controls the lamp power according to the variation rate of the lamp voltage. In this embodiment, as shown in II of FIG. 5, the power increase rate is changed based on the magnitude of the fluctuation rate.

  In this case, when the variation rate is small, in other words, when the flicker is small, the rate of increase of the lamp power is controlled, and when the rate of variation is large, the rate of increase of the lamp power is increased.

  Thereby, when the flicker is small, the control is performed to increase the lamp power while suppressing the increase of the lamp power. Therefore, it is possible to suppress the input of power more than necessary and contribute to prolonging the lamp life. .

  The present invention is not limited to the above embodiment, and the switch elements SW1 to SW4 constituting the DC / AC inverter 15 are full bridges, but may be half bridges using two switch elements.

The circuit block diagram for demonstrating one Embodiment regarding the discharge lamp lighting device of this invention. Explanatory drawing for demonstrating the operation | movement of FIG. The flowchart for demonstrating the flicker reduction of FIG. Explanatory drawing for magnifying a part of waveforms of Drawing 1, and explaining flicker reduction. The circuit block diagram for demonstrating other embodiment regarding the discharge lamp lighting device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Power supply 12 Converter 13 Lamp voltage detection part 14 Lamp current detection part 15 Inverter 16 Lamp start part 17 Discharge lamp 18 Control part 19 PWM control part 20 Full bridge driver

Claims (2)

A converter that boosts or steps down an input DC voltage, converts it to a desired DC voltage, and outputs it;
An inverter that converts the DC voltage into AC power and throws it into a high-pressure discharge lamp;
A high-pressure pulse generator for applying a high voltage to the discharge lamp at start-up;
A control unit that controls the lighting state of the discharge lamp based on the DC voltage,
The control unit is in a state where the discharge lamp is controlled to be in a normal lighting state, detects a lamp voltage from the converter, and determines that the lamp voltage during a predetermined period in the normal lighting state is higher than a voltage outside the predetermined period. The discharge lamp lighting device is characterized in that the discharge lamp is lit at a higher power than normal power.   2. The discharge lamp lighting device according to claim 1, wherein when flicker is detected by the flicker detection means, the input power at the beginning of lighting is reduced.

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