JP5589586B2 - Discharge lamp lighting device - Google Patents

Description

  The present invention relates to a discharge lamp lighting device for lighting a discharge lamp.

  Conventionally, as this type of discharge lamp lighting device, Patent Document 1 discloses a discharge lamp lighting device in which a discharge lamp is turned on by applying an AC voltage as shown in FIG. This discharge lamp lighting device uses a full bridge circuit. The step-down chopper circuit steps down a DC voltage input from a DC power source, outputs a desired DC voltage, and applies it to a full bridge circuit composed of four switching elements. The direct current voltage is converted into an alternating voltage by the full bridge circuit, and the LC series circuit is connected so that the alternating voltage is applied. Discharge lamps are connected to both ends of the capacitor of the LC series circuit. At the time of starting the discharge lamp, an AC voltage having a high switching frequency near the resonance frequency (for example, 150 kHz) of the LC series circuit is applied to supply a high voltage necessary for starting the discharge lamp. After the discharge lamp is lit, the switching frequency is shifted to a steady frequency (several tens to several hundreds Hz) to perform a steady operation.

JP 2004-327117 A

  An inductor of an LC series circuit is usually a ferrite core with a winding. When an AC voltage is applied to this inductor, a periodic magnetic field change occurs due to the current flowing through the winding. Due to the change in the magnetic field, the ferrite core is distorted by the magnetostrictive effect, and mechanical vibration is generated. On the other hand, the magnetostriction constant of the ferrite core has temperature dependence, and the magnetostriction constant is large when the temperature of the ferrite core is low. Therefore, since the ferrite core temperature is low and the magnetostriction constant is large for a while after the transition to the steady frequency, there is a problem that audible noise is generated by mechanical vibration due to the magnetostriction effect. This is because the stationary frequency of several tens to several hundreds of Hz is a frequency in the human audible range, and mechanical vibration at this frequency becomes audible noise. Here, the human audible range is 20 Hz to 20 kHz, of which 1 to 10 kHz is the easiest to hear. The farther away from this frequency band, the harder it is to hear. In the measurement with a sound level meter, the A characteristic mode is used internationally in which correction by weighting is performed for each frequency band in consideration of the ease of hearing to the human ear. In the A characteristic mode, for example, the audible noise is measured with correction of −20 dB for the 100 Hz component, −5 dB for the 400 Hz component, and 0 dB (no correction) for the 1 kHz component.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a discharge lamp lighting device in which audible noise due to mechanical vibration of a ferrite core is reduced.

In order to solve the above problems, a discharge lamp lighting device according to the present invention includes a DC voltage input terminal to which a first value of DC voltage is supplied, a first value of DC voltage, and a second value of DC voltage. A DC-DC converter circuit including a switching element, DC voltage detecting means for detecting an output voltage of the DC-DC converter circuit, and a DC output from the DC-DC converter circuit. A voltage is converted into an AC voltage having an arbitrary switching frequency, and a lamp-current flowing through a DC-AC inverter circuit including a switching element and an LC series circuit and a discharge lamp connected to the LC series circuit is detected. Current detecting means for detecting the value of the DC voltage detected by the DC voltage detecting means and the value of the lamp current detected by the current detecting means. A discharge lamp lighting device comprising: a control circuit for controlling on / off of switching elements of the DC-DC converter circuit and the DC-AC inverter circuit, wherein the LC series circuit is wound around a ferrite core. The magnetostriction constant of the ferrite core is temperature-dependent, the magnetostriction constant is large when the temperature is low, and temperature detection means for detecting the temperature of the ferrite core is provided. The control circuit sets the switching frequency to a frequency lower than the steady frequency when the temperature of the ferrite core detected by the temperature detection means is lower than a predetermined temperature.

  In this discharge lamp lighting device, when the temperature of the ferrite core of the inductor is low, the switching frequency can be operated at a frequency lower than the steady-state frequency. Noise can be reduced.

  In the present invention, the temperature detecting means is a thermistor element.

  In the present invention, the temperature detecting means detects the temperature of the ferrite core from the DC resistance value of the winding.

  In this case, the temperature of the ferrite core can be detected more easily.

  According to the present invention, when the temperature of the ferrite core of the inductor in the discharge lamp lighting device is low, the switching frequency can be operated at a frequency lower than the steady frequency, so that the switching frequency can be kept away from the audible range. Audible noise from the core can be reduced.

1 is a circuit diagram showing a configuration of a discharge lamp lighting device according to a first embodiment of the present invention. It is a schematic graph which shows the relationship between a ferrite core temperature and a magnetostriction constant. It is a timing chart which shows the relationship between the core temperature after shifting to a steady operation, a magnetostriction constant, and switching frequency. It is a circuit diagram which shows the structure of the discharge lamp lighting device which concerns on the 2nd Embodiment of this invention. It is a circuit diagram of the conventional discharge lamp lighting device.

Hereinafter, embodiments of a discharge lamp lighting device according to the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 shows a configuration of a discharge lamp lighting device 1 according to the first embodiment of the present invention. A low-pass filter including an inductor L21 and a capacitor C21 is connected to the connector CN1 to which a DC external power supply voltage is input. A regulator 9 is connected to the next stage, and a step-down chopper circuit 7 is connected to the subsequent stage. The step-down chopper circuit 7 includes a switching element Q11 made of a semiconductor switching element such as an FET, a diode D11, an inductor L11, and a capacitor C11. The digital control circuit 3 is connected to the switching element Q11 via the driver 8.

  The low-pass filter including the inductor L21 and the capacitor C21 stabilizes the external power supply voltage input from the connector CN1 and removes noise. The regulator 9 is for generating a power supply voltage for the digital control circuit 3.

  The step-down chopper circuit 7 is a circuit that steps down an input DC voltage and outputs a DC voltage having a desired voltage value. The digital control circuit 3 controls on / off of the switching element Q11 to obtain a desired DC voltage. The output voltage output from the step-down chopper circuit 7 is divided by the resistors R 1 and R 2, and the divided voltage is input to the digital control circuit 3. As a result, the digital control circuit 3 can monitor and control the output voltage of the step-down chopper circuit 7.

  In the first embodiment, since it is assumed that the input voltage is high, a step-down chopper circuit is used. It is possible to

 The output of the step-down chopper circuit 7 is further connected to the DC-AC inverter circuit 2. The DC-AC inverter circuit 2 includes four switching elements Q1 to Q4, a driver 4 for driving the four switching elements Q1 to Q4, and an LC series circuit including an inductor L1 and a capacitor C1. The four switching elements Q1 to Q4 form a so-called full bridge circuit, and convert a DC voltage into an AC voltage. The driver 4 complementarily turns on / off the switching elements Q1 and Q4 and Q2 and Q3 by a command signal from the digital control circuit 3. The LC series circuit of the inductor L1 and the capacitor C1 is connected to a full bridge circuit, and a converted AC voltage is applied. An AC voltage is applied to a discharge lamp (not shown) via connectors CN2 connected to both ends of the capacitor C1.

  In the first embodiment, a full bridge circuit is used for the DC-AC inverter circuit 2, but a half bridge circuit, a push-pull circuit, or the like can be used depending on the situation.

  The inductor L1 is configured by winding a winding around a ferrite core. In the vicinity of the ferrite core, a thermistor element as the ferrite core temperature detecting means 6 is provided. The thermistor element is connected to the digital control circuit 3 to monitor the temperature of the ferrite core.

  The lamp current flowing through the discharge lamp corresponding to the load coincides with the current flowing through the inductor L1 in the steady operation. Therefore, the lamp current is detected by the current detection means 5 provided on the low voltage side of the output of the step-down chopper circuit 7 and monitored by the digital control circuit 3. For example, a resistor can be used as the current detection means 5.

  The discharge lamp lighting device of the first embodiment is for lighting a high-pressure mercury lamp used for a front projector, for example, and the connector CN3 connected to the digital control circuit 3 is such a front projector or the like. This is for connection with a microcomputer or the like on the device side. Through this connector, it is possible to communicate the operating status of the discharge lamp lighting device and the exchange of command signals for the output voltage and output current.

  Next, the operation of the discharge lamp lighting device 1 will be described. At the time of starting the discharge lamp, the digital control circuit 3 sets the switching frequency of the AC voltage applied to the LC series circuit of the inductor L1 and the capacitor C1 to obtain a high voltage necessary for starting the discharge lamp. Near the frequency or near the frequency obtained by dividing the resonance frequency by an odd number. For example, if the value of the inductor L1 is 275 μH and the value of the capacitor C1 is 550 pF, the resonance frequency is 409 kHz. A high voltage capable of starting the discharge lamp can be obtained by applying an alternating voltage having a switching frequency near 136 kHz, which is in the vicinity of the frequency obtained by dividing the resonance frequency by 3.

  If the voltage required for starting the discharge lamp can be obtained, the resonance frequency is not limited to the value obtained by dividing by 3, but the frequency obtained by dividing the resonance frequency by an odd number of 1, 5, 7, 9 or more. Also good. Such starting of the discharge lamp is accomplished in a short period of time within approximately one second.

  When the discharge lamp is lit, the switching frequency is shifted to the steady frequency and the steady operation is performed. For example, 370 Hz is suitable as a switching frequency as a steady frequency for continuously lighting the discharge lamp. This is because the life characteristics of the discharge lamp and the efficiency characteristics of the discharge lamp lighting device 1 are good.

  However, immediately after the start of the discharge lamp, the ferrite core of the inductor L1 is near the room temperature (for example, 25 ° C.), which is the operating atmosphere, and the ferrite core has a large magnetostriction constant λ. FIG. 2 is a schematic graph showing the relationship between the ferrite core temperature and the magnetostriction constant λ, and shows that the magnetostriction constant λ near the room temperature is large.

  Due to the alternating magnetic field generated by the alternating lamp current flowing through the inductor L1, the ferrite core is distorted by the magnetostriction effect, and mechanical vibrations mainly at the period of the switching frequency are generated. When the temperature of the ferrite core is low, since the magnetostriction constant is large, the vibration becomes large, and if the switching frequency is 370 Hz, it is a frequency close to 1 to 10 kHz that is most easily audible to humans in the human audible range. The mechanical vibration of the ferrite core becomes audible noise that can be heard by the human ear. The audible noise can be measured by a sound level meter, for example. When a standard value of audible noise is set based on the usage environment or the like, this standard value may not be satisfied when the temperature of the ferrite core is low and the magnetostriction constant is large.

  Therefore, in the first embodiment, the digital control circuit 3 controls the switching frequency when the temperature of the ferrite core is low immediately after starting the discharge lamp so as to operate at 100 Hz, which is lower than the steady frequency. . When lighting a high-pressure mercury lamp, etc., by setting the frequency lower than the steady frequency, it can be moved away from 1 to 10 kHz, which is the most audible area in the human audible range, thus reducing the audible noise caused by the vibration of the ferrite core. can do.

  However, it is not preferable to continue the operation at 100 Hz in consideration of the life characteristics of the discharge lamp and the efficiency characteristics of the discharge lamp lighting device 1. Here, the temperature of the ferrite core of the inductor L1 rises as the operation of the discharge lamp lighting device 1 continues. The cause of the temperature rise of the ferrite core is heat generation due to iron loss of the ferrite core and heat generation due to resistance loss (copper loss) of the winding wound around the ferrite core. If the operation is in the vicinity of 370 Hz, which is a steady frequency, the frequency is low, so heat generated by copper loss is dominant.

  When the temperature of the ferrite core rises, the magnetostriction constant decreases as shown in FIG. Therefore, the mechanical vibration of the ferrite core is also reduced, and the audible noise reduced by the 100 Hz operation is further reduced. In the magnetostriction constant region, audible noise is reduced even when operating at a steady frequency of 370 Hz.

  In the first embodiment, when the temperature of the ferrite core detected by the ferrite core temperature detecting means 6 exceeds a predetermined temperature of 60 ° C., the digital control circuit 3 is configured to shift the switching frequency to a steady frequency of 370 Hz. Control. By controlling in this way, at the ferrite core temperature at which the audible noise is reduced, the operation is not continued at 100 Hz, and the life characteristics of the discharge lamp and the efficiency characteristics of the discharge lamp lighting device 1 are made to operate favorably. Can do.

  FIG. 3 is a timing chart showing the relationship between the core temperature, magnetostriction constant, and switching frequency after the transition from the lamp start to the steady operation. Since the ferrite core temperature is low immediately after the transition to the steady operation, the switching frequency operates at 100 Hz.

  When the operation of the discharge lamp lighting device 1 continues, the ferrite core temperature rises and the magnetostriction constant decreases accordingly. As described above, when the ferrite core temperature detected by the thermistor element that is the ferrite core temperature detecting means 6 exceeds a predetermined temperature of 60 ° C., the digital control circuit 3 controls the switching frequency to shift to 370 Hz.

In this embodiment, the switching frequency is shifted when the ferrite core temperature reaches 60 ° C., but the ferrite core temperature at which the switching frequency is shifted can be set according to the audible noise and its standard value.
(Second Embodiment)
FIG. 4 shows a configuration of a discharge lamp lighting device 10 according to the second embodiment of the present invention. Portions corresponding to those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. The second embodiment differs from the first embodiment in that it includes voltage detection means for resistors R3 and R4.

  In the second embodiment, the DC resistance value of the winding of the inductor L1 is detected by the digital control circuit 3, and the ferrite core temperature is detected. Since the metal used as the winding material has a temperature change coefficient of resistance, the winding temperature can be derived from the DC resistance value of the winding. Further, in the inductor L1, the winding is close because it is wound around the ferrite core, and the temperature of the ferrite core can be derived from the temperature of the winding. In the digital control circuit 3, the relationship between the DC resistance value of the winding and the ferrite core temperature is programmed in advance.

  The voltage applied to the winding of the inductor L1 is monitored by the digital control circuit 3 by a DC voltage detection means comprising resistors R1 and R2 and a voltage detection means comprising resistors R3 and R4. The current flowing through the inductor L1 is monitored by the digital control circuit 3 via the current detection means 5. The DC resistance value of the winding of the inductor L1 can be derived from Ohm's law from the voltage and current values applied to the winding. Here, since the switching frequency in the steady operation of the DC-AC inverter circuit 2 is about 370 Hz, the frequency for deriving the DC resistance value in this way is a sufficiently low frequency.

  In the second embodiment, the temperature of the ferrite core can be detected by detecting the voltage and current, and the configuration can be simplified.

  Here, it is desirable to use a DSP (digital signal processor) as the digital control circuit 3. As another digital control circuit, a microcomputer or the like can be considered, but a DSP is effective in terms of a high processing speed.

DESCRIPTION OF SYMBOLS 1, 10: Discharge lamp lighting device 2: DC-AC inverter circuit 3: Digital control circuit 4, 8: Driver 5: Current detection means 6: Ferrite core temperature detection means 7: Step-down chopper circuit 9: Regulator CN1-CN3: Connector Q1-Q4, Q11: Switching elements R1, R2: Resistance (DC voltage detecting means)
R3, R4: Resistance (voltage detection means)
L1, L11, L21: Inductors C1, C11, C21: Capacitors D11: Diodes

Claims (3)

A DC voltage input terminal to which a first value DC voltage is supplied;
A DC-DC converter circuit including a switching element for converting the first value DC voltage into a second value DC voltage;
DC voltage detection means for detecting the output voltage of the DC-DC converter circuit;
A DC voltage output from the DC-DC converter circuit is converted into an AC voltage having an arbitrary switching frequency, and includes a DC-AC inverter circuit including a switching element and an LC series circuit,
Current detecting means for detecting a lamp current flowing in a discharge lamp connected to the LC series circuit;
The switching elements of the DC-DC converter circuit and the DC-AC inverter circuit are turned on / off according to the value of the DC voltage detected by the DC voltage detecting means and the value of the lamp current detected by the current detecting means. A discharge lamp lighting device having a control circuit for controlling each of off,
The LC series circuit is composed of an inductor and a capacitor in which a winding is applied to a ferrite core,
The magnetostriction constant of the ferrite core has temperature dependence, the magnetostriction constant is large when the temperature is low, and a temperature detection means for detecting the temperature of the ferrite core is provided,
The discharge lamp lighting device, wherein when the temperature of the ferrite core detected by the temperature detecting means is lower than a predetermined temperature, the control circuit sets the switching frequency to a frequency lower than a steady frequency. The temperature detecting means is a thermistor element, a discharge lamp lighting device according to claim 1. The discharge lamp lighting device according to claim 1 or 2, wherein the temperature detection means detects the temperature of the ferrite core from a DC resistance value of the winding.