JP4703626B2 - Discharge lamp lighting device - Google Patents

Description

  The present invention relates to a discharge lamp lighting device having a function of preventing partial non-lighting of a discharge lamp such as a fluorescent lamp in a multi-lamp backlight such as a large-screen liquid crystal television.

  2. Description of the Related Art Conventionally, backlights for large liquid crystal televisions and large liquid crystal displays employ a multi-lamp system that uses a plurality of discharge lamps such as external electrode fluorescent tubes and cold cathode fluorescent tubes. Conventionally, a multi-lamp type backlight inverter has been used in which a single or two discharge lamps are controlled by a single control system (a so-called 1-by1 system). Therefore, a large-sized backlight lighting device using more than a dozen discharge lamps is expensive.

  Therefore, recently, the electric circuit has been simplified by driving a plurality of discharge lamps connected in parallel using a small control system circuit and an integrated large transformer, thereby reducing the number of parts of the device and reducing the cost. I'm trying to go down.

  When an external electrode fluorescent tube (EEFL) is used as a discharge lamp, the external electrode fluorescent tube has a resistance characteristic in the positive direction, and therefore can be directly connected in parallel without using a balancer element. For this reason, there is an advantage that a discharge lamp lighting device can be configured with a small number of parts since circuit parts for balancing current are not required.

  When a cold cathode fluorescent tube (CCFL) is used as a discharge lamp, since the cold cathode fluorescent tube has negative resistance characteristics, it cannot be used by directly connecting the fluorescent tubes in parallel. Is used. This has a current balance function in which a ballast coil, a ballast capacitor, and the like are connected in series with an electrode, so that fluorescent tubes can be connected in parallel and used.

  Examples of the multi-lamp type discharge lamp lighting device as described above include a multi-lamp discharge lamp lighting device disclosed in JP-A-2006-173024 and a multi-lamp discharge device disclosed in JP-A-2006-173023. Discharge lamp lighting device, inverter device disclosed in Japanese Patent Application Laid-Open No. 2002-027762, discharge lamp lighting device disclosed in Japanese Patent Application Laid-Open No. 07-245186, and high frequency power supply device for parallel multi-lamp lighting disclosed in Japanese Patent Application Laid-Open No. 07-211467 Etc. are known.

  In addition, when a cold cathode fluorescent tube (CCFL) or an external electrode type fluorescent tube (EEFL) is used as a discharge lamp, these cold cathode fluorescent tube and external electrode type fluorescent tube are activated by the gas inside the tube in a low temperature environment. Therefore, the discharge start voltage rises and the discharge lamp is difficult to light. In addition, if the lamp itself is stored in a cool and dark place without lighting for a long time, the lamp itself cannot generate initial electrons for enabling the discharge to start. There is a property that requires a high discharge start voltage.

  In the case of an external electrode fluorescent tube (EEFL) in which a plurality of discharge lamps are connected in parallel, the discharge lamp connected in parallel has a difference in lighting delay time, lighting start voltage characteristics, startability after standing in the dark, etc. In some cases, all tubes may not light up at the same time. If there is a time delay in lighting with the fluorescent tubes connected in parallel, the tube voltage will be reduced by the previously lighted fluorescent tube, so the fluorescent tube with the time delay will not start discharging, or will not light up, or In a semi-lighting state in which discharge occurs only in the vicinity of the electrodes, uneven brightness of the backlight occurs.

  In addition, one of the causes of the discharge lamp not lighting is dark lighting. Discharge lamps such as external electrode discharge tubes and cold cathode discharge tubes cannot generate initial electrons that trigger discharge at start-up, and in bright places, the initial electrons are generated in the tube by ambient light, and after energization Lights up immediately, but lighting is impossible or difficult in dark places. The initial electrons that trigger the discharge include thermionic electrons, photoelectrons, electrons emitted by high electric fields, natural cosmic rays, etc., but if a discharge lamp is placed in a place where no external light exists, photoelectrons Since there is no light, it becomes difficult to light up.

For this reason, in the case of dark lighting, a high lighting start voltage is required. Therefore, in order to increase the lighting start voltage at start-up and to facilitate discharge from the electrode section, the operating frequency is increased only at start-up. A method of shifting to a frequency and returning to a normal frequency after lighting is known. In general, a metal casing or reflector of a backlight forms a capacitance with an electrode of a discharge lamp, and serves as a proximity conductor that promotes high-frequency discharge. In this case, the frequency is returned to a predetermined normal lighting frequency after lighting.
JP 2006-173024 A JP 2006-173023 A Japanese Patent Laid-Open No. 2002-027762 JP 07-245186 A Japanese Patent Application Laid-Open No. 07-212467

  However, when an LCD panel in which a plurality of discharge lamps are connected in parallel is turned on by a method in which the operating frequency is shifted to a higher frequency when the discharge lamp lighting device is started up, the non-lighted or half-lighted light is not emitted due to variations in the characteristics of the discharge lamp. There is a case where an electric lamp is present and luminance unevenness is partially generated when viewed on the screen.

  That is, when started in a low temperature environment, there is a problem that some (one to several) of discharge lamps connected in parallel are not lit, and luminance unevenness occurs on the TV screen. Partial non-lighting occurs when the discharge lamps are connected in parallel due to variations in characteristics such as lighting start time, dark startability, and tube voltage. Since it is difficult to sort and rank according to the characteristics of the discharge lamps, partial discharge of light tends to occur at low temperatures because of the presence of discharge lamps with different starting characteristics on the same panel.

  When partial non-lighting occurs, it takes time for the panel to warm up sufficiently and all the discharge lamps to light up completely, and uneven brightness on the screen is maintained for a long time, thereby degrading the screen quality.

Thus, the problem of partial non-lighting becomes apparent in a low temperature environment where the discharge lamp is difficult to light. The following methods are known as means for eliminating such partial non-lighting.
• Increase the voltage applied to the fluorescent tube at startup.
Increase the voltage applied to the fluorescent tube at startup and lengthen the time during which a high voltage is applied.
・ A large current is applied for a short time during startup.

  However, these methods have the following problems.

  In the method of increasing the applied voltage at start-up, an output voltage that is about twice that of the normal operating voltage is output, which requires a transformer withstand voltage, making it difficult to reduce the size and thickness of the transformer. In addition, if the turn ratio is increased in order to produce a high voltage, there is a problem that the efficiency during normal operation is lowered and the heat generation of the transformer is increased. Further, when a high voltage is generated, a roaring sound is generated due to the magnetostriction of the transformer, and this roaring sound becomes annoying.

  In the method of flowing a large current at the time of start-up, partial non-lighting is not eliminated with a current increase of about 20%. In addition, a transformer designed in consideration of efficiency during steady operation does not have an ability to flow an overcurrent of about 150% of the rated current in normal operation. For this reason, it has been difficult to completely eliminate partial non-lighting in a low temperature environment.

  The present invention has been made in view of the above-mentioned problems, and the object thereof is to prevent partial non-lighting of the discharge lamp and realize lighting without uneven brightness from the start even in a low temperature environment. It is an object of the present invention to provide a discharge lamp lighting device capable of minimizing the occurrence of a roaring sound of a transformer.

  In order to achieve the above object, the present invention aims at lighting a discharge lamp to which a voltage is applied to each of both end electrodes and a voltage is applied via the capacitance, and is connected to a plurality of discharge lamps connected in parallel. The relationship between the inverter driving frequency and the output voltage when one of the discharge lamps is lit, and the relationship between the inverter driving frequency and the output voltage when one or more discharge lamps are lit. A resonance frequency characteristic that represents a lighting resonance frequency characteristic, a DC voltage is input, and a resonance that is lower than a resonance frequency indicating a maximum voltage value in the resonance frequency characteristic when not lit and indicates a maximum voltage value in the lighting resonance frequency characteristic In a discharge lamp lighting device comprising an inverter circuit that generates an alternating voltage of a normal lighting frequency higher than a frequency and applies the alternating voltage to the plurality of discharge lamps, the discharge Detecting the ambient temperature of the sensor, and operating when the drive signal is output, operating means for outputting a drive signal when the detected ambient temperature is a low temperature below a predetermined threshold, Low temperature driving frequency control means for operating the inverter circuit at a predetermined low frequency lower than the normal lighting frequency that is higher than the voltage of the normal lighting frequency in the lighting resonance frequency characteristics is provided.

  The discharge lamp lighting device of the present invention is intended for lighting a discharge lamp having a capacitance at each of both end electrodes and to which a voltage is applied via the capacitance. The output voltage of the inverter circuit applied to the discharge lamp is the sum of the voltage applied to the capacitance of both end electrodes and the voltage applied between the both end electrodes. At this time, the voltage applied to each capacitance of both end electrodes depends on the impedance component and current of the capacitance determined by the operating frequency of the inverter circuit.

  When the ambient temperature of the discharge lamp is detected by the low temperature operation means and the detected temperature is a low temperature below the threshold value, the inverter circuit operates at a predetermined low frequency lower than the normal lighting frequency by the low temperature drive frequency control means. Controlled to work.

  For this reason, at the time of low temperature, the capacitance and the voltage between both end electrodes change to a voltage based on the resonance frequency characteristic at the time of lighting. That is, the resonance frequency characteristic shifts from the resonance frequency characteristic when not lit to the resonance frequency characteristic when lit, and the inverter circuit operates at the low frequency, so there is a discharge lamp that does not light by the applied voltage based on the resonance frequency characteristic when not lit. However, due to the operation at the low frequency in the lighting resonance frequency characteristic, the impedance of the capacitance increases, and the voltage applied to both ends of the capacitance increases more than the voltage at the normal lighting frequency. Increases the voltage applied to the discharge lamp including Thereby, lighting of the discharge lamp is promoted. Further, when the ambient temperature is higher than the threshold value, the inverter circuit is controlled to operate at the normal lighting frequency in the lighting resonance frequency characteristic.

  In order to achieve the above object, the present invention is directed to a discharge lamp having a capacitance at each of both end electrodes and to which a voltage is applied via the capacitance, and is connected to a plurality of discharge lamps connected in parallel. The relationship between the inverter driving frequency and the output voltage when all the discharge lamps are not lit, the resonance frequency characteristic when not lit and the inverter driving frequency and the output voltage when one or more discharge lamps are lit And having a resonance frequency characteristic at the time of lighting representing the relationship, a DC voltage is input, and the maximum voltage value in the resonance frequency characteristic at the time of lighting is lower than the resonance frequency indicating the maximum voltage value in the resonance frequency characteristic when not lit. An inverter circuit that generates an alternating voltage with a normal lighting frequency higher than the indicated resonance frequency and applies it to the plurality of discharge lamps, and a current value flowing through the discharge lamps are detected. And a means for increasing the power supplied from the inverter circuit to the discharge lamp as the current value is smaller, detecting the ambient temperature of the discharge lamp, and the detected ambient temperature is a predetermined value. Low temperature operation means for outputting a drive signal when the temperature is lower than a threshold, and when the drive signal is output, the current flowing through the discharge lamp is lower than the actual current value. Correction means for correcting the detected current value is provided.

  The discharge lamp lighting device of the present invention is intended for lighting a discharge lamp having a capacitance at each of both end electrodes and to which a voltage is applied via the capacitance. The output voltage of the inverter circuit applied to the discharge lamp is the sum of the voltage applied to the capacitance of both end electrodes and the voltage applied between the both end electrodes. At this time, the voltage applied to each capacitance of both end electrodes depends on the impedance component and current of the capacitance determined by the operating frequency of the inverter circuit.

  When the ambient temperature of the discharge lamp is detected by the low temperature operation means and the detected temperature is a low temperature below the threshold value, the current flowing through the discharge lamp by the correction means is lower than the actual current value. The detected current value is corrected. For this reason, the electric power supplied from the inverter circuit to the discharge lamp is increased, and the voltage applied to the discharge lamp including the capacitance is increased. Thereby, lighting of the discharge lamp is promoted. When the ambient temperature is higher than the threshold value, the inverter circuit is controlled to operate based on the detected current value that is not corrected.

  In order to achieve the above object, the present invention is directed to a discharge lamp having a capacitance at each of both end electrodes and to which a voltage is applied via the capacitance, and is connected to a plurality of discharge lamps connected in parallel. The relationship between the inverter driving frequency and the output voltage when all the discharge lamps are not lit, the resonance frequency characteristic when not lit and the inverter driving frequency and the output voltage when one or more discharge lamps are lit And having a resonance frequency characteristic at the time of lighting representing the relationship, a DC voltage is input, and the maximum voltage value in the resonance frequency characteristic at the time of lighting is lower than the resonance frequency indicating the maximum voltage value in the resonance frequency characteristic when not lit. An inverter circuit that generates an alternating voltage with a normal lighting frequency higher than the indicated resonance frequency and applies it to the plurality of discharge lamps, and a current value flowing through the discharge lamps are detected. And a means for increasing the power supplied from the inverter circuit to the discharge lamp as the current value is smaller, detecting the ambient temperature of the discharge lamp, and the detected ambient temperature is a predetermined value. Low temperature operation means for outputting a drive signal when the temperature is lower than a threshold, and when the drive signal is output, the current flowing through the discharge lamp is lower than the actual current value. The correction means for correcting the detected current value, and the normal lighting frequency that operates when the drive signal is output and is higher than the voltage of the normal lighting frequency in the lighting resonance frequency characteristic. Low temperature driving frequency control means for operating the inverter circuit at a predetermined low frequency.

  The discharge lamp lighting device of the present invention is intended for lighting a discharge lamp having a capacitance at each of both end electrodes and to which a voltage is applied via the capacitance. The output voltage of the inverter circuit applied to the discharge lamp is the sum of the voltage applied to the capacitance of both end electrodes and the voltage applied between the both end electrodes. At this time, the voltage applied to each capacitance of both end electrodes depends on the impedance component and current of the capacitance determined by the operating frequency of the inverter circuit.

  When the ambient temperature of the discharge lamp is detected by the low temperature operation means and the detected temperature is a low temperature below the threshold value, the current flowing through the discharge lamp by the correction means is lower than the actual current value. The detected current value is corrected and the power supplied from the inverter circuit to the discharge lamp is increased, and the inverter circuit is controlled to operate at a predetermined low frequency lower than the normal lighting frequency by the low temperature driving frequency control means. The For this reason, the voltage applied to the discharge lamp including the capacitance increases, and changes to a voltage based on the resonance frequency characteristics during lighting. That is, in addition to increasing the applied voltage by correcting the detection current value to be small, the resonance frequency characteristic shifts from the resonance frequency characteristic when not lit to the resonance frequency characteristic when lit and the inverter circuit Since it operates at a low frequency, even if there is a discharge lamp that does not light by an applied voltage based on the resonance frequency characteristics when not lit, the low frequency operation in the resonance frequency characteristics during lighting increases the impedance of the capacitance, The voltage applied to both ends of the capacitance increases more than the voltage at the normal lighting frequency, and the voltage applied to the discharge lamp including the capacitance increases. Thereby, lighting of the discharge lamp is promoted. Further, when the ambient temperature is higher than the threshold value, the inverter circuit is controlled to operate at the normal lighting frequency in the lighting resonance frequency characteristic based on the detected current value that is not corrected.

  According to the discharge lamp lighting device of the present invention, since the inverter circuit operates at the low frequency after the resonance frequency characteristic shifts from the unlit resonance frequency characteristic to the lighting resonance frequency characteristic, Even if there is a discharge lamp that does not light up due to the applied voltage based on the low frequency operation in the lighting resonance frequency characteristic, the voltage applied to the discharge lamp increases and lighting of the discharge lamp is promoted. Even when the discharge lamps are driven in parallel, it is possible to prevent some of the discharge lamps from becoming unlit or semi-lit. Furthermore, it is possible to prevent partial non-lighting particularly in a low-temperature environment where the discharge lamp is difficult to turn on, and to improve the uniformity of the screen brightness without brightness unevenness from the start. In addition, since a voltage higher than the normal lighting voltage is applied to the discharge lamp only at startup and at a low temperature to prevent the occurrence of non-lighting or partial non-lighting, the magnetostriction of the transformer when a high voltage is applied to the discharge lamp It is possible to minimize the generation of the roaring sound caused by.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a discharge lamp lighting device according to a first embodiment of the present invention. In the figure, 101 is a discharge lamp lighting device, eight field effect transistors (hereinafter referred to as FETs) Q1 to Q4, Q21 to Q24, capacitors C1 and C21, inverter transformers T1 and T21, and a resistor R1 for current detection. , R21, drive control circuits 11, 21, current detection circuits 12, 22, oscillation circuit 13, lighting frequency shift circuit 15, low temperature operation on circuit 18, frequency change circuit 19, discharge lamps Lamp-1 to Lamp-n ( n is a natural number) and has a full-bridge inverter circuit. In this embodiment, as the discharge lamps Lamp-1 to Lamp-n, for example, external electrode fluorescent lamps (External Electrode Fluorescent Lamps) are used.

  The drain of the FET Q1 is connected to the positive electrode of the DC power source Vcc1 and the drain of the FET Q3, and the negative electrode of the DC power source Vcc1 is grounded. The source of the FET Q1 is connected to the drain of the FET Q2, and is connected to one end of the primary winding of the transformer T1 through the capacitor C1, and the source of the FET Q2 is grounded.

  The source of FETQ3 is connected to the drain of FETQ4 and to the other end of the primary winding of transformer T1. One end of the secondary winding of the transformer T1 is connected to one end of the discharge lamps Lamp-1 to Lamp-n connected in parallel, and the other end of the secondary winding is connected to the current detection circuit 12 and the resistor R1 is connected. Is grounded. Thereby, the current detection circuit 12 can detect the value of the current flowing through the discharge lamps Lamp-1 to Lamp-n based on the voltage across the resistor R1. Further, the current detection circuit 12 outputs the detection result to the drive control circuit 11 and the lighting frequency shift circuit 15.

  The gates of the FETs Q1 to Q4 are connected to the drive control circuit 11, and the FETs Q1 to Q4 are switched on and off by a control signal output from the drive control circuit 11. That is, the drive control circuit 11 outputs a control signal based on the frequency of the AC signal oscillated by the oscillation circuit 13 to the gates of the FETs Q1 to Q4, and switches the FETs Q1 to Q4 to perform the primary operation of the inverter transformer T1. The energization direction of the winding is reversed at a predetermined cycle, and a high-voltage AC voltage is generated in the secondary winding of the inverter transformer T1. The oscillation frequency (inverter drive frequency) of the oscillation circuit 13 is set to 54 KHz, which is a normal lighting frequency, during startup and in a steady state. Accordingly, during start-up and steady state, the drive control circuit 11 performs switching control of the on / off states of the FETs Q1 to Q4 so that an AC voltage having a frequency of 54 KHz is applied to the discharge lamps Lamp-1 to Lamp-n. To do.

  Further, the voltage output from the current detection circuit 12 is input to the drive control circuit 11. This voltage changes in proportion to the current flowing through the secondary winding of the inverter transformer T1, and the lamp current flowing through the discharge lamps Lamp-1 to Lamp-n corresponds to the current flowing through the secondary winding. Therefore, the drive control circuit 11 controls the operation of each of the FETs Q1 to Q4 based on the voltage output from the current detection circuit 12, changes the on / off duty, and starts from the secondary winding of the transformer T1. The generated electric power, ie, the lamp current is controlled. That is, when the current flowing through the discharge lamps Lamp-1 to Lamp-n is small, the power supplied to the discharge lamps Lamp-1 to Lamp-n is increased by increasing the time during which the FETs Q1 to Q4 are turned on. Thereby, the brightness adjustment of the discharge lamps Lamp-1 to Lamp-n is performed.

  When the lighting frequency shift circuit 15 is activated, the current flowing through the discharge lamps Lamp-1 to Lamp-n detected by the current detection circuit 12 is within a predetermined allowable range including the rated current value (for example, 70 of the rated current value). %), The frequency of the oscillation circuit 13 is switched from the normal lighting frequency to a predetermined low frequency, and the drive control circuit 11 is operated. After a predetermined time, the frequency of the oscillation circuit 13 is switched to the normal lighting frequency.

  The low temperature operation ON circuit 18 operates the frequency change circuit 19 when the ambient temperature becomes a predetermined threshold value or less, and when the ambient temperature becomes higher than the above threshold value, the frequency change circuit 19 Stop operation.

  When the operation is started by the low temperature operation on circuit 18, the frequency change circuit 19 switches the frequency of the oscillation circuit 13 from the normal lighting frequency to a predetermined low frequency to operate the drive control circuit 11, and operates at a low temperature operation on circuit. When the operation is stopped by 18, the drive control circuit 11 is operated by switching the frequency of the oscillation circuit 13 from the low frequency to the normal lighting frequency.

  The drain of the FET Q21 is connected to the positive electrode of the DC power source Vcc21 and the drain of the FET Q23, and the negative electrode of the DC power source Vcc21 is grounded. The source of the FET Q21 is connected to the drain of the FET Q22 and is connected to one end of the primary winding of the transformer T21 via the capacitor C21, and the source of the FET Q22 is grounded.

  The source of the FET Q23 is connected to the drain of the FET Q24 and to the other end of the primary winding of the transformer T21. One end of the secondary winding of the transformer T21 is connected to the other end of the discharge lamps Lamp-1 to Lamp-n connected in parallel, and the other end of the secondary winding is connected to the current detection circuit 22 and the resistor R21. Is grounded. Thereby, the current detection circuit 22 can detect the value of the current flowing through the discharge lamps Lamp-1 to Lamp-n based on the voltage across the terminals of the resistor R21. Further, the current detection circuit 22 outputs the detection result to the drive control circuit 21. Note that the outputs of the transformers T1 and T21 are output in opposite phases.

  The gates of the FETs Q21 to Q24 are connected to the drive control circuit 21, and the FETs Q21 to Q24 are switched on and off by a control signal output from the drive control circuit 21. In other words, the drive control circuit 21 outputs a control signal based on the frequency of the AC signal oscillated by the oscillation circuit 13 to the gates of the FETs Q21 to Q24, and switches the FETs Q21 to Q24 to perform the primary operation of the inverter transformer T21. The energization direction of the winding is reversed at a predetermined cycle, and a high-voltage AC voltage is generated in the secondary winding of the inverter transformer T21. In the start-up and steady state, the drive control circuit 21 performs switching control of the on / off states of the FETs Q21 to Q24 so that an alternating voltage having a frequency of 54 KHz is applied to the discharge lamps Lamp-1 to Lamp-n. Further, the voltage output from the current detection circuit 22 is input to the drive control circuit 21. This voltage changes in proportion to the current flowing through the secondary winding of the inverter transformer T21, and the lamp current flowing through the discharge lamps Lamp-1 to Lamp-n corresponds to the current flowing through the secondary winding. Therefore, the drive control circuit 21 controls the operation of each of the FETs Q21 to Q24 based on the voltage output from the current detection circuit 22, changes the ON / OFF duty, and starts from the secondary winding of the transformer T21. The generated electric power, ie, the lamp current is controlled. That is, when the current flowing through the discharge lamps Lamp-1 to Lamp-n is small, the electric power supplied to the discharge lamps Lamp-1 to Lamp-n is increased by increasing the time during which the FETs Q21 to Q24 are turned on. Thereby, the brightness adjustment of the discharge lamps Lamp-1 to Lamp-n is performed. In the drive control circuit 21, the phase of the applied voltage to the other end side electrodes of the discharge lamps Lamp-1 to Lamp-n is a phase obtained by inverting the phase of the applied voltage to the one end side electrode, that is, a phase shifted by 180 degrees. As described above, the on / off states of the FETs Q21 to Q24 are switched.

  FIG. 2 is a block diagram showing an example of the lighting frequency shift circuit 15, and FIG. 3 is a circuit diagram showing an example of the lighting frequency shift circuit 15, the low temperature operation on circuit 18 and the frequency change circuit 19. In FIG. 2, 151 is a buffer & hold & delay circuit, 152 is a differentiation circuit, and 153 is a switch circuit.

  The buffer & hold & delay circuit 151 detects the tube current detection voltage input from the current detection circuit 12, that is, the lamp current flowing through the discharge lamps Lamp-1 to Lamp-n, and inputs the voltage converted into the voltage. The voltage is temporarily held, delayed for a predetermined time, and output to the differentiation circuit 152. The differentiation circuit 152 differentiates the input voltage and outputs it to the switch circuit 153. The switch circuit 153 turns on the switching element and grounds one end of the capacitor CX while the voltage input from the differentiation circuit 152 is equal to or higher than a predetermined threshold voltage. The other end of the capacitor CX is connected to the CT terminal of the oscillation circuit 13, that is, a capacitor connection terminal for setting the oscillation frequency. Further, the CT terminal of the oscillation circuit 13 is grounded via the capacitor CT.

  As shown in FIG. 3, the lighting frequency shift circuit 15 includes capacitors 161 to 164 and CX, NPN transistors 165 and 166, diodes 167 and 168, and resistors 169 to 172. One end of the capacitor 161 is connected to the input terminal of the power source + Vcc, the collector of the transistor 165, and the cathode of the diode 168, and the other end is grounded.

  The base of the transistor 165 is connected to the input terminal of the tube current detection voltage V1 output from the current detection circuit 12, and the emitter is connected to the anode of the diode 167 and grounded through the resistor 169. The cathode of the diode 167 is connected to one end of the resistor 170, and the other end of the resistor 170 is connected to the anode of the diode 168 and one end of each of the capacitors 162 and 163. The other end of the capacitor 162 is grounded, the other end of the capacitor 163 is connected to one end of the resistor 172, and is grounded via the resistor 171. The other end of the resistor 172 is connected to the base of the transistor 166 and grounded via the capacitor 164. The collector of the transistor 166 is connected to one end of the capacitor CX, and the emitter is grounded. The other end of the capacitor CX is connected to the CT terminal of the oscillation circuit 13.

  The low temperature operation ON circuit 18 includes a thermistor Rth, resistors 181 to 184, and a comparator 185 including an operational amplifier. The power supply + Vcc is applied to one end of the thermistor Rth via resistors 182 and 182 connected in series, the connection point of these resistors 181 and 182 is connected to the inverting input terminal of the comparator 185, and the other end of the thermistor 181 is grounded. Has been. A voltage obtained by dividing the power source + Vcc by two resistors 183 and 184 connected in series to the non-inverting input terminal of the comparator 185, that is, a power source voltage + Vcc is divided by the ground side resistor 183 and the power source side resistor 184. Applied voltage. As a result, the output of the comparator 185 is output when the ambient temperature detected by the thermistor 181 is within a low temperature range below a predetermined threshold value that causes the discharge lamps Lamp-1 to Lamp-n to be unlit or partially unlit. When the ambient temperature is higher than the threshold temperature, the output of the comparator 185 is set to low level. That is, for the threshold voltage Vth1 obtained by dividing the voltage + Vcc by the resistors 183 and 184, the resistance values of the resistors 183 and 184 are set so as to correspond to the above threshold temperature. Furthermore, when the temperature below the threshold is detected by the thermistor Rth, the voltage divided by the combined resistance of the resistor 181 and the thermistor Rth and the resistor 182 is equal to or higher than the threshold voltage Vth1. The resistance value and characteristics of the thermistor Rth are selected, and the resistance values of the resistors 181 and 182 are set.

  The frequency changing circuit 19 includes a capacitor 191, a diode 192, resistors 193 and 194, and an N-channel FET 195. A tube current detection voltage V 1 output from the current detection circuit 12 is applied to one end of the capacitor 191, and the other end of the capacitor 191 is connected to the cathode of the diode 192 and one end of the resistor 193. The anode of the diode 192 is grounded, and the other end of the resistor 193 is grounded via the resistor 194 and is connected to the gate of the FET 195. The drain of the FET 195 is connected to the collector of the transistor 166 and one end of the capacitor CX.

  With the above configuration, at the time of start-up, as shown in FIG. 4, when the lamp current falls within a predetermined allowable range including the rated current values of the discharge lamps Lamp-1 to Lamp-n, the differential signal is output from the differentiating circuit 152. Is output, the switching element is kept on for a predetermined time, for example, 0.5 seconds, and the capacitance connected to the CT terminal of the oscillation circuit 13 is a capacitance obtained by connecting the capacitor CT and the capacitor CX in parallel, which is 46 KHz. A frequency signal is output from the oscillation circuit 13 to the drive control circuits 11 and 21. Thus, the drive control circuits 11 and 21 perform switching control of the on / off states of the FETs Q1 to Q4 so that an AC voltage having a frequency of 46 KHz is applied to the discharge lamps Lamp-1 to Lamp-n.

  Since the switching element of the switch circuit 153 is in the off state at the start-up and steady state, only the capacitor CT is connected to the CT terminal of the oscillation circuit 13, and a signal having a frequency of 54 KHz is output from the oscillation circuit 13. Is output to the drive control circuits 11 and 21, and the drive control circuits 11 and 21 turn on / off the FETs Q1 to Q4 so that an AC voltage having a frequency of 54 KHz is applied to the discharge lamps Lamp-1 to Lamp-n. Control switching.

  For example, the current detection resistor R1 detects that the discharge lamps Lamp-1 to Lamp-n are turned on and a current flows. As a result, the tube current detection voltage (about 5V) is input from the current detection circuit 12 to the frequency shift circuit 15 at the time of lighting, which is received by the buffer, rectified, and held by a capacitor of several μF. Furthermore, it is delayed by a resistor provided in series on the input side of the capacitor. The delayed signal is differentiated to pick up the rising edge at which current begins to flow. The switching element is turned on at the rising edge of the differential signal to switch the time constant of the oscillation circuit only for a predetermined time. As an example, when starting up at 54 KHz at the time of starting and the tube current flows about 70% (70 mAmma) or more of the rated current (for example, 100 mArms), it is switched to a low frequency of 46 KHz and is normally maintained for about 0.5 seconds. An operation for returning the lighting frequency to 54 KHz is performed.

  Note that the time for turning on the switching elements of the switch circuit 153 takes into account the characteristics of the circuit and the discharge lamps Lamp-1 to Lamp-n, etc., and all of the discharge lamps Lamp-1 to Lamp-n shift to the lighting state. Thus, it is preferable to appropriately set the time between 0.3 seconds and 3.0 seconds.

  On the other hand, when the ambient temperature is a low temperature that is less than the specified threshold value, at which the discharge lamps Lamp-1 to Lamp-n are not easily lit or partially lit, the output of the comparator 185 of the low temperature operation on circuit 18 is open. The frequency changing circuit 19 is driven. That is, when the ambient temperature is higher than the above threshold, the output of the comparator 185 is low level, so the gate of the FET 195 is low level, the FET 195 is off, and the capacitor CX controls the frequency shift circuit 15 at the time of lighting described above. Only connected in parallel to the capacitor CT. However, when the discharge lamps Lamp-1 to Lamp-n are not lit or partially unlit, the output of the comparator 185 of the low temperature operation on circuit 18 is open at the low temperature below a predetermined threshold, and the FET 195 gate Since a pulse-like high level voltage corresponding to the voltage V1 is applied to and intermittently applied, the FET 195 is repeatedly turned on and off correspondingly. As a result, the capacitor CX is intermittently connected in parallel to the capacitor CT in accordance with the on / off state of the FET 195, so that the drive control circuits 11 and 21 are driven at a low frequency of 46 kHz and at a normal lighting frequency of 54 KHz. The driving of is repeated alternately.

  In the present embodiment, the oscillation frequency (operating frequency of the inverter circuit) is set based on the resonance frequency characteristics of the discharge lamp lighting device 101 shown in FIG. That is, the normal lighting frequency f0 is set between the resonance frequency f1 of the unlit resonance frequency characteristic curve A1 of the discharge lamp lighting device 101 and the resonance frequency f2 of the lighting resonance frequency characteristic curve A2. In this embodiment, at the time of start-up, after the voltage at the point B1 whose operating frequency on the unlit resonance frequency characteristic curve A1 is 54 KHz is applied to the discharge lamps Lamp-1 to Lamp-n, the resonance frequency characteristic is the resonance frequency at lighting. The frequency at which the drive control circuit 11 operates after shifting to the characteristic curve A2 is switched to 46 KHz, and the voltage at the point B2 of the frequency 46 KHz on the lighting resonance frequency characteristic curve A2 is applied to the discharge lamps Lamp-1 to Lamp-n. Then, all the discharge lamps Lamp-1 to Lamp-n are promoted to be in the lighting state, and thereafter, the voltage at the point B3 of the normal lighting frequency 54 KHz on the lighting resonance frequency characteristic curve A2 is changed to the discharge lamps Lamp-1 to Lamp. Applied to -n to maintain the lighting state. Further, when the discharge lamps Lamp-1 to Lamp-n are not lit or partially unlit, the drive control circuit 11 operates at a frequency of 46 KHz at a low temperature below a predetermined threshold, and the lighting resonance frequency. A voltage at a point B2 having a frequency of 46 KHz on the characteristic curve A2 is applied to the discharge lamps Lamp-1 to Lamp-n to promote all the discharge lamps Lamp-1 to Lamp-n to be in a lighting state.

  As shown in FIG. 6, the equivalent circuit of the external electrode type fluorescent tube (EEFL) includes capacitances Ca1 and Ca2 and a discharge lamp portion Lamp that are connected in series to both end electrodes.

  The voltage VL applied to the discharge lamp is composed of voltages Vca1 and Vca2 shared by the capacitances Ca1 and Ca2 and a voltage Vlamp shared by the discharge lamp portion Lamp.

  When partial unlighting occurs at startup, the ratio of the voltages Vca1, Vca2 shared by the capacitances Ca1, Ca2 and the voltage Vlamp shared by the discharge lamp portion Lamp is changed by lowering the frequency of the inverter circuit output. If the current and temperature are constant, the voltage Vlamp of the discharge lamp portion Lamp is substantially constant even if the frequency changes. The voltages Vca1 and Vca2 shared by the capacitances Ca1 and Ca2 increase with the relationship of Xc = 1 / ωC as the frequency decreases.

  That is, the voltage VL applied to the entire discharge lamp load increases by lowering the operating frequency. If there is a non-lighted discharge lamp, no current flows through the non-lighted discharge lamp, so that a voltage drop due to the capacitances Ca1 and Ca2 does not occur, and the voltage VL is applied to the discharge lamp portion Lamp. That is, by lowering the operating frequency, the voltage at both ends of the non-lighting discharge lamp is increased to facilitate lighting.

  Assuming that the capacitances Ca1 and Ca2 are 39 pF, the voltage Vlamp of the discharge lamp portion Lamp is 1255 Vrms, the current flowing through the discharge lamp is 5 mArms and the case of differential driving is calculated as an example, as shown in FIG. By reducing the normal operating frequency from the normal lighting frequency 54KHz to the low lighting frequency 46KHz, which is the partial lighting cancellation frequency, the voltage Vca1.Vca2 shared by the capacitances Ca1 and Ca2 rises by about 130Vrms in total at two locations, and the non-lighting discharge lamp The brightness unevenness of the screen is improved by facilitating lighting or improving the degree of non-lighting.

  In addition, by lowering the operating frequency of the drive control circuits 11 and 21, the operation is performed in a portion where the gain of the resonance frequency characteristic when all the discharge lamps are lit is increased, and the voltage applied to the discharge lamp is increased or the current is increased. The performance for eliminating the partial non-lighting by increasing can be obtained.

  As described above, according to the present embodiment, after the resonance frequency characteristic shifts from the non-lighting resonance frequency characteristic curve A1 to the lighting resonance frequency characteristic curve A2, the inverter circuit operates at a low frequency of 46 KHz. Even if there are discharge lamps Lamp-1 to Lamp-n that are not lit by an applied voltage based on the resonance frequency characteristic curve A1, the discharge lamps Lamp-1 to Lamp-1 are operated by a low frequency 46 KHz operation in the lighting resonance frequency characteristic curve A2. Since the voltage applied to -n is increased and the lighting of the discharge lamps Lamp-1 to Lamp-n is promoted, even when a plurality of discharge lamps Lamp-1 to Lamp-n are connected in parallel, It is possible to prevent the discharge lamps Lamp-1 to Lamp-n of the unit from being unlit or semi-lit. Furthermore, it is possible to prevent partial non-lighting particularly in a low temperature environment where the discharge lamps Lamp-1 to Lamp-n are difficult to turn on, and to improve the uniformity of screen brightness without brightness unevenness from the start.

  In the present embodiment, the discharge lamps Lamp-1 to Lamp-n are applied with a voltage higher than the normal lighting voltage only at startup and at a low temperature to prevent the occurrence of non-lighting or partial non-lighting. Generation of a roaring sound due to magnetostriction of the transformers T1 and T21 when a high voltage is applied to the lamps Lamp-1 to Lamp-n can be minimized.

  In the present embodiment, the normal lighting frequency f0 is set to 54 KHz and the low frequency which is the partial lighting release frequency is set to 46 KHz. However, the present invention is not limited to this. For example, the low frequency that is the partial lighting release frequency may be set to a frequency that is higher than the voltage of the normal lighting frequency f0 on the lighting resonance frequency characteristic curve A2. However, if the low frequency, which is the partial lighting release frequency, is set to a frequency equal to or lower than the resonant frequency f2 of the resonant frequency characteristic curve A2 during lighting, a surge is generated to pass the resonant frequency when shifting from the low frequency to the normal lighting frequency f0. Therefore, it is preferable to set the low frequency, which is the partial lighting release frequency, to a frequency between the resonance frequency f2 of the lighting resonance frequency characteristic curve A2 and the normal lighting frequency f0.

  Next, a second embodiment of the present invention will be described.

  FIG. 8 is a block diagram showing a discharge lamp lighting device 102 in the second embodiment. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. Further, the difference between the second embodiment and the first embodiment is that a ballast capacitor is provided for each of both end electrodes instead of each of the plurality of discharge lamps Lamp-1 to Lamp-n made of an external electrode type fluorescent tube (EEFL). That is, a cold cathode fluorescent tube (CCFL) 41 in which capacitances 42 called in series are connected in series is used as a discharge lamp. The same effect as that of the first embodiment described above can also be obtained by the configuration of the present embodiment.

  Next, a third embodiment of the present invention will be described.

  FIG. 9 is a block diagram showing a discharge lamp lighting device 103 in the third embodiment. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The difference between the third embodiment and the first embodiment is that a current detection value correction circuit 20 is provided in place of the frequency change circuit 19 in the first embodiment.

  As shown in FIG. 10, the current detection value correction circuit 20 includes a capacitor 201, a diode 202, resistors 203 and 204, and an N-channel FET 205. The tube current detection voltage V1 output from the current detection circuit 12 is applied to one end of the capacitor 201, and the other end of the capacitor 201 is connected to the cathode of the diode 202 and one end of the resistor 203. The anode of the diode 202 is grounded, and the other end of the resistor 203 is grounded via the resistor 204 and is connected to the gate of the FET 205. The drain of the FET 205 is connected to the other end of the resistor R6 of the current detection circuits 12 and 22.

  Each of the current detection circuits 12 and 22 includes resistors R2 to R6, diodes D1 and D2, a capacitor C2, and a variable resistor VR1, and includes a secondary winding of the transformers T1 and T21 and resistors R1 and R21. The connection point is connected to the anode of the diode D2 and the cathode of the diode D1. The cathode of the diode D2 is connected to one end of the resistor R2 and grounded via the capacitor C2, and the other end of the resistor R2 is grounded via the resistor R3 and the variable resistor VR1 connected in series. Also connected to the drive control circuits 11 and 21 via resistors R4 and R5 connected in series. One end of the resistor R6 is connected to the connection point of the resistors R4 and R5.

  Although not shown here, a triangular wave voltage is applied to the cathode of the diode D2. Here, the value of the capacitor C2 is set so that the impedance is sufficiently high with respect to the frequency of the triangular wave voltage (burst frequency).

  Thereby, the tube current flowing through the discharge lamps Lamp-1 to Lamp-n is converted into a voltage by the resistor R1, and this detection voltage is combined with the triangular wave voltage at the anode of the diode D2, and then the resistors R2, R3 and the variable When the voltage is divided by the resistor VR1 and the current detection value correction circuit 20 is not operating, the divided voltage is supplied to the drive control circuits 11 and 21 via the resistors R4 and R5 connected in series as a feedback voltage. Is output. The level of the feedback voltage can be changed by the variable resistor VR1. Further, when the current detection value correction circuit 20 is operating, the voltage divided by the resistors R2, R3 and the variable resistor VR1 is further divided by the resistors R4, R6, and this divided voltage is Is output as a feedback voltage to the drive control circuits 11 and 21 via the resistor R5.

  Therefore, when the current detection value correction circuit 20 is operating, the detection current value is corrected so that the current flowing through the discharge lamps Lamp-1 to Lamp-n is lower than the actual current value. The current sensing voltage V1 is output to the drive control circuits 11 and 21 as the feedback voltage. As a result, when the current detection value correction circuit 20 is operating, that is, when the discharge lamps Lamp-1 to Lamp-n are not lit or partially unlit, they are normally lit by the drive control circuits 11, 21. Since a voltage higher than the voltage is applied to the discharge lamps Lamp-1 to Lamp-n, it is possible to prevent the discharge lamps Lamp-1 to Lamp-n from being unlit or partially unlit at a low temperature.

  In the present embodiment, the discharge lamps Lamp-1 to Lamp-n are applied with a voltage higher than the normal lighting voltage only at startup and at a low temperature to prevent the occurrence of non-lighting or partial non-lighting. Generation of a roaring sound due to magnetostriction of the transformers T1 and T21 when a high voltage is applied to the lamps Lamp-1 to Lamp-n can be minimized.

  Next, a fourth embodiment of the present invention will be described.

  FIG. 11 is a block diagram showing a discharge lamp lighting device 104 in the fourth embodiment. In the figure, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted. The difference between the fourth embodiment and the first embodiment is that a current detection value correction circuit 20 in the third embodiment is provided in addition to the configuration of the first embodiment.

  By providing both the frequency changing circuit 19 and the current detection value correcting circuit 20 in this way, the discharge lamps Lamp-1 to Lamp-n are not lit up or partially lit up at low temperatures below a predetermined threshold value. Then, the frequency at which the drive control circuit 11 operates is switched to 46 KHz, and the voltage at the point B2 of the frequency 46 KHz on the lighting resonance frequency characteristic curve A2 is applied to the discharge lamps Lamp-1 to Lamp-n. Drive control is performed by correcting the detected current value so that the current flowing through the discharge lamps Lamp-1 to Lamp-n is lower than the actual current value, while facilitating the 1 to Lamp-n to be lit. The circuits 11 and 21 apply voltage discharge lamps Lamp-1 to Lamp-n higher than the normal lighting voltage to promote all the discharge lamps Lamp-1 to Lamp-n to be in a lighting state. Thereby, it is possible to prevent the discharge lamps Lamp-1 to Lamp-n from being unlit or partially unlit at a low temperature.

  Also in the present embodiment, the discharge lamps Lamp-1 to Lamp-n are applied with a voltage higher than the normal lighting voltage only at startup and at low temperatures to prevent the occurrence of non-lighting and partial non-lighting. Generation of a roaring sound due to magnetostriction of the transformers T1 and T21 when a high voltage is applied to the discharge lamps Lamp-1 to Lamp-n can be minimized.

  In addition, when performing luminance adjustment (dimming) in each of the above-described embodiments, particularly when performing well-known burst dimming (also referred to as duty dimming or time ratio dimming), the voltage is applied in the same manner as at startup. It is possible to promote lighting of the discharge lamp by changing the inverter operating frequency. In this case, the lighting frequency shift circuit 15 is used at the time of burst dimming, and the time constant of the buffer & hold & delay circuit 151 in the lighting frequency shift circuit 15 is set small, that is, the capacitor 162 has a small electrostatic capacity. It is necessary to reduce the time constant by switching to.

  That is, in burst dimming, the brightness of the discharge lamp is adjusted by changing the ratio between the voltage application period and the voltage non-application period to the discharge lamp to alternately switch between the lighting state and the extinguishing state of the discharge lamp. . At this time, it is possible to promote lighting by changing the inverter operating frequency as shown in FIG. 12 or FIG. 13 within the voltage application period.

  In the burst dimming waveform shown in FIG. 12, the frequency is changed in the voltage application period in the same manner as in the start-up of the first embodiment. That is, at the start of voltage application, after applying the voltage at point B1 whose operating frequency is 54 KHz on the unlit resonance frequency characteristic curve A1 to the discharge lamps Lamp-1 to Lamp-n, the resonance frequency characteristic is the resonance frequency characteristic curve at lighting. The frequency at which the drive control circuit 11 operates after shifting to A2 is switched to 46 KHz, and the voltage at the point B2 of the frequency 46 KHz on the lighting resonance frequency characteristic curve A2 is applied to the discharge lamps Lamp-1 to Lamp-n. The discharge lamps Lamp-1 to Lamp-n are promoted to be in the lighting state, and thereafter, the voltage at the point B3 of the normal lighting frequency 54 KHz on the lighting resonance frequency characteristic curve A2 is changed to the discharge lamps Lamp-1 to Lamp-n. To maintain the lighting state.

  In the burst dimming waveform shown in FIG. 13, at the start of voltage application, after applying the voltage at the point B1 whose operating frequency is 46 kHz on the resonance frequency characteristic curve A1 when not lit to the discharge lamps Lamp-1 to Lamp-n, After the characteristic shifts to the lighting resonance frequency characteristic curve A2, the voltage at the point B3 at the normal lighting frequency of 54 KHz on the lighting resonance frequency characteristic curve A2 is applied to the discharge lamps Lamp-1 to Lamp-n to maintain the lighting state is doing.

  In the above embodiment, inverter circuits are provided on both electrode sides of the discharge lamps Lamp-1 to Lamp-n. For example, as a modification of the fourth embodiment, the discharge lamp lighting of the fifth embodiment shown in FIG. As in the device 105, an inverter circuit may be provided only on one electrode side of the discharge lamps Lamp-1 to Lamp-n, and the other electrode may be grounded, or the discharge lamp lighting of the sixth embodiment shown in FIG. The same effects as described above can be obtained by using a known half-bridge driving method such as the device 106 or a known push-pull driving method such as the discharge lamp lighting device 107 of the seventh embodiment shown in FIG. Needless to say, you can.

  Further, when changing the lighting frequency, the frequency may be changed step by step, or the lighting frequency may be changed by continuous scanning.

The block diagram which shows the discharge lamp lighting device of 1st Embodiment of this invention. The block diagram which shows an example of the frequency shift circuit at the time of lighting in 1st Embodiment of this invention The circuit diagram which shows an example of the frequency shift circuit at the time of lighting in 1st Embodiment of this invention, a low temperature operation ON circuit, and a frequency change circuit The figure which shows the transition of the lighting frequency in 1st Embodiment of this invention. The figure which shows the relationship between the resonant frequency characteristic curve and lighting frequency in 1st Embodiment of this invention. The figure explaining the equivalent circuit of the external electrode type | mold fluorescent tube in 1st Embodiment of this invention, and the applied voltage of each part The figure explaining the relationship between the applied voltage to the discharge lamp in 1st Embodiment of this invention, and a lighting frequency. The block diagram which shows the discharge lamp lighting device of 2nd Embodiment of this invention. The block diagram which shows the discharge lamp lighting device of 3rd Embodiment of this invention. The figure which shows the current detection circuit and current detection value correction circuit in 3rd Embodiment of this invention. The block diagram which shows the discharge lamp lighting device of 4th Embodiment of this invention. The figure explaining an example of the burst dimming control in one Embodiment of this invention The figure explaining an example of the burst dimming control in one Embodiment of this invention The block diagram which shows the discharge lamp lighting device of 5th Embodiment of this invention. The block diagram which shows the discharge lamp lighting device of 6th Embodiment of this invention. The block diagram which shows the discharge lamp lighting device of 7th Embodiment of this invention.

Explanation of symbols

  101 to 107 ... discharge lamp lighting device, Q1 to Q4, Q21 to Q24 ... field effect transistor (FET), C1, C21 ... capacitor, T1, T21 ... inverter transformer, R1, R21 ... resistor for current detection, 11, 21 ... Drive control circuit, 12, 22 ... Current detection circuit, 13 ... Oscillation circuit, 15 ... Lighting frequency shift circuit, 18 ... Low temperature operation on circuit, 19 ... Frequency change circuit, 20 ... Current detection value correction circuit, Lamp-1 ~ Lamp-n ... Discharge lamp.

Claims (7)

Inverter drive when each discharge electrode has a capacitance at each end electrode and a voltage is applied via the capacitance, and is connected to a plurality of discharge lamps connected in parallel, and all the discharge lamps are not lit An unlit resonance frequency characteristic representing the relationship between the frequency and the output voltage, and a lighting resonance frequency characteristic representing the relationship between the inverter drive frequency and the output voltage when one or more discharge lamps are lit, When a DC voltage is input, an AC voltage having a normal lighting frequency that is lower than a resonance frequency indicating the maximum voltage value in the resonance frequency characteristics when not lit and higher than a resonance frequency indicating the maximum voltage value in the resonance frequency characteristics when lit. In a discharge lamp lighting device comprising an inverter circuit that generates and applies to the plurality of discharge lamps,
Low temperature operation means for detecting the ambient temperature of the discharge lamp and outputting a drive signal when the detected ambient temperature is a low temperature below a predetermined threshold value;
Operates when the drive signal is output, and operates the inverter circuit at a predetermined low frequency lower than the normal lighting frequency that is higher than the voltage of the normal lighting frequency in the lighting resonance frequency characteristic. A discharge lamp lighting device comprising a low-temperature driving frequency control means. Inverter drive when each discharge electrode has a capacitance at each end electrode and a voltage is applied via the capacitance, and is connected to a plurality of discharge lamps connected in parallel, and all the discharge lamps are not lit An unlit resonance frequency characteristic representing the relationship between the frequency and the output voltage, and a lighting resonance frequency characteristic representing the relationship between the inverter drive frequency and the output voltage when one or more discharge lamps are lit, When a DC voltage is input, an AC voltage having a normal lighting frequency that is lower than a resonance frequency indicating the maximum voltage value in the resonance frequency characteristics when not lit and higher than a resonance frequency indicating the maximum voltage value in the resonance frequency characteristics when lit. An inverter circuit that is generated and applied to the plurality of discharge lamps, and a current value that flows through the discharge lamp is detected. In the discharge lamp lighting device and means for increasing the power supplied to the discharge lamp from,
Low temperature operation means for detecting the ambient temperature of the discharge lamp and outputting a drive signal when the detected ambient temperature is a low temperature below a predetermined threshold value;
And a correction unit that operates when the drive signal is output and corrects the detected current value so that the current flowing through the discharge lamp is lower than the actual current value. Electric light lighting device. Inverter drive when each discharge electrode has a capacitance at each end electrode and a voltage is applied via the capacitance, and is connected to a plurality of discharge lamps connected in parallel, and all the discharge lamps are not lit An unlit resonance frequency characteristic representing the relationship between the frequency and the output voltage, and a lighting resonance frequency characteristic representing the relationship between the inverter drive frequency and the output voltage when one or more discharge lamps are lit, When a DC voltage is input, an AC voltage having a normal lighting frequency that is lower than a resonance frequency indicating the maximum voltage value in the resonance frequency characteristics when not lit and higher than a resonance frequency indicating the maximum voltage value in the resonance frequency characteristics when lit. An inverter circuit that is generated and applied to the plurality of discharge lamps, and a current value that flows through the discharge lamp is detected. In the discharge lamp lighting device and means for increasing the power supplied to the discharge lamp from,
Low temperature operation means for detecting the ambient temperature of the discharge lamp and outputting a drive signal when the detected ambient temperature is a low temperature below a predetermined threshold value;
A correction unit that operates when the drive signal is output and corrects the detected current value so that the current flowing through the discharge lamp is lower than the actual current value;
Operates when the drive signal is output, and operates the inverter circuit at a predetermined low frequency lower than the normal lighting frequency that is higher than the voltage of the normal lighting frequency in the lighting resonance frequency characteristic. A discharge lamp lighting device comprising a low-temperature driving frequency control means. The discharge lamp lighting device according to claim 1 or 3, wherein the low frequency is set between a resonance frequency in the lighting resonance frequency characteristic and the normal lighting frequency.   The discharge lamp lighting device according to any one of claims 1 to 3, wherein the discharge lamp to be lit is an external electrode fluorescent tube.   The discharge lamp lighting device according to any one of claims 1 to 3, wherein the discharge lamp to be lit is a cold cathode fluorescent tube having a ballast capacitor connected in series with an electrode. After the start-up, the ratio of the voltage application period and the voltage non-application period to the discharge lamp is changed to alternately switch between the lighting state and the extinguishing state of the discharge lamp, and the inverter circuit at the low frequency within the voltage application period The discharge lamp lighting according to any one of claims 1 to 3, further comprising: burst dimming means for adjusting brightness by operating the inverter circuit at the normal lighting frequency after operating the lamp. apparatus.

Images