JP2006012660A - Discharge lamp lighting circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp lighting circuit capable of providing satisfactory lighting characteristics without using a ballast element for each discharge lamp or increasing the output voltage of a transformer, and eliminating the dispersion of current of discharge lamps. <P>SOLUTION: This circuit comprises an inverter 3 converting DC voltage to high frequency voltage, a plurality of discharge lamps 11-15 lighted by the high frequency voltage of the inverter 3, and a plurality of current transformers CT1-CT5 provided in conformation to the discharge lamps 11-15. Secondary winding wires 21b-25b of the current transformers CT1-CT5 are connected in series to each discharge lamp 11-15. Between two adjacent current transformers among the plurality of current transformers CT1-CT5, the primary winding wire of the other current transformer is serially connected to the secondary winding wire of one current transformer. Each serial circuit of the discharge lamp, the secondary winding wire of the one current transformer and the primary winding wire of the other current transformer is connected to both output ends of the inverter 3 in parallel. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a discharge lamp lighting circuit that lights a plurality of cold cathode fluorescent lamps (CCFLs), discharge lamps such as external electrode fluorescent lamps and fluorescent lamps with one inverter, and particularly, lights a plurality of discharge lamps connected in parallel. The present invention relates to a simple and inexpensive discharge lamp lighting circuit.

  Conventionally, in a discharge lamp lighting circuit, one cold-cathode tube is lit using one inverter. However, as the number of cold-cathode tube lamps increases, the number of inverters increases proportionally. The cost has increased considerably.

  Therefore, a discharge lamp lighting circuit that lights a large number of cold cathode tubes with one inverter has come to be used. FIG. 8 shows a conventional discharge lamp lighting circuit of this type. In FIG. 8, an AC power source Vac that generates a high-frequency voltage and a transformer T1 constitute an inverter. The primary winding 1a (the number of turns n3) of the transformer T1 is connected to both ends of the AC power supply Vac. Ballast elements C1 to C5 made of capacitors are connected in series to the cold cathode tubes 11 to 15 that are lit by the high frequency voltage from the AC power supply Vac, and are connected to both ends of the secondary winding 1b (number of turns n4) of the transformer T1. Each of the series circuits of the cold cathode tubes 11 to 15 and the ballast elements C1 to C5 is connected.

  The cold cathode tubes 11 to 15 are different in starting voltage and lighting voltage, and the starting voltage needs to be higher than the lighting voltage. For this reason, the ballast elements C1 to C5 are inserted for each of the cold cathode tubes 11 to 15, and the voltage of the secondary winding 1b of the transformer T1 is made higher than the starting voltage to light the cold cathode tubes 11 to 15. When the cold cathode fluorescent lamps 11 to 15 are lit, the voltage is lowered to the lighting voltage and stabilized by the impedance of the ballast elements C1 to C5.

  However, when the cold cathode tubes 11 to 15 are turned on when the power is turned on, the impedance of the load decreases, and the output voltage of the transformer T1 also decreases every time one cold cathode tube is turned on. For this reason, when the last cold-cathode tube is about to be lit, the output voltage of the transformer T1 is further lowered, and the last cold-cathode tube is difficult to light or is not lit.

  Further, in order to surely light up to the last cold cathode tube, the output voltage of the transformer T1 must be further increased, and the impedance of the ballast elements C1 to C5 is further increased to increase the ballast element. It was necessary to increase the voltage drop of C1 to C5.

For example, Patent Document 1 is known as a related technique of the conventional technique. The discharge lamp lighting device described in Patent Document 1 includes an inverter unit, a first resonance circuit connected to an output stage of the inverter unit, and an inductor and a capacitor connected in series, and at least one capacitor. In a discharge lamp lighting device comprising: a second resonance circuit having a load circuit composed of a plurality of discharge lamps; and an oscillation control unit for dimming and lighting the discharge lamp by changing the oscillation frequency of the inverter unit. A second resonant circuit and a load circuit are connected in series at both ends of the capacitor of the resonant circuit. The second resonant circuit and the load circuit are configured so that the lamp currents of the respective discharge lamps are equal to each other, and are adjusted. The oscillation frequency of the inverter part at the time of lighting is set in the vicinity of the natural vibration frequency of the first resonance circuit. For this reason, a plurality of discharge lamps can be stably lit up to a low luminous flux, and the light output difference between the discharge lamps can be reduced.
JP-A-11-238589

  However, in the discharge lamp lighting circuit shown in FIG. 8, the lighting characteristics are improved by inserting the ballast elements C1 to C5 having high impedance, but the power factor of the load is deteriorated. Further, the efficiency is lowered by increasing the output voltage of the transformer T1, the loss is increased, the cost is increased, and the size cannot be reduced.

  Further, in the discharge lamp lighting device of Patent Document 1, since the first resonance circuit, the second resonance circuit, the oscillation control unit, and the like are provided, the configuration of the device is complicated and expensive. It was.

  The present invention is capable of obtaining a favorable lighting characteristic without using a ballast element for each discharge lamp and without increasing the output voltage of the transformer, and discharge lamp lighting that can eliminate variations in the current of each discharge lamp. It is to provide a circuit.

  In order to solve the above-mentioned problems, an invention according to claim 1 is provided corresponding to an inverter that converts a DC voltage into a high-frequency voltage, a plurality of discharge lamps that are lit by the high-frequency voltage of the inverter, and the plurality of discharge lamps. And a secondary winding of the transformer is connected in series to each discharge lamp, and a secondary winding of one transformer is disposed between two adjacent transformers of the plurality of transformers. The primary winding of the other transformer is connected in series, and each of the series circuit of the discharge lamp, the secondary winding of the one transformer, and the primary winding of the other transformer is connected to both ends of the output of the inverter. It is characterized by being connected in parallel.

  The invention of claim 2 is characterized in that, in the discharge lamp lighting circuit according to claim 1, a ballast element is connected in series to a series circuit in which the discharge lamp and the secondary winding of the transformer are connected in series. To do.

  According to a third aspect of the present invention, in the discharge lamp lighting circuit according to the second aspect, the ballast element includes at least one of a capacitor, a reactor, and a leakage inductance of the transformer.

  According to a fourth aspect of the present invention, there is provided the discharge lamp lighting circuit according to any one of the first to third aspects, wherein the detecting means detects the state of the discharge lamp based on the voltage generated in the secondary winding of the transformer. It is characterized by providing.

  According to a fifth aspect of the present invention, in the discharge lamp lighting circuit according to any one of the first to fourth aspects, the inverter is a self-excited oscillation type inverter, and includes a direct current power source and the direct current power source from the direct current power source. And an oscillating unit that oscillates the high-frequency voltage using a DC voltage, and the current flowing through the discharge lamp is changed by changing the DC voltage from the DC power source supplied to the oscillating unit.

  According to a sixth aspect of the present invention, in the discharge lamp lighting circuit according to any one of the first to fourth aspects, the inverter is a separately-excited oscillation type inverter, and includes a DC power source and the DC power source. A converter that converts a DC voltage into the high-frequency voltage, and the current flowing through the discharge lamp is changed by changing a switching frequency of the converter.

  According to a seventh aspect of the present invention, in the discharge lamp lighting circuit according to any one of the first to sixth aspects, a preheating circuit for supplying a preheating current to a filament of the discharge lamp based on the high frequency voltage from the inverter. It is characterized by providing.

  According to the first aspect of the present invention, the secondary winding of the transformer is connected in series to each discharge lamp, and the secondary winding of one transformer is connected to the other secondary winding between two adjacent transformers of the plurality of transformers. Since the primary windings of the transformer are connected in series, the currents of adjacent discharge lamps are the same. That is, since all the discharge lamps can have the same current value, there is no variation in the discharge lamp current. Further, when only one discharge lamp is not lit, the secondary side of the transformer is opened, and a high voltage is output, and the discharge lamp when not lit is lit immediately. Therefore, good lighting characteristics can be obtained without using a ballast element for each discharge lamp and without increasing the output voltage of the transformer.

  According to the invention of claim 2, since the ballast element is connected in series to the series circuit in which the discharge lamp and the secondary winding of the transformer are connected in series, the maximum voltage of the transformer when not lit can be lowered. .

  According to the invention of claim 4, the state of the discharge lamp can be detected by the detecting means based on the voltage generated in the secondary winding of the transformer.

  According to the invention of claim 5, the current flowing through the discharge lamp can be changed by changing the DC voltage from the DC power source supplied to the oscillating unit.

  According to invention of Claim 6, the electric current which flows into a discharge lamp can be changed by changing the switching frequency of a conversion part.

  According to invention of Claim 7, a discharge lamp can be lighted favorably by supplying a preheating current to the filament of a discharge lamp by a preheating circuit.

  Hereinafter, embodiments of a discharge lamp lighting circuit according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of a discharge lamp lighting circuit according to a first embodiment of the present invention. In FIG. 1, an AC power source Vac that generates a high-frequency voltage and a transformer T1 constitute an inverter 3. The primary winding 1a (the number of turns n3) of the transformer T1 is connected to both ends of the AC power supply Vac. Secondary windings 21b to 25b (number of turns n2) of current transformers CT1 to CT5 (current transformer) are connected in series to the cold cathode tubes 11 to 15 that are lit by a high-frequency voltage from the AC power supply Vac.

  Between the two adjacent current transformers (for example, CT1, CT2) among the current transformers CT1 to CT5, the other current transformer (for example, 21b) is connected to the secondary winding (for example, 21b) of one current transformer (for example, CT1). For example, a primary winding (for example, 22a) of CT2) is connected in series, and a series circuit of cold cathode tubes 11 to 15, a secondary winding of one current transformer, and a primary winding of the other current transformer. Are connected in parallel to the secondary winding 1b (number of turns n4) of the transformer T1.

  Next, the operation of the discharge lamp lighting circuit according to the first embodiment configured as described above will be described. First, in each of the current transformers CT1 to CT5, I1 (primary winding current) × n1 (number of turns of the primary winding) = I2 (secondary winding current) × n2 (number of turns of the secondary winding). There is a relationship. The secondary winding 21b of the current transformer CT1 is connected in series to the cold cathode tube 11, and the primary winding 21a of the current transformer CT2 is connected in series to the secondary winding 21b of the current transformer CT1. Yes. For this reason, the current of the cold cathode tube 11 and the cold cathode tube 12 becomes the same current by the current transformer CT2. Similarly, the current in the cold cathode tube 12 and the cold cathode tube 13 becomes the same current by the current transformer CT3. Thus, all the cold cathode tubes of the cold cathode tubes 11 to 15 can have the same current value. Accordingly, there is no variation in the currents of the cold cathode tubes 11 to 15. Further, the power factor becomes approximately 1.

  Moreover, since the hot ends of the cold cathode tubes 11 to 15 are connected in parallel, it is possible to prevent variations in current of the cold cathode tubes 11 to 15 due to stray capacitance.

  Next, the operation at the time of starting the cold cathode tubes 11 to 15 will be described. When the inverter 3 operates to output a high voltage to the secondary winding 1b of the transformer T1, and the high voltage exceeds the starting voltage, the five cold-cathode tubes 11 to 15 are turned on one after another.

  Here, for example, when the four cold-cathode tubes 11 to 14 are turned on and the cold-cathode tube 15 is not lit, the secondary winding 25b side of the current transformer CT1 and the current transformer CT5 is close to no load. It becomes the same as the state where the secondary winding 25b side of the current transformer CT1 and the current transformer CT5 is opened (opened), and a high voltage is generated. For this reason, since a high voltage is applied to the cold cathode tube 15, the cold cathode tube 15 is turned on immediately.

  Therefore, even if the cold cathode tube is turned on late, the supplied voltage increases, the last cold cathode tube 15 is more likely to be turned on, and it is not possible to turn on only one cold cathode tube. That is, when the starting voltage of the cold-cathode tubes that are easily lit among the five lamps is exceeded, all the cold-cathode tubes can be lit. Further, the secondary winding 1b of the transformer T1 can also be a low voltage and the reliability can be improved. Also, since there is no impedance of the ballast element, the voltage can be low when the lamp is lit, and the transformer T1 can be a low voltage and the reliability is improved. . That is, good lighting characteristics can be obtained without using a ballast element for each cold cathode tube and without increasing the output voltage of the transformer.

  After each cold-cathode tube 11-15 is lit, the current of each cold-cathode tube 11-15 is kept at the same value according to the above relational expression. When there is a variation in the voltage of each cold cathode tube 11-15, the difference voltage is applied to each current transformer CT1-CT5 and each current transformer CT1-CT5 absorbs. That is, a voltage that varies among the current transformers CT1 to CT5 is applied, and the current flowing through all the cold cathode tubes 11 to 15 is a constant current determined by the primary winding current and the turn ratio of the current transformers CT1 to CT5. Flows.

  FIG. 2 is a configuration diagram of a discharge lamp lighting circuit according to the second embodiment of the present invention. In the discharge lamp lighting circuit of Example 2 shown in FIG. 2, ballast elements C1 to C5 made of capacitors are connected in series to the cold cathode tubes 11 to 15 in addition to the configuration of Example 1 shown in FIG. It is characterized by that. Since other configurations are the same as those of the first embodiment shown in FIG. 1, the same reference numerals are given to the same portions, and details thereof are omitted.

  The ballast element includes at least one of the capacitor, the reactor, and the leakage inductance of the transformer.

  In the above configuration, assuming that the voltage of the ballast elements C1 to C5 is, for example, AC 200V, the output voltage of the transformer T1 in the steady state is AC 700V + AC 200V = AC 900V.

  On the other hand, when one lamp is not lit, the output voltage of the transformer T1 is increased to AC 960V by AC 60V, and AC 60V is generated in the current transformers CT1 to CT4 of the lit cold cathode tubes 11 to 14. AC240V (AC60V × 4) is generated in the device CT5, and the voltage of the unlit cold cathode tube 15 is AC960V + AC240V = AC1200V. Therefore, the maximum voltage of the current transformer CT5 can be lowered to 240V AC.

  FIG. 3 is a configuration diagram of a discharge lamp lighting circuit according to the third embodiment of the present invention. The discharge lamp lighting circuit of Example 3 shown in FIG. 3 is further provided with diodes D1 to D10 and a voltage detector 27 with respect to the configuration of Example 1 shown in FIG. It is characterized by detecting an abnormality of the above.

  The diodes D1 to D5 are provided corresponding to the cold cathode tubes 11 to 15, and the anodes are connected to the connection points between the cold cathode tubes 11 to 15 and the secondary windings 21b to 25b of the current transformers CT1 to CT5. Each cathode is connected to the input terminal IN 1 of the voltage detector 27. The diodes D6 to D10 are provided corresponding to the cold cathode tubes 11 to 15, and the cathodes are connected to connection points between the cold cathode tubes 11 to 15 and the secondary windings 21b to 25b of the current transformers CT1 to CT5. Each anode is connected to the input terminal IN <b> 2 of the voltage detector 27.

  The voltage detector 27 receives the cathode voltages of the diodes D1 to D5, receives the anode voltages of the diodes D6 to D10, and detects abnormalities of the cold cathode tubes 11 to 15 based on these voltages.

  FIG. 4 is a specific configuration diagram of a voltage detector provided in the discharge lamp lighting circuit according to the third embodiment. The voltage detector 27 shown in FIG. 4 has a Zener diode ZD1 whose cathode is connected to the input terminal IN1 and whose anode is grounded via the resistor R1, and an anode which is connected to the input terminal IN2 and whose cathode is grounded via the resistor R2. And a Zener diode ZD2.

  In the above configuration, when, for example, one of the cold cathode tubes 15 of the cold cathode tubes 11 to 15 is not lit, the voltage of the cold cathode tube 15 becomes a voltage of about AC 1200V, and the current transformer CT5 has an AC of 400V. A voltage will be applied.

  At this time, if the breakdown voltage of the Zener diode ZD1 is set to 400V AC, the Zener diode ZD1 breaks down and a current flows through the path 25b → D5 → ZD1 → R1 → ground. For this reason, the voltage detector 27 can detect the voltage of AC400V of the current transformer CT5 by the voltage across the resistor R1. Therefore, it is possible to detect whether or not there is an unlit cold cathode tube by this detection voltage.

  In addition, when the cold cathode tube is not connected or damaged, a higher voltage is output, so detecting the secondary winding voltage of the current transformer CT detects the unconnected or damaged cold cathode tube. it can.

  FIG. 5 is a configuration diagram of a discharge lamp lighting circuit according to Embodiment 4 of the present invention. Example 4 shown in FIG. 5 is a specific example of the inverter 3a, and the inverter 3a is formed of a self-excited oscillation type AC power source. The inverter 3a converts the DC voltage from the DC power source Vdc1 into a high-frequency voltage by alternately switching the switching elements Q1 and Q2 made of MOSFETs at a switching frequency, and this high-frequency voltage is converted into a transformer T3, a reactor L2, and a capacitor Co. To the cold cathode tubes 11 to 14.

  In the inverter 3a, a second primary winding 1a2 (number of turns n3) is connected in series to the first primary winding 1a1 (number of turns n3) of the transformer T3, and the first primary winding 1a1 and the second primary winding 1a1 The connection point with the primary winding 1a2 is connected to the positive electrode of the DC power supply Vdc1 through the reactor L1. A resonance capacitor Cp is connected to both ends of the series circuit of the first primary winding 1a1 and the second primary winding 1a2, and a series circuit of the switching element Q1 and the switching element Q2 is connected to both ends of the series circuit. . A connection point between the switching element Q1 and the switching element Q2 is grounded.

  One end of the feedback winding 1c (number of turns n5) of the transformer T3 is connected to the gate of the switching element Q2, and the other end of the feedback winding 1c is connected to the gate of the switching element Q1 and one end of the resistor R3. The other end is connected to a connection point between the positive electrode of DC power supply Vdc1 and reactor L1. One end of the secondary winding 1b (number of turns n4) of the transformer T3 is connected to each of the cold cathode tubes 11 to 14 via a reactor L2, and a connection point between the reactor L2 and each of the cold cathode tubes 11 to 14 is connected to a capacitor Co. The other end of the capacitor Co and the other end of the secondary winding 1b are grounded. Here, the reactor L2 is the leakage inductance of the transformer T3, and Co is the stray capacitance of the winding of the transformer T3.

  Switching elements Q1, Q2, resonance capacitor Cp, and transformer T3 constitute a self-excited oscillation unit that oscillates a high-frequency voltage by a DC voltage from DC power supply Vdc1.

  Next, the operation of the inverter 3a will be described. First, when the switching element Q1 is turned on, a current flows through a path of Vdc1-> L1-> 1a1-> Q1-> ground. Next, when the switching element Q1 is turned off and the switching element Q2 is turned on, a current flows through a path of Vdc1-> L1-> 1a2-> Q2-> ground. For this reason, a high frequency voltage is generated in the secondary winding 1b of the transformer T3, and this high frequency voltage is supplied to each of the cold cathode tubes 11 to 14 via the reactor L2 and the capacitor Co.

  Further, since the inductances of the first primary winding 1a1 and the second primary winding 1a2 have the same value and are wound around the same core, the inductance of the first primary winding 1a1 Is LP1, the series combined inductance Lp is Lp = 4 × LP1. The resonance frequency is substantially determined by the series combined inductance Lp and the resonance capacitor Cp. Further, since the switching element Q1 and the switching element Q2 are driven by a resonance voltage generated in the feedback winding 1c of the transformer T3, the switching frequency also matches the resonance frequency.

  Moreover, the high frequency voltage can be changed by changing the DC voltage of the DC power supply Vdc1, and the current flowing through the cold cathode tubes 11 to 14 can be changed by the changed high frequency voltage.

  FIG. 6 is a configuration diagram of a discharge lamp lighting circuit according to the fifth embodiment of the present invention. A fifth embodiment shown in FIG. 6 is a specific example of the inverter 3b, and the inverter 3b includes a separately-excited oscillation type AC power supply. The inverter 3b alternately switches the DC voltage from the DC power supply Vdc1 by switching the switching elements Q1 and Q2 made of MOSFETs via the drive circuit 31 with a high-frequency signal (switching frequency) oscillated by the oscillation control unit 29. This voltage is converted into a voltage, and this high-frequency voltage is supplied to the cold cathode tubes 11 to 14 via a transformer T1 and a resonance circuit including a reactor L2 and a capacitor Cf.

  In the inverter 3b, a series circuit of a switching element Q1, a capacitor Cc, a reactor L1, and a primary winding 1a (number of turns n3) of a transformer T1 is connected to both ends of the DC power supply Vdc1. The source of the switching element Q1 is connected to the drain of the switching element Q2, and the source of the switching element Q2 is grounded. A high frequency signal (switching frequency) is input from the drive circuit 31 to each gate of the switching elements Q1 and Q2.

  One end of the secondary winding 1b (the number of turns n4) of the transformer T1 is connected to each of the cold cathode tubes 11 to 14 via the reactor L2, and the connection point between the reactor L2 and each of the cold cathode tubes 11 to 14 includes a capacitor Cf. The other end of the capacitor Cf and the other end of the secondary winding 1b are grounded. Here, the reactor L2 is the leakage inductance of the transformer T1, and Cf is the stray capacitance of the winding of the transformer T1.

  Next, the operation of the inverter 3b will be described. First, when the switching element Q1 is turned on by a high frequency signal from the drive circuit 31, a current flows through a path of Vdc1 → Q1 → Cc → L1 → 1a → ground. Next, when the switching element Q1 is turned off and the switching element Q2 is turned on, a current flows through a path of 1a → L1 → Cc → Q2 → ground. For this reason, a high frequency voltage is generated in the secondary winding 1b of the transformer T1, and this high frequency voltage is supplied to the cold cathode tubes 11 to 14 through a resonance circuit of the reactor L2 and the capacitor Cf. The high frequency voltage is changed by changing the switching frequency of the oscillation control unit 29, and the changed high frequency voltage is supplied to the cold cathode tubes 11 to 14. Therefore, the current flowing through the cold cathode tubes 11 to 14 can be changed by the changed high frequency voltage.

  In addition, when the inductance of reactor L2 is insufficient, the reactor may be externally attached, and when the capacity of capacitor Cc is insufficient, a capacitor may be externally attached.

  FIG. 7 is a configuration diagram of a discharge lamp lighting circuit according to Embodiment 6 of the present invention. The discharge lamp lighting circuit of Example 6 shown in FIG. 7 is an example applied to a fluorescent lamp as a discharge lamp.

  In the discharge lamp lighting circuit shown in FIG. 7, the DC voltage from the DC power supply Vdc1 is alternately switched between switching elements Q1 and Q2 made of MOSFETs via a drive circuit 31 by a high-frequency signal oscillated by the oscillation control unit 29. The high-frequency voltage is converted into a high-frequency voltage, and the high-frequency voltage is supplied to the fluorescent lamps 11a to 14a through the resonance circuit constituted by the reactor L1 and the capacitor C1 and the coupling capacitor Co.

  The transformer T4 includes a reactor L1 including a primary winding, and secondary windings 41 to 48 that are provided two for each fluorescent lamp 11a to 14a. Capacitors C11 to C18 are connected to the secondary windings 41 to 48 in series. One secondary winding (for example, 41) of the pair of secondary windings (for example, 41 and 42) is connected to one end of a fluorescent lamp (for example, 11a) via a capacitor (for example, C11), and the other secondary winding. The winding (for example, 42) is connected to the other end of the fluorescent lamp (for example, 11a) through a capacitor (for example, C12).

  The secondary windings 41 to 48 constitute a preheating circuit that supplies a preheating current to the filaments of the fluorescent lamps 11a to 14a by the generated high frequency voltage, that is, a heater power source. That is, since the secondary windings 41 to 48 supply a preheating current to the filaments of the fluorescent lamps 11a to 14a, the fluorescent lamps 11a to 14a can be lit well.

  In addition, this invention is not limited to the discharge lamp lighting circuit of Example 1 thru | or Example 6 mentioned above, For example, the discharge lamp lighting which combined the 2 or more Example of Example 1 thru | or Example 6 was combined. Of course, the present invention can also be applied to a circuit.

  The present invention is applicable to a discharge lamp lighting circuit that lights a plurality of cold cathode tubes, discharge lamps such as external electrode fluorescent lamps and fluorescent lamps.

It is a block diagram of the discharge lamp lighting circuit of Example 1 of this invention. It is a block diagram of the discharge lamp lighting circuit of Example 2 of this invention. It is a block diagram of the discharge lamp lighting circuit of Example 3 of this invention. It is a specific block diagram of the voltage detector provided in the discharge lamp lighting circuit of Example 3 of the present invention. It is a block diagram of the discharge lamp lighting circuit of Example 4 of this invention. It is a block diagram of the discharge lamp lighting circuit of Example 5 of this invention. It is a block diagram of the discharge lamp lighting circuit of Example 6 of this invention. It is a block diagram of the conventional discharge lamp lighting circuit.

Explanation of symbols

1a, 21a-25a Primary windings 1b, 21b-25b Secondary windings 11-15 Cold-cathode tubes 11a-14a Fluorescent lamp Vac AC power supply Vdc1 DC power supplies T1, T3, T4 Transformers CT1-CT5 Current transformers C1-C5 , Ballast element 27 voltage detector 29 oscillation control unit 31 drive circuit Q1, Q2 switching element L1, L2 reactor R1-R3 resistance ZD1, ZD2 Zener diode

Claims (7)

An inverter that converts a DC voltage into a high-frequency voltage, a plurality of discharge lamps that are lit by the high-frequency voltage of the inverter, and a plurality of transformers that are provided corresponding to the plurality of discharge lamps,
The secondary winding of the transformer is connected in series to each discharge lamp, and the primary winding of the other transformer is connected to the secondary winding of one transformer between two adjacent transformers of the plurality of transformers. A series circuit of the discharge lamp, the secondary winding of the one transformer, and the primary winding of the other transformer is connected in series, and is connected in parallel to both ends of the output of the inverter. A discharge lamp lighting circuit.   2. The discharge lamp lighting circuit according to claim 1, wherein a ballast element is connected in series to a series circuit in which the discharge lamp and the secondary winding of the transformer are connected in series.   The discharge lamp lighting circuit according to claim 2, wherein the ballast element includes at least one of a capacitor, a reactor, and a leakage inductance of the transformer.   The discharge lamp lighting circuit according to any one of claims 1 to 3, further comprising detection means for detecting a state of the discharge lamp based on a voltage generated in a secondary winding of the transformer.   The inverter is a self-excited oscillation type inverter, and includes a direct current power source and an oscillating unit that oscillates the high frequency voltage by the direct current voltage from the direct current power source, from the direct current power source supplied to the oscillating unit The discharge lamp lighting circuit according to any one of claims 1 to 4, wherein the current flowing through the discharge lamp is changed by changing the DC voltage.   The inverter is a separately-excited oscillation type inverter, and includes a direct-current power source and a conversion unit that converts the direct-current voltage from the direct-current power source into the high-frequency voltage, and changing the switching frequency of the conversion unit The discharge lamp lighting circuit according to any one of claims 1 to 4, wherein a current flowing through the discharge lamp is changed. The discharge lamp lighting circuit according to any one of claims 1 to 6, further comprising a preheating circuit that supplies a preheating current to a filament of the discharge lamp based on the high-frequency voltage from the inverter.

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