JP2016225256A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize the filament current, while down-sizing and standardizing a lighting device, and to add various functions related to the output to a filament in an appropriate mode, in a discharge lamp lighting device for lighting a low voltage discharge lamp having a pair of thermal cathode filaments.SOLUTION: A discharge lamp lighting device (1) includes a first power supply circuit (2) for supplying a low voltage discharge lamp (5) with a lamp voltage or current, a second power supply circuit (3) having an insulated DC/DC converter (30) for supplying first and second filaments (51, 52), respectively, with first and second DC filament currents, converted from a DC voltage inputted from a part of first power supply circuit, and first and second current detection circuits (31, 33) for detecting the first and second filament currents, respectively, and a control section (4) for controlling the DC/DC converter so that the first current detection value matches a target value, and stopping the output operation of the DC/DC converter when the second current detection value deviates from a predetermined range.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a discharge lamp lighting device for lighting a low pressure discharge lamp having a hot cathode filament.

  Patent Document 1 discloses a discharge lamp lighting device capable of supplying a low-frequency filament current. The lighting device includes a commercial power transformer as a filament power source, the primary side of the transformer is connected to the commercial power source, and the two secondary windings are connected to a pair of filaments. That is, a low frequency voltage generated by stepping down from the commercial power supply voltage is applied to the filament, and a filament current flows.

  Patent Document 2 discloses a discharge lamp lighting device that supplies a lamp current and a filament current of a fluorescent lamp from a half-bridge circuit. In this discharge lamp lighting device, the current flowing through the filament is converted into a voltage value by a shunt resistor inserted and connected to one filament current path, and the driving frequency of the half-bridge circuit is controlled based on this voltage. Thereby, the filament current, that is, the amount of preheating is controlled.

Japanese Patent Laid-Open No. 6-251883 JP-A-10-340791

However, the filament current supply configuration (hereinafter referred to as “commercial power transformer system”) as in Patent Document 1 has the following problems.
First, there is a problem that the startability of the discharge lamp is lowered and further the lighting characteristics are lowered. Specifically, there is a problem that the filament current can be reduced due to a voltage drop due to the resistance component of the output wiring between the lighting device (filament power supply transformer) and the discharge lamp. For example, when the resistance value of the filament is 2.5Ω, the length of the output wiring is 50 m, and the conductor cross-sectional area of the output wiring is 0.75 mm ² , the resistance value of the output wiring is about 2. 5Ω. Since the commercial power transformer acts as a voltage source and the output wiring is connected in series with the filament, in the above case, only about half the voltage, that is, about half of the current is supplied to the filament compared to when the output wiring is sufficiently short. It will be. As a result, in the preheating period before starting the lamp, the electron emitting material emitted from the filament becomes insufficient, and the startability of the discharge lamp decreases. In addition, it is not preferable from the viewpoint of lighting characteristics of the discharge lamp that an appropriate value of current is not supplied to the filament even during stable lighting after starting the lamp. To reduce the influence of this voltage drop, use a wire with a large conductor cross-sectional area to reduce the resistance value of the output wire, or unify the length of the output wire for all lighting devices. Although it is theoretically possible to design in consideration of the influence in advance, these measures are not practical from the viewpoint of wiring cost and wiring management. Therefore, according to the commercial power transformer system, it is difficult to optimize the filament current according to the length of the output wiring, and the startability of the discharge lamp is lowered and proper lighting characteristics cannot be ensured.

  Secondly, there are problems of increasing the size of the lighting device and increasing the lineup. As described above, in the commercial power supply transformer system, since it is necessary to use a transformer for commercial frequency, its size and weight increase. Also, since a transformer with a turn ratio corresponding to the voltage of the commercial power supply and the assumed filament voltage is required, it is necessary to prepare different transformers according to the specifications of the commercial power supply and the discharge lamp. Standardization is difficult. Therefore, according to the commercial power transformer system, it is difficult to reduce the size and standardize the filament power source or the lighting device.

  Thirdly, appropriate addition of various functions related to output to the filament becomes a problem. Specifically, it is desirable to add a function of supplying a desired current to the filament as described above. On the other hand, there is a possibility that a short-circuit state or an open state may occur in the output to the filament, and it is necessary to add a function for preventing failure of the filament power supply or lighting device due to such a short-circuit state or open state. . In addition, the lamp has a pair of filaments, but it is desirable that the balance of the filament currents of both is not disturbed by the added circuit elements while adding the above functions. As an example in which the balance of the filament current is lost, as in Patent Document 2, in a configuration in which a resistance for current detection is inserted and connected to one filament, the current of the filament becomes the current of the other filament due to loss at this resistance. Will be less than. Of course, if two sets of circuit configurations for realizing all the functions described above are added to both filaments, the balance of the filament current is ensured, but this complicates and increases the cost of the lighting device. Therefore, it is necessary to provide a simple and low-cost configuration for various functions related to output to both filaments while maintaining the balance of the filament current.

  Therefore, the present invention provides a discharge lamp lighting device for lighting a low-pressure discharge lamp having a pair of hot cathode filaments, optimizes the filament current regardless of the length of the output wiring, and achieves downsizing and standardization of the lighting device, and It is an object to add various functions related to output to a hot cathode filament in an appropriate manner.

  A discharge lamp lighting device for lighting a low pressure discharge lamp having first and second hot cathode filaments according to the present invention includes a first power supply circuit for supplying a lamp voltage or a lamp current to the low pressure discharge lamp, and a first power supply. An insulating type that converts a DC voltage input from a part of the circuit into a DC first and second filament current and supplies the first and second filament currents to the first and second hot cathode filaments, respectively. A DC / DC converter, a first current detection circuit for detecting a first filament current, a second power supply circuit having a second current detection circuit for detecting a second filament current, and a first current detection circuit Constant current control is performed to control the DC / DC converter so that the detected first current detection value matches the target value, and the second current detection value detected by the second current detection circuit is And a configured controlled unit to execute the protection operation to stop the output operation of the DC / DC converter when the constant range.

  According to the discharge lamp lighting device of the present invention, the direct current voltage input from a part of the main power supply circuit is converted into direct current first and second filament currents by the DC / DC converter of the filament power supply circuit. While the filament current is constant-current controlled by the control unit, the output operation of the DC / DC converter is stopped when the second filament current is out of the predetermined range. With such a configuration, a desired value of current can be applied to the filament regardless of the voltage drop caused by the resistance component of the output wiring from the discharge lamp lighting device to the low pressure discharge lamp. As a result, the filament current is optimized regardless of the length of the output wiring, and it becomes possible to improve the startability of the low-pressure discharge lamp and ensure proper lighting characteristics during stable lighting. In addition, since the second power supply circuit is constituted by a DC / DC converter, the discharge lamp lighting device is greatly reduced in size as compared with a commercial power transformer system using a commercial power transformer. Further, since the second power supply circuit is constituted by a DC / DC converter, the second power supply circuit having substantially the same circuit configuration regardless of the value of the input power supply voltage or the type of the low pressure discharge lamp. Since it can be employed, it is possible to standardize the discharge lamp lighting device. Furthermore, since the second power supply circuit is protected when the second filament current is abnormal while the constant current control of the first filament current is being performed, protection against abnormal output to both hot cathode filaments is performed. Function is realized. Since the constant current control is not required in the circuit that realizes the protection operation of the second filament current, it is more than the case where two sets of constant current control circuits are provided for the first and second hot cathode filaments. A simple and low-cost configuration is realized.

  Here, the first current detection circuit comprises a first resistance element inserted and connected to the first filament current path, and the second current detection circuit is inserted and connected to the second filament current path. Preferably, the resistance values of the first and second resistance elements are set so that the first filament current and the second filament current are equal. Thereby, the balance of the 1st and 2nd filament current is ensured.

  The second power supply circuit detects the output voltage of the first output circuit that outputs the first filament current, the second output circuit that outputs the second filament current, and the first output circuit. And the control unit is configured to control the DC / DC converter so that a voltage detection value detected by the first voltage detection circuit is equal to or lower than an upper limit value. Thereby, the protection function with respect to the open state of the output to the 1st hot cathode filament is strengthened.

  The second power supply circuit detects the output voltage of the first output circuit that outputs the first filament current, the second output circuit that outputs the second filament current, and the second output circuit. And the control unit is configured to perform a protection operation when the voltage detection value detected by the second voltage detection circuit is outside a predetermined range. Thereby, the protection function against the open state of the output to the second hot cathode filament is reinforced with a simple and low-cost configuration.

  Further, in the preheating period after the start of the DC / DC converter and before the lamp voltage is output from the first power supply circuit, the control unit sets the target value stepwise or continuously in a predetermined period immediately after the start of the preheating period. May be configured to be raised. As a result, even if the output to the second hot cathode filament is short-circuited or opened, the protection operation is performed during the predetermined period, and thereafter, it is prevented that a large stress is applied to the circuit component. The

  Further, in a predetermined period including a part of the preheating period after the start of the DC / DC converter and before the lamp voltage is output from the first power supply circuit, the control unit sets the target value in the stable lighting period. And the protection operation may be invalidated. As a result, the filament heating is accelerated in the predetermined period, so that the preheating period is shortened to obtain a quick lighting operation and prevent the malfunction of the protective function.

  Moreover, it is preferable that a DC / DC converter consists of a flyback converter. Thereby, each of the advantageous effects described above is realized with a simple configuration.

It is a figure which shows the circuit structure of the discharge lamp lighting device by the 1st Embodiment of this invention. It is a figure which supplements 1st Embodiment. It is a figure explaining operation | movement of the discharge lamp lighting device by 1st Embodiment. It is a figure which shows the circuit structure of the discharge lamp lighting device by the 2nd and 3rd embodiment of this invention. It is a figure which supplements 2nd and 3rd embodiment. It is a figure which shows the alternative circuit structure of the discharge lamp lighting device by 2nd and 3rd embodiment. It is a figure explaining operation | movement of the discharge lamp lighting device by 2nd Embodiment. It is a figure explaining an example of operation of a discharge lamp lighting device by a 3rd embodiment. It is a figure explaining the other example of operation | movement of the discharge lamp lighting device by 3rd Embodiment. It is a figure which shows partially the circuit structure of the discharge lamp lighting device by the modification of this invention.

<First Embodiment>
FIG. 1 shows a circuit configuration of a discharge lamp lighting device 1 (hereinafter referred to as “lighting device 1”) according to a first embodiment of the present invention. The lighting device 1 includes a main power supply circuit 2, a filament power supply circuit 3, and a control unit 4. The lighting device 1 is supplied with power from an AC power source AC such as a commercial power source, and supplies power to the low-pressure discharge lamp 5 (hereinafter referred to as “discharge lamp 5”) through output wirings W1, W2, W3, and W4. The igniter 6 is connected to the discharge lamp 5 side on the output wirings W3 and W4 as necessary. Specifically, the lighting device 1 has output terminals T1, T2, T3, and T4, and the discharge lamp 5 (or a unit that includes the discharge lamp 5 and the igniter 6, hereinafter the same) has input terminals T5, T6, T7, and The output wirings W1, W2, W3, and W4 are connected between the terminals T1, T2, T3, and T4 and the terminals T5, T6, T7, and T8, respectively.

  The discharge lamp 5 has a pair of hot cathode filaments 51 and 52 (hereinafter referred to as “filaments 51 and 52”, respectively). Filament 51 is connected to terminals T7 and T8, and filament 52 is connected to terminals T5 and T6 (via igniter 6 if igniter 6 is connected). When the filaments 51 and 52 are heated, an electron discharge substance contributing to the discharge is released.

  In addition, the definition of the term in this specification is as follows. The voltage applied to both ends of the discharge lamp 5 (that is, between the filaments 51-52) and the energized current are referred to as “lamp voltage” and “lamp current”, respectively. The currents flowing through the filaments 51 and 52 are collectively referred to as “filament current”, and the currents flowing through the filament 51 and the filament 52 are referred to as “filament current i51” and “filament current i52”, respectively. In addition, the operation of starting discharge when the discharge lamp 5 breaks down is called “lamp start”, the operation in which the filament current is energized before starting the lamp is called “preheating”, and the lamp current is energized after starting the lamp. This operation is called “stable lighting”. As for the filament current, the filament current flowing during the preheating period is also referred to as “preheating current”. The constant current control of the filament current refers to a control for matching the filament current value with a certain target value, and whether the target value is fixed or fluctuates does not affect the definition of this term. In the following description, the division of each circuit element into each circuit is for convenience of description and does not restrict the present invention.

  The main power supply circuit 2 includes a rectifier circuit 20, a boost converter 22, a step-down converter 24, and a full bridge circuit 25. In general, the input voltage from the AC power supply AC is rectified by the rectifier circuit 20, the rectified output of the rectifier circuit 20 is boosted by the boost converter 22, and the boosted output of the boost converter 22 is stepped down by the step-down converter 24. Is converted into an alternating current by the full bridge circuit 25. The power converted by the full bridge circuit 25 is supplied between both ends of the discharge lamp 5 via the output wirings W1 and W4. That is, the main power supply circuit 2 forms a DC / AC converter by the boost converter 22, the step-down converter 24, and the full bridge circuit 25, and supplies a low-frequency lamp voltage or current to the discharge lamp 5 as will be described later.

  The rectifier circuit 20 includes a full-wave rectifier circuit such as a diode bridge. When the input power source is not an AC power source but a DC power source such as a battery, the rectifier circuit 20 is not necessary. In addition, an input circuit (not shown) such as a noise filter, a current fuse, or a varistor is provided in front of or after the rectifier circuit 20 as necessary.

  The boost converter 22 includes a switching element 221 such as a MOSFET, an inductor 222, a diode 223, and a smoothing capacitor 224, and boosts and smoothes the rectified output of the rectifier circuit 20. When the switching element 221 is turned on, a current flows from the inductor 222 to the switching element 221, and energy is stored in the inductor 222. When the switching element 221 is turned off, the current stored in the inductor 222 causes a current to flow from the inductor 222 to the diode 223 to the smoothing capacitor 224, and the smoothing capacitor 224 is charged. The switching element 221 is PWM-driven by the control unit 4 (control circuit 40) so that the boosted output voltage of the boost converter 22 becomes a predetermined value. A node having the same potential as the low potential side electrode of the smoothing capacitor 224 is referred to as a ground G1.

  The step-down converter 24 includes a switching element 241 such as a MOSFET, an inductor 242, a diode 243, and a capacitor 244, and generates a limited current from the step-up output of the step-up converter 22. When the switching element 241 is turned on, a current flows through the switching element 241 → the inductor 242 → the full bridge circuit 25 → the discharge lamp 5 → the full bridge circuit 25 → the current detection resistor 246, and energy is stored in the inductor 242. When the switching element 241 is turned off, current flows in the inductor 242 → the full bridge circuit 25 → the discharge lamp 5 → the full bridge circuit 25 → the current detection resistor 246 → the diode 243 due to the energy stored in the inductor 242. Capacitor 244 smoothes the output of step-down converter 24. The switching element 241 is PWM-driven by the control unit 4 (control circuit 40), and the ON width (ON duty) is determined by the control circuit 40.

  Step-down converter 24 includes a voltage detection circuit 245 and a current detection circuit 246. The voltage detection circuit 245 includes a resistance voltage dividing circuit connected in parallel to the output terminal of the step-down converter 24, and a divided voltage value (hereinafter referred to as “detected value A”) indicated by the node A is input to the control circuit 40. Thereby, the output voltage of step-down converter 24 is detected. The ramp voltage value is substantially equal to the output voltage value of step-down converter 24. The current detection circuit 246 is formed of a low resistance element, is inserted into the output current path of the step-down converter 24, and a voltage value (hereinafter referred to as “detection value B”) generated in the current detection circuit 246 shown at the node B is supplied to the control circuit 40. Entered. Thereby, the output current of step-down converter 24 is detected. The lamp current value is substantially equal to the output current value of the step-down converter 24.

  The full bridge circuit 25 constitutes a full bridge including switching elements 251, 252, 253 and 254 made of MOSFET or the like, and converts the direct current output of the step-down converter 24 into alternating current. A connection point between the switching elements 251 and 252 is connected to the output wiring W1 through the terminal T1, and a connection point between the switching elements 253 and 254 is connected to the output wiring W4 through the terminal T4. As a result, the AC output from the full bridge circuit 25 is supplied to the discharge lamp 5. The switching elements 251 and 254 and the switching elements 252 and 253 are alternately turned on and off at a frequency of about 50 Hz to 1 kHz (hereinafter referred to as “low frequency”) by a driver included in the control circuit 40. Thereby, a voltage or current of a low frequency rectangular wave is applied or energized to the discharge lamp 5 via the output wirings W1 and W4.

  The filament power supply circuit 3 includes a DC / DC converter 30, a current detection circuit 31, a voltage detection circuit 32, a current detection circuit 33, and a voltage detection circuit 34. As an outline, the filament power supply circuit 3 converts a DC voltage input from the output terminal of the boost converter 22 into a two-output DC current. One output is supplied to the filament 51 via the output wirings W3 and W4, and the other output is supplied to the filament 52 via the output wirings W1 and W2. As a result, a DC filament current is supplied to each of the filaments 51 and 52.

  The DC / DC converter 30 includes a switching element 301 made of a MOSFET or the like, a transformer 302, a diode 303 and an output capacitor 304 of the output circuit 30a, and a diode 305 and an output capacitor 306 of the output circuit 30b. A step-down converter). The primary-side reference potential of the DC / DC converter 30 is the ground G1, and the secondary-side reference potential is a node having the same potential as the low-potential-side electrode of the output capacitor 304 (hereinafter referred to as “ground G2”). In FIG. 1, electrolytic capacitors are illustrated as the output capacitors 304 and 306, but the output capacitors 304 and 306 may be film capacitors or the like as long as the high-frequency ripple due to the switching operation of the switching element 301 can be removed.

  In the DC / DC converter 30, energy is accumulated by the primary winding of the transformer 302 during the ON period of the switching element 301, and the energy is output to the secondary winding side of the transformer 302 during the OFF period of the switching element 301. The switching element 301 is PWM-driven by the control circuit 40 at a high frequency of about several tens kHz to 100 kHz. In the output circuit 30a, the output of one secondary winding is charged to the capacitor 304 via the diode 303, and in the output circuit 30b, the output of the other secondary winding is charged to the capacitor 306 via the diode 305. The output of the DC / DC converter 30 is determined by the ON duty (ON width) in the PWM drive of the switching element 301, the turn ratio of the secondary winding to the primary winding of the transformer 302, and the like. The output current from the output circuit 30a flows from terminal T4 → output wiring W4 → terminal T8 → igniter 6 (transformer 604) → filament 51 → igniter 6 (transformer 604) → terminal T7 → output wiring W3 → terminal T3. i51. On the other hand, the output current from the output circuit 30b flows through the terminal T1, the output wiring W1, the terminal T5, the filament 52, the terminal T6, the output wiring W2, and the terminal T2, and becomes a filament current i52.

  The current detection circuit 31 includes a current detection resistor 310, and detects the output current of the output circuit 30a (that is, the filament current i51). The current detection resistor 310 is a low resistance element inserted and connected between the ground G2 and the terminal T3 (output wiring W3), and a voltage proportional to the filament current i51 is generated in the current detection resistor 310. A detected current value detected by the current detection resistor 310 is input to a feedback circuit 41 described later.

  The voltage detection circuit 32 comprises a voltage dividing resistor circuit connected in parallel to the output capacitor 304, and detects the output voltage of the output circuit 30a. This output voltage is a voltage obtained by subtracting the voltage drop across the wires W3 and W4 and the secondary winding of the transformer 604 from the voltage across the filament 51, and is also a voltage that indirectly indicates the voltage across the filament 51. The output voltage value of the output circuit 30a detected by the voltage detection resistor 32 is input to a feedback circuit 41 described later.

  The current detection circuit 33 includes a current detection resistor 330 and a photocoupler 331, and detects an output current (that is, a filament current i52) of the output circuit 30b. The current detection resistor 330 is composed of a low resistance element inserted and connected between the negative terminal of the output capacitor 306 and the terminal T2 (output wiring W2), and a voltage proportional to the filament current i52 is generated in the current detection resistor 330. The anode end of the photodiode of the photocoupler 331 is connected to the high potential end of the current detection resistor 330, and the cathode end of the photodiode is connected to the low potential end of the current detection resistor 330. The phototransistor of the photocoupler 331 is connected to the control circuit 40 with the reference potential as the ground G1. For example, the collector terminal of the phototransistor may be connected to the control power supply of the control circuit 40 via a resistor (not shown), and the emitter terminal may be connected to the ground G1. Alternatively, the collector terminal of the phototransistor may be connected to the control power supply of the control circuit 40, and the emitter terminal may be connected to the ground G1 via a resistor (not shown). In any case, the output value D (hereinafter referred to as “detected value D”) of the phototransistor of the photocoupler 331 changes in accordance with the increase or decrease of the voltage of the current detection resistor 330 (that is, the filament current i52).

  The current detection circuit 33 realizes a protection function when the output circuit 30a is short-circuited. For example, the voltage of the current detection resistor 330 increases when a short circuit occurs between the output wirings W1 and W2 due to erroneous wiring or when the filament 52 has a short circuit failure. When the voltage of the current detection resistor 330 increases and the detection value D falls outside the predetermined range, the control circuit 40 determines the output short-circuit state, and stops the output operation of the DC / DC converter 30, that is, the driving of the switching element 301.

  Here, the resistance value of the current detection resistor 310 and the resistance value of the current detection resistor 330 are set so that the filament current i51 and the filament current i52 are substantially equal. This ensures a balance between both filament currents. For example, when the igniter 6 is connected, the voltage at both ends of the filaments 51 and 52 is equalized in consideration of the voltage drop due to the secondary winding of the transformer 604 of the igniter 6 described later. The resistance value of the voltage detection resistor 330 is set to be slightly larger than the resistance value. Note that the number of turns of the secondary winding of the transformer 302 is limited due to the design of the DC / DC converter 30 (the number of turns needs to be reduced), and by adjusting the ratio of the secondary turns to the output circuits 30a and 30b. It is difficult to adjust the balance between the filament currents i51 and i52. More specifically, if the current detection resistor 310 is connected to the filament 51 while the current detection resistor 330 is not connected to the filament 52, i51 < i52. In such a case, it is difficult to cancel the difference between the two currents by adjusting the turns ratio of the secondary winding of the transformer 302 so that i51 = i52. This problem is the same when the igniter 6 (secondary winding of the transformer 604) is inserted and connected to the filament current path as described above. On the other hand, since the resistance value of the resistance element can be adjusted at a relatively fine pitch, if the current detection resistor 330 is connected, the resistance value of the current detection resistor 330 can be appropriately selected to select the filament. The current i51 and the filament current i52 can be made substantially equal. Thus, the current detection resistor 330 also plays a role of balancing the filament currents i51 and i52.

  In this embodiment, the resistance values of the current detection resistors 310 and 330 are set so that the filament currents i51 and i52 are substantially equal. However, the resistance values are set so that the filament currents i51 and i52 are intentionally different. Different flow detection resistors 310 and 330 may be employed. For example, when the filament 51 and the filament 52 have different specifications in a DC lighting discharge lamp or the like, the resistances of the current detection resistors 310 and 330 so that the filament current i51 and the filament current i52 have a desired ratio. A ratio may be set.

  The voltage detection circuit 34 includes a resistor 341, a Zener diode 342, and a photocoupler 343, and detects the output voltage of the output circuit 30b. This output voltage is a voltage obtained by subtracting the voltage drop across the wires W1 and W2 from the voltage across the filament 52, and is also a voltage that indirectly indicates the voltage across the filament 52. A series circuit of a resistor 341, a Zener diode 342, and a photodiode of a photocoupler 343 is connected in parallel to the output capacitor 306, and a phototransistor of the photocoupler 343 is connected to the control circuit 40 with a reference potential as the ground G1. For example, the collector terminal of the phototransistor may be connected to the control power supply of the control circuit 40 via a resistor (not shown), and the emitter terminal may be connected to the ground G1. Alternatively, the collector terminal of the phototransistor may be connected to the control power supply of the control circuit 40, and the emitter terminal may be connected to the ground G1 via a resistor (not shown). In either case, the output value E (hereinafter referred to as “detected value E”) of the phototransistor of the photocoupler 343 changes according to the increase or decrease of the output voltage of the output circuit 30b.

  The voltage detection circuit 34 realizes a protection function when the output of the output circuit 30b is opened. For example, when the discharge lamp 5 is not connected to the lighting device 1, when the wirings W1 and W2 are not connected to the filament 52 due to miswiring or the like, or when the filament 52 has an open failure, the output voltage of the output circuit 30b Will increase. As a result, when the Zener diode 342 is turned on and the detected value E falls outside the predetermined range due to an increase in the current flowing through the photodiode of the photocoupler 343, the control circuit 40 determines the output open state and outputs the output of the DC / DC converter 30. The operation, that is, the driving of the switching element 301 is stopped.

  In the present embodiment, in the output circuit 30b, the current detection circuit 33, and the control circuit 40, an abnormality due to an output short circuit is detected when the voltage value of the current detection resistor 330 exceeds a predetermined range (upper threshold). However, the abnormality due to the output opening may be detected when the voltage value of the current detection resistor 330 falls below a predetermined range (lower threshold). Similarly, in the present embodiment, in the output circuit 30b, the voltage detection circuit 34, and the control circuit 40, an abnormality due to output opening is detected when the detected output voltage exceeds a predetermined range (upper threshold). An abnormality due to an output short circuit may be detected when the output voltage falls below a predetermined range (lower threshold).

  The control unit 4 includes a control circuit 40 and a feedback circuit 41. As an outline, the control unit 4 controls the operations of the main power supply circuit 2 and the filament power supply circuit 3. In particular, the DC / DC converter 30 is controlled so that the current detection value detected by the current detection circuit 31 matches the current target value, and the voltage detection value detected by the voltage detection circuit 32 is the voltage target value (upper limit value). The DC / DC converter 30 is controlled to be as follows. That is, in the control unit 4, the output current (filament current i51) is subjected to constant current control while the output voltage of the output circuit 30a is maintained below the upper limit value. Further, as described above, the control unit 41 stops the output operation of the DC / DC converter 30 when the output current (filament current i52) or the output voltage of the output circuit 30b is out of the predetermined range.

  The control circuit 40 controls driving of the switching element 221, the switching element 241, the switching elements 251-254, and the switching element 301 with the ground G1 as a reference potential. Specifically, the control circuit 40 PWM-drives the switching element 221 so that the output voltage of the boost converter 22 becomes a predetermined value. The control circuit 40 also PWM-drives the switching element 241 of the step-down converter 24 so that the detected value A is equal to or lower than the target value (upper limit value) and the detected value B matches the target value. That is, the step-down converter 24 and the control circuit 40 feedback control the lamp current while maintaining the output voltage below the upper limit value. Alternatively, the control circuit 40 may PWM drive the switching element 241 of the step-down converter 24 so that the product of the detection value A and the detection value B matches the power target value. In this case, the step-down converter 24 and the control circuit 40 feedback control the lamp power while maintaining the output voltage below the upper limit value. Further, the control circuit 40 drives the switching elements 251 to 254 of the full bridge circuit 25 at a low frequency as described above.

  Further, for the DC / DC converter 30, the control circuit 40 PWM-drives the switching element 301 with an ON width determined based on a detection value C generated by a feedback circuit 41 described later. Furthermore, as described above, the control circuit 40 can stop the switching element 301 when the detection values D and E are out of the predetermined range. At this time, the control circuit 40 stops some or all of the operations of the step-up converter 22 (switching element 221), the step-down converter 24 (switching element 241), and the full bridge circuit 25 (switching elements 251 to 254). It may be.

  The control voltage of the control circuit 40 is appropriately supplied based on the voltage generated in the auxiliary winding (not shown) of the inductor 222, the inductor 242 or the transformer 302 or the electric power obtained from the voltage of the smoothing capacitor 224. To do.

  During the preheating period, the control circuit 40 drives the switching elements 221 and 301 to substantially stop the switching element 241 and to stop the switching elements 251 to 254. Further, the control circuit 40 drives the switching elements 221, 241, 251 to 254 and 301 at the time of starting the lamp and during stable lighting.

  The feedback circuit 41 includes operational amplifiers 411 and 412, voltage sources 413 and 414, diodes 415 and 416, a voltage source 417, a resistor 418, and a photocoupler 419, and uses the ground G2 as a reference potential. As an outline, the operational amplifier 411 is a constant current control operational amplifier that has a function of making the output current (that is, the filament current i51) of the output circuit 30a constant, and the operational amplifier 412 has a function of making the output voltage of the output circuit 30a constant. It is an operational amplifier for constant voltage control. Then, according to the output state of the output circuit 30a, one of constant current control and constant voltage control is selected by a diode OR circuit composed of diodes 415 and 416, and the input state of the photocoupler 419 in the photodiode is determined. In response to this, the output of the phototransistor of the photocoupler 419 is input to the control circuit 40 as the detection value C. That is, the switching element 301 is PWM-controlled by the control circuit 40 and the feedback circuit 41 so as to perform either constant current control or constant voltage control. In practice, the output current (that is, the filament current i51) is constant-current controlled while the output voltage of the output circuit 30a is maintained below the upper limit value.

  The current detection value detected by the current detection circuit 31 is input to the negative input terminal (−) of the constant current control operational amplifier 411, and the voltage value corresponding to the target value of the filament current i51 is input to the positive input terminal (+). Is input from the voltage source 413. Note that a feedback element (not shown) (a resistor, a capacitor, or a series circuit or a parallel circuit thereof) is connected between the negative input terminal and the output terminal of the operational amplifier 411. The operational amplifier 411 amplifies and outputs an error between the current detection value input to the negative input terminal and the voltage value input to the positive input terminal. In other words, when the diode 415 is turned on and the constant current control is selected, the operational amplifier 411 determines the ON width in the PWM control of the switching element 301 so that the current detection value matches the voltage value of the voltage source 413. Will do. This constant current control can also prevent the output current from becoming excessive when the output circuit 30a is short-circuited.

  The voltage detection value detected by the voltage detection circuit 32 is input to the negative input terminal (−) of the operational amplifier 412 for constant voltage control, and the target value (upper limit value) of the output voltage corresponds to the positive input terminal (+). The voltage value to be input is input from the voltage source 414. Note that a feedback element (not shown) is also connected between the negative input terminal and the output terminal of the operational amplifier 412. The operational amplifier 412 amplifies and outputs an error between the voltage detection value input to the negative input terminal and the voltage value input to the positive input terminal. In other words, when the diode 416 is turned on and constant voltage control is selected, the operational amplifier 412 determines the ON width in the PWM control of the switching element 301 so that the voltage detection value matches the voltage value of the voltage source 414. Will do. This constant voltage control can prevent the output voltage from becoming excessive when the output of the output circuit 30a is opened.

  The diode OR circuit including the diodes 415 and 416 is turned on with respect to the lower one of the output terminal voltage of the operational amplifier 411 and the output terminal voltage of the operational amplifier 412. The common anode of the diode OR circuit is connected to the cathode side of the photodiode of the photocoupler 419. The anode of the photodiode of the photocoupler 419 is connected to the output of the voltage source 417 via a resistor 418. The phototransistor of the photocoupler 419 outputs the detection value C corresponding to the current (light emission) flowing through the photodiode with the ground G1 as a reference potential. The control circuit 40 generates a PWM drive signal having a pulse width corresponding to the detected value C, and outputs it as the gate voltage of the switching element 301.

  Then, when the filament current i51 is constant-current controlled to the target value by the feedback circuit 41 and the control circuit 40, the filament current i52 is similarly determined (assuming that the output circuit 30b to the filament 52 are in a normal state). Current controlled. Further, the output circuit 30b is controlled by the feedback circuit 41 and the control circuit 40 so that the output voltage of the output circuit 30a is equal to or lower than the upper limit value (assuming that the output circuit 30b to the filament 52 are in a normal state). The output voltage is also controlled at a constant voltage.

  The control voltage of the feedback circuit 41 may be obtained from the auxiliary winding of the transformer 302. FIG. 2 shows an example of the auxiliary power supply circuit 42 for generating the control voltage of the feedback circuit 41 and the voltage of each voltage source. The auxiliary power circuit 42 includes an auxiliary winding S3 of the transformer 302, a diode 421, a capacitor 422, a transistor 423, a resistor 424, a Zener diode 425, a diode 426, and a capacitor 427. The voltage generated in the auxiliary winding S3 is rectified and smoothed by the diode 421 and the capacitor 422, and the smoothed voltage is stepped down by a series regulator constituted by the transistor 423, the resistor 424, and the Zener diode 425. The stepped down voltage is smoothed by the capacitor 427 via the diode 426, and the control voltage Vcc of the feedback circuit 41 is generated. The voltage source 417 is the control voltage Vcc, and each of the voltage sources 413 and 414 may be a resistance voltage dividing circuit that divides the control voltage Vcc. The auxiliary power circuit 42 may be configured using a three-terminal regulator, a shunt regulator, or the like.

  The igniter 6 includes a resistor 601, a capacitor 602, a discharge gap 603, and a transformer 604, and a secondary winding of the transformer 604 is connected between the terminals T7 and T8 and the filament 51. The igniter 6 superimposes a pulse voltage on the lamp voltage (no-load secondary voltage of the full bridge circuit 25) between the output wirings W1 and W4 at the time of starting the lamp, thereby promoting the starting of the lamp. However, when the lamp can be started only by the no-load secondary voltage of the full bridge circuit 25, the igniter 6 does not operate or is unnecessary. At the time of starting the lamp, the no-load secondary voltage of the full bridge circuit 25 is charged into the capacitor 602 via the resistor 601. When the voltage of the capacitor 602 exceeds the breakdown voltage of the discharge gap 603, the discharge gap 603 becomes conductive. As a result, a pulse voltage is generated in the primary winding of the transformer 604, and this pulse voltage is boosted according to the turns ratio of the transformer 604, and becomes a high-voltage pulse voltage in the secondary winding and superimposed on the no-load secondary voltage. Is done. After the lamp starts, the output voltage of the full bridge circuit 25 becomes lower than the no-load secondary voltage, and the voltage charged in the capacitor 602 does not exceed the breakdown voltage of the discharge gap 603. That is, the igniter 6 does not operate after starting the lamp.

  The operation of the lighting device 1 will be described with reference to FIG. In FIG. 3, the output current (filament current) of the DC / DC converter 30 of the filament power supply circuit 3 is shown on the upper vertical axis, and the output voltage (lamp voltage) of the full bridge circuit 25 of the main power supply circuit 2 is shown on the lower vertical axis. Time is shown on the horizontal axis.

  At time t0, the control circuit 40 starts the output operation of the DC / DC converter 30. It is assumed that boost converter 22 has started operating at time t0. After time t0, constant current control is performed by the DC / DC converter 30 and the control unit 4 so that the filament current (filament current i51) becomes the current value I1. It is assumed that the current value I1 is a current value for allowing the discharge lamp 5 to keep lighting stably even after starting the lamp.

  At time t1, the control circuit 40 starts the output operation of the full bridge circuit 25, whereby the no-load voltage Vo is temporarily output until the lamp start is completed (the igniter 6 can operate during this time, hereinafter the same). Thereafter, after the lamp is started, the output voltage of the full bridge circuit 25 decreases to a voltage value VL substantially equal to the lamp voltage during stable lighting. That is, in the stable lighting period after starting the lamp, a low-frequency lamp current corresponding to the lamp voltage (VL) is supplied from the main power supply circuit 2 to the discharge lamp 5 and the DC filament current (I1) is supplied to the filament power supply circuit 3. To the filaments 51 and 52 respectively. In addition, although the time between time t0-t1 depends on the kind of discharge lamp, it may be about 1 to 3 seconds.

  As described above, according to the lighting device 1 of the present embodiment, the DC voltage input from a part of the main power supply circuit 2 is converted into the DC filament currents i51 and i52 by the DC / DC converter 30 of the filament power supply circuit 3. Is done. Then, the filament current i51 is controlled at a constant current by the controller 4, and the output operation of the DC / DC converter 30 is stopped when the filament current i52 is out of the predetermined range. With such a configuration, the following effects can be obtained.

(1) Improving startability of discharge lamp 5 by optimizing preheating current As described above, a direct current filament current controlled by constant current is supplied from the lighting device 1 to the discharge lamp 5. Therefore, a desired value of current can be supplied to the filaments 51 and 52 regardless of the length of the output wirings W1 to W4, that is, the voltage drop caused by the resistance component. Thereby, regardless of the lengths of the output wirings W1 to W4, the filaments 51 and 52 are sufficiently heated at the time of starting the lamp, the emission of the electron emitting material from the filaments 51 and 52 is promoted, and the startability of the discharge lamp 5 is improved. Is possible. Further, since a predetermined filament current is applied even in stable lighting, appropriate lighting characteristics are ensured.

(2) Miniaturization of the lighting device 1 The filament power supply circuit 3 is constituted by a DC / DC converter 30, and the transformer 302 is a high-frequency switching transformer. Therefore, the filament power supply 3 is greatly reduced in size compared to the conventional configuration in which a commercial power transformer is used in the filament power supply circuit. Thereby, the small lighting device 1 is realized.

(3) Standardization of the lighting device 1 The DC / DC converter 30 of the filament power supply circuit 3 has a desired value of filament by controlling its switching operation (ON width, etc.) even for different input voltages. A current can be output. Further, on the output side of the filament power supply circuit 3, by adjusting the target value of the filament current for different types of discharge lamps 5 (that is, the discharge lamps 5 having different necessary filament currents), a filament having a desired value can be obtained. A current can be output. That is, since the filament power supply circuit 3 having substantially the same circuit configuration can be adopted regardless of the specification of the AC power supply AC or the type of the discharge lamp 5, the lighting device 1 can be standardized. . In particular, when the output voltage of the boost converter 22 that is the input of the DC / DC converter 30 is configured to be constant regardless of the voltage of the AC power supply AC, the filament power supply circuit 3 can be used for all AC power supply specifications. The line-up can have substantially the same configuration, and standardization of the lighting device 1 is further promoted.

(4) Addition of protection function with simple and low-cost configuration In the control circuit 40 and the feedback circuit 41, constant current control of the output current of the output circuit 30a or constant voltage control of the output voltage (control to make the output voltage not more than the upper limit value) ) Is secured, the protection function for preventing overcurrent when the output circuit 30a of the output circuit 30a relating to the filament 51 is short-circuited and preventing overvoltage when the output is opened is secured. On the other hand, when the current detection circuit 33 and the voltage detection circuit 34 are added to the filament 52, and the detection value D or the detection value E is outside the predetermined range in the control circuit 40, the output operation of the DC / DC converter 30 is performed. Is stopped. Thereby, the function of the overcurrent prevention at the time of the output short circuit of the output circuit 30b regarding the filament 52 and the overvoltage prevention at the time of the output opening are also realized. The circuit configuration including the current detection circuit 33 and the voltage detection circuit 34 is larger in circuit scale than the circuit configuration including the current detection circuit 31, the voltage detection circuit 32, the feedback circuit 41, and the auxiliary power supply circuit 42 (see FIG. 2). Small and low cost. Therefore, according to the configuration of the present embodiment, the lighting device is more than the case where two sets of the circuit configuration including the current detection circuit 31, the voltage detection circuit 32, the feedback circuit 41, and the auxiliary power supply circuit 42 are provided for both the filaments 51 and 52. 1 is simple and low cost. Thus, the protection function regarding the output to both filaments 51 and 52 is realized in a simple and low-cost manner.

(5) Ensuring balance of filament current The current detection resistor 310 is connected in series to the filament 51, and the current detection resistor 330 is connected in series to the filament 52. Then, by appropriately selecting the resistance values of the current detection resistors 310 and 330 in consideration of the voltage drop in the path of the filament currents i51 and i52, the ratio of the filament current i51 and the filament current i52 is set to be equal, for example. It becomes possible to adjust. This makes it possible to ensure the balance between the filament currents i51 and i52.

<Second Embodiment>
Although the filament current is a fixed value in the first embodiment, the present embodiment shows a configuration in which the filament current can be switched. FIG. 4 shows a circuit configuration of the lighting device 1 according to the present embodiment. The difference between the lighting device 1 of the present embodiment and the lighting device 1 of the first embodiment is in the configuration and operation of the control unit 4, and other configurations are common to both embodiments. In the present embodiment, the same reference numerals are given to substantially the same components as those in the first embodiment, and detailed description thereof will be omitted.

  In the present embodiment, as a rule, the current value of the filament current i51 in the predetermined period T1 immediately after the start of the preheating period is reduced from the period T2 in the subsequent preheating period and the current value I1 in the stable lighting period. In this period T1, the control unit 4 makes an abnormality in the output of the output circuit 30b prior to the period T2 (for example, an open state when the discharge lamp 5 is not attached, a short circuit state and an open state due to incorrect wiring of the wiring W1 or W2, filaments 52) is determined.

  In the control circuit 40 and the feedback circuit 41 of the control unit 4 of the present embodiment, the voltage of the voltage source 413 connected to the operational amplifier 411 of the feedback circuit 41 is configured to be switched from the control circuit 40. Specifically, the switching signal S0 from the output unit of the control circuit 40 is output to the feedback circuit 41 as the switching signal S1 through the photocoupler 401, and the voltage value of the voltage source 413 is switched by the switching signal S1. Note that the reference potential on the input side (photodiode) of the photocoupler 401 is the ground G1, and the reference potential on the output side (phototransistor) of the photocoupler 401 is the ground G2.

  For example, as shown in FIG. 5, the voltage source 413 includes a series circuit of a resistor 413 c and a transistor 413 d connected in parallel to the resistor 413 b in addition to the resistors 413 a and 413 b that divide the control voltage Vcc. That's fine. Then, the phototransistor of the photocoupler 401 may be connected to the control voltage Vcc via the resistor 413e, and the collector terminal of the phototransistor may be connected to the base terminal of the transistor 413d. When the switching signal S0 is at a low level and the switching signal S1 is at a high level, the transistor 413d is turned on, and the voltage value of the voltage source 413 (the voltage at the positive input terminal of the operational amplifier 411) is decreased. In the example shown in FIG. 5, when the switching signal S0 is switched from the low level to the high level, the switching signal S1 is switched from the high level to the low level, the voltage value (target value) of the voltage source 413 increases, and the operational amplifier 411. The filament current increases as a result of constant current control by. The switching timing at which the switching signal S0 is output is determined by the internal timer of the control circuit 40.

  As an alternative example, as illustrated in FIG. 6, the feedback circuit 41 may include a timer circuit 431 and a switching circuit 432 having the ground G2 as a reference potential. In this configuration, when the DC / DC converter 30 is activated and the control voltage Vcc is supplied to the feedback circuit 41, the timer circuit 431 is activated. Then, when the timer circuit 431 times the predetermined period, the switching circuit 432 outputs the switching signal S1. The timer circuit 431 may be, for example, an RC integration circuit in which a resistor and a capacitor are connected in series.

  With reference to FIG. 7, operation | movement of the lighting device 1 of this embodiment is demonstrated. In FIG. 7, the output current (filament current) of the DC / DC converter 30 of the filament power supply circuit 3 is shown on the upper vertical axis, and the output voltage (lamp voltage) of the full bridge circuit 25 of the main power supply circuit 2 is shown on the lower vertical axis. Time is shown on the horizontal axis.

  Period T1 starts at time t0. At this time, the control circuit 40 starts the output operation of the DC / DC converter 30. It is assumed that boost converter 22 has started operating at time t0. In the period T1, the constant current control of the filament current i51 is performed by the DC / DC converter 30 and the control unit 4 so that the filament current matches the current value I0 lower than the current value I1. The duration of the period T1 is preferably set to be short as long as the current detection circuit 33, the voltage detection circuit 34, and the control circuit 40 can perform the protection function. For example, about 100 msec (for example, 50 msec to 150 msec) Degree).

  Period T2 starts at time t2. At this time, in the control unit 4, the switching signal S1 is output, the target value of constant current control (that is, the voltage value of the voltage source 413) is increased, and the filament current increases from the current value I0 to the current value I1. Also in the period T2, the current detection circuit 33 and the voltage detection circuit are prepared for the occurrence of a subsequent output short-circuit state or output-open state (for example, when the discharge lamp 5 is removed or the filament 52 is short-circuited or opened). 34 and the control circuit 40 continue to detect.

  The period T2 ends at time t3. At this time, the control circuit 40 starts the output operation of the full bridge circuit 25, and thereby, the no-load voltage Vo is temporarily output until the lamp start is completed. After starting the lamp, the output voltage of the full bridge circuit 25 decreases to a voltage value VL substantially equal to the lamp voltage during stable lighting. That is, in the stable lighting period after starting the lamp, a low-frequency lamp current corresponding to the lamp voltage (VL) is supplied from the main power supply circuit 2 to the discharge lamp 5 and the DC filament current (I1) is supplied to the filament power supply circuit 3. To the filaments 51 and 52 respectively.

  As described above, according to the lighting device 1 of the present embodiment, in addition to the advantageous effects (1) to (5) described in the first embodiment, the following advantageous effects can be obtained.

(6) Suppression of component stress at the time of filament failure In the present embodiment, during the preheating period, the control unit 4 increases the target value of the filament current i51 stepwise, whereby the filament current is smaller than the current value I1. A period T1 in which the value is I0 is provided. As described above, even when an abnormality occurs in the output of the output circuit 30b, the protection operation is executed in the low output period T1, and thereafter, it is possible to prevent a large stress from being applied to the circuit components. .

<Third Embodiment>
In the second embodiment, the filament current in the preheating period (period T2) and the filament current in the stable lighting period are the same. However, in the present embodiment, the filament current in the preheating period is in the stable lighting period. A configuration in which the preheating period is shortened by increasing the filament current is shown. The circuit configuration of the lighting device 1 according to the present embodiment is the same as that of the second embodiment shown in FIGS. 4 to 6, and the lighting device 1 of the present embodiment and the lighting device 1 of the second embodiment are the same. The difference is in the operation of the control unit 4.

  In the present embodiment, the current value of the filament current i51 in the predetermined period T3 including a part of the preheating period is increased from the current value I1 for stable lighting. In general, the resistance value of the filament greatly depends on the temperature, and the resistance value of the filament is low at a low temperature before starting the lamp. Therefore, by increasing the filament current during the preheating period, the output power of the DC / DC converter 30 is not greatly increased as compared with that during stable lighting. In this period T3, the control unit 4 makes an abnormality in the output of the output circuit 30b (for example, an open state due to the discharge lamp 5 not being attached, a short-circuit state and an open state due to incorrect wiring of the wiring W1 or W2, and a short circuit of the filament 52). Disable the protection function against the status and open state. That is, in the period T3, even if the detection value D or E is outside the predetermined range, the control circuit 40 causes the DC / DC converter 30 to continue the output operation.

  With reference to FIG. 8A, operation | movement of the lighting device 1 of this embodiment is demonstrated. In FIG. 8A, the output current (filament current) of the DC / DC converter 30 of the filament power supply circuit 3 is shown on the upper vertical axis, and the output voltage (lamp voltage) of the full bridge circuit 25 of the main power supply circuit 2 is shown on the lower vertical axis. Time is shown on the horizontal axis.

  Period T1 starts at time t0. At this time, the control circuit 40 starts the output operation of the DC / DC converter 30. It is assumed that boost converter 22 has started operating at time t0. In the period T1, constant current control is performed by the DC / DC converter 30 and the control unit 4 so that the filament current i51 coincides with the current value I0 (similar to the second embodiment).

  Period T3 starts at time t4. At this time, in the control unit 4, the switching signal S1 is output, the target value of constant current control (that is, the voltage value of the voltage source 413) is increased, and the filament current increases from the current value I0 to the current value I2. The current value I2 is larger than the current value I1 for stable lighting. In this period T3, the protection operation by the current detection circuit 33, the voltage detection circuit 34, and the control circuit 40 is invalidated (masked). In other words, the protection operation is performed outside the period T3.

  Period T3 ends at time t5. At this time, the switching signal S1 is output, the target value of the constant current control is reduced, and the filament current is decreased from the current value I2 to the current value I1.

  At time t6, the control circuit 40 starts the output operation of the full bridge circuit 25, whereby the no-load voltage Vo is temporarily output until the lamp start is completed. After starting the lamp, the output voltage of the full bridge circuit 25 decreases to a voltage value VL substantially equal to the lamp voltage during stable lighting. That is, in the stable lighting period after starting the lamp, a low-frequency lamp current corresponding to the lamp voltage (VL) is supplied from the main power supply circuit 2 to the discharge lamp 5 and the DC filament current (I1) is supplied to the filament power supply circuit 3. To the filaments 51 and 52 respectively.

  The operation of the lighting device 1 of the present embodiment may be a mode as shown in FIG. 8B. Similarly to FIG. 8A, also in FIG. 8B, the output current (filament current) of the DC / DC converter 30 of the filament power supply circuit 3 is shown on the upper vertical axis, and the full bridge circuit 25 of the main power supply circuit 2 is shown on the lower vertical axis. The output voltage (lamp voltage) is shown, and the horizontal axis shows time.

  The period T1 ′ starts at time t0. At this time, the control circuit 40 starts the output operation of the DC / DC converter 30. It is assumed that boost converter 22 has started operating at time t0. In the period T1 ′, constant current control is performed by the DC / DC converter 30 and the control unit 4 so that the filament current i51 matches the current value I1 (similar to the first embodiment). Note that the duration of the period T1 ′ may be approximately the same as the duration of the period T1 in the second embodiment.

  Period T3 starts at time t7. At this time, in the control unit 4, the switching signal S1 is output, the target value of constant current control (that is, the voltage value of the voltage source 413) is increased, and the filament current increases from the current value I1 to the current value I2. In this period T3, the protection operation by the current detection circuit 33, the voltage detection circuit 34, and the control circuit 40 is invalidated (masked). In other words, the protection operation is performed outside the period T3.

  At time t8, the control circuit 40 starts the output operation of the full bridge circuit 25, whereby the no-load voltage Vo is temporarily output until the lamp start is completed. After starting the lamp, the output voltage of the full bridge circuit 25 decreases to a voltage value VL substantially equal to the lamp voltage during stable lighting. That is, after starting the lamp, a low-frequency lamp current corresponding to the lamp voltage (VL) is supplied from the main power supply circuit 2 to the discharge lamp 5.

  Period T3 ends at time t9. At this time, the switching signal S1 is output, the target value of the constant current control is reduced, and the filament current is decreased from the current value I2 to the current value I1. Thus, during the stable lighting period, a low-frequency lamp current is supplied from the main power supply circuit 2 to the discharge lamp 5, and a DC filament current (I1) is supplied from the filament power supply circuit 3 to each of the filaments 51 and 52. The Thereby, filament heating is sufficiently performed even at the moment of starting the lamp, and the startability of the discharge lamp 5 is further improved. In this example, for example, the period T1 is about 100 msec, the period T3 is about 3 sec, and the time t9 may be about 1 sec after the lamp starts lighting.

  8A and 8B, in the control circuit 40, the end timing of the period T3 may be determined by an internal timer, or may be determined based on the detection value A or B. Good. In any case, the end timing of the period T3 may be approximately in the vicinity of the lamp start timing, for example, within about ± 1 sec at the time of lamp start. When the lamp is started, a rapid decrease in the lamp voltage is detected by the detection value A, the generation of the lamp current is detected by the detection value B, and the end timing of the period T3 is determined by one or both of these detection results. . Since filament heating is accelerated by increasing the filament current during the preheating period, the preheating period is set shorter than in the case of the first and second embodiments.

  As described above, according to the lighting device 1 of the present embodiment, in addition to the advantageous effects (1) to (6) described with respect to the first and second embodiments, the following advantageous effects can be obtained.

(7) Shortening the preheating period and preventing malfunction of the protection function In this embodiment, the filament current in the preheating period (period T3) can be increased with respect to the filament current for stable lighting. Heating can be accelerated, the preheating period can be shortened, and a quick lighting operation can be obtained. In the period T3 in which the filament current increases, the overcurrent protection and the overvoltage protection related to the output circuit 30b are invalidated, so that the malfunction of the protection function can be prevented while shortening the preheating period.

<Modification>
Although preferred embodiments of the present invention have been described above, the present invention can be modified into various modes as shown below, for example.

(1) Modification Regarding Main Power Supply Circuit 2 In each of the above embodiments, the configuration in which the discharge lamp 5 for AC lighting is lit at a low frequency is shown, but the present invention is also applied to a configuration in which the discharge lamp for DC lighting is lit by DC. Is applicable. In this case, the main power supply circuit 2 comprises a DC / DC converter that outputs a DC voltage and a DC current.

(2) Modification Regarding Filament Power Supply Circuit 3 In the above embodiments, the configuration in which the input voltage of the DC / DC converter 30 is supplied from the output section of the boost converter 22 is shown. The voltage may be input from another location. For example, as shown in FIG. 9, the input voltage of the DC / DC converter 30 may be supplied from the input section of the boost converter 22 (that is, the output section of the rectifier circuit 20). In this case, as the input capacitor 201, it is desirable to use a capacitor having a relatively small capacity so as not to decrease the power factor of the lighting device 1. Therefore, the input voltage to the DC / DC converter 30 is a non-smooth pulsating voltage. As the output capacitors 304 and 306, it is preferable to use a capacitor having a relatively large capacity when it is desired to prevent a ripple caused by the power supply frequency of the AC power supply AC from appearing in the filament current.

  Further, the advantageous effects “(2) downsizing of the lighting device 1” and “(3) standardization of the lighting device 1” described in the first embodiment are the flyback converter having a simple configuration of the DC / DC converter 30. However, the present invention can also be realized by other types of isolated DC / DC converters. For example, the DC / DC converter may be a forward converter, a push-pull converter, or the like.

(3) Modification related to the control unit 4 (switching signals S0 and S1) In the second and third embodiments, the switching signals S0 and S1 are switched stepwise in the control unit 4 and the filament current increases stepwise. Alternatively, the configuration in which the filament current is decreased is shown, but the control unit 4 may generate the switching signals S0 and S1 that change linearly, and the filament current may be continuously increased or decreased.

(4) Modification concerning operation during stable lighting In each of the above embodiments, the filament current is supplied to the filaments 51 and 52 at the time of stable lighting after starting the lamp. When the discharge lamp does not require the filament current, the control unit 4 (control circuit 40) may stop the operation of the filament power supply circuit 3 (DC / DC converter 30). Thereby, the power consumption during stable lighting is reduced, and a more efficient lighting device 1 is realized.

1 Discharge lamp lighting device 2 Main power circuit (first power circuit)
3 Filament power circuit (second power circuit)
4 Control Unit 5 Low Pressure Discharge Lamp 30 DC / DC Converter 30a Output Circuit (First Output Circuit)
30b Output circuit (second output circuit)
31 Current detection circuit (first current detection circuit)
32 Voltage detection circuit (first voltage detection circuit)
33 Current detection circuit (second current detection circuit)
34 Voltage detection circuit (second voltage detection circuit)
51 Hot cathode filament (first hot cathode filament)
52 Hot cathode filament (second hot cathode filament)
310 Current detection resistor (first resistance element)
330 Current detection resistor (second resistor element)

Claims (7)

A discharge lamp lighting device for lighting a low-pressure discharge lamp having first and second hot cathode filaments,
A first power supply circuit for supplying a lamp voltage or a lamp current to the low-pressure discharge lamp;
A direct current voltage input from a part of the first power supply circuit is converted into direct current first and second filament currents, and the first and second filament currents are converted into the first and second hot cathode filaments. And a second power supply circuit having a first current detection circuit for detecting the first filament current and a second current detection circuit for detecting the second filament current. When,
Constant current control is performed to control the DC / DC converter so that a first current detection value detected by the first current detection circuit matches a target value, and is detected by the second current detection circuit. A discharge lamp lighting device comprising: a control unit configured to execute a protective operation for stopping the output operation of the DC / DC converter when the second detected current value is outside a predetermined range.   2. The discharge lamp lighting device according to claim 1, wherein the first current detection circuit includes a first resistance element inserted and connected to a path of the first filament current, and the second current detection circuit includes the first current detection circuit. A second resistor element inserted and connected to the path of the second filament current, and the resistances of the first and second resistor elements so that the first filament current and the second filament current are equal to each other. A discharge lamp lighting device with a set value. In the discharge lamp lighting device according to claim 1 or 2,
The second power supply circuit detects a first output circuit that outputs the first filament current, a second output circuit that outputs the second filament current, and an output voltage of the first output circuit. A first voltage detection circuit that
The discharge lamp lighting device, wherein the control unit is configured to control the DC / DC converter so that a voltage detection value detected by the first voltage detection circuit is equal to or lower than an upper limit value. In the discharge lamp lighting device according to any one of claims 1 to 3,
The second power supply circuit detects a first output circuit that outputs the first filament current, a second output circuit that outputs the second filament current, and an output voltage of the second output circuit. A second voltage detection circuit that
The discharge lamp lighting device, wherein the control unit is configured to perform the protection operation when a voltage detection value detected by the second voltage detection circuit is outside a predetermined range. In the discharge lamp lighting device according to any one of claims 1 to 4,
In the preheating period after the start of the DC / DC converter and before the lamp voltage is output from the first power supply circuit, the control unit sets the target value in a predetermined period immediately after the start of the preheating period. A discharge lamp lighting device configured to raise the lamp stepwise or continuously. In the discharge lamp lighting device according to any one of claims 1 to 5,
In a predetermined period including a part of a preheating period after the start of the DC / DC converter and before the lamp voltage is output from the first power supply circuit, the control unit sets the target value to a stable lighting period. The discharge lamp lighting device is configured to be higher than a target value and invalidate the protection operation. The discharge lamp lighting device according to any one of claims 1 to 6, wherein the DC / DC converter is a flyback converter.

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