JP6417844B2 - Discharge lamp lighting device - Google Patents

Description

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

  In recent years, the frequency of lighting devices for low-pressure discharge lamps has been increasing. However, in the high-frequency lighting method, when the output wiring between the lighting device and the discharge lamp is relatively long (for example, about several tens of meters), the decrease in the no-load secondary voltage due to the parasitic capacitance of the output wiring, and the output A decrease in lamp current due to wiring inductance cannot be ignored. Therefore, it is not preferable to apply the high frequency lighting method to a lighting device connected to the discharge lamp through a long output wiring. Therefore, a low-frequency lighting method for lighting a discharge lamp with a low-frequency rectangular wave current or the like is suitable for a lighting device that assumes a long output wiring. The same applies to the filament current supplied to the filament of the discharge lamp as well as the lamp current.

  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. Such a configuration of the filament power supply is applicable regardless of whether the lighting device is a high frequency lighting system or a low frequency lighting system.

Japanese Patent Laid-Open No. 6-251883

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. Although it is theoretically possible to reduce the resistance value of the output wiring by using wiring with a large conductor cross-sectional area in order to reduce the influence of this voltage drop, it is not practical from the viewpoint of wiring cost and wiring management. Absent. Therefore, according to the commercial power transformer system, it is difficult to optimize the filament current when the output wiring is long, 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.

  Therefore, the present invention is capable of optimizing the filament current and miniaturizing and standardizing the lighting device regardless of the length of the output wiring in the discharge lamp lighting device for lighting the low pressure discharge lamp having the hot cathode filament. It is an object to provide a simple configuration.

  In the discharge lamp lighting device of the present invention, a low-pressure discharge lamp having a hot cathode filament is lit, a first power supply circuit for supplying a low-frequency or direct-current lamp voltage or current to the low-pressure discharge lamp, Insulating DC / DC converter that converts a DC voltage input from a part of a power supply circuit into a DC filament current and supplies the filament current to a hot cathode filament, and a current detection circuit that detects the current value of the filament current And a control unit that controls the DC / DC converter so that the current detection value detected by the current detection circuit matches the target value.

  According to the discharge lamp lighting device of the present invention, a DC voltage input from a part of the main power supply circuit is converted into a DC filament current by the DC / DC converter of the filament power supply circuit, and this filament current is converted into a constant current by the control unit. Be controlled. 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. Furthermore, 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. Therefore, it is possible to standardize the discharge lamp lighting device.

  Here, the controller may reduce the filament current to the DC / DC converter after a predetermined time has elapsed since the filament current was output from the DC / DC converter. Thereby, since the filament current in the preheating period can be relatively increased, the heating of the hot cathode filament can be accelerated and the preheating period can be shortened. In addition, since the filament current during stable lighting can be reduced more than the filament current during the preheating period, it is possible to prevent power from being supplied to the hot cathode filament during the stable lighting period to save power. It becomes possible. In addition, since different filament currents can be set during the preheating period and the stable lighting period, the startability of the discharge lamp is improved by optimizing the filament current during the preheating period, and the discharge is achieved by optimizing the filament current during stable lighting. It is possible to effectively improve the lighting characteristics of electric lamps.

  Further, the controller may reduce the filament current to the DC / DC converter after the filament current is output from the DC / DC converter and before the lamp voltage is output from the first power supply circuit. . According to this, since the increase in filament current by the second power supply circuit and the increase in output voltage at the time of lamp start by the first power supply circuit are not included in the same period, the output power of the discharge lamp lighting device as a whole is greatly increased. This is preferable from the viewpoint of reliability management of the discharge lamp lighting device.

  Further, the controller may reduce the filament current to the DC / DC converter after the filament current is output from the DC / DC converter and the lamp voltage is output from the first power supply circuit. Thereby, even when the discharge is unstable immediately after the start of the discharge lamp, the discharge of the electron discharge substance is continued by energizing the filament current, so that the startability of the discharge lamp is further improved.

  Moreover, you may comprise so that a control part may temporarily stop the output operation of a DC / DC converter over a predetermined period including the time of starting of a discharge lamp. As a result, the second power supply circuit is brought into a non-operating state at the time of starting the lamp, so that noise that may occur in the output wiring is prevented from inducing a malfunction of the second power supply circuit.

  The DC / DC converter includes a first output circuit that supplies a filament current to one filament of the low-pressure discharge lamp, and a second output circuit that supplies a filament current to the other filament of the low-pressure discharge lamp, A current detection circuit is provided in one output circuit, a voltage detection circuit for detecting an output voltage of the second output circuit is provided in a second output circuit, and a detection voltage detected by the voltage detection circuit has a predetermined value. When it exceeds, you may comprise so that a control part may stop the output operation of a DC / DC converter. This prevents the output of the DC / DC converter from entering an overvoltage state when the filament is disconnected or when the discharge lamp is not connected.

  Furthermore, in the output path of the second output circuit, a current fuse connected in series to the hot cathode filament may be provided on the hot cathode filament side of the voltage detection circuit. This prevents the output of the DC / DC converter from entering an overcurrent state when the filament is short-circuited.

  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 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. It is a figure which shows 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 T5 and T6, and filament 52 is connected to terminals T7 and T8 (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 between both ends of the discharge lamp 5 (that is, between the filaments 51 and 52) and the energized current are referred to as “lamp voltage” and “lamp current”, respectively. The current flowing through each of the filaments 51 and 52 is referred to as “filament”. It is called “current”. 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 divider 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”) shown at 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 composed of a low resistance element, and is inserted into the output current path of the step-down converter 24. A voltage value (hereinafter referred to as “detection value B”) generated in the current detection circuit 246 shown at the node B 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, and a protection circuit 33. 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 52 via the output wirings W3 and W4, and the other output is supplied to the filament 51 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 through terminal T4 → output wiring W4 → terminal T8 → igniter 6 → filament 52 → igniter 6 → terminal T7 → output wiring W3 → terminal T3 and becomes the filament current of the filament 52. 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 51, the terminal T6, the output wiring W2, and the terminal T2, and becomes the filament current of the filament 51.

  The current detection circuit (voltage detection resistor) 31 includes a low resistance element inserted between the ground G2 and the terminal T3 (output wiring W3). A voltage proportional to the filament current flowing in the filament 52 is generated in the current detection resistor 31. Hereinafter, the value of the filament current of the filament 52 detected by the current detection resistor 31 is referred to as a detected current value.

  The voltage detection circuit (voltage detection resistor) 32 includes a voltage dividing resistor circuit connected in parallel to the output capacitor 304. Hereinafter, the output voltage value of the output circuit 30a detected by the voltage detection resistor 32 is referred to as a voltage detection value.

  The protection circuit 33 is connected to the output circuit 30b, and includes a voltage detection circuit 330 including a resistor 331, a Zener diode 332, and a photocoupler 333, and a current fuse 335. In the voltage detection circuit 330, a series circuit of a resistor 331, a Zener diode 332, and a photodiode of a photocoupler 333 is connected in parallel to the output capacitor 306, and the phototransistor of the photocoupler 333 is connected to the control circuit 40 with a reference potential as the ground G1. The The current fuse 335 is connected in series with the filament 51 and the output wiring W2 on the filament 51 side of the voltage detection circuit 330.

  The voltage detection circuit 330 implements a protection function when output opening is detected. For example, if the output voltage of the output circuit 30b becomes excessive when the filament 51 is opened or when the discharge lamp 5 is not connected to the lighting device 1, the current flowing through the photodiode of the photocoupler 333 increases. The output value of the phototransistor of the photocoupler 333 (hereinafter referred to as “detection value D”) decreases. In response to the decrease in the detected value D, the control circuit 40 specifies the output open state, and stops the output operation of the DC / DC converter 30, that is, the driving of the switching element 301.

  The current fuse 335 realizes a protection function when an output short circuit is detected. For example, when the output current of the output circuit 30b becomes excessive when the filament 51 is short-circuited or when a short-circuit failure occurs between the output wirings W1 and W2, the current fuse 335 is blown and the output of the output circuit 30b is output. Opened. In this open state, as described above, the control circuit 40 stops the output operation of the DC / DC converter 30 by the protection function when the voltage detection circuit 330 detects the output open.

  The control unit 4 includes a control circuit 40 and a feedback circuit 41. As an outline, the control unit 4 controls the DC / DC converter 30 so that the current detection value detected by the current detection circuit 31 matches the target value, and the voltage detection value detected by the voltage detection circuit 32 is the target value. The DC / DC converter 30 is controlled to be equal to or less than the (upper limit value). That is, in the control unit 4, the filament current of the filament 52, which is the output current, is subjected to constant current control while the output voltage of the output circuit 30a is maintained below the upper limit value.

  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 voltage target value (upper limit value) and the detected value B matches the current 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.

  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 described later. The detection value C is determined by the feedback circuit 41 as will be described later. Further, the control circuit 40 can stop the switching element 301 based on the detection value D.

  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 (ie, filament current) 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. This 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) is controlled at a constant current 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 operational amplifier 411 for constant current control, and the voltage value corresponding to the target value of the filament current is input to the positive input terminal (+). 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.

  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.

  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.

  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, a transformer 604, and a capacitor 605. 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 turn ratio of the transformer 604, and is superimposed on the no-load secondary voltage as a high voltage pulse voltage. 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 (that is, the filament current) of the DC / DC converter 30 of the filament power supply circuit 3 is shown in the upper part of the vertical axis, and the output voltage (ie, the full bridge circuit 25 of the main power supply circuit 2 is shown in the lower part of the vertical axis. Lamp voltage), and the horizontal axis represents time.

  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 becomes the current value I1. It is assumed that the current value I1 is a current value necessary for the discharge lamp 5 to keep lighting stably even after the lamp is started.

  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. 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, after the lamp is started, 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 a DC filament current (I1) is supplied from the filament power supply circuit 3 to the filament 51 and Supplied to each of 52. 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, a DC voltage input from a part of the main power supply circuit 2 is converted into a DC filament current by the DC / DC converter 30 of the filament power supply circuit 3. The filament current is subjected to constant current control by the control unit 4. 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 applied to the filament 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.

<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 circuit 4, and the 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 general rule, the control unit 4 causes the DC / DC converter 30 to reduce the filament current after a predetermined time has elapsed since the start of energization of the filament current. In other words, in the present embodiment, the filament current is increased more than the filament current in the first embodiment during the preheating period. 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.

  The control unit 4 of this embodiment includes a control circuit 40 and a feedback circuit 41, and is configured such that the voltage of the voltage source 413 connected to the operational amplifier 411 of the feedback circuit 41 is 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 high level to the low level, the switching signal S1 is switched from the low level to the high level, the voltage value (target value) of the voltage source 413 decreases, and the operational amplifier 411 As a result of constant current control by the filament current, the filament current decreases.

  In the control circuit 40, the switching timing at which the switching signal S0 is output may be determined by an internal timer, or may be determined based on the detection value A or B. In any case, the switching timing may be approximately in the vicinity of the lamp start timing (may be before the lamp start or after the lamp start). The detection value A detects a rapid decrease in the lamp voltage accompanying the lamp start, and the detection value B detects the generation of the lamp current accompanying the lamp start. Therefore, when the switching timing is determined based on the detection value A or B, the switching timing is after the lamp is started.

  When the switching signals S0 and S1 are output before the lamp start and the filament current is reduced, the increase in the filament current by the filament power supply circuit 3 and the increase in the output voltage at the lamp start by the main power supply circuit 2 are in the same period. Not included. Therefore, a period during which the output power of the lighting device 1 as a whole increases significantly does not occur, which is preferable from the viewpoint of reliability management of the lighting device 1. On the other hand, when the switching signals S0 and S1 are output after the lamp is started and the filament current is reduced, even when the discharge is unstable immediately after the lamp is started (if any), the discharge of the electron discharge substance by the energization of the filament current is performed. Therefore, the lamp startability is further improved.

  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 (that is, the filament current) of the DC / DC converter 30 of the filament power supply circuit 3 is shown in the upper stage of the vertical axis, and the output voltage (ie, the full bridge circuit 25 of the main power supply circuit 2 is shown in the lower stage of the vertical axis. Lamp voltage), and the horizontal axis represents time.

  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 matches the current value I2. It is assumed that the current value I2 is larger than the current value I1 in the first embodiment.

  At time t2, the control unit 4 outputs the switching signal S1, the target value for constant current control (that is, the voltage value of the voltage source 413) is reduced, and the filament current decreases from the current value I2 to the current value I1.

  At time t3, 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 the lamp is started, 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 a DC filament current (I1) is supplied from the filament power supply circuit 3 to the filament 51 and Supplied to each of 52. As described above, the switching timing (t2) may occur after time t3.

  As described above, according to the lighting device 1 of the present embodiment, the following advantageous effects can be obtained in addition to the advantageous effects (1) to (3) described in the first embodiment.

(4) Coexistence of shortening of preheating period and power saving In the present embodiment, the filament current is reduced after a lapse of a predetermined time from the start of energization of the filament current. Thereby, since the filament current in the preheating period can be relatively increased, heating of the filaments 51 and 52 can be accelerated to shorten the preheating period. In addition, since the filament current during stable lighting can be reduced more than the filament current during the preheating period, it is possible to prevent power from being supplied to the filaments 51 and 52 during the stable lighting period, thereby saving power. It becomes possible to plan.

(5) Setting of optimum filament current for each period In the present embodiment, different filament currents can be set in the preheating period and the stable lighting period. Optimization of the filament current (current value I2) during the preheating period contributes to improvement of startability of the discharge lamp 5, and optimization of the filament current (current value I1) during the stable lighting period is the discharge stability of the discharge lamp 5. Contributes to improved lighting characteristics such as life. Therefore, by optimizing the current values I1 and I2, the startability of the discharge lamp 5 connected to the lighting device 1 and the lighting characteristics can be effectively realized.

<Third Embodiment>
In the second embodiment, the filament power supply circuit 3 continues to supply the filament current before and after the lamp start. In this embodiment, the output operation of the filament power supply circuit 3 is stopped during the lamp start period. The structure to be shown 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, as a general rule, the control circuit 40 temporarily stops the output operation of the DC / DC converter 30 (that is, driving of the switching element 301) over a predetermined period including when the lamp is started. This prevents noise that may occur during the lamp starting period from affecting the operation of the DC / DC converter 30.

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

  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. At time t0, constant current control is performed by the DC / DC converter 30 and the control unit 4 so that the filament current becomes the current value I2. The setting of the current values I1 and I2 is the same as in the second embodiment.

  At time t4, the control unit 4 outputs the switching signal S1, the voltage value of the voltage source 413 (that is, the target value for constant current control) is reduced, and the filament current is decreased from the current value I2 to the current value I1.

  At time t5, the control circuit 40 stops the operation of the DC / DC converter 30. That is, the switching element 301 of the DC / DC converter 30 is turned off.

  At time t6, the full bridge circuit 25 of the main power supply circuit 2 starts the output operation, and the no-load voltage Vo is temporarily output until the lamp start is completed. Thereafter, when the lamp start is completed at time t7, the output voltage of the full bridge circuit 25 becomes a lamp voltage VL substantially equal to the lamp voltage during stable lighting. That is, after starting the lamp, a low-frequency lamp current corresponding to the voltage value (VL) is supplied from the main power supply circuit 2 to the discharge lamp 5.

  At time t8, the control circuit 40 resumes the output operation of the DC / DC converter 30, whereby constant current control at the filament current value I1 is resumed. Note that the switching (t4) of the filament current from the current value I2 to the current value I1 may occur after time t5. If this switching occurs between times t5 and t8, the filament current drop itself does not appear in FIG. Moreover, it is preferable that the timing at which the control circuit 40 resumes the output operation of the DC / DC converter 30 at time t8 is determined based on the detected value A or B or both. As previously mentioned. Since the detection value A detects a rapid decrease in the lamp voltage accompanying the lamp start, and the detection value B detects the generation of the lamp current accompanying the lamp start, the control circuit 40 can detect the completion of the lamp start. .

  Although this embodiment is configured as an extension of the second embodiment, it may be configured as an extension of the first embodiment. That is, the filament current may be fixed to the current value I1 except for the stop period (t5 to t8) of the DC / DC converter 30.

  As described above, according to the lighting device 1 of the present embodiment, the advantageous effects (1) to (3) described in relation to the first embodiment and the advantageous effects (4) and (4) described in relation to the second embodiment. In addition to 5), the following advantageous effects can be obtained.

(6) Reduction of influence of noise on filament power supply circuit 3 According to the present embodiment, the output operation of the DC / DC converter 30 is stopped during the lamp starting period. Here, the lamp voltage and the lamp current are applied and energized to the output wirings W1 and W4 (and substantially the output wirings W2 and W3) to which the filament power supply circuit 3 is connected. At the time of starting the lamp, the lamp voltage and the lamp current largely fluctuate in a short time, so that noise may occur in the output wirings W1 to W4. However, according to the present embodiment, since the filament power supply circuit 3 is in an inoperative state at the time of starting the lamp, noise that may occur in the output wirings W1 to W4 may induce a malfunction of the filament power supply circuit 3. Is prevented.

<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. 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 signal S1) In the second and third embodiments, the control unit 4 generates the binary signal switching signal S1 and switches the filament current in two stages. Although shown, it is good also as a structure which the switching signal S1 of a multi-value signal is produced | generated in the control part 4, and a filament electric current is switched in multistep. Further, the controller 4 may be configured to generate a linearly variable switching signal S1 so that the filament current is gently switched.

(4) Modification concerning preheating configuration In each of the above embodiments, it is assumed that a preheating current is applied to both filaments 51 and 52. However, the startability and lighting characteristics of the discharge lamp 5 are improved by preheating only one filament. When secured (especially in the case of a discharge lamp for direct current lighting, etc.), the filament power supply circuit 3 may be connected to only one filament. In this case, for example, as shown in FIG. 10, the filament power supply circuit 3 includes a DC / DC converter 30, a current detection circuit 31, and a voltage detection circuit 32 having only one output circuit 30a. The filament current flowing in the filament 52 connected to the output wirings W3 and W4 is subjected to constant current control by the control unit 4. The other filament 51 is opened or short-circuited and is not substantially energized. Thereby, output wiring W2 becomes unnecessary and the installation ease of the lighting device 1 and the discharge lamp 5 increases.

(5) Modification concerning operation during stable lighting In each of the above embodiments, the filament current is supplied to each filament at the time of stable lighting after starting the lamp. When the discharge lamp does not require 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 31 Current Detection Circuit 32 Voltage Detection Circuit 33 Protection Circuit 51, 52 Hot Cathode Filament 330 Voltage Detection Circuit 335 Current Fuse

Claims (8)

A discharge lamp lighting device for lighting a low pressure discharge lamp having a hot cathode filament,
A first power supply circuit for supplying a low-frequency or direct-current lamp voltage or current to the low-pressure discharge lamp;
An insulated DC / DC converter that converts a DC voltage input from a part of the first power supply circuit into a DC filament current and supplies the filament current to the hot cathode filament, and a current value of the filament current A second power supply circuit having a current detection circuit to detect;
A discharge lamp lighting device comprising: a control unit that controls the DC / DC converter so that a current detection value detected by the current detection circuit matches a target value.   2. The discharge lamp lighting device according to claim 1, wherein the controller is configured to reduce the filament current to the DC / DC converter after a predetermined time has elapsed since the filament current was output from the DC / DC converter. Discharge lamp lighting device.   3. The discharge lamp lighting device according to claim 2, wherein after the filament current is output from the DC / DC converter and before the lamp voltage is output from the first power supply circuit, the control unit includes: A discharge lamp lighting device configured to reduce the filament current in the DC / DC converter.   The discharge lamp lighting device according to claim 2, wherein after the filament current is output from the DC / DC converter and the lamp voltage is output from the first power supply circuit, the control unit A discharge lamp lighting device configured to reduce the filament current in a DC / DC converter.   5. The discharge lamp lighting device according to claim 1, wherein the control unit temporarily stops the output operation of the DC / DC converter for a predetermined period including when the discharge lamp is started. 6. Discharge lamp lighting device configured in the above. In the discharge lamp lighting device according to any one of claims 1 to 5,
The DC / DC converter includes a first output circuit for supplying a filament current to one filament of the low-pressure discharge lamp, and a second output circuit for supplying a filament current to the other filament of the low-pressure discharge lamp;
The current detection circuit is provided in the first output circuit;
A voltage detection circuit for detecting an output voltage of the second output circuit is provided in the second output circuit,
The discharge lamp lighting device configured to stop the output operation of the DC / DC converter when the detected voltage detected by the voltage detection circuit exceeds a predetermined value.   7. The discharge lamp lighting device according to claim 6, wherein a current fuse connected in series to the hot cathode filament is provided on the hot cathode filament side of the voltage detection circuit in an output path of the second output circuit. A discharge lamp lighting device. The discharge lamp lighting device according to any one of claims 1 to 7, wherein the DC / DC converter is a flyback converter.

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