JP2006202682A - Discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device capable of realizing stable ignition and continuation of oscillation without generating abnormal sound of a transformer and deterioration of performance thereof. <P>SOLUTION: This discharge lamp lighting device is provided with: a control circuit 114 for outputting high-speed switching signals; switching elements S1 and S2 executing switching operations by the switching signals 1 and 2 outputted by the control circuit for creating a rectangular wave voltage from a constant voltage power source Vcc; a step-up transformer T1 for boosting the rectangular-wave voltage generated by the switching operations of the switching elements; a discharge lamp 13 discharged and lit by a high-frequency lamp current IL generated in the secondary winding of the step-up transformer; and an input voltage soft-start circuit 16 for gradually boosting, from a cut-off state to a constant voltage, a voltage from the constant voltage power source supplied to the primary winding of the step-up transformer or the switching element connected to the primary winding when the control circuit is shifted from a lighting-off mode to a lighting mode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a discharge lamp lighting device, for example, a discharge lamp lighting device suitable for a backlight light source of a liquid crystal display device used in a personal computer or a navigation system.

  Conventionally, an external electrode type dielectric barrier discharge type cold cathode fluorescent lamp using a rare gas instead of mercury, which is a harmful substance, has been developed from the viewpoint of environmental problems. An example of such an outer surface electrode type dielectric barrier discharge type cold cathode fluorescent lamp using a rare gas is shown in FIGS.

  In the lamp structure shown in FIGS. 11 and 12, reference numeral 1 denotes a glass tube having an inner wall coated with a phosphor 2, and a discharge medium containing at least xenon is sealed inside the glass tube 1. At least one end of the glass tube 1 is sealed with an internal electrode 4 via an introduction wire 3. On the outer wall of the glass tube 1, a conductive wire constituting the external electrode 5 is spirally wound along the tube axis direction. The external electrode 5 is covered with a translucent heat-shrinkable tube 6 and fixed to the surface of the glass tube 1, so that the position is not shifted.

  In this cold cathode fluorescent lamp of the outer surface electrode type dielectric barrier discharge type, the voltage supply line 8 is connected to the internal electrode 4 via the lead-in wire 3, and the voltage supply line is connected to the external electrode 5 via the fixing metal rod 7. 8 'is connected, and a high-frequency positive and negative lamp current IL is supplied between the internal electrode 4 and the external electrode 5 by using the inverter power supply 9. By supplying the high-frequency lamp current IL, the cold cathode fluorescent lamp starts discharging between the internal electrode 4 and the external electrode 5, and emits ultraviolet rays from the discharge medium xenon, which is converted into visible light by the phosphor 2. Can be used as a light source.

  In order to light the cold cathode fluorescent lamp efficiently, it is optimal to apply a rectangular wave voltage having a steep slope of the lamp voltage to the primary side of the step-up transformer whose secondary winding is directly connected to the lamp. . FIGS. 13 and 14 are circuit diagrams of a conventional discharge lamp lighting device, and FIG. 15 is a timing chart of each signal when shifting from the extinguishing mode to the lighting mode. In the case of the conventional circuit, the constant voltage input voltage Vcc is always supplied to the switching elements S1 and S2 and the capacitors C1 and C2 that drive the transformer T1 for generating a high voltage regardless of whether the fluorescent lamp 13 is turned off or on. Z1 and Z2 are resistors, inductors, diodes, or a combination of them.

  FIG. 13 shows a state in which a positive lamp current IL is created when the switching element S1 is turned off by the drive signal 1 from the control circuit 10 and the switching element S2 is turned on by the drive signal 2. FIG. 14 shows a state in which a negative lamp current IL is created when the switching element S1 is turned on by the drive signal 1 from the control circuit 10 and the switching element S2 is turned off by the drive signal 2. That is, as shown in the timing chart of FIG. 15, the primary winding voltage of the lamp driving transformer T1 is “L → H → L → H → L → H. By repeating the oscillation, positive and negative lamp currents IL are supplied to the cold cathode fluorescent lamp 13 connected to the secondary winding of the transformer T1. Then, the control circuit 10 determines the dimming signal 17 and repeats a series of these operations as many times as necessary, thereby continuously applying positive and negative lamp currents IL having a steep slope to the fluorescent lamp 13 and high output efficiency. The lamp is lit.

  However, when the conventional discharge lamp lighting device shifts from the above-described extinguishing mode (0% dimming mode) to the lighting mode (dimming mode other than 0%), the power circuit elements S1, S2, C1, and C2 are grouped. When the power circuit element group drives the primary winding of the transformer T1 at a high frequency while the constant-voltage power supply voltage (= Vcc) to be supplied is sufficiently supplied, the energy remaining in the transformer T1 is superimposed on it, so that at the initial stage of oscillation Excessive current flows to the transformer T1, which causes noises from the transformer T1, and sometimes has a problem that performance may be deteriorated and the life may be shortened.

  Further, in the circuit system of the conventional discharge lamp lighting device, as shown in FIG. 16, when an oscillation detection circuit 18 for the purpose of detecting oscillation of the transformer T1, for example, is directly connected to the primary winding side of the transformer T1, a neutral capacitor C2 From this, the current Ib flows to the oscillation detection circuit 18 to a minimum, but this may cause the start of the transformer T1 when the voltage (VC0) of the primary winding of the transformer T1 is reduced. appear. Further, when lighting is started after being extinguished for a while (after about 2 minutes or more), it is conceivable that the capacitors C1 and C2 are naturally discharged and fall to the GND potential. Thus, when the transformer T1 is started in a state where the voltage VC0 of the primary winding of the transformer T1 is reduced, an excessive current flows through the transformer driving switching element S1 as compared with the other switching element S2. The balance of the charge / discharge current of the capacitor C2 is lost, and as shown in FIG. 15, a spike-like high voltage SPK may be generated in the primary winding, and as a result, the spike current SPK also appears in the lamp current IL. .

  FIG. 17 shows an actual waveform when the oscillation of the primary winding is unstable only at the start of the transformer T1, and FIG. 18 shows an actual waveform when the unstable state continues. As shown in FIG. 17, the midpoint voltage (VC0) greatly fluctuates due to the influence of the spike-like voltage SPK, and in the worst case, the oscillation of the transformer T1 may continue to be unstable as shown in FIG. There is also. For this reason, the lamp light becomes unstable during a period in which a normal rectangular wave voltage is not applied to the fluorescent lamp 13, and spike-like voltage noise exceeds the breakdown voltage of the semiconductor switching elements S1 and S2 for driving the transformer. There was a problem that could cause surge destruction.

  As a countermeasure against abnormal driving noise (= abnormal noise) generated by excessive current flowing to the transformer at the initial stage of such transformer oscillation, transformer performance deterioration and life, and countermeasures against abnormal transformer oscillation In general, an element group having a capacitive component having a damping effect is provided on the primary winding side of the transformer. However, in order to light a cold cathode fluorescent lamp such as the xenon fluorescent lamp described above with high brightness, it is necessary to increase the peak of the lamp current by making the slope of the rectangular wave voltage of the primary winding of the transformer steep. When the element group having the capacitance component as described above is provided on the primary winding side, the slope of the voltage waveform is dull and the brightness is lowered, so that the above technical problem cannot be solved. .

  The present invention has been made in view of the above-described conventional technical problems, and does not include an element group having a capacitive component, so that there is no generation of abnormal sound or deterioration of performance of the transformer, and further, stability of the transformer. An object of the present invention is to provide a discharge lamp lighting device capable of extending the life of equipment by realizing continuous start-up and continuous oscillation, in particular, extending the life of transformers and lighting cold cathode fluorescent lamps with high brightness. .

  The discharge lamp lighting device of the invention of claim 1 is a control circuit that outputs a high-speed switching signal, a switching element that performs a switching operation by the switching signal output from the control circuit, and creates a rectangular wave voltage from a constant pressure power source, A step-up transformer for stepping up the rectangular wave voltage generated by the switching operation of the switching element; a discharge lamp that is turned on by a high-frequency lamp current generated in a secondary winding of the step-up transformer; Input voltage soft start for gradually increasing the voltage from the constant-voltage power source supplied to the primary winding of the step-up transformer or the switching element connected to the primary winding from the cutoff state to a constant pressure when shifting to the lighting mode And a circuit.

  According to a second aspect of the present invention, in the discharge lamp lighting device according to the first aspect, the input voltage soft start circuit has a soft start characteristic with a gentle slope over 20 [ms] from the input voltage of the constant pressure power source. A voltage is generated and supplied to the primary winding of the step-up transformer or the switching element connected to the primary winding.

  According to a third aspect of the present invention, in the discharge lamp lighting device according to the second aspect, the control circuit is configured until the soft start voltage output from the input voltage soft start circuit reaches a voltage that is ¼ of a constant pressure from 0 [V]. During this period, output of the high-speed switching signal is started.

  According to the discharge lamp lighting device of the present invention, when shifting from the extinguishing mode to the lighting mode, the input voltage soft-start circuit drives the transformer with a high frequency connected to the primary winding and the primary winding of the transformer. By gradually raising the voltage supplied to the circuit element group, the high-frequency voltage of the primary winding of the transformer gradually rises in proportion to this so that the voltage and current of the primary winding of the transformer do not increase suddenly. The step-up transformer can always start oscillation stably and can continue to oscillate.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  (First Embodiment) FIG. 1 shows a circuit configuration of a discharge lamp lighting device according to a first embodiment of the present invention. The discharge lamp lighting device of the present embodiment is a discharge lamp lighting device for lighting the cold cathode fluorescent lamp 13 which is the outer surface electrode type dielectric barrier discharge type shown in FIGS. 11 and 12, and is the conventional one shown in FIG. Similarly to the circuit, it includes a high-frequency step-up transformer T1, switching elements S1 and S2, capacitors C1 and C2, resistors, inductors, diodes or elements Z1 and Z2 that combine them as a power circuit element group, and switching elements S1 and S2. Are provided with a control circuit 14 that outputs a drive signal 1 and a drive signal 2 that are alternately turned on / off, and a transformer oscillation detection circuit 18. In the case of the present embodiment, the constant voltage input voltage Vcc is input, and the soft start circuit 16 that gradually increases the voltage from 0 [V] to Vcc within a predetermined time t as the output SW-Vcc on the power circuit element group side. It is characterized by having. The control circuit 14 is set to give the input voltage switching signal 15 to the soft start circuit 16 at a timing τ2 delayed by a predetermined time from the output start points τ1 of the drive signals 1 and 2.

  Next, the lighting operation of the xenon fluorescent lamp which is the cold cathode fluorescent lamp 13 by the discharge lamp lighting device having the above configuration will be described with reference to the timing chart of FIG.

  <Normal lighting state> In the normal lighting state, the control circuit 14 alternately turns on / off the switching elements S1 and S2 at a high speed by the driving signal 1 and the driving signal 2 that are alternately turned on / off, and the primary winding of the transformer T1. By applying a high-frequency rectangular wave voltage to and repeating oscillation “L → H → L → H → L → H...”, The cold cathode fluorescent lamp 13 connected to the secondary winding of the transformer T1 has positive and negative polarity. A lamp current IL is supplied. Then, the control circuit 14 determines the dimming signal 17 and repeats a series of operations as many times as necessary for each lighting cycle, thereby continuously applying a positive and negative lamp current IL with a steep slope to the fluorescent lamp 13. Light up efficiently.

  <Soft start operation> When the light-emitting mode is switched to the lighting mode, the control circuit 14 first starts outputting the drive signal 1 and the drive signal 2 at the timing τ1. Then, the input voltage soft start signal 15 is given to the input voltage soft start circuit 16 at the timing τ2 delayed by a predetermined time to start. The input voltage soft start circuit 16 starts the input voltage soft start operation at the timing τ2 when the input voltage soft start signal 15 is received, and is driven at a high frequency connected to the primary winding or the primary winding of the transformer T1. As a power system voltage to be supplied to the circuit element group, a power system voltage SW-Vcc having a gradual slope having a rising time t of 20 [ms] or more created from the constant pressure input voltage Vcc is supplied. As a result, the rectangular wave voltage VT1 of the primary winding of the transformer T1 is increased, and the high-frequency lamp current IL generated in the secondary winding is not distorted. Timing τ3 indicates the arrival timing of the steady state.

  As described above, in the discharge lamp lighting device according to the first embodiment of the present invention, stable start-up of the transformer T1 and continuation of stable oscillation can be achieved without providing a power circuit element group having a capacitive component. The generation of abnormal noise at the initial stage of the transformer drive and the sudden increase in current of the transformer primary winding can be suppressed, and the slope of the rectangular wave voltage of the primary winding of the transformer T1 is steep, so that the fluorescent lamp 13 is made high. Further, a zener diode can be added for surge protection of the semiconductor switching elements S1 and S2 for driving the transformer because a spike-like steep voltage is not generated in the primary winding of the transformer T1. Can be reduced.

  FIG. 3 is an actual waveform diagram at the time of starting the transformer in the discharge lamp lighting device of the first embodiment, and FIG. 4 is an actual waveform diagram at the time of stable lighting. From this, it can be confirmed that a spike-like steep voltage does not appear in the primary voltage of the transformer T1 and is stable.

  (Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The discharge lamp lighting device of the second embodiment is provided with gate voltage generation circuits 21 and 22 as means for performing a soft start operation with respect to the constant pressure input voltage Vcc, and receives a gate voltage generation start signal 24 from the control circuit 23. In this case, the control is performed to increase the rectangular wave voltage VT1 on the primary side of the transformer T1 by increasing / decreasing the gate voltages of the FET1 and FET2, which are switching elements. In FIG. 5, circuit elements common to the first embodiment shown in FIG. 1 are denoted by common reference numerals.

  Next, the operation of the discharge lamp lighting device of the second embodiment will be described with reference to the timing chart of FIG. When the control circuit 23 enters the lighting operation from the extinguished state, the control signal 23 outputs the driving signal 1 and the driving signal 2 to the switching elements S3 and S4 alternately at the timing τ11. The switching elements S3 and S4 function to intermittently apply the gate voltages created by the gate voltage creation circuits 21 and 22 to the gates of the FET1 and FET2, respectively, by an on / off operation. Each of FET1 and FET2 conducts when a gate voltage is applied, and applies a rectangular wave voltage of voltage VT1 to the primary winding of the transformer T1. The rectangular wave voltage IL to the secondary winding of the transformer T1 is induced by the rectangular wave voltage with respect to the primary winding, thereby causing the fluorescent lamp 13 to discharge.

  As a result, in the discharge lamp lighting device of the second embodiment, stable start-up of the transformer T1 and continuation of stable oscillation can be achieved without including an element group having a capacitive component, and as a result, the transformer drive initial stage Noise and a sudden increase in current of the primary winding of the transformer can be improved, and since the slope of the rectangular wave voltage of the primary winding of the transformer T1 is steep, the fluorescent lamp 13 can be lit with high brightness. Furthermore, since a spike-like steep voltage is not generated in the primary winding of the transformer, there is an advantage that it is possible to reduce countermeasure parts such as a Zener diode added for surge protection of the semiconductor switching element for driving the transformer.

  FIG. 7 is an actual waveform diagram at the time of starting the transformer in the discharge lamp lighting device according to the second embodiment, and FIG. 8 is an actual waveform diagram at the time of stable lighting. From this, it can be confirmed that a spike-like steep voltage does not appear in the primary voltage of the transformer T1 and is stable.

  FIG. 9 shows a circuit configuration of a discharge lamp lighting device that enables stable lighting even at a low dimming rate. In this discharge lamp lighting device, the control circuit 30 outputs the drive signal 1 and the drive signal 2 that alternately turn on / off the switching elements S1 and S2 at high speed, and outputs the drive signal 3 to the switching circuit S5. Yes. This switching circuit S5 is for short-circuiting both ends of the primary winding of the transformer T1 to suppress secondary voltage ringing and to reduce flickering when the fluorescent lamp 13 is turned on.

  In a region where the dimming rate is extremely low, the control circuit 30 turns on the switching element S6 by turning on the drive signal 3 and turns off S7 by turning on the third switching element S8, and is connected in parallel to the primary side of the step-up transformer T1. By passing a current through the resistor R1 and making the resonance frequency of the primary side of the step-up transformer extremely lower than when the third switching element S8 is turned off, the voltage of the transformer T1 and thus the secondary supplied to the fluorescent lamp 13 are supplied. Suppresses side voltage ringing (lamp voltage oscillation) and enables stable lamp lighting without flickering. On the other hand, if the dimming rate is increased, the control circuit 30 turns off the switching element S6 and turns on the switching element S7 by the drive signal 3, thereby turning off the switching element S8, and the resistor R1 from the primary winding of the transformer T1. Disconnect and move to normal operation.

  However, by always turning on the third switching element S8 at the time of low dimming, which may cause the lamp light to flicker, the ringing of the lamp voltage is suppressed, enabling stable lamp lighting without flickering. A phenomenon occurs in which the lamp current IL when the switching element S8 is on is reduced compared to the lamp current IL when the third switching element S8 is off. Therefore, depending on the performance of the lamp to be used, if the lamp current IL is reduced by always turning on the third switching element S8 at the time of low dimming, a sufficient starting current for the initial lighting of the lamp 13 cannot be secured. The lamp 13 may flicker due to causes other than lamp voltage ringing. Therefore, in the circuit shown in FIG. 9, the delay circuit 31 is provided so that the third switching element S8 is prevented from suddenly turning from off to on or suddenly from on to off. As a result, it is possible to avoid a factor that induces ringing of the voltage of the secondary winding of the transformer T1 (lamp voltage oscillation).

  It is a timing chart of operation | movement of the discharge lamp lighting device of FIG. In FIG. 10, the signal for turning on the third switching element S8, that is, the timing when the drive signal 3 is turned on is turned on after the delay time DT1 after the drive signal 1 and the drive signal 2 are output for at least one cycle. I am doing so. Further, since the lamp current IL does not decrease during the period in which the drive signal 3 is off, the absolute value of the first cycle of the lamp current IL in FIG. 10 is greater than when the delay circuit 31 is not provided (broken line waveform). It can be increased.

  Also in the discharge lamp lighting device having such a circuit configuration, the soft start circuit 16 as in the first embodiment is provided, or the gate voltage generation circuits 21 and 22 as in the second embodiment are provided. The power voltage SW-Vcc can be supplied to the primary side of the transformer T1 with respect to the constant voltage input voltage Vcc.

1 is a circuit diagram of a discharge lamp lighting device according to a first embodiment of the present invention. The timing chart of the lamp lighting operation by the said embodiment. The measured waveform figure of the drive signal at the time of starting by the said embodiment, and a transformer primary winding voltage. The measured waveform figure of the capacitor middle point voltage at the time of stable lighting by the said embodiment, and a transformer primary winding voltage. The circuit diagram of the discharge lamp lighting device of the 2nd Embodiment of this invention. The timing chart of the lamp lighting operation by the said embodiment. The measured waveform figure of the drive signal at the time of starting by the said embodiment, and a transformer primary winding voltage. The measured waveform figure of the capacitor middle point voltage at the time of stable lighting by the said embodiment, and a transformer primary winding voltage. The circuit diagram of the discharge lamp lighting device of the 3rd Embodiment of this invention. The timing chart of the lamp lighting operation of the embodiment. The front view of the conventional external electrode type dielectric barrier discharge type cold cathode fluorescent lamp. Sectional drawing of the said conventional cold cathode fluorescent lamp. Explanatory drawing 1 of the lighting operation of the conventional discharge lamp lighting device. Explanatory drawing 2 of the lighting operation of the said conventional discharge lamp lighting device. The timing chart of the lamp lighting operation of the conventional discharge lamp lighting device. The circuit diagram of the discharge lamp lighting device of another prior art example. The measured waveform figure of the drive signal and transformer primary winding voltage at the time of starting by the conventional discharge lamp lighting device. The measured waveform figure of the capacitor middle point voltage at the time of steady lighting by the said conventional discharge lamp lighting device and a transformer primary winding voltage.

Explanation of symbols

DESCRIPTION OF SYMBOLS 13 Fluorescent lamp 14 Control circuit 15 Input voltage soft start signal 16 Soft start circuit 17 Dimming signal 18 Oscillator detection circuit 21 Gate voltage generation circuit 22 Gate voltage generation circuit 23 Control circuit 24 Gate voltage generation start signal 30 Control circuit T1 Transformer S1, S2 Switching element Z1, Z2 Resistor, inductor, diode, or a combination of these elements C1, C2 Mid-point bias capacitor Vcc Input voltage SW-Vcc Power system voltage VT1 Primary winding voltage IL Lamp current Ib Leakage current

Claims (3)

A control circuit that outputs a high-speed switching signal;
A switching element that performs a switching operation by a switching signal output from the control circuit and creates a rectangular wave voltage from a constant-voltage power source;
A step-up transformer for stepping up the rectangular wave voltage generated by the switching operation of the switching element;
A discharge lamp that is ignited by a high-frequency lamp current generated in the secondary winding of the step-up transformer;
When the control circuit shifts from the light-off mode to the light-up mode, the voltage from the constant-voltage power source supplied to the primary winding of the step-up transformer or the switching element connected to the primary winding is gradually constant from the cut-off state. A discharge lamp lighting device comprising an input voltage soft start circuit that boosts the voltage to a maximum.   The input voltage soft start circuit creates a soft start voltage having a gradually rising characteristic over 20 [ms] or more from the input voltage of the constant voltage power supply, thereby generating a primary winding or a primary winding of the step-up transformer. The discharge lamp lighting device according to claim 1, wherein the discharge lamp lighting device is supplied to the switching element connected to a line. The control circuit starts outputting the high-speed switching signal until the soft start voltage output from the input voltage soft start circuit reaches a voltage of ¼ of a constant pressure from 0 [V]. The discharge lamp lighting device according to claim 2.

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