JP2006004669A - Discharge lamp driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp driving device which enables a discharge lamp to be stably lit without flicker even at an area of low-rate light control by supplying a current sufficient for discharge by impressing sufficient voltage to a primary winding 12 of a transformer 1 at the first cycle of start of lighting when switching from a turn-off period to a turn-on period. <P>SOLUTION: This discharge lamp driving device comprises: a discharge lamp 11 with an external electrode lit by a high-frequency rectangular wave current supplied to a secondary winding 13 side of the transformer 1; first and second capacitors 3 and 4 for forming a middle point bias connected in parallel with the first winding 12 of the transformer; first and second switching elements 7 and 8 for supplying current to the primary winding of the transformer; and a control circuit 2 impressing driving signals to the respective switching elements. A stable voltage can be supplied in starting the transformer 1 by turning on a third switching element 9 before a driving signal is applied to the primary winding of the transformer through the switching elements from the control circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a discharge lamp driving device for lighting an external electrode type discharge lamp.

  Conventionally, cold-cathode fluorescent lamps in which mercury is enclosed as a light source have been used for backlights for liquid crystal panels. Recently, external electrode fluorescent lamps in which xenon is enclosed instead of mercury, which is a harmful substance, have been developed. Yes.

  The outer surface electrode fluorescent lamp 11 shown in FIGS. 5 and 6 has a phosphor coating 22 deposited on the inner surface of a bulb 21 constituting a sealed discharge space, and an inner electrode 23 is sealed to one end of the bulb 21. In addition, an external electrode 24 formed by winding a conductive wire in a spiral shape is provided on the outer peripheral surface of the bulb 21, and a translucent resin film 25 having insulating properties for preventing a short circuit is wound. In order to turn on the outer electrode fluorescent lamp 11, the internal electrode 23 is connected to the voltage supply line 27 via the lead-in line 26, and the external electrode 24 is connected to the voltage supply line 27 ′ via the fixing metal rod 28. Then, using a power source (inverter) 29, for example, a high frequency rectangular wave voltage is applied to start discharging. By this discharge, ultraviolet light is emitted from xenon as a discharge medium, which is converted into visible light by the phosphor 22 and emitted to the outside, and used as a light source.

  In order to turn on the outer electrode fluorescent lamp 11 described above, it is optimal to apply a rectangular wave voltage. FIGS. 7, 8, and 9 are conventional circuit diagrams of a discharge lamp driving device, and FIG. 10 is a timing chart thereof. Is shown. In the case of the conventional circuit, the input voltage Vcc is always supplied to the circuit element group that drives the transformer 1 for generating high voltage regardless of whether the lamp 11 is turned off or on.

  FIG. 8 shows a state in which a positive lamp current is created when the switching element 7 is turned off by the drive signal a output from the control circuit 10 and the switching element 8 is turned on by the drive signal b. FIG. 9 shows a state in which a negative lamp current is created when the switching element 7 is turned on by the drive signal A and the switching element 8 is turned off by the drive signal B. That is, as shown in the timing chart of FIG. 10, the primary winding voltage of the lamp driving transformer 1 oscillates as “L → H → L → H → L → H →. By repeating the above, positive and negative lamp currents are supplied to the outer electrode fluorescent lamp 11 connected to the secondary winding 13 of the transformer 1. The control circuit 10 determines a given dimming signal 19 and repeats a series of operations as many times as necessary, thereby continuously applying positive and negative lamp currents to the lamp 11 to realize lamp lighting with high output efficiency. .

  However, in the conventional circuit system, as shown in FIG. 7, when the oscillation detection circuit 20 or the like for the purpose of detecting oscillation of the transformer 1 is directly connected to the primary winding 12 side of the transformer 1, a capacitor for creating a midpoint bias is used. Since the current Ib flows from 4 to the oscillation detection circuit 20 even though it is very small, the transformer 1 may start to start with the voltage (VC0) of the primary winding 12 of the transformer 1 lowered. Further, when lighting is started after being extinguished for a while (about 2 minutes or more), it is conceivable that the capacitors 3 and 4 are naturally discharged and fall to the GND potential. Note that, depending on the circuit system, the direction of the current Ib may be opposite to that in FIG. 7, but in this conventional example, an explanation will be given by taking a circuit that flows in for convenience.

  When the transformer 1 is started in a state where the voltage of the primary winding 12 of the transformer 1 is lowered, an excessive current flows through the semiconductor switching element 7 for driving the transformer as compared with the other semiconductor switching element 8. , 4 may be unbalanced and a spike-like high voltage may be generated in the primary winding 12 in some cases. FIG. 11 shows an actual waveform when the oscillation of the primary winding 12 is unstable only at the initial start of the transformer 1, and FIG. 12 shows an actual waveform when the unstable state continues.

  When the spike-like voltage described above is generated, the midpoint voltage (VC0) greatly fluctuates due to the influence, and in the worst case, the oscillation of the transformer 1 may continue to be unstable. For this reason, a period in which a normal rectangular wave voltage is not applied to the lamp 11 occurs, and the lamp light may flicker during this period. Further, when spike voltage noise exceeds the breakdown voltage of the semiconductor switching elements 7 and 8 for driving the transformer. There is a risk of surge destruction.

  The present invention has been made in view of such conventional problems, and a sufficient voltage is applied to the primary winding of the transformer by applying a sufficient voltage to the primary winding of the lighting in the first lighting start cycle that switches from the off period to the on period. An object of the present invention is to provide a discharge lamp driving device capable of stably lighting a discharge lamp without flickering even when the dimming rate is as low as about 1% by flowing a lamp current.

  The discharge lamp driving device according to the first aspect of the present invention is connected to the secondary winding side of the transformer, and is connected in parallel with the primary winding of the transformer, and an external electrode discharge lamp that is lit by passing a high-frequency rectangular wave lamp current. Connected first and second capacitors for creating a midpoint bias, first and second switching elements for passing a current through the primary winding of the transformer, and a drive signal applied to each of the switching elements And an input voltage supply circuit for turning on / off the input voltage supplied to the first and second capacitors for creating the midpoint bias connected to the primary winding side of the transformer. It is a feature.

  According to a second aspect of the present invention, in the discharge lamp driving device according to the first aspect, the input voltage supply circuit determines a dimming signal input to the control circuit, and the dimming rate is 0% when the lamp is turned off. The input voltage is sometimes cut off, and the input voltage is supplied when the dimming rate is other than 0%.

  According to the present invention, since the third switching element is turned on immediately before one of the first and second switching elements is turned off, the neutral bias capacitor is used. The transformer can be started after raising the midpoint voltage to almost ½ of the input voltage, and the reduction of the lamp current in the first lighting cycle can be improved, and stable lighting in a low dimming rate region is possible.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram of a discharge lamp driving device according to one embodiment of the present invention. In FIG. 1, a discharge lamp driving device includes a power source Vcc, a control circuit 2, first and second capacitors 3 and 4 on the primary side of a transformer 1, and elements having first and second resistance components. 5, 6, first, second, and third switching elements 7, 8, and 9, and the secondary side of the transformer 1 includes a discharge lamp 11 as a load. More specifically, first and second capacitors 3 and 4 are connected in series to the DC power source Vcc, and the side of the second capacitor 4 not connected to the first capacitor 3 is grounded. Yes. Further, one terminal of the primary winding 12 of the transformer 1 is connected to the DC power source Vcc via the first capacitor 3. A first switching element 7 is connected to the DC power source Vcc, and the first and second switching elements 7 and 8 are connected in series via elements 5 and 6 having first and second resistance components. It is connected.

  The control circuit 2 shapes the power supply voltage Vcc into a rectangular wave DC voltage, generates three waveform data, assigns this waveform to the drive signals A, B, and the input voltage switching signal C and outputs them. The drive signal a to be output operates the first switching element 7, the drive signal B operates the second switching element 8, and the input voltage switching signal C operates the third switching element 9. After the input voltage switching signal C is switched from the OFF state to the ON state, the signals A, B, and C are output as drive signals A, B, which are pulse signals whose phases are inverted, and the first switching element 7 and the first switching signal 7 The two switching elements 8 are alternately turned on and off.

  The side not connected to the element 6 having the second resistance component of the second switching element 8 is grounded. The other terminal of the primary winding 12 of the transformer 1 is connected between the element 5 having the first resistance component and the element 6 having the second resistance component. The other terminal of the primary winding 12 of the transformer 1 is, for example, a coil, a diode, a resistor, an element having a resistance component, or a combination of these as described in JP-A-2002-75682. 7 and 8 may be configured to input a rectangular wave DC voltage drive signal A, B.

  A third switching element 9 is connected immediately after the input end of the power supply Vcc, and constitutes an input voltage supply circuit 50. When the third semiconductor switching element 9 is turned on by the input voltage switching signal C output from the control circuit 2, the charging current Ia is supplied to the capacitors 3 and 4 during the charging period. If the charging current Ia is approximately equal to the leakage current Ib to the oscillation detection circuit 20 of the transformer 1, the voltage (Vcc / 2) when the power is turned on is maintained, and the initial voltage when the transformer 1 is started up is secured. The secondary winding 13 of the transformer 1 is connected to the outer surface electrode fluorescent lamp 11 as in the prior art.

FIG. 2 is a timing chart showing the relationship between the signals A, B, C, the primary winding voltage of the transformer 1 and the lamp current. In the discharge lamp driving device of the present embodiment, the third switching element 9 is turned on by the signal of the input voltage switching signal C immediately before the lighting mode is changed to the lighting mode, and the first and second capacitors 3 and 4 are connected. By raising the voltage supply from the cut-off state to Vcc at once, the input voltage Vcc is supplied to the drive circuit element group and the midpoint bias circuit, the midpoint bias generating capacitors 3 and 4 are charged uniformly, and the midpoint potential V _C1. Becomes approximately half of the input voltage Vcc (Vcc / 2), and it is possible to secure an initial voltage (generally Vcc / 4 to 3 Vcc / 4) of the primary winding 12 that is optimal for stable starting of the transformer 1. For this reason, an excessive spike-like current does not flow from the semiconductor switching element → the primary winding of the transformer → the midpoint bias capacitor, so that the voltages of the midpoint bias capacitors 3 and 4 are not disturbed, and the stable transformer 1 Startup and stable oscillation are possible continuously. As a result, the charging and discharging currents of the midpoint bias capacitors 3 and 4 after the second cycle become equal, so that the midpoint potential of the capacitors 3 and 4 can be maintained at a voltage of approximately Vcc / 2. In addition, the oscillating operation of the transformer can be continued, and the external electrode fluorescent lamp 11 such as a xenon fluorescent lamp can be lit with high brightness.

FIG. 3 shows an actual waveform when the transformer 1 according to the present embodiment is started. 3 that the transformer primary voltage V _T1 is stable even when the transformer 1 is started. Further, FIG. 4 showing the actual waveform when the lamp is lit in this embodiment shows that a stable voltage can be supplied even when the lamp is lit.

  As described above, in the discharge lamp driving device according to the present embodiment, even if a circuit for detecting the oscillation of the transformer is directly connected to the primary winding side of the transformer, it is used to create a midpoint bias immediately before entering the lighting mode. By starting voltage supply to the capacitor, the initial voltage on the primary side required for stable oscillation of the transformer can be optimized, and the semiconductor switching element → transformer primary winding → midpoint bias creation Since the excessive spike-like current does not flow to the capacitor for use, the voltage of the capacitor for creating the midpoint bias is not disturbed, and stable starting of the transformer and stable oscillation are continuously obtained. Such an external electrode fluorescent lamp can be lit without flickering even at a low dimming rate of about 1%.

The circuit diagram of the discharge lamp drive device of one embodiment of the present invention. The timing chart of the discharge lamp drive device of the said embodiment. The actual waveform figure at the time of the trans | transformer starting by the said embodiment. The actual waveform at the time of the lamp lighting by the said embodiment. The front view of an outer surface electrode fluorescent lamp. Front sectional drawing of an outer surface electrode fluorescent lamp. The circuit diagram of a prior art example. The conventional circuit diagram when the switch 8 is turned on. The conventional circuit diagram when the switch 7 is turned on. The timing chart figure of a conventional circuit. The actual waveform figure at the time of the transformer starting of a conventional circuit. The actual waveform figure at the time of unstable lighting of a conventional circuit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transformer 2 Control circuit 3, 4 Capacitor 7 1st switching element 8 2nd switching element 9 3rd switching element 11 External electrode fluorescent lamp 12 Primary winding 13 Secondary winding 19 Dimming signal 20 Oscillation of transformer Detection circuit 21 Valve 22 Phosphor film 23 Internal electrode 24 External electrode 50 Input voltage supply circuit Vcc power supply

Claims (2)

An external electrode discharge lamp that is connected to the secondary winding side of the transformer and is lit by passing a high-frequency rectangular wave lamp current;
First and second capacitors for creating a midpoint bias connected in parallel with the primary winding of the transformer;
First and second switching elements for passing a current through the primary winding of the transformer;
A control circuit for applying a drive signal to each of the switching elements;
A discharge lamp comprising: an input voltage supply circuit for turning on / off an input voltage supplied to the first and second capacitors for creating the midpoint bias connected to the primary winding side of the transformer. Drive device. The input voltage supply circuit determines a dimming signal input to the control circuit, cuts off the input voltage when the lamp is turned off and when the dimming rate is 0%, and the input voltage when the dimming rate is other than 0%. The discharge lamp driving device according to claim 1, wherein a voltage is supplied.

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