JP2005150026A - Discharge lamp driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To light, with high luminance, a dielectric barrier discharge type discharge lamp where the temperature rise of a component is small and power efficiency is high even when a small MOSFET is used as an unidirectional current element. <P>SOLUTION: This discharge lamp driving device is provided with a power feed device for applying a periodical rectangular-wave high voltage between two electrodes of the discharge lamp 13. The power feed device is composed of: a control circuit 10 serially connected to a D.C. power source Vcc for generating first to third rectangular-wave driving signals; a step-up transformer T1 for which first and second rectangular-wave driving signals 11 and 12 outputted from the control circuit are inputted between its primary terminals and the respective electrodes of the discharge lamp are connected between its secondary terminals; first and second elements S1 and S2 interlaid by corresponding to the respective first and second rectangular-wave driving signals; and a flicker prevention circuit interlaid between the first and second elements and having a MOSFET S3 switched in response to a third driving signal 14 from the control circuit and an impedance element Z1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a discharge lamp driving device for lighting an outer surface electrode type discharge lamp such as a dielectric barrier discharge type discharge lamp.

  Cold cathode discharge lamps in which mercury is enclosed in lamp tubes have been used as backlight sources for liquid crystal display devices used in displays such as personal computers and navigation systems, but in recent years, instead of mercury, a harmful substance. A discharge lamp enclosing a rare gas such as xenon has been developed, and a discharge lamp driving device for lighting it has also been developed.

  6 and 7 show the structure of a dielectric barrier discharge type discharge lamp using xenon as a discharge medium as a conventional outer electrode type discharge lamp using a rare gas as a discharge medium. FIGS. 8 and 9 show the discharge lamp. FIG. 10 shows a timing chart of discharge lamp lighting control. FIG. 10 shows a circuit configuration of a half-bridge discharge lamp driving device for lighting the lamp.

  In the rare gas outer surface electrode type discharge lamp shown in FIGS. 6 and 7, a film of phosphor 2 is formed on the inner wall of the glass tube 1, and a discharge medium containing at least xenon is enclosed in the glass tube 1. . An internal electrode 4 is sealed to at least one end of the glass tube 1 via an introduction wire 3, and an electrically conductive substance having an arbitrary shape is installed as an external electrode 5 along the tube axis direction on the outer wall of the glass tube 1. It is. The external electrode 5 is formed, for example, by winding a linear conductive material in a spiral shape around the outer peripheral surface of the glass tube 1, and is fixed to the surface of the glass tube 1 by covering with a translucent heat shrinkable tube 6. is there. A voltage supply line 8 is connected to the internal electrode 4 via an introduction line 3, and a voltage supply line 8 ′ is connected to the external electrode 5 via a fixing metal rod 7.

  In this rare gas outer surface electrode type discharge lamp, a high-frequency rectangular wave voltage is applied between these electrodes 8 and 8 'by using an inverter power supply device 9 to start discharge in the glass tube 1, and xenon as a discharge medium. Then, ultraviolet rays are emitted from the phosphor 2, and the phosphor 2 is irradiated with the ultraviolet rays to emit visible light, which is used as a light source.

  In order to light this rare gas outer electrode type discharge lamp, it is optimal to apply a rectangular wave voltage between both electrodes of the discharge lamp from the inverter power supply device. Conventionally, the discharge of the circuit configuration shown in FIGS. It is turned on by an electric light driving device. In this discharge lamp driving device, a rare gas outer surface electrode type fluorescent lamp 13 is connected to the secondary winding side of the step-up transformer T1, and capacitors C1 and C2 for creating a midpoint bias are connected in parallel to one end of the primary winding side. Is connected to the power supply Vcc and the ground GND through the capacitors C1 and C2, and the other end on the primary winding side is directly or an impedance element having an impedance component such as a coil, a diode or a resistor. A high-frequency rectangular wave voltage is supplied from the semiconductor switching elements S1 and S2 via Z1 or an element group in which Z1 is combined. 8 and FIG. 9, the impedance switching element Z1 is connected to the semiconductor switching element S1 side, and the semiconductor switching element S2 side is directly connected to the step-up transformer T1. This will be described using a circuit configuration.

  The control circuit 10 includes an oscillator, a counter, and a microcomputer. Each time a predetermined number of pulses of the oscillator are counted, an on (H) signal and an off (L) signal are alternately output, and the first and second drive signals are output. Generate two rectangular wave signals so as to have opposite phases to each other, and output them as a first drive signal (1) 11 and a second drive signal (2) 12, and the drive signal (1) 11 One switching element S1 is operated, and the drive signal (2) 12 operates the second switching element S2.

  FIG. 8 shows a state in which the switching element S1 is turned off by the driving signal (1) 11 output from the control circuit 10 and the switching element S2 is turned on by the driving signal (2) 12, thereby generating a positive lamp current. ing. FIG. 9 shows a state in which a negative lamp current is created when the switching element S1 is turned on by the drive signal (1) 11 and the switching element S2 is turned off by the drive signal (2) 12.

  As shown in the timing chart of FIG. 10, the primary winding voltage of the lamp driving transformer T1 is “L → H → L → H → L →” while the drive signal (1) 11 and the drive signal (2) 12 are on. By repeating “H...”, Positive and negative lamp currents are supplied to the outer surface electrode type discharge lamp 13 connected to the secondary winding of the transformer T1. By repeating these operations, the rectangular wave voltage is continuously supplied to the lamp 13 in the conventional discharge lamp driving device shown in FIGS. 8 and 9, thereby the rare gas outer surface electrode type discharge lamp 13 having a capacity component. The positive and negative lamp currents IL are continuously applied to the lamps, and a lamp with high brightness can be realized.

  However, in the conventional example, in order to further increase the luminance, it is necessary to pass a large amount of lamp current through the outer electrode type discharge lamp 13 (for example, 2 mA or more per lamp) or the kind of rare gas sealed in the lamp 13 If the lamp current in the positive or negative ringing state occurs after a steep lamp current flows at the rise or fall of the lamp voltage due to the influence of the gas pressure, the time constant of the step-up transformer T1, etc., the normal polarity The lamp current opposite to that is a reactive current and does not contribute to light emission. In particular, as shown in the waveform of the lamp current IL in FIG. 10, a linking current opposite to the direction flows during a current period (= tp) in which the positive charge is applied to the inside of the glass tube wall of the lamp 13. As a result, there is a phenomenon that the luminance is lowered and the luminance is low for every time power is applied. In this specification, the direction of the current flowing in the direction in which a positive charge is applied to the inside of the glass tube wall of the lamp 13 is defined as a positive current. In this case, however, the negative lamp current particularly contributes greatly to the light emission of the lamp 13. Current.

  FIG. 11 shows an actual waveform of the conventional example. In this figure, the waveform VG2 is a gate control signal when a general N-channel MOSFET is used as the semiconductor switching element S2, and the voltage of the portion directly connected to the semiconductor switching element S2 on the primary side of the transformer T1 is shown. The waveform is V1, and the waveform of the current flowing from the primary side of the transformer T1 to the semiconductor switching element S2 is represented by I1, but the current waveform I1 is opposite to the normal polarity as seen in the part surrounded by the broken line circle. It can be seen that the reactive current flows.

  In order to improve the ringing of the lamp current with respect to such a conventional example, Japanese Patent Laid-Open No. 2002-246196 (Patent Document 1) describes a diode or MOSFET as a unidirectional current element that allows a current to flow in one direction. A technique is described in which a parasitic diode is connected in series to at least one of the semiconductor switching elements S1 or S2 to improve luminance efficiency.

  12 and 13 show a circuit configuration of a second conventional example using a diode D1 as a unidirectional current element. The diode D1 in the drawing may use a MOSFET parasitic diode. The control method for the discharge lamp driving apparatus of the second conventional example is the same as that of FIGS. 8 and 9 of the previous conventional example, but can be seen in the lamp current (= IL) shown in the timing chart of FIG. Since such a ringing state does not occur, the circuit configuration of the second conventional example has an advantage that there is no invalid lamp current and the lamp can be lit with higher brightness.

However, in the second conventional example, in order to light the rare gas outer surface electrode type discharge lamp 13 connected to the secondary side of the step-up transformer T1, a high-voltage rectangular wave lamp voltage is required. When a diode D1 or a MOSFET parasitic diode is used as an element, a forward current (= VF) is small because a large current of several amperes to several tens of amperes needs to flow through the primary side of the step-up transformer T1. If the parts of the large package are not used, there is a problem that the surface temperature of the diode becomes higher by 50 ° C. or more than the ambient temperature. Further, in the case of a MOSFET using a parasitic diode, there is a problem that the component temperature rises more remarkably and the surface temperature becomes as high as 70 ° C. than the ambient temperature.
JP 2002-246196 A

  The present invention has been made in view of the above-described conventional technical problems. Even when a small MOSFET is used as a unidirectional current element, the temperature rise of the component is small, the power efficiency is high, and the dielectric barrier discharge type discharge is performed. An object of the present invention is to provide a discharge lamp driving device capable of lighting a lamp with high brightness.

  The invention of claim 1 is a discharge lamp driving device comprising an outer surface electrode type discharge lamp and a power feeding device for applying a periodic rectangular wave high voltage between two electrodes of the outer surface electrode type discharge lamp. The power supply device is connected in series to a DC power source, and generates a first, second and third drive signals, and first and second drive signals output from the control circuit as primary. A step-up transformer that is input between the side terminals, and each electrode of the outer electrode type discharge lamp is connected between the secondary side terminals, and the first and second drive signals output from the control circuit. A first and a second switching element interposed between the first and second switching elements, and a MOSFET that opens and closes in response to a third drive signal output from the control circuit. And a circuit element having a resistance component in series A flicker prevention circuit connected to and connected in parallel to the primary side of the step-up transformer with respect to the DC power source, and having one of the primary side terminals of the step-up transformer and one end of the MOSFET connected thereto. The MOSFET has a drain side and a source side connected to each other in a reverse manner, and the third drive signal applied to the gate of the MOSFET is at least during the ON period of the first and second switching elements. It is characterized in that the signals are different in two or more states.

  According to a second aspect of the present invention, in the discharge lamp driving device according to the first aspect, the third drive signal is obtained when the first switching element is off, the second switching element is on, and The MOSFET is turned on during a period when a large current flows through the second switching element having a steep regular polarity, and the parasitic diode of the MOSFET is operated during the subsequent ringing period. Is a signal in a state of turning off.

  According to the present invention, a MOSFET is used as a unidirectional current element, and at least two kinds of control signals having different states are supplied as a gate signal of the MOSFET while the semiconductor switching element is on. Even if a small MOSFET is used, the temperature rise of the parts is small, the power efficiency is high, and the outer electrode type discharge lamp can be lit with high brightness.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1, 2, and 3 each show a circuit configuration of one embodiment of the present invention, showing three different switching states, and FIG. 4 shows a timing chart. The discharge lamp driving device of the illustrated embodiment is a half-bridge type as in the first and second conventional examples, but as a circuit method for controlling the primary winding side of the step-up transformer T1 Any of a full-bridge method, a half-bridge method, a push-pull method, and a mid-tap method can be employed. In addition, common reference numerals are used for those common to the circuit elements of the conventional example.

  The discharge lamp driving device according to the present embodiment is one of the primary windings of the step-up transformer T1, either directly to at least one primary winding or the impedance element Z1 having an impedance component such as an inductor or a resistor. The flicker prevention circuit 20 is configured by connecting a MOSFET serving as the unidirectional current element S3 with the first and second semiconductor switching elements S1 and S2 connected in series with the MOSFET. It is a feature.

  The control circuit 10 generates the drive signal (1) 11 and the drive signal (2) 12 whose on / off phases are opposite to each other as in the conventional example, and as the third drive signal (3) 14, During the on period of the drive signal (2) for the second semiconductor switching element S2, at least two kinds of different signals are generated. The control circuit 10 includes an oscillator, a counter, and a microcomputer. Each time a predetermined number of pulses of the oscillator are counted, an on (H) signal and an off (L) signal are alternately output. Two rectangular wave signals are generated so as to have opposite phases with each other in the drive signal, and these are output as the first drive signal (1) 11 and the second drive signal (2) 12, and the drive signal (1) 11 Operates the first switching element S1, and the drive signal (2) 12 operates the second switching element S2. The control circuit 10 further generates the drive signal (1) 11 and the drive signal (2) 12 whose on / off phases are opposite to each other as described above, and as the third drive signal (3) 14, During the on period of the drive signal (2) for the second semiconductor switching element S2, at least two kinds of different signals are generated.

  The circuit configuration of the discharge lamp driving device of the present embodiment shown in the figure is such that the portion of the diode D1, which is a unidirectional current element, is a MOSFET so that it can be easily compared with the second conventional circuit example shown in FIGS. The configuration is replaced with. However, in the MOSFET as the unidirectional current element S3, the drain side and the source side are connected in the opposite direction, and the gate is connected to the second semiconductor switching element S2 connected in series with the MOSFET. Further, at least two kinds of drive signals (3) 14 having different states are supplied from the control circuit 10. That is, as shown in FIG. 4, two types of signals having different states of tA and tB are supplied as the drive signal (3) 14 during the ON period of the second semiconductor switching element S2.

  Next, the operation of the discharge lamp driving device configured as described above will be described.

  I) As shown in FIG. 1, when the first switching element S1 is off and the second switching element S2 is on, the regular semiconductor has a steep and large steep polarity during the on-period of the second semiconductor switching element S2. In the period in which the current flows (period corresponding to the period tA in FIG. 4), the drive signal (3) is set to “H” in order to operate the MOSFET which is the unidirectional current element S3 as a switching element having an extremely low ON voltage. To do.

  II) Then, in the subsequent ringing period (a period corresponding to the period tB in FIG. 4), the parasitic diode of the MOSFET (S3) operates so as to cut the current in the reverse direction as shown in FIG. The drive signal (3) 14 is set to “L”.

  By controlling the MOSFET (S3) in this way, in the period during which a large current flows (= tA), the on-voltage of the MOSFET (S3) is very small, so that the temperature rise is kept very low and the ringing period (= During tB), the current in the normal direction in which the parasitic diode is turned on is extremely small and the flowing time is short, so that the heat generation of the parasitic diode can be kept low.

  III) As shown in FIG. 3, even when the first switching element S1 is on and the second switching element S2 is off, the gates of the MOSFETs as the unidirectional current element S3 are I) and II). Similarly to the state, two types of signals having different states of tA and tB are supplied as the drive signal (3) 14. However, during the period in which the second switching element S2 is off, no current flows through this branch regardless of whether the MOSFET (S3) is on or off.

  FIG. 5 shows an actual waveform of the present embodiment. 5 is a specific circuit example in the case where an N-channel MOSFET is used for the second semiconductor switching element S2 and the MOSFET as the unidirectional current element S3 in the circuit shown on the left of the actual waveform in FIG. It is. In other words, the circuit configuration is such that the drains D of the N-channel MOSFETs are connected to each other.

  From the actual waveform of FIG. 5, the current (= I2) flowing from the primary side MOSFET (S3) of the transformer T1 to the second semiconductor switching element S2 is the same as the actual waveform of the conventional example shown in FIG. It can be seen that there is no reactive current of reverse polarity. In particular, during the ON period of the second semiconductor switching element S2 in FIG. 5, a period during which a steep lamp current flows when the lamp voltage rises or falls, that is, a period during which a steep large current of normal polarity flows. The diode shown in FIGS. 12 and 13 is further optimized by optimizing the phase difference with the ON period of the third drive signal (3) 14 (period corresponding to the period tA in the timing chart of FIG. 4). Since the on-voltage is smaller than that of the second conventional circuit using, power supply efficiency is further improved.

  As described above, in the discharge lamp driving device according to the present embodiment, since the current flowing through the MOSFET as the unidirectional current element S3 is small, the component temperature is lowered as much as the diode of the large package even if the small MOSFET is employed. In addition, since the reactive current in the reverse direction is suppressed, the power efficiency is increased and the luminance can be increased. In addition, the board area can be reduced as compared with the prior art. Therefore, as a lighting circuit for a backlight light source of a liquid crystal display device used in navigation and TV monitors that require a reduced component temperature, board area, and high luminance. It can be introduced.

The circuit diagram of the switching state of the 1st state of the discharge lamp drive device of one embodiment of this invention. The circuit diagram of the 2nd switching state of the said embodiment. The circuit diagram of the 3rd switching state of the said embodiment. The operation | movement timing chart of each circuit element of the said embodiment. FIG. 6 is a waveform diagram of voltage and current of each circuit element in the embodiment. The front view of the conventional dielectric barrier discharge type discharge lamp. Sectional drawing of said dielectric barrier discharge type discharge lamp. The circuit diagram of the 1st switching state of a 1st prior art example. The circuit diagram of the 2nd switching state of a 1st prior art example. The operation | movement timing chart of each circuit element of a 1st prior art example. FIG. 6 is a waveform diagram of voltage and current of each circuit element of the first conventional example. The circuit diagram of the 1st switching state of a 2nd prior art example. The circuit diagram of the 2nd switching state of a 2nd prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass tube 2 Phosphor 4 Internal electrode 5 External electrode 9 Feeding device 10 Control circuit 11 Drive signal (1)
12 Drive signal (2)
13 External electrode discharge lamp 14 Drive signal (3)
20 Flicker prevention circuit S1 First switching element S2 Second switching element S3 MOSFET
T1 Step-up transformer C1, C2 Middle bias capacitor Z1 Impedance element V1 Voltage of primary winding of transformer V2 Voltage of source side of MOSFET VG2 Gate signal of second switching element VG3 Gate signal of MOSFET IL Lamp current I2 of MOSFET Source current tA MOSFET on period tB MOSFET off period

Claims (2)

A discharge lamp driving device comprising: an outer surface electrode type discharge lamp; and a power feeding device for applying a periodic rectangular wave high voltage between both electrodes of the outer surface electrode type discharge lamp,
The power supply device
A control circuit connected in series to the DC power source and generating the first, second and third drive signals;
A step-up transformer in which first and second drive signals output from the control circuit are input between primary terminals, and each electrode of the outer surface electrode type discharge lamp is connected between the secondary terminals;
The first and second switching elements inserted corresponding to the first and second drive signals output from the control circuit, respectively, are inserted between the first and second switching elements, A MOSFET that opens and closes in response to the third drive signal output from the control circuit and a circuit element having a resistance component are connected in series, and are arranged and connected in parallel to the primary side of the step-up transformer with respect to the DC power supply. And a flicker prevention circuit having one of primary terminals of the step-up transformer and one end of the MOSFET connected thereto,
The MOSFET has its drain side and source side connected in the opposite direction,
The discharge lamp driving device according to claim 1, wherein the third driving signal given to the gate of the MOSFET is a signal having at least two different states during the ON period of the first and second switching elements. In the third drive signal, a large current flows through the second switching element having a steep normal polarity when the first switching element is off, the second switching element is on. 2. A signal for turning on the MOSFET during a period, and a signal for turning off the MOSFET so that a parasitic diode of the MOSFET operates in a subsequent ringing period. The discharge lamp driving device described.

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