JP2007109606A - Discharge lamp driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp driving circuit capable of instantly stopping lighting of a discharge lamp when conductive contact occurs. <P>SOLUTION: This discharge lamp driving device 1 is equipped with a driving circuit 6 to drive a transformer 5 for lighting the discharge lamp 2, a control circuit 7 to control the driving circuit 6, a current detecting circuit 8 to detect a current on the high voltage side of the transformer 5 as a conductive contact voltage, and a stop circuit 9 to instruct the control circuit 7 to stop driving the transformer 5 when comparing the conductive contact voltage detected by the current detecting circuit 8 with a conductive contact voltage reference voltage to detect occurrence of conductive contact, and determining that the conductive contact voltage is larger than the conductive contact reference voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a discharge lamp driving device.

  The discharge lamp driving device is used as a backlight device for a liquid crystal display device used in, for example, a portable information terminal, a computer, and a television. The discharge lamp driving device includes a plurality of discharge lamps, an inverter circuit that lights these discharge lamps, a control circuit that controls the inverter circuit, and the like. Among such discharge lamp driving devices, there has been proposed a discharge lamp driving device that instructs the control circuit to stop the output of the inverter circuit when an abnormality occurs in the discharge lamp (see, for example, Patent Document 1).

  For example, as shown in FIG. 4, the discharge lamp driving device 101 includes four discharge lamps 102 and an inverter circuit 103 that lights the discharge lamps 102. The inverter circuit 103 includes four connectors 104 to which the respective discharge lamps 102 are respectively connected, two transformers 105 connected in correspondence to the connectors 104, and two drive circuits 106 that drive the transformers 105, respectively. A control circuit 107 that controls the drive circuit 106, a high-voltage side current of each transformer 105, that is, an open current detection circuit 108 that detects an open current as an open voltage, and a detection result of the open current detection circuit 108 On the basis of this, a stop circuit 109 that instructs the control circuit 107 to stop driving the transformer 105 is configured.

In the discharge lamp driving device 101 having such a configuration, for example, when the discharge lamp 102 is opened due to disconnection or breakage, the open current detection circuit 108 detects the open current as an open voltage, and the stop circuit 109 detects the open voltage. Is determined to be input for a predetermined time or more, and when it is determined that the open current is input for a predetermined time, the control circuit 107 is instructed to stop driving all the transformers 105. As a result, when the discharge lamp 102 is opened due to disconnection or breakage, all the discharge lamps 102 are turned off.
JP-A-5-182773

  However, in the above-described discharge lamp driving device 101, when a conductive contact is caused by a person or an object, all the discharge lamps 102 remain lit. When the cause of the conductive contact is the human body, current continues to flow through the human body.

  Usually, attention is paid to the fact that a person disassembles or touches the discharge lamp driving device 101. For example, the discharge lamp driving device 101 is disassembled ignoring the attention. There is a possibility. At this time, if a human hand, a driver, or the like contacts a high voltage portion on the high voltage side of the transformer 105, a large current continues to flow through the human body. For this reason, when the conductive contact occurs, it is necessary to stop the lighting of the discharge lamp 102 instantaneously.

  In particular, with the recent increase in the screen size of the display device, the length of the discharge lamp 102 of the discharge lamp driving device 101 has become longer, and the voltage required for good lighting of the discharge lamp 102 has increased. Therefore, the voltage on the high voltage side of the transformer 105 is set high. For this reason, it is important to stop the lighting of the discharge lamp 102 instantaneously when a conductive contact occurs.

  The present invention has been made in view of the above, and an object thereof is to provide a discharge lamp driving device capable of instantaneously stopping lighting of a discharge lamp when conductive contact occurs.

  According to an embodiment of the present invention, in a discharge lamp driving device, a driving circuit for driving a transformer for lighting a discharge lamp, a control circuit for controlling the driving circuit, and a current on the high voltage side of the transformer are in conductive contact Compares the current detection circuit detected as a voltage with the conductive contact voltage detected by the current detection circuit and the conductive contact reference voltage for detecting the occurrence of conductive contact, and determines that the conductive contact voltage is greater than the conductive contact reference voltage. In this case, a stop circuit that instructs the drive control circuit to stop driving the transformer is provided.

  In the feature according to the embodiment of the present invention, when it is determined that the conductive contact voltage is larger than the conductive contact reference voltage, the occurrence of the conductive contact is detected by providing a stop circuit instructing the drive stop of the transformer in the drive control circuit. Then, since the drive of the transformer is stopped, the discharge lamp is turned off instantaneously.

  ADVANTAGE OF THE INVENTION According to this invention, the discharge lamp drive device which can stop lighting of a discharge lamp instantaneously when a conductive contact generate | occur | produces can be provided.

  The best mode for carrying out the present invention will be described with reference to FIGS.

  As shown in FIGS. 1 and 2, the discharge lamp driving device 1 according to the embodiment of the present invention includes, for example, four discharge lamps 2 and an inverter circuit 3 that lights those discharge lamps 2.

  The inverter circuit 3 includes four connectors 4 to which the respective discharge lamps 2 are respectively connected, two transformers 5 connected in correspondence with the connectors 4, and two drive circuits 6 that drive the transformers 5, respectively. A control circuit 7 for controlling the drive circuit 6, a current detection circuit 8 for detecting a current on the high voltage side of each transformer 5, and the control circuit 7 based on the detection result by the current detection circuit 8 It comprises a stop circuit 9 for instructing to stop driving.

  The high voltage side electrode of the discharge lamp 2 is connected to the transformer 5 via the connector 4. Moreover, the low voltage side electrode of the discharge lamp 2 is grounded. For example, a cold cathode discharge lamp is used as the discharge lamp 2.

  The transformer 5 includes a core (not shown) serving as a magnetic core, a primary winding 5a wound around the core, and two secondary windings 5b wound around the core. The number of turns of the secondary winding 5b is larger than the number of turns of the primary winding 5a. Thereby, the transformer 5 becomes a step-up transformer, and the primary winding 5a becomes the low voltage side and the secondary winding 5b becomes the high voltage side.

  A drive circuit 6 is connected to the primary winding 5 a of the transformer 5. Resonating capacitors C1 to C4 are connected in parallel to the two secondary windings 5b of the transformer 5, respectively. The high-voltage terminals of the two discharge lamps 2 are connected to the high-voltage terminals of the two secondary windings 5 b of the transformer 5 via the corresponding connectors 4. Furthermore, capacitors C5 to C8, resistors R1 to R4, and a current detection circuit 8 are connected to the low voltage terminals of the two secondary windings 5b of the transformer 5, respectively.

  The drive circuit 6 converts a DC voltage from the DC power supply VDD into an AC voltage, that is, a high-frequency and high-frequency AC voltage, and supplies the AC voltage to the transformer 5. In response to this, the transformer 5 performs driving for boosting the voltage.

  The control circuit 7 controls the drive circuit 6 so as to keep the lamp voltage (for example, amplitude and frequency, for example, see FIG. 3) of each discharge lamp 2 constant. The control circuit 7 is connected to a DC power supply VDD.

  The current detection circuit 8 is a conductive contact between an open current detection circuit 8a that detects a current on the high voltage side of each transformer 5, that is, an open current as an open voltage for open detection, and a high voltage side current of each transformer 5, that is, a limited current. And a limited current detection circuit 8b that detects the conductive contact voltage for detection.

  The open current detection circuit 8a includes four diodes D1 to D4 for rectification connected to the low voltage terminals of the secondary windings 5b of the two transformers 5 and four resistors connected to the diodes D1 to D4, respectively. R5 to R8. The open-circuit current detection circuit 8a converts the open-circuit current on the high voltage side of each transformer 5 by the resistors R5 to R8 and detects it as an open-circuit voltage. Note that when the discharge lamp 2 is opened due to disconnection or breakage, the open-circuit voltage becomes very small but does not drop to the ground voltage. One of the factors is that current flows through the primary winding 5a of the transformer 5 when the discharge lamp 2 is opened due to disconnection or breakage.

  The limiting current detection circuit 8b includes four Zener diodes ZD1 to ZD4 respectively connected to the four diodes D1 to D4 of the open current detection circuit 8a, and four resistors R9 to R12 respectively connected to the respective Zener diodes ZD1 to ZD4. And four capacitors C9 to C12 and four diodes D5 to D8 respectively connected to the resistors R9 to R12. The limit current detection circuit 8b converts the limit current (zener current) generated at a voltage equal to or higher than the zener voltage of each of the zener diodes ZD1 to ZD4 by the resistors R9 to R12 and detects it as the conductive contact voltage A.

  The stop circuit 9 includes a first comparison circuit 9a connected to the open current detection circuit 8a, a second comparison circuit 9b connected to the limiting current detection circuit 8b, and the first comparison circuit 9a and the second comparison circuit 9a. And a determination circuit 9c connected to the comparison circuit 9b.

  The first comparison circuit 9a includes two comparators H1 each having two terminals for inputting a voltage, a plus terminal (+) and a minus terminal (−), and an output terminal for outputting a voltage. The open circuit voltage from the open circuit current detection circuit 8a is input to the plus terminal of the comparator H1. An open reference voltage for detecting occurrence of open is input to the negative terminal of the comparator H1. This open reference voltage is preset to a predetermined voltage by the resistor R13 and the resistor R14. Here, for example, a comparator or an operational amplifier is used as the comparator H1.

  In the comparator H1, when the voltage at the plus terminal is larger than the voltage at the minus terminal, the voltage at the output terminal is the ground voltage. On the other hand, when the voltage at the plus terminal is smaller than the voltage at the minus terminal, the voltage at the output terminal is an open voltage.

  Therefore, the first comparison circuit 9a compares the open-circuit voltage input from the open-circuit current detection circuit 8a with the open-circuit reference voltage. If the open-circuit voltage is larger than the open-circuit reference voltage, the first comparison circuit 9a outputs the ground voltage from the output terminal and opens the circuit. When the voltage is smaller than the open reference voltage, an open voltage is output from the output terminal.

  The second comparison circuit 9b includes a comparator H2 having two terminals for inputting a voltage, a plus terminal (+) and a minus terminal (−), and an output terminal for outputting the voltage. The conductive contact voltage A from the limited current detection circuit 8b is input to the negative terminal of the comparator H2. A conductive contact reference voltage B for detecting the occurrence of conductive contact is input to the plus terminal of the comparator H2. The conductive contact reference voltage B is preset to a predetermined voltage by the resistors R15 and R16. Here, for example, a comparator or an operational amplifier is used as the comparator H2.

  In the comparator H2, when the voltage at the minus terminal is larger than the voltage at the plus terminal, the voltage at the output terminal becomes the ground voltage. On the other hand, when the voltage at the minus terminal is smaller than the voltage at the plus terminal, the voltage at the output terminal is an open voltage.

  Therefore, as shown in FIG. 3, the second comparison circuit 9b compares the conductive contact voltage A input from the limit current detection circuit 8b with the conductive contact reference voltage B, and the conductive contact voltage A is the conductive contact reference voltage. When it is larger than B, a ground voltage is outputted from the output terminal, and when the conductive contact voltage A is smaller than the conductive contact reference voltage B, an open voltage is outputted from the output terminal.

  The determination circuit 9c determines and detects the occurrence of opening based on the voltage input from the first comparison circuit 9a, and further detects the occurrence of conductive contact based on the voltage input from the second comparison circuit 9b. Determine and detect.

  That is, the determination circuit 9c determines whether the voltage input from the first comparison circuit 9a is a ground voltage or an open voltage, and detects that an open has occurred when determining that the voltage is an open voltage. To do. In addition, the determination circuit 9c determines whether the voltage input from the second comparison circuit 9b is a ground voltage or an open voltage, and when it is determined that the voltage is the ground voltage, the conductive contact is generated. Detect.

  Furthermore, the determination circuit 9c determines whether or not the open voltage from the first comparison circuit 9a has been input for a predetermined time (for example, 10 seconds) or more, and if it is determined that the open voltage has been input for a predetermined time or more, the control circuit The circuit 7 is instructed to stop the driving of the transformer 5 and the lighting of the discharge lamp 2 is stopped. The determination circuit 9c determines whether or not the ground voltage from the second comparison circuit 9b has been input for a predetermined time (for example, 1 second) or more, and determines that the ground voltage has been input for a predetermined time or more. The circuit 7 is instructed to stop the driving of the transformer 5 and the lighting of the discharge lamp 2 is stopped. Each predetermined time is set in advance.

  In the discharge lamp driving device 1 having such a configuration, the control circuit 7 controls the drive circuit 6, and the drive circuit 6 supplies an AC voltage to each transformer 5 to drive each transformer 5. Turn on the light.

  Here, in the discharge lamp driving device 1 in the lit state, when the discharge lamp 2 is opened due to disconnection or breakage, the open current detection circuit 8a detects the open current as the open voltage, and the first comparison The circuit 9a compares the open-circuit voltage with the open-circuit reference voltage, and based on the comparison result, the determination circuit 9c detects the occurrence of open-circuit, and instructs the control circuit 7 to stop driving all the transformers 5. As a result, the driving of all the transformers 5 is stopped, and all the discharge lamps 2 are turned off.

  Further, in the discharge lamp driving device 1 in the lit state, when a conductive contact is generated by a human hand or a driver, the limited current detection circuit 8b detects the limited current as the conductive contact voltage A, and the second comparison circuit. The conductive contact voltage A is compared with the conductive contact reference voltage B by 9b, the occurrence of the conductive contact is detected by the determination circuit 9c based on the comparison result, and the control circuit 7 is instructed to stop driving all the transformers 5. . Thereby, the drive of all the transformers 5 is stopped, and all the discharge lamps 2 are extinguished instantaneously.

  As described above, according to the embodiment of the present invention, the conductive contact voltage A detected by the limited current detection circuit 8b is compared with the conductive contact reference voltage B, and the conductive contact voltage A is compared with the conductive contact reference voltage B. If it is determined that it is larger, by instructing the control circuit 7 to stop driving all the transformers 5, the occurrence of conductive contact by a human hand or a driver is detected, and the driving of all the transformers 5 is stopped. All the discharge lamps 2 are turned off instantaneously. In this way, lighting of all the discharge lamps 2 can be stopped instantaneously when conductive contact occurs. As a result, it is possible to prevent a large current from continuing to flow through the human body even when a person contacts the high voltage portion on the high voltage side of the transformer with a hand or a driver.

  Furthermore, the open circuit voltage detected by the open circuit current detection circuit 8a is compared with the open circuit reference voltage for detecting the occurrence of the open circuit. By instructing the stop of driving of the transformer 5, the occurrence of opening due to disconnection or breakage of the discharge lamp 2 is detected, and the driving of all the transformers 5 is stopped, so that all the discharge lamps 2 are turned off. become. In this way, it is possible to stop the lighting of all the discharge lamps 2 even when the opening occurs.

  Moreover, the malfunction of the discharge lamp drive device 1 can be prevented by determining the occurrence of opening and the occurrence of conductive contact based on a predetermined time by the determination circuit 9c.

  Here, even when such a discharge lamp driving device 1 is connected to a touch current circuit based on a touch current measurement method (contact current measurement method: IEC60990), the control circuit 7 is instructed to stop driving the transformer 5 quickly. It was confirmed that the lighting of the discharge lamp 2 can be stopped instantaneously. Note that the contact current is a current that flows through the human body when a person touches one or more accessible parts of the apparatus under a normal operation state or a failure state.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention.

  For example, in the above-described embodiment, a straight tube is used as the discharge lamp 2. However, the present invention is not limited to this. For example, a U-shaped or L-shaped bent tube may be used.

  In the above-described embodiment, four discharge lamps 2 are provided. However, the present invention is not limited to this. For example, eight, ten, or twelve discharge lamps 2 may be provided. There is no limit to the number. When the number of the discharge lamps 2 is increased, the connector 4, the transformer 5, the drive circuit 6 and the like are added according to the number of the discharge lamps 2.

  In the above-described embodiment, the open reference voltage and the conductive contact reference voltage B are fixed and used. However, the present invention is not limited to this, and for switching between the open reference voltage and the conductive contact reference voltage B. A switching circuit or the like may be provided.

  In the above-described embodiment, each predetermined time of the determination circuit 9c is set in advance. However, the present invention is not limited to this. For example, a selection circuit for selecting each predetermined time is provided. May be.

  In the above-described embodiment, the determination circuit 9c determines the occurrence of opening and the occurrence of conductive contact based on a predetermined time. However, the present invention is not limited to this. For example, the determination based on the predetermined time is performed. You may make it determine generation | occurrence | production of an open | release and generation | occurrence | production of a conductive contact, without performing.

It is a block diagram which shows schematic structure of the discharge lamp drive device which concerns on one Embodiment of this invention. It is a circuit diagram which shows schematic structure of the discharge lamp drive device shown in FIG. It is explanatory drawing for demonstrating generation | occurrence | production detection of the conductive contact in the discharge lamp drive device shown in FIG. It is a block diagram which shows schematic structure of the discharge lamp drive device which concerns on a prior art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Discharge lamp drive device 2 Discharge lamp 5 Transformer 6 Drive circuit 7 Control circuit 8 Current detection circuit 9 Stop circuit A Conductive contact voltage B Conductive contact reference voltage

Claims (3)

A drive circuit for driving a transformer for lighting a discharge lamp;
A control circuit for controlling the drive circuit;
A current detection circuit for detecting a current on the high voltage side of the transformer as a conductive contact voltage;
When the conductive contact voltage detected by the current detection circuit is compared with a conductive contact reference voltage for detecting the occurrence of conductive contact, and it is determined that the conductive contact voltage is greater than the conductive contact reference voltage, the driving A stop circuit that instructs the control circuit to stop driving the transformer;
A discharge lamp driving device comprising: The current detection circuit detects a current on the high voltage side of the transformer as an open voltage,
The stop circuit compares the open-circuit voltage detected by the current detection circuit with an open-circuit reference voltage for detecting occurrence of open-circuit, and determines that the open-circuit voltage is smaller than the open-circuit reference voltage, the drive The discharge lamp driving device according to claim 1, wherein a control circuit is instructed to stop driving the transformer.   The discharge lamp driving device according to claim 1, further comprising the discharge lamp.

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