JP2009048906A - Protection circuit and lamp driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protection circuit which certainly protects a lamp driving device even when an output terminal of a high voltage side and an output terminal of a low voltage side of a transformer circuit are short-circuited, and the lamp driving device having the protection circuit. <P>SOLUTION: The protection circuit has a detection circuit 403 which detects a voltage from an electric current flowing between an high-voltage side output terminal T1 and a low-voltage side output terminal T2 of a transformer circuit 20 that supplies the current from the high voltage side output terminal T2 to a lamp 30 in which a discharge medium is filled inside and electrodes are formed on the both end external face, and, when the current flows between the both output terminals, outputs a detection voltage in which the detected voltage is stepped down to a prescribed permitted voltage or lower, and when the current does not flow between the both output terminals, outputs a detection voltage equivalent to zero, and a control circuit 402 which controls the current to be supplied to the lamp 30 according to the value of detection voltage output. A lamp driving device having the protection circuit is provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a protection circuit that protects a lamp driving device that drives an external electrode fluorescent lamp, and a technology of a lamp driving device that includes the protection circuit.

  In general, a liquid crystal display device used for a personal computer or a liquid crystal television includes a backlight using a plurality of lamps arranged in parallel and a lamp driving device that drives each lamp to light.

  The types of lamps are cold cathode fluorescent lamps (CCFLs) that have internal electrodes in both ends of the lamp, and external electrodes are formed on the outer surfaces of both ends of the lamp, depending on the position of the electrodes. There are two types of external electrode fluorescent lamps (EEFLs). When lighting a plurality of cold cathode fluorescent lamps arranged in parallel at the same time, a plurality of transformer circuits for supplying voltages to each of the plurality of cold cathode fluorescent lamps are required, which increases the number of cold cathode fluorescent lamps. Along with this, the number of transformer circuits increases and the manufacturing cost of the lamp driving device increases.

  On the other hand, when an external electrode fluorescent lamp is used, the glass between the external electrode and the discharge space acts as a ballast component as a dielectric (capacitor) to adjust the amount of current flowing through the external electrode fluorescent lamp. A plurality of external electrode fluorescent lamps connected in parallel using one transformer circuit can be lit simultaneously. Therefore, unlike the case of using a cold cathode fluorescent lamp, it is possible to provide a lamp driving device that satisfies the cost reduction in a liquid crystal display device whose size is rapidly increasing in order to suppress an increase in the number of transformer circuits.

  FIG. 4 is a configuration diagram showing a configuration of a conventional lamp driving device. A conventional lamp driving device 1 includes an oscillation circuit 10 that oscillates an alternating current obtained by converting a direct current power source into an alternating current in response to an input of a lighting signal, and boosts the oscillated current to a high current to increase the high voltage side of a secondary winding. The transformer circuit 20 that outputs from the output terminal T1, the external electrode fluorescent lamp 30 connected to the output terminal T1 on the high voltage side of the transformer circuit 20, and the lamp drive device due to the failure of lighting due to damage to the external electrode fluorescent lamp 30 or the like And a protection circuit 40 for preventing malfunctions and malfunctions. In addition, the protection circuit 40 includes a detection circuit 401 that detects a voltage obtained from the current output from the output terminal T2 on the low voltage side of the transformer circuit 20, and an AC that oscillates in the oscillation circuit 10 based on the detected voltage. And a control circuit 402 for controlling current.

  The lamp driving device 1 includes an oscillation circuit 10 ′, a transformation circuit 20 ′, and a protection circuit 40 ′ having the same functions as those of the oscillation circuit 10, the transformer circuit 20, and the protection circuit 40 described above. In this case, the lighting drive is realized by applying a high voltage having a phase difference of 180 ° to both electrodes of the external electrode fluorescent lamp 30.

  Here, when the lamp cannot be lit, the current output condition changes due to fluctuations in the load distribution capacity of the current supplied to the lamp by the transformer circuit 20, and from the output terminal T2 on the low-voltage side than in the steady state. Excessive current flows. Therefore, the protection circuit 40 can protect the lamp driving device by controlling the current supplied to the lamp 30 in accordance with the value of the detection voltage output from the output terminal T2 on the low voltage side.

A technique using such a protection circuit is disclosed in Patent Document 1.
JP 2004-311396 A

  However, the high-voltage output terminal T1 and the low-voltage output terminal T2 of the transformer circuit 20 are very narrow, and the two output terminals are short-circuited (short-circuited) due to the influence of minute dust or dust that cannot be visually confirmed. there is a possibility. In the case of a short circuit, the high voltage of several hundred volts supplied to the external electrode fluorescent lamp 30 flows to the output terminal T2 on the low voltage side, so that the diode constituting the detection circuit 401 and the tolerance of each part constituting the other circuit There is a problem that the voltage drive value is exceeded and the lamp driving device cannot be reliably protected without the protection circuit 40 operating properly.

  Further, since the voltage output from the output terminal T1 on the high voltage side of the transformer circuit 20 increases due to the increase in the number of the external electrode fluorescent lamps 30 connected in parallel, a discharge phenomenon occurs between the printed circuit board foils of the lamp driving device. There is a problem that peripheral parts are ignited or burnt out due to arcing.

  The present invention has been made in view of the above, and a protection circuit that reliably protects the lamp driving device even when the output terminal on the high voltage side and the output terminal on the low voltage side of the transformer circuit are short-circuited, It is an object of the present invention to provide a lamp driving device including the protection circuit.

  According to a first aspect of the present invention, there is provided a protection circuit according to a first aspect of the present invention, comprising: a high-voltage side output terminal of a transformer means for supplying current from a high-voltage side output terminal to a lamp in which a discharge medium is enclosed and electrodes are formed on the outer surfaces of both ends When the voltage is detected from the current flowing between the low-voltage side output terminal and the current flows, the detection voltage obtained by stepping down the detected voltage to a predetermined allowable voltage or less is output, and the current does not flow The gist of the present invention is to include detection means for outputting a detection voltage equivalent to zero and control means for controlling a current supplied to the lamp in accordance with the output value of the detection voltage.

  In the present invention, the high voltage side output terminal and the low voltage side output terminal of the transformer means for supplying current from the high voltage side output terminal to the lamp in which the discharge medium is enclosed and electrodes are formed on the outer surfaces of both ends are provided. When a voltage is detected from the current flowing between the two terminals, and a current flows between the two output terminals, a detection voltage is output by dropping the detected voltage below a predetermined allowable voltage, and the current flows between the two output terminals. Since there is a detection means that outputs a detection voltage equivalent to zero when there is no current, both the output terminals are shorted when the current flows between both output terminals and when the high voltage output terminal and the low voltage output terminal are shorted. Can be clearly distinguished from an abnormal time when the electric potential of the lamp is the same and the current does not flow. Further, since there is a control means for controlling the current supplied to the lamp according to the value of the output detection voltage, The output end on the high pressure side and the output end on the low pressure side Even when it is possible to provide a protection circuit to reliably protect the lamp driver.

  According to a second aspect of the present invention, there is provided a lamp driving apparatus comprising: an oscillating means that oscillates an alternating current obtained by converting a direct current power source into an alternating current; and a lamp having a discharge medium sealed therein and electrodes formed on both outer surfaces. A voltage is detected from a current flowing between a transformer means connected to the output terminal and supplying a current obtained by transforming the alternating current to the lamp, and an output terminal on the high voltage side and an output terminal on the low voltage side of the voltage transformer means. First detection means for outputting a detection voltage obtained by stepping down the detected voltage to a predetermined allowable voltage or lower when the current flows, and outputting a detection voltage equivalent to zero when the current does not flow; , A second detection means for detecting a voltage from the current output from the output terminal on the low-voltage side and outputting the detected voltage, a value of the detection voltage output from the first detection means, and the second The detection output from the detection means Depending on the value of the pressure, it is summarized in that and a control means for controlling the current supplied to the lamp.

  In the present invention, the high voltage side output terminal and the low voltage side output terminal of the transformer means for supplying current from the high voltage side output terminal to the lamp in which the discharge medium is enclosed and electrodes are formed on the outer surfaces of both ends are provided. When a voltage is detected from the current flowing between the two terminals, and a current flows between the two output terminals, a detection voltage is output by dropping the detected voltage below a predetermined allowable voltage, and the current flows between the two output terminals. Since there is a first detection means that outputs a detection voltage equivalent to zero when there is no current, a normal current flows between both output terminals, and the high-voltage side output terminal and the low-voltage side output terminal are short-circuited. It is possible to clearly distinguish between abnormal conditions in which the electric potentials at both output terminals are the same and no current flows, and there is a control means for controlling the current supplied to the lamp according to the value of the output detection voltage. Therefore, the output end on the high voltage side and the output end on the low voltage side of the transformer means Even when Yoto, it is possible to provide a lamp driving device having a protection circuit to reliably protect the lamp driver.

  According to the present invention, even when the output terminal on the high voltage side and the output terminal on the low voltage side of the transformer circuit are short-circuited, the protection circuit that reliably protects the lamp driving device, and the lamp drive including the protection circuit An apparatus can be provided.

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

  FIG. 1 is a configuration diagram illustrating a configuration of a protection circuit according to the present embodiment and a lamp driving device including the protection circuit. The lamp driving device 1 according to the present embodiment has a configuration including an oscillation circuit 10, a transformer circuit 20, a lamp 30, and a protection circuit 40.

Oscillation circuit 10, when the lighting signal is inputted, to oscillate the alternating current converted direct current to alternating current power source V _in the transformer circuit 20.

  The transformer circuit 20 boosts the alternating current oscillated by the oscillation circuit 10 to a predetermined current, and outputs the boosted current from the output terminal T1 on the high voltage side.

  The lamp 30 is an external electrode fluorescent lamp (EEFL) in which a discharge medium is sealed inside and external electrodes are formed on the outer surfaces of both ends. For example, a dielectric barrier discharge lamp can be used. In this lamp 30, the glass between the external electrode and the discharge space acts as a ballast component as a dielectric (capacitor), and adjusts the amount of current flowing through the external electrode fluorescent lamp. A plurality of lamps can be connected in parallel to the output terminal T1.

  The protection circuit 40 includes a first detection circuit 403, a second detection circuit 401, and a control circuit 402.

  The first detection circuit 403 is connected between the output terminal T1 on the high voltage side and the output terminal T2 on the low voltage side of the transformer circuit 20, and is obtained from the current flowing from the output terminal T1 on the high voltage side to the output terminal T2 on the low voltage side. The detected voltage is detected. When a current flows between these output terminals, a detection voltage obtained by stepping down the detected voltage to a voltage equal to or lower than a predetermined allowable voltage is output to the control circuit 402 at the subsequent stage, and when no current flows between these output terminals, A detection voltage equivalent to zero is output to the control circuit 402 at the subsequent stage. By providing the first detection circuit 403, it is possible to reliably protect the lamp driving device 1 even when the output terminal T1 on the high voltage side and the output terminal T2 on the low voltage side are short-circuited. It is said. The operation of the first detection circuit 403 will be described later.

  The second detection circuit 401 is connected to the output terminal T2 on the low voltage side of the transformer circuit 20, detects a voltage obtained from the current output from the output terminal T2 on the low voltage side, and detects the detected voltage as a detection voltage. To the control circuit 402 in the subsequent stage. By providing the second detection circuit 401, the lamp driving device 1 can be surely protected even when the lamp 30 cannot be lit.

  When the lamp 30 cannot be lit due to breakage of the lamp 30 or disconnection of the lead wire connected to the external electrode of the lamp 30, the voltage distribution circuit 20 is supplied to the lamp 30 due to fluctuations in the load distribution capacity, etc. The current output condition changes, and an excessive current flows from the low-pressure side output terminal T2 as compared with the steady state. Therefore, since the value of the detected voltage detected is different between the normal state in the lighting state and the abnormal state in which the lighting is impossible, the lighting state of the lamp 30 can be reliably determined.

  The control circuit 402 receives the first detection voltage output from the first detection circuit 403 and the second detection voltage output from the second detection circuit 401, and according to the values of the detection voltages. The current supplied to the lamp 30 is controlled. For example, when the value of the first detection voltage is zero [V], it can be determined that the output terminal T1 on the high voltage side and the output terminal T2 on the low voltage side of the transformer circuit 20 are short-circuited. Control is performed to turn off the supply of the alternating current output from the oscillation circuit 10 to the transformer circuit 20 to the oscillation circuit 10. Alternatively, the transformer circuit 20 may be controlled to reduce the step-up rate of the current output to the output terminal T1 on the high voltage side.

  In addition, when the value of the second detection voltage is higher than the detection voltage detected in the normal state in the lighting state, it can be determined that the lamp 30 is in a lighting-incapable state, and thus the control circuit 402 oscillates in the same manner as described above. The circuit 10 or the transformer circuit 20 is controlled.

  In addition to the method of judging the short-circuit state and the lighting state of the lamp using the first detection voltage value and the second detection voltage value, the detection voltage is compared with a certain reference voltage, and the comparison is made. The same effect can be obtained by controlling the oscillation circuit 10 or the transformer circuit 20 according to the result.

  The lamp driving device 1 is configured such that the oscillation circuit 10 ′, the transformation circuit 20 ′, and the protection circuit 40 ′ having the same functions as the oscillation circuit 10, the transformation circuit 20, and the protection circuit 40 described above are connected to the other electrode side of the lamp 30. In preparation for this, lighting drive is realized by applying high voltages with a phase difference of 180 ° to both electrodes of the lamp 30.

  Next, the operation of the first detection circuit 403 will be described. As shown in FIG. 1, the first detection circuit 403 includes a capacitor C1 and a capacitor C2 connected in series between a high-voltage side output terminal T1 and a low-voltage side output terminal T2, and a capacitor C1 and a capacitor C2. A capacitor C3 and a capacitor C4 connected in series between the first connection point and the ground are provided, and a voltage obtained from a current flowing through the second connection point between the capacitor C3 and the capacitor C4 is output to the control circuit 402 as a detection voltage. To do.

  FIG. 2 is a configuration diagram showing a part of the circuit configuration of the first detection circuit 403. For example, when the transformer circuit 20 outputs a voltage of 1000 [V] from the output terminal T1 on the high voltage side, the capacitor is set so that 980 [V] is between the output terminal T1 on the high voltage side and the first connection point. C1 is selected, and the capacitor C2 is selected so that 20 [V] is applied between the first connection point and the output terminal T2 on the low voltage side. As a result, the potential at the first connection point is 20 [V]. Further, the capacitor C3 is selected so that 15 [V] is applied between the first connection point and the second connection point, and the capacitor C4 is selected so that 5 [V] is applied between the second connection point and the ground. select. As a result, the potential at the second connection point becomes 5 [V].

  In other words, the first detection circuit 403 can output a detection voltage obtained by reducing the potential of 1000 [V] supplied to the output terminal T1 on the high voltage side to a potential of 5 [V]. Therefore, when a current flows from the high-voltage side output terminal T1 to the low-voltage side output terminal T2, the first detection circuit 403 can output a voltage of several volts reduced to an allowable potential by the control circuit 402. It becomes possible.

  On the other hand, when the output terminal T1 on the high voltage side and the output terminal T2 on the low voltage side of the transformer circuit 20 are short-circuited, the potential of the output terminal T2 on the low voltage side is the same as the potential of the output terminal T1 on the high voltage side. No current flows between the ends, and the detection voltage becomes 0 (zero) [V].

  Accordingly, the first detection circuit 403 can output a detection voltage of several volts when the output terminals are not short-circuited, and can output a detection voltage of 0 [V] when the short-circuit is abnormal. Since the potential difference between the normal time and the abnormal time is clear, the control circuit 402 can reliably determine the short-circuit state between the output terminals.

  Note that the first detection circuit 403 only needs to be able to reduce the potential of the output terminal T1 on the high-voltage side in a normal state to a potential allowable by the control circuit 402. As shown, a capacitor C5 and a capacitor C6 are connected in series between the second connection point and the ground, and a capacitor C7 and a capacitor C8 are connected in series between the third connection point of the capacitor C5 and the capacitor C6 and the ground. The voltage obtained from the current flowing through the fourth connection point between the capacitor C7 and the capacitor C8 is used as the detection voltage, and the detection voltage can be adjusted to be smaller than that shown in FIG.

  According to the present embodiment, the output terminal T1 on the high voltage side of the transformer circuit 20 for supplying current from the output terminal T2 on the high voltage side to the lamp 30 in which the discharge medium is enclosed and electrodes are formed on the outer surfaces of both ends. When the voltage is detected from the current flowing between the low-voltage output terminal T2 and the current flows between the two output terminals, the detected voltage obtained by stepping down the detected voltage to a predetermined allowable voltage or less is output. When the current does not flow between the terminals, the detection circuit 403 outputs a detection voltage equivalent to zero. Therefore, when the current flows between the two output terminals, the high voltage side output terminal T1 and the low voltage side output terminal It is possible to clearly distinguish from an abnormal time when T2 is short-circuited and the potentials of both output terminals are the same potential and current does not flow, and the current supplied to the lamp 30 according to the value of the output detection voltage. Control circuit 402 for controlling the Even when the output terminal T1 on the high voltage side and the output terminal T2 on the low voltage side of the circuit 20 are short-circuited, a protection circuit that reliably protects the lamp driving apparatus 1 and the lamp driving apparatus 1 including the protection circuit 40 are provided. Can be provided.

It is a block diagram which shows the structure of the protection circuit which concerns on this Embodiment, and the lamp drive device provided with this protection circuit. It is a block diagram which shows a part of circuit structure of a 1st detection circuit. It is a block diagram which shows a part of other circuit structure of a 1st detection circuit. It is a block diagram which shows the structure of the conventional lamp drive device.

Explanation of symbols

C1 to C8 ... Capacitor D1 ... Diodes T1 and T2 ... Output terminal 1 ... Lamp drive device 10 ... Oscillator circuit 20 ... Transformer circuit 30 ... Lamp, external electrode fluorescent lamp 40 ... Protection circuit 401 ... Detection circuit, second detection circuit 402: Control circuit 403: First detection circuit

Claims (2)

A current flowing between the high-voltage side output terminal and the low-voltage side output terminal of the transformer means for supplying current from the high-voltage side output terminal to the lamp in which the discharge medium is sealed and electrodes are formed on the outer surfaces of both ends. When the current flows, the detection voltage obtained by stepping down the detected voltage below the predetermined allowable voltage is output, and when the current does not flow, the detection voltage equivalent to zero is output. Means,
Control means for controlling the current supplied to the lamp according to the output value of the detected voltage;
A protection circuit comprising: An oscillation means for oscillating an alternating current obtained by converting a direct current power source into an alternating current;
A transformer having a discharge medium enclosed therein and electrodes formed on the outer surfaces of both ends connected to the output end on the high voltage side, and a transformer for supplying the lamp with a current obtained by transforming the alternating current;
A detection voltage obtained by detecting a voltage from a current flowing between the output terminal on the high voltage side and the output terminal on the low voltage side of the transformer, and reducing the detected voltage below a predetermined allowable voltage when the current flows. And when the current does not flow, first detection means for outputting a detection voltage equivalent to zero;
Second detection means for detecting a voltage from a current output from the low-voltage side output terminal and outputting the detected voltage as a detection voltage;
Control means for controlling the current supplied to the lamp according to the value of the detection voltage output from the first detection means and the value of the detection voltage output from the second detection means;
A lamp driving device comprising:

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