JP2010055818A - Lamp driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a lamp driving device to detect even a minute abnormal discharge. <P>SOLUTION: The lamp driving device is provided with a power source device, a transformer with a primary winding side connected to the power source device and a secondary winding side to lamps, a detection circuit connected to a secondary winding side of the transformer, equipped with capacitors and an impedance element connected in series with the capacitors, and further, connected in parallel with the lamps, and a protective means performing protective movement for the power source device against abnormal discharge based on potential differences generated at both ends of the impedance element contained in the detection circuit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a lamp driving device.

For example, Japanese Patent Laid-Open No. 2007-80797 discloses a circuit as shown in FIG. Briefly, in FIG. 1, when an abnormal discharge occurs in the lamp LP or the like for some reason, the discharge noise at the time of abnormal discharge is detected by the impedance element Z connected in series with the secondary winding of the transformer TR. There is disclosed a lamp driving circuit that performs and stops operation by a control circuit. However, the method of connecting the impedance element Z in series with the secondary winding of the transformer TR has a problem that minute noise is difficult to detect due to the secondary winding of the transformer TR. For example, in the circuit of FIG. 1, the discharge around the portion A close to the secondary winding of the transformer TR becomes a very large discharge, and a voltage waveform with discharge noise as shown in FIG. 2A is obtained. A relatively large discharge noise portion as shown in FIG. 2B is detected at the connection point C between the impedance element Z and the current detection portion, and the output of the rectifier circuit included in the abnormal discharge detection portion is shown in FIG. A relatively large voltage as shown in FIG. However, the discharge at the portion B of each lamp LP is relatively small, and a voltage waveform with a relatively small discharge noise as shown in FIG. 3A is obtained. A small discharge noise portion as shown in b) is detected, and a small voltage as shown in FIG. 3C is obtained at the output of the rectifier circuit included in the abnormal discharge detector. When only such a small voltage can be detected, the abnormal discharge detector may not reach the threshold value and cannot be determined as abnormal discharge. Further, the system in which the impedance element Z is connected in series to the secondary winding of the transformer TR cannot be adapted to the floating system in which a lamp is connected to drive both ends of the secondary winding of the transformer TR.
JP 2007-80797 A

  As described above, the conventional technique has a problem that it is difficult to detect fine abnormal discharge.

  Accordingly, an object of the present invention is to provide a lamp driving device including an abnormal discharge detection function capable of detecting even a minute abnormal discharge.

  The lamp driving device according to the first aspect of the present invention includes a power supply device, a transformer having a primary winding connected to the power supply, a secondary winding connected to the lamp, and a secondary winding connected to the transformer. And a detection circuit connected in parallel with the lamp, and a protection against abnormal discharge based on a potential difference generated at both ends of the impedance element included in the detection circuit. Protective means for performing the operation on the power supply device.

  By introducing the detection circuit in parallel with the lamp in this way, it becomes possible to detect a fine discharge without being affected by the secondary winding of the transformer.

  Note that the impedance element described above may be an element having a high impedance in a frequency band included in abnormal discharge. In a normal case, since the impedance remains low, the protection means does not operate, the impedance becomes high against discharge noise related to abnormal discharge, and the potential difference generated at both ends of the impedance element increases and the protection means operates. It becomes like this.

  Note that there are a plurality of capacitors described above, which may be used for overvoltage detection. In this way, it may be shared with overvoltage detection, or may be provided separately.

  Furthermore, the protection means described above includes a rectifier circuit that rectifies the voltage at the connection point between the impedance element and the capacitor included in the detection circuit, and a comparator that compares the output from the rectifier circuit with a predetermined threshold value. It may be.

  Furthermore, when a lamp is connected to both ends of the secondary winding of the transformer, a detection circuit may be connected to each end of the secondary winding. It is also possible to handle the case where the lamp is driven by a floating method.

  A lamp driving device according to a second aspect of the present invention is a lamp driving device that differentially drives a lamp with a first power supply device and a second voltage device that outputs a voltage having a phase opposite to that of the first power supply device. A first detection circuit connected to one end of the lamp, having a first capacitor and a first impedance element connected in series to the first capacitor, and connected to the other end of the lamp; A second detection circuit having a second capacitor and a second impedance element connected in series to the second capacitor, and a potential difference generated at both ends of the first impedance element included in the first detection circuit And a protection means for performing a protection operation against abnormal discharge on the first and second power supply devices based on a potential difference generated at both ends of the second impedance element included in the second detection circuit.

  Thus, even in the case of differential driving, it becomes possible to detect a fine discharge.

  There are a plurality of circuits for realizing the above configuration, and specific examples are shown below, but the present invention is not limited to these.

  According to the present invention, even a minute abnormal discharge can be detected in a lamp driving device.

[Embodiment 1]
FIG. 4 shows an example of a lamp driving device in the present embodiment. The lamp driving apparatus according to the present embodiment supplies power to n lamps L1 to L3 (for example, a cold cathode ray tube: CCFL (Cold Cathode Fluorescent Lamp), but not limited thereto, the same applies hereinafter). Driver 1, boost transformer T1 for boosting the voltage output from driver 1, capacitors C1 and C2 used for overvoltage detection and discharge detection, and overvoltage state generated on the secondary winding side of boost transformer T1 Overvoltage detection unit 5 that is connected in series with capacitors C1 and C2 and used for discharge detection, rectifier circuit 9 used for discharge detection, comparator 11 used for discharge detection, and comparator 11 A reference voltage power supply 13 for outputting a reference voltage used in the above, a current detection unit 7 for detecting an overcurrent on the secondary winding side of the transformer T1, Detection signal of the comparator 11, and a control circuit 3 stops the operation of the driver 1 in accordance with the detection signal of the detection signal and the current detection unit 7 of the excess voltage detectors 5.

  The driver 1 is connected to the primary winding side of the step-up transformer T1. One end of the secondary winding of the step-up transformer T1 is connected to one end of the lamps L1 to L3, and the other end of the lamps L1 to L3 is grounded. One end of the secondary winding of the step-up transformer T1 is also connected to one end of the capacitor C1. The other end of the capacitor C1 is connected to the input of the overvoltage detection unit 5 and one end of the capacitor C2. The other end of the capacitor C <b> 2 is connected to one end of the impedance element Z and the input of the rectifier circuit 9. The other end of the impedance element Z is grounded. The output of the rectifier circuit 9 is connected to the first input of the comparator 11, and one end of the reference voltage power supply 13 is connected to the second input of the comparator 11. The other end of the reference voltage power supply 13 is grounded. The other end of the secondary winding of the step-up transformer T1 is connected to the current detection unit 7, and the current detection unit 7 is grounded. The output of the overvoltage detector 5, the output of the comparator 11, and the output of the current detector 7 are connected to the control circuit 3, and the output of the control circuit 3 is connected to the driver 1.

  In the present embodiment, discharge detection will be described. Therefore, the current detection unit 7 and the overvoltage detection unit 5 which are conventional techniques will not be described further. Further, since the rectifier circuit 9 and the comparator 11 can adopt the same circuit configuration as that of the prior art, the description of the specific configuration is omitted here.

  The impedance element Z has a frequency characteristic as shown in FIG. 5, for example. In FIG. 5, the horizontal axis represents frequency, and the vertical axis represents level. In FIG. 5, the frequency spectrum 50 of the tube current flowing through the lamps L1 to L3 exists in a low frequency region of 60 kHz, and the frequency spectrum 52 of electrostatic noise exists in about 100 MHz, for example. The frequency spectrum 54 of the discharge to be detected ranges from several MHz to several hundred MHz. Here, it is assumed that the impedance element Z in the present embodiment has a characteristic such that the impedance is higher in the spectrum 30 that covers a part of the frequency spectrum 54 of discharge at a frequency higher than the frequency spectrum 52 of electrostatic noise. For example, it can be realized with a ferrite bead or a multilayer high-loss inductor.

  In the present embodiment, an impedance element Z is further connected in series to capacitors C1 and C2 conventionally used for overvoltage detection, and a discharge detection circuit constituted by the capacitors C1 and C2 and impedance element Z is provided as a lamp. It is provided in parallel with L1 to L3.

  Next, the discharge detection operation in the present embodiment will be described. The output voltage of the driver 1 is boosted by the step-up transformer T1 and supplied to the lamps L1 to L3, and the lamps L1 to L3 are lit. If the lamps L1 to L3 are lit and no discharge is generated, the impedance is reduced in a circuit in which the capacitors C1 and C2 and the impedance element Z are connected in series (a path shared by overvoltage detection and discharge detection). Since the impedance of the element Z is low, the potential difference generated at both ends of the impedance element Z is small, and even if it is output to the comparator 11 via the rectifier circuit 9, it is below the reference voltage, No discharge detection signal is output.

  On the other hand, when a discharge occurs in the portion E closer to the step-up transformer T1 than the lamps L1 to L3, a waveform as shown in FIG. 6A is detected. That is, it is a waveform in which a relatively large noise generated by discharge is applied to a sine wave having a large amplitude. On the other hand, when a discharge occurs in each of the lamps L1 to L3 (for example, part F), a waveform as shown in FIG. 7A is detected. That is, it is a waveform in which a relatively small noise generated by discharge is applied to a sine wave having a small amplitude.

  The impedance of the impedance element Z is high for a signal having a high frequency such as discharge noise, and the voltage drop due to the current flowing in the capacitors C1 and C2 and the path of the impedance element Z is increased due to the discharge noise. Accordingly, the voltage at the connection point G between the capacitor C2 and the impedance element Z has a waveform as shown in FIG. 6B when discharge occurs in the portion E and discharge noise occurs, and the discharge occurs in the portion F. When discharge noise is generated, a waveform as shown in FIG. 7B is obtained. Unlike the prior art, even when discharge occurs in each of the lamps L1 to L3, a relatively large amplitude can be obtained as shown in FIG. 7B.

  As a result, when rectified by the rectifier circuit 9, the voltage at the output portion H of the rectifier circuit 9 has a waveform as shown in FIG. 6C when discharge occurs in the portion E and discharge noise occurs. When discharge occurs in the portion F and discharge noise occurs, the waveform is as shown in FIG. As described above, even when discharge occurs in each of the lamps L1 to L3, a relatively high voltage output can be obtained as shown in FIG. 7C.

  Therefore, by appropriately setting the reference voltage, the output from the rectifier circuit 9 at the time of discharge in the comparator 11 exceeds the reference voltage, and discharge can be detected. That is, the comparator 11 outputs a discharge detection signal to the control circuit 3, and the control circuit 3 performs a protection operation such as stopping the driver 1.

  As described above, even minute discharges in the individual lamps L1 to L3 can be appropriately detected.

  The circuit described above can be modified. For example, apart from the capacitors C1 and C2 for detecting overvoltage, the capacitor and the impedance element Z are connected in series and connected in parallel to the lamps L1 to L3. You may do it.

[Embodiment 2]
In this embodiment, discharge detection when the lamp is driven in a floating manner will be described with reference to FIG.

  The lamp driving apparatus according to the present embodiment includes a driver 21 that supplies electric power to the lamps L4 and L5, a step-up transformer T2 that boosts a voltage output from the driver 21, and a capacitor that is used to detect discharge of the lamp L4. C3 and C4, capacitors C5 and C6 used for detecting discharge of the lamp L5, impedance element Z1 used for detecting discharge of the lamp L4, impedance element Z2 used for detecting discharge of the lamp L5, and used for detecting discharge Control for stopping the operation of the driver 21 according to the detection signal of the rectifier circuit 23, the comparator 25 used for discharge detection, the reference voltage power supply 29 for outputting the reference voltage used in the comparator 25, and the comparator 25, etc. Circuit 27. In the present embodiment, the illustration of an overvoltage detection unit and the like that are the same as those in the prior art is omitted.

  Also in the present embodiment, a detection circuit in which a capacitor and an impedance element are connected in series is connected in parallel with the lamp L4. The capacitors C3 and C4 are used for an overvoltage detection unit (not shown). Capacitors C5 and C6 are also used in an overvoltage detection unit (not shown). However, when using another configuration that is not configured to detect an overvoltage by dividing the voltage with a capacitor, one capacitor may be provided for each detection circuit.

  In the present embodiment, the driver 21 is connected to the primary winding side of the transformer T2. One end of the secondary winding of the transformer T2 is connected to one end of the lamp L4 and one end of the capacitor C3. The other end of the secondary winding of the transformer T2 is connected to one end of the lamp L5 and the capacitor C5. One end is connected. In this way, the lamps are connected to both ends of the secondary winding of the transformer T2, and a floating system is adopted. The other ends of the lamps L4 and L5 are grounded.

  The other end of the capacitor C3 is connected to one end of the capacitor C4, and the other end of the capacitor C4 is connected to one end of the impedance element Z1 and the rectifier circuit 23. The other end of the impedance element Z1 is grounded. The other end of the capacitor C5 is connected to one end of the capacitor C6, and the other end of the capacitor C6 is connected to one end of the impedance element Z2 and the rectifier circuit 23. The other end of the impedance element Z2 is grounded.

  The rectifier circuit 23 is connected to the first input of the comparator 25, and one end of the reference voltage power supply 29 is connected to the second input of the comparator 25. The other end of the reference voltage power supply 29 is grounded. The output of the comparator 25 is connected to the control circuit 27, and the output of the control circuit 27 is connected to the driver 21.

  The basic operation of the lamp driving device in the present embodiment is the same as that in the first embodiment. However, if a discharge occurs on the lamp L4 side, a signal having a relatively large potential difference is generated at both ends of the impedance element Z1. When the voltage higher than the reference voltage is detected by the comparator 25 after being rectified by the rectifier circuit 23, a discharge detection signal is output to the control circuit 27. Even when a discharge occurs on the lamp L5 side, a signal having a relatively large potential difference is generated at both ends of the impedance element Z2, rectified by the rectifier circuit 23, and then compared with the reference voltage by the comparator 25. If a voltage higher than the voltage is detected, a discharge detection signal is output to the control circuit 27.

  The rectifier circuit 23 rectifies the result of, for example, diode ORing the two inputs from the impedance elements Z1 and Z2, and outputs the rectified signal to the comparator 25. That is, the higher voltage signal is rectified and output to the comparator 25. When receiving the discharge detection signal from the comparator 25, the control circuit 27 performs a protection operation such as stopping the driver 21.

  Even when the floating method is employed as described above, even a fine discharge can be detected by introducing a detection circuit in parallel with the lamp.

  Although only one lamp L4 and one lamp L5 are illustrated, a plurality of lamps may be provided.

[Embodiment 3]
In the present embodiment, a lamp driving device in the case of differentially driving a lamp will be described with reference to FIG.

  The lamp driving apparatus according to the present embodiment includes a driver 31, a driver 33 that outputs a voltage having a phase opposite to that of the driver 31, transformers T3 and T4, capacitors C7 to C10 used for discharge detection, and discharge detection. The impedance elements Z3 and Z4 used, a rectifier circuit 35, a comparator 37, a control circuit 39, and a reference voltage power supply 41 are included.

  The driver 31 is connected to the primary winding of the transformer T3, and one end of the secondary winding of the transformer T3 is connected to one end of the lamp L6 and one end of the capacitor C7. The other end of the secondary winding of the transformer T3 is grounded. The driver 33 is connected to the primary winding of the transformer T4, and one end of the secondary winding of the transformer T4 is connected to the other end of the lamp L6 and one end of the capacitor C9. The other end of the secondary winding of the transformer T4 is grounded.

  The other end of the capacitor C7 is connected to one end of the capacitor C8, and the other end of the capacitor C8 is connected to one end of the impedance element Z3 and the rectifier circuit 35. The other end of the impedance element Z3 is grounded. Similarly, the other end of the capacitor C9 is connected to one end of the capacitor C10, and the other end of the capacitor C10 is connected to one end of the impedance element Z4 and the rectifier circuit 35.

  The output of the rectifier circuit 35 is connected to the first input of the comparator 37, and one end of the reference voltage power supply 41 is connected to the second input of the comparator 37. The other end of the reference voltage power supply 41 is grounded. The output of the comparator 37 is connected to the input of the control circuit 39, and the output of the control circuit 39 is connected to the drivers 31 and 33.

  The basic operation of the lamp driving device in the present embodiment is the same as that of the first embodiment, but since it is differentially driven, the lamp L6 and the detection circuit cannot be connected in parallel. In order to detect discharge at both ends, a detection circuit is connected to both ends of the lamp L6.

  If a discharge occurs on the left end side of the lamp L6, a signal having a relatively large potential difference is generated at both ends of the impedance element Z3. After rectification by the rectifier circuit 35, the comparator 37 compares the reference voltage with the reference voltage. If a higher voltage is detected, a discharge detection signal is output to the control circuit 39. Even when a discharge occurs on the right end side of the lamp L6, a signal having a relatively large potential difference is generated at both ends of the impedance element Z4, rectified by the rectifier circuit 35, and then compared with the reference voltage by the comparator 37. If a voltage higher than the reference voltage is detected, a discharge detection signal is output to the control circuit 39. The control circuit 39 performs a protection operation to stop the drivers 31 and 33 according to the discharge detection signal.

  The rectifier circuit 35 rectifies the result of, for example, diode ORing the two inputs from the impedance elements Z3 and Z4, and outputs the rectified signal to the comparator 37. That is, a signal having a certain potential difference is also generated at both ends of the impedance element in the detection circuit on the opposite side of the lamp, but the potential difference generated at both ends of the impedance element in the detection circuit where discharge has occurred is larger. The other signal is rectified by the rectifier circuit 35 and output to the comparator 37.

  Even in the case of employing differential driving in this way, even a fine discharge can be detected by introducing detection circuits at both ends of the lamp.

  Although only one lamp L6 is illustrated, a plurality of lamps may be provided. It is possible to employ both differential driving and floating systems. In that case, a detection circuit may be provided at the right end of the first lamp and the left end of the second lamp.

  Although the embodiment of the present invention has been described above, the present invention is not limited to this. For example, the number of lamps is arbitrary. Further, a combination of known overvoltage detection and overcurrent detection is also arbitrary. Furthermore, the configuration of the driver is also arbitrary.

It is a figure which shows an example of the lamp drive device which concerns on a prior art. (A) is a waveform diagram when discharge occurs at point A, (b) is a waveform diagram detected at point C, and (c) is an output waveform diagram of the rectifier circuit in the abnormal discharge detector. . (A) is a waveform diagram when discharge occurs at point B, (b) is a waveform diagram detected at point C, and (c) is an output waveform diagram of the rectifier circuit in the abnormal discharge detector. . It is a figure which shows the lamp drive device which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating the characteristic of an impedance element. (A) is a waveform diagram when a discharge occurs at point E, (b) is a waveform diagram detected at point G, and (c) is a waveform diagram detected at point H. (A) is a waveform diagram when a discharge occurs at point F, (b) is a waveform diagram detected at point G, and (c) is a waveform diagram detected at point H. It is a figure which shows the lamp drive device which concerns on the 2nd Embodiment of this invention. It is a figure which shows the lamp drive device which concerns on the 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Driver T1 Step-up transformer 3 Control circuit 5 Overvoltage detection part C1, C2 Capacitor L1-L3 Lamp Z Impedance element 7 Current detection part 9 Rectifier circuit 11 Comparator 13 Reference voltage power supply

Claims (6)

A power supply;
A transformer in which a primary winding side is connected to the power supply device and a secondary winding side is connected to a lamp;
A detection circuit connected to the secondary winding side of the transformer, having a capacitor and an impedance element connected in series to the capacitor, and connected in parallel to the lamp;
Protecting means for performing a protection operation against abnormal discharge on the power supply device based on a potential difference generated at both ends of the impedance element included in the detection circuit;
A lamp driving device. The lamp driving apparatus according to claim 1, wherein the pre-impedance element is an element that has a high impedance in a frequency band included in the abnormal discharge. The lamp driving device according to claim 1, wherein a plurality of capacitors are used for overvoltage detection. The protective means is
A rectifier circuit for rectifying a voltage at a connection point between the impedance element and the capacitor included in the detection circuit;
The lamp driving device according to claim 1, further comprising: a comparator that compares an output from the rectifier circuit with a predetermined threshold value. The lamp driving device according to claim 1, wherein when a lamp is connected to both ends of the secondary winding of the transformer, the detection circuit is connected to both ends of the secondary winding. A lamp driving device that differentially drives a lamp with a first power supply device and a second voltage device that outputs a voltage having a phase opposite to that of the first power supply device,
A first detection circuit connected to one end of the lamp and having a first capacitor and a first impedance element connected in series to the first capacitor;
A second detection circuit connected to the other end of the lamp and having a second capacitor and a second impedance element connected in series to the second capacitor;
Protection operation against abnormal discharge based on a potential difference generated at both ends of the first impedance element included in the first detection circuit and a potential difference generated at both ends of the second impedance element included in the second detection circuit Protection means for implementing the first and second power supply devices;
A lamp driving device.

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