JP2010094003A - Device and method for detecting failure of inverter for backlight - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and method for detecting a failure of an inverter for a backlight, capable of detecting an abnormal voltage generated in discharging. <P>SOLUTION: The device includes: an oscillation circuit 6 for oscillating a rectangular wave; a frequency-duty control unit 8 for controlling a frequency and a duty; piezoelectric transformers 2a-2d for allowing output voltage to be applied to primary terminals via a switching circuit 5; and fluorescent lamps 1a, 1b connected to secondary terminals of the piezoelectric transformers 2a-2d. The device further includes: a zero cross detection units 10a, 10b for measuring the phase of an output voltage waveform of each of the piezoelectric transformers; a pulse interval detection unit 11 for calculating an interval between a pulse measured by the zero cross detection units 10a, 10b and a pulse of the rectangular wave from the oscillation circuit 6; and a failure determination section 12 for detecting a failure on the basis of the pulse interval selected by the pulse interval detection unit 11. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention protects an inverter for a backlight using a piezoelectric transformer used in a high voltage generator such as a fluorescent lamp driving device, a television receiver, an electronic copying machine, and a mobile phone, from an abnormal voltage generated at the time of discharging. The present invention relates to an abnormality detection method and a backlight inverter provided with the abnormality detection method.

  For a backlight of a liquid crystal display device, a fluorescent lamp such as a cold cathode tube is used as a light source, and an inverter is used as a lighting device. This inverter employs a constant current circuit for brightness adjustment and the like, and the fluorescent lamp is lit with a high voltage of about 1.5 kV and a low current of about several mA, for example. And the current route including the fluorescent lamp to which the AC output is supplied from the inverter is the wiring section from the high voltage side terminal of the transformer to the fluorescent lamp, the terminal of the transformer, the conductor pattern on the printed wiring board, the connector, the wiring, etc. Since it passes through many members, it is long, and the circuit wiring is thin and easily deformed by external pressure. In mobile phones and notebook personal computers, the installation space for the fluorescent lamp lighting device is particularly narrow, and the thin wiring from the inverter to the fluorescent lamp is susceptible to deformation due to external pressure.

  When disconnection or loose contact of the connector occurs in the current route of such an inverter, the current is cut off at that point, but since the current is a high-voltage constant current, the voltage increases in the current route of the fluorescent lamp when the disconnection occurs. May occur, and the discharge generated at the disconnection point may continue and the current route may be maintained. If the current route is maintained, the tube current flows and the lighting of the fluorescent lamp continues, so that it is impossible to know the operation abnormality from the lighting state, and the discovery of the operation abnormality is delayed. Therefore, it is necessary to detect abnormalities such as disconnection discharge of circuit wiring, breakdown discharge between high and low pressure parts, ground fault discharge, etc., for inverters that supply AC output to various loads such as fluorescent lamps for backlights of liquid crystal display devices. .

In order to solve the above problem, in an inverter that converts a direct current input into an alternating current output and supplies the alternating current output to a load such as a fluorescent lamp, an abnormal voltage due to discharge or the like is detected, and the direct current input is blocked by the abnormal voltage. There is a discharge protection circuit (see Patent Document 1). In this circuit, when a disconnection discharge occurs in the load of the inverter, an abnormal voltage is applied to the load of the inverter. The abnormal voltage causes the Zener diode provided in the detection circuit and the transistor to conduct, and the current flowing through the detection circuit. As a result, the transistor provided between the DC input and the inverter control circuit can be turned off and shut off.
JP 05-168230 A

  However, in the above prior art, an abnormal voltage due to discharge or the like is detected by the above detection circuit, and the direct current input is cut off by the current flowing through the detection circuit. Therefore, a dedicated detection circuit is required, and the inverter circuit is complicated. There was a problem of becoming.

  The present invention has been made in view of various problems as described above, and an object of the present invention is to provide an inverter for a backlight that can detect an abnormal voltage generated at the time of discharge with a simpler circuit than the above-described discharge protection circuit. It is an object of the present invention to provide an abnormality detection apparatus and method.

  In order to achieve the above object, an abnormality detection device for a backlight inverter according to the present invention includes an oscillation circuit that oscillates a rectangular wave, and a frequency and duty control that controls the frequency and duty of the rectangular wave that the oscillation circuit oscillates. A switching circuit having a plurality of switching elements that are turned on and off by a rectangular wave output from the oscillation circuit, a DC power source connected to the input side of the switching circuit, and connected to the output side of the switching circuit A piezoelectric transformer in which an output voltage from the DC power supply is applied to a primary terminal as an AC voltage via the switching circuit, and a fluorescent lamp connected to a secondary terminal of the piezoelectric transformer, The zero cross point that detects the zero cross point of the output voltage waveform and outputs a pulse based on the zero cross point A pulse interval detector for detecting a pulse time difference between a detection unit, an output pulse from the zero cross detector and a rectangular wave pulse from the oscillation circuit, and a fluctuation value of the pulse time difference detected by the pulse interval detector And an abnormality determination unit that determines an abnormality when a predetermined reference range is exceeded.

  In another aspect of the present invention, the oscillation circuit outputs two types of rectangular waves whose phases are shifted, and a plurality of the piezoelectric transformers are provided, and each of the piezoelectric transformers corresponds to the rectangular wave of the oscillation circuit. The output voltage of the waveform shifted in phase is output, and the zero-cross detector detects the zero-cross point of each output voltage waveform and outputs a plurality of pulses shifted in phase with reference to the zero-cross point. The pulse interval detection unit detects a plurality of rectangular wave pulses whose phases are shifted from the oscillation circuit and a plurality of phase-shifted output voltage pulses from the zero cross detection unit, and each pulse having a phase shift The time difference between the two is measured from the phase of the rectangular wave pulse output from the oscillation circuit and the phase of the pulse of the output voltage from the corresponding piezoelectric transformer.

  In another aspect of the present invention, the abnormality determination unit includes a short-time average calculation unit that calculates a short-time average value of a time difference between pulses detected by the pulse interval detection unit, and a pulse selected by the pulse interval detection unit. A long-time average calculation unit that calculates a long-time average value of a time difference, and a pulse interval fluctuation detection unit that detects that the short-time average value and the long-time average value of the time difference of the pulses exceed a preset reference range It is characterized by providing.

  In another aspect of the present invention, the abnormality determination unit is based on the time difference between the pulses detected by the pulse interval detection unit, the time difference between the lower limit pulse and the upper limit pulse appropriate for maintaining the lighting of the fluorescent lamp. And a lighting maintenance range detection unit for detecting whether or not the time difference of the pulses detected by the pulse interval detection unit is within a time difference range suitable for maintaining the lighting of the fluorescent lamp.

  Note that a method for detecting an abnormal voltage generated at the time of discharge with a simple circuit using the above-described backlight inverter abnormality detection device is also one embodiment of the present invention.

  According to the present invention, an abnormal voltage generated at the time of discharging can be detected with a simple circuit. Further, it is possible to provide an abnormality detection apparatus and method for a backlight inverter that does not require a dedicated detection circuit for detecting an abnormal voltage generated during discharge.

  In particular, when detecting a voltage pulse (AC zero cross) on the input side and output side of a piezoelectric transformer as in the prior art to detect a phase shift, two zero cross detections are required. According to the present invention, the phase of the pulse of the voltage on the output side is detected by the zero cross detector, but the phase of the pulse of the voltage on the input side uses the phase of the rectangular wave pulse from the oscillation circuit. By utilizing the phase of the square wave pulse from the oscillation circuit, it is not necessary to install a new zero cross detection unit or pulse measuring device on the input side of the piezoelectric transformer, and processing can be performed with the functions in the oscillation circuit. An abnormal voltage generated at the time of discharging can be detected with a simple circuit.

[Configuration of the embodiment]
Hereinafter, an embodiment of the present invention will be specifically described with reference to FIGS. In FIG. 1, reference numerals 1a and 1b denote fluorescent lamps to be lit, and 2a to 2d denote piezoelectric transformers that supply a lighting start voltage and a lighting sustain voltage to the fluorescent lamps 1a and 1b. The piezoelectric transformers 2a to 2d have a pair of primary terminals 3a and 3b and one secondary terminal 3c.

  A pair of primary terminals 3a and 3b of the piezoelectric transformers 2a to 2d are connected to a switching circuit 5 configured by a full bridge circuit having four FETs 4a to 4d. The input side of the switching circuit 5 is connected to a constant voltage DC power source 15, and the output side is grounded via the FETs 4a to 4d and the primary terminals 3a and 3b of the piezoelectric transformers 2a to 2d.

  This switching circuit 5 connects two FETs 4a and 4b that open and close alternately and two FETs 4c and 4d that open and close alternately, in series, and two sets of FETs connected in series are connected in parallel. Is connected to. Between the FETs 4a and 4b and an intermediate portion between 4c and 4d are connected to primary terminals 3a and 3b of the piezoelectric transformers 2a to 2d.

  An oscillation circuit 6 is connected to the switching circuit 5, and the FETs 4 a and 4 b and the FETs 4 c and 4 d are alternately opened and closed by a high-frequency rectangular wave from the oscillation circuit 6. That is, from the first output terminal of the oscillation circuit 6, a rectangular wave as indicated by (1) in the figure is inverted with respect to the FET 4a, and the same rectangular wave (1) is inverted with respect to the FET 4b via the inverter 7b. Supplied with From the second output terminal of the oscillating circuit 6, the rectangular wave as shown in (2) in the figure which is 180 degrees out of phase with the rectangular wave of (1) with respect to the FET 4c is the same rectangular wave with respect to the FET 4d. (2) is supplied in an inverted state via the inverter 7a.

  The input voltage is input to the pair of primary terminals 3a and 3b of the piezoelectric transformers 2a to 2d by the switching circuit 5 by the rectangular waves (1) and (2) output from the oscillation circuit 6. The piezoelectric transformers 2a to 2d output an output voltage corresponding to the input voltage from the secondary terminal 3c based on the frequency of the AC voltage input to the pair of primary terminals 3a and 3b.

  A frequency and duty control unit 8 is connected to the oscillation circuit 6. The control unit 8 determines the frequency f and the duty duty of the rectangular waves (1) and (2) output from the oscillation circuit 6. A voltage detector 9 that detects output voltages of the piezoelectric transformers 2 a to 2 d is connected to the input side of the frequency and duty controller 8.

  For the backlight inverter having such a configuration, the abnormality detection device of the present invention having the following configuration is provided. That is, in the backlight inverter, the lighting start voltage and the lighting maintenance voltage are supplied to the fluorescent lamps 1a and 1b by the outputs from the secondary terminals 3c of the piezoelectric transformers 2a to 2d. In order to measure the phase of the waveform of the output voltage of the piezoelectric transformers 2a to 2d, zero-cross detectors 10a and 10b are arranged on the output side of the piezoelectric transformers 2a to 2d.

  The zero-cross detectors 10a and 10b detect the point (zero-cross point) where the polarity of the waveform of the output voltage of the piezoelectric transformers 2a to 2d is reversed, thereby detecting the zero-cross point of the phase of the waveform of the output voltage of the piezoelectric transformers 2a to 2d. Outputs a square wave pulse according to the timing. That is, the zero cross detector 10a detects the output voltage zero cross points of the piezoelectric transformers 2a and 2c. The waveforms of the output voltages of the piezoelectric transformers 2a and 2c correspond to the rectangular wave (1) output from the oscillation circuit 6, and basically vary although there are fluctuations due to the characteristic difference between the piezoelectric transformers 2a and 2c. Are equal in phase. From the zero cross detection unit 10a, a rectangular wave pulse (3) according to the detected timing of the zero cross point is output.

  Similarly, a rectangular wave pulse (4) is output from the zero cross detector 10b according to the zero cross points of the output voltages of the piezoelectric transformers 2b and 2d having the same phase. The output voltages of the piezoelectric transformers 2b and 2d correspond to the rectangular wave (2) output from the oscillation circuit 6, and the phases of both are shifted by 180 ° from the output waveforms from the piezoelectric transformers 2a and 2c. Yes.

  A pulse interval detection unit 11 and an abnormality determination unit 12 are connected to the output side of the zero cross detection units 10a and 10b. The input of the pulse interval detector 11 includes a rectangular wave pulse (3) (4) based on the detected zero cross point measured by the zero cross detectors 10a and 10b and a rectangular wave pulse (1) output from the oscillation circuit 6. (2) is entered. The pulse interval detector 11 detects the pulse interval of the input rectangular wave pulses (1) to (4). The abnormality determination unit 12 determines an abnormality of the circuit based on the pulse interval selected by the pulse interval detection unit 11, and stops the output of the oscillation circuit 6 if there is an abnormality. That is, in the present embodiment, the pulse interval detection unit 11 and the abnormality determination unit 12 perform the following processing, and therefore have each unit as shown in FIG.

(1) Pulse interval detector 11
(A) Oscillator circuit output pulse measurement unit 111
The phase of rectangular pulses (1) and (2) output from the oscillation circuit 6 input to the pulse interval detector 11 is measured.
(B) Piezoelectric transformer output pulse measuring unit 112
The phases of the pulses (3) and (4) generated based on the zero cross points detected by the zero cross detection units 10a and 10b input to the pulse interval detection unit 11 are measured.

(C) Pulse time difference calculation unit 113
A time difference P13 between the output pulse (1) of the rectangular wave output from the oscillation circuit 6 and the pulse (3) generated by the zero cross detector 10a is calculated. A time difference P24 between the rectangular wave output pulse (2) output from the oscillation circuit 6 and the pulse (4) generated by the zero cross detector 10a is calculated.
(D) Pulse time difference selection unit 114
The smaller one of the time differences P13 and P24 between the rectangular wave output pulse (1) (2) calculated by the pulse time difference calculation unit 113 and the pulses (3) (4) generated by the zero cross detection units 10a, 10b is selected. Let Ps be the time difference between the selected pulses.

(2) Abnormality determination unit 12
(A) Short-time average calculation unit 121 of the pulse time difference Ps
A short-time average Ps1 that is an average of a short time (for example, 20 msec) of the time difference Ps of the pulses selected by the pulse time difference selection unit 114 is obtained.
(B) Long-time average calculation unit 122 of the pulse time difference Ps
A long-time average Ps2 that is an average of long-time (for example, 200 msec) of the time difference Ps of the pulses selected by the pulse time difference selection unit 114 is obtained.

(C) Pulse interval fluctuation detection unit 123
The absolute value of the difference between the short time average Ps1 of the pulse time difference Ps calculated by the pulse time difference Ps short time average calculation unit 121 and the long time average Ps2 of the pulse time difference Ps calculated by the pulse time difference Ps long time average calculation unit 122 is Then, the pulse interval fluctuation is detected by determining whether or not the pulse fluctuation width is within a pulse fluctuation reference value Pw1 that has been determined in advance to determine abnormality.
(D) Lighting maintenance range detection unit 124
The time difference Ps of the pulses selected by the pulse time difference selection unit 114, the lower limit pulse Pth1 that can maintain the lighting of the fluorescent lamp, the upper limit pulse Pth2 that can maintain the lighting, and the lighting maintenance that has been determined in advance to determine abnormality Based on the possible reference value Pw2, it is detected whether the pulse interval is within the range in which the fluorescent lamp can be kept on.
(E) Stop signal output unit 125
When the pulse interval fluctuation detection unit 123 detects the pulse interval fluctuation, or when the lighting maintenance range detection unit 124 detects that the pulse interval is outside the lighting maintenance possible range, a stop signal is sent to the oscillation circuit 6. Output.

[Operation of the embodiment]
Next, the operation of the embodiment of the present invention having the above-described configuration will be described with reference to the flowchart of FIG.

  When the fluorescent lamp is turned on, as described above, the switching circuit 5 is turned on / off by the rectangular wave pulses (1) and (2) from the oscillation circuit 6, and the output of the DC constant voltage power supply 15 is accordingly changed to the piezoelectric transformers 2a to 2a. 2d is applied as a pseudo sine wave. As a result, the AC power boosted from the piezoelectric transformers 2a to 2d is output to the fluorescent lamps 1a and 1b, and the fluorescent lamps are turned on.

  In this embodiment, in such an apparatus, the pulse interval between the pulses (3) and (4) from the zero cross detectors 10a and 10b and the pulses (1) and (2) from the oscillation circuit 6 is detected. When the fluctuation value exceeds a preset reference range, it is determined as abnormal. The above operation will be described with reference to the flowchart of FIG.

  In step 1, the pulse time difference calculation unit 113 calculates a time difference P13 between the pulse (1) measured by the oscillation circuit output pulse measurement unit 111 and the pulse (3) measured by the piezoelectric transformer output pulse measurement unit 112. In step 2, the pulse time difference calculation unit 113 calculates the time difference P24 between the pulse (2) measured by the oscillation circuit output pulse measurement unit 111 and the pulse (4) measured by the piezoelectric transformer output pulse measurement unit 112.

  In step 3, the pulse time difference selection unit 114 selects the smaller one of the time differences P13 and P24 between the rectangular wave pulse from the oscillation circuit and the piezoelectric transformer output pulse calculated by the pulse time difference calculation unit 113, and the time difference of the selected pulse is selected. Let Ps.

  It is determined whether the time difference Ps of the pulses selected in step 3 is within a range in which the fluorescent lamp can be kept on. That is, in step 4, the lighting maintenance range detection unit 124 determines the magnitude of the absolute value of the difference between the pulse time difference Ps and the lower limit pulse time difference Pth1 of lighting maintenance and the lighting maintenance possible reference value Pw2. If the absolute value is larger than the lighting sustainable reference value Pw2, it is detected that the pulse interval is outside the lighting sustainable range, and it is an abnormal time such as abnormal heat generation of the piezoelectric transformer, cracking or gas leakage of the fluorescent lamp. The process proceeds to step 9 (Y in step 4 in FIG. 3). On the other hand, if the absolute value is smaller than the lighting maintenance possible reference value Pw2, it is determined that there is no abnormality in the circuit, and the process proceeds to the next step (N in step 4 in FIG. 3).

  In step 5, as in step 4, it is determined whether or not the time difference Ps of the pulses selected in step 3 is within the lighting maintaining range. The lighting maintenance range detection unit 124 determines the magnitude of the absolute value of the difference between the pulse time difference Ps and the maximum sustaining pulse Pth2 and the lighting sustainability reference value Pw2. If the absolute value is larger than the lighting maintaining maintainable reference value Pw2, it is determined that there is an abnormality, and the process proceeds to Step 9 (Y in Step 5 in FIG. 3). On the other hand, when the absolute value is smaller than the lighting maintenance possible reference value Pw2, it is determined that there is no abnormality in the circuit, and the process proceeds to the next step (N in step 5 in FIG. 3).

  In step 6 to step 8, it is determined whether or not there is a certain fluctuation in the pulse interval. That is, in step 6, the short time average calculation unit 121 of the pulse time difference Ps obtains a short time average Ps1 that is an average of a short time (for example, 20 msec) of the pulse time difference Ps. In step 7, the long time average calculation unit 122 of the pulse time difference Ps obtains a long time average Ps2 that is an average of the long time (eg, 200 msec) of the pulse time difference Ps.

  In step 8, the pulse interval fluctuation detecting unit 123 obtains the absolute value of the difference between the short time average Ps1 of the pulse time difference Ps and the long time average Ps2 of the pulse time difference Ps in order to detect the fluctuation of the pulse interval. The magnitude of the absolute value and the pulse fluctuation width reference value Pw1 is determined. If the absolute value is larger than the pulse fluctuation width reference value Pw1, it is determined that the pulse interval fluctuation is large (Y in step 8 in FIG. 3). On the other hand, if the absolute value is smaller than the pulse fluctuation width reference value Pw1, it is determined that there is no abnormality in the circuit, and the process returns to step 1 to continue monitoring (N in step 8 in FIG. 3). In step 9, when it is determined in steps 4, 5 and step 8 that there is an abnormality, the stop signal output unit 125 outputs a stop signal to the oscillation circuit 6.

[Effect of the embodiment]
According to this embodiment in which the above processing is performed, when an abnormality occurs such as abnormal heat generation or cracking of the piezoelectric transformer, gas leakage of a fluorescent lamp, or discharge due to loose contact of a connector, the piezoelectric transformers 2a to 2b. A large change will appear in the phase of the wavemeter of the 2d output voltage.

  In this embodiment, the smaller one of the time differences P13 and P24 between the rectangular wave pulse from the oscillation circuit calculated by the pulse time difference calculation unit 113 and the piezoelectric transformer output pulse is selected. That is, the voltage of the backlight inverter circuit is different between lighting and lighting, and the temperature of the fluorescent lamp rises and the voltage flowing through the fluorescent lamp changes in a short time (minute order). For this reason, a large change tends to appear also in the phase of the waveform of the voltage pulse output from the piezoelectric transformers 2a to 2d. Depending on how the reference range Pw1 set in advance is set, it may be determined that there is an abnormality even if there is no abnormal part in the circuit. By selecting the smaller one of the time differences P13 and P24, it is possible to determine abnormality detection with less error.

  In general, when an abnormality occurs, the phase of the output voltage waveform of the piezoelectric transformer fluctuates in the order of msec. In the present embodiment, in order to detect the phase fluctuation that changes in the order of msec, the short time average (eg, 20 msec) of the pulse time difference Ps is compared with the long time average (eg, 200 msec). That is, when an abnormality occurs, first, a large change appears in the short-time average Ps1. The long time average Ps2 does not change as much as the short time average Ps1.

  By detecting whether the absolute value of the difference between the greatly changed short-time average Ps1 and the long-time average Ps2 that is less affected when an abnormality occurs is within the pulse fluctuation width reference value Pw1, the fluctuation of the pulse interval of the order of msec is detected. can do. As a result, if the fluctuation of the pulse interval is equal to or greater than the pulse fluctuation width reference value Pw1, it is possible to safely stop the circuit by outputting a stop signal to the oscillation circuit 6 even if an abnormality is detected by the inverter circuit. .

[Other Embodiments]
The present invention is not limited to the above-described embodiment, and the numbers of fluorescent lamps, piezoelectric transformers, and zero-cross detection units described in the embodiments are merely examples, and the present invention is not limited thereto. Other embodiments such as the following are also included.

(A) When detecting an abnormality by the pulse time difference Ps, the smaller one of the time differences P13 and P24 between the rectangular wave pulse from the oscillation circuit calculated by the pulse time difference calculation unit 113 and the piezoelectric transformer output pulse is not selected. The larger of P13 and P24 can be selected.

  By making the pulse time difference Ps the larger of P13 and P24, an abnormality can be detected even when the change in the pulse time difference is small when Pw1 is constant, compared to when the pulse time difference Ps is small. Can do. That is, since it is possible to determine that there is an abnormality with a small change in pulse and stop the circuit, a large burden is not imposed on the piezoelectric transformer, FET, and the like in the circuit.

(B) One of the time differences P13 and P24 between the rectangular wave pulse from the oscillation circuit calculated by the pulse time difference calculation unit 113 and the piezoelectric transformer output pulse may not be selected. A time difference between a rectangular wave pulse from an oscillation circuit corresponding to an arbitrary piezoelectric transformer output pulse can be defined as a pulse time difference Ps, and an abnormality can be detected based on the pulse time difference Ps.

(C) The zero-cross detectors 10a and 10b detect the point (zero-cross point) where the polarity of the waveform of the output voltage of the piezoelectric transformers 2a to 2d is reversed, and output the rectangular wave pulses (3) and (4) according to the timing of the zero-cross point. Output. That is, in the above-described embodiment, the rectangular wave pulse (3) is generated based on the zero cross point of the output voltage of the piezoelectric transformers 2a and 2c, and the rectangular wave pulse (4) is the zero cross point of the output voltage of the piezoelectric transformers 2b and 2d. The phase of the output voltage of the piezoelectric transformers 2a and 2c and the phase of the output voltage of the piezoelectric transformers 2b and 2d are equal to each other. However, the present invention is not limited to such a case, and the phase of the output voltages of the piezoelectric transformers 2a and 2c or the phase of the output voltages of the piezoelectric transformers 2b and 2d may be different.

  For example, a rectangular wave pulse output according to the timing of the zero cross point of the voltage waveform output from the piezoelectric transformer 2a and a rectangular wave pulse output according to the timing of the zero cross point of the voltage waveform output from the piezoelectric transformer 2c. Is a rectangular wave pulse (b), the rectangular wave pulse (3) output from the zero cross detector can be an average of the rectangular wave pulse (a) and the rectangular wave pulse (b). Further, as the rectangular wave pulse (3), both the rectangular wave pulse (a) and the rectangular wave pulse (b) are output, and the rectangular wave (1) and the rectangular wave pulse (a) (b) output from the oscillation circuit 6 are output. ) Can be compared individually. The method of comparing the rectangular wave pulse (4) with the rectangular wave (2) output from the oscillation circuit 6 is also the same.

(D) The present invention is not limited to the order of the flowchart of FIG. 3, but the order of step 4 and step 5 (part A in FIG. 3) and step 6 and step 7 (part B in FIG. 3). Can also be replaced. Further, the order of steps 4 and 5 and steps 6 to 8 can be changed (part C in FIG. 3). When the order of the portion C in FIG. 3 is changed, if the determination in step 8 is Y, the process proceeds to step 9. If N, the process proceeds to step 4 instead of returning to step 1.

The block diagram which shows the structure of embodiment of this invention. The block diagram which shows the internal structure of the pulse space | interval detection part 11 and the abnormality determination part 12 in embodiment of FIG. The flowchart of the abnormality detection by the pulse interval of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1a, 1b ... Fluorescent lamp 2a-2d ... Piezoelectric transformer 3a, 3b ... Primary terminal 3c of piezoelectric transformer ... Secondary terminal 4a-4d of piezoelectric transformer ... FET
DESCRIPTION OF SYMBOLS 5 ... Switching circuit 6 ... Oscillator circuit 7a, 7b ... Inverter 8 ... Frequency and duty control part 9 ... Voltage detection part 10a, 10b ... Zero cross detection part 11 ... Pulse space | interval detection part 12 ... Abnormality determination part 15 ... Constant voltage DC power supply

Claims (8)

An oscillation circuit that oscillates a rectangular wave;
A frequency and duty control unit for controlling the frequency and duty of the rectangular wave oscillated by the oscillation circuit;
A switching circuit having a plurality of switching elements that are turned on and off by a rectangular wave output from the oscillation circuit;
A DC power source connected to the input side of the switching circuit;
A piezoelectric transformer connected to the output side of the switching circuit and having an output voltage from the DC power supply applied to a primary terminal as an AC voltage via the switching circuit;
In an abnormality detection device for an inverter for backlight comprising a fluorescent lamp connected to the secondary terminal of this piezoelectric transformer,
Detecting a zero-cross point of an output voltage waveform of the piezoelectric transformer, and outputting a pulse based on the zero-cross point; and
A pulse interval detection unit for detecting a pulse time difference between the output pulse from the zero-cross detection unit and the rectangular wave pulse from the oscillation circuit;
An abnormality of the backlight inverter characterized by comprising an abnormality determination unit that determines that an abnormality occurs when the fluctuation value of the pulse time difference detected by the pulse interval detection unit exceeds a preset reference range Detection device. The oscillation circuit outputs two types of rectangular waves whose phases are shifted,
A plurality of the piezoelectric transformers are provided, and an output voltage having a phase shift corresponding to the rectangular wave of the oscillation circuit is output from each piezoelectric transformer,
The zero-cross detector detects a zero-cross point of each output voltage waveform, and outputs a plurality of pulses whose phases are shifted with reference to the zero-cross point.
The pulse interval detector
A plurality of rectangular wave pulses with a phase shift from the oscillation circuit and a plurality of output voltage pulses with a phase shift from the zero cross detection unit are detected, and a rectangle output from the oscillation circuit for each pulse with a shifted phase. 2. The abnormality detection device for a backlight inverter according to claim 1, wherein a time difference between the two is measured from the phase of the wave pulse and the phase of the pulse of the output voltage from the corresponding piezoelectric transformer. The abnormality determination unit
A short-time average calculation unit that calculates a short-time average value of a time difference between pulses detected by the pulse interval detection unit;
A long-time average calculation unit for calculating a long-time average value of a time difference between pulses detected by the pulse interval detection unit;
The pulse interval fluctuation detection part which detects that the short time average value and long time average value of the time difference of the said pulse exceeded the preset reference range is provided, The pulse interval fluctuation | variation detection part is provided. An abnormality detector for backlight inverters. The abnormality determination unit
Based on the time difference between the pulses detected by the pulse interval detection unit and the time difference between the lower limit pulse and the upper limit pulse suitable for maintaining the lighting of the fluorescent lamp, the time difference between the pulses detected by the pulse interval detection unit is The back of any one of Claims 1-3 provided with the lighting maintenance range detection part which detects whether it exists in the range of the time difference appropriate for maintaining lighting of a fluorescent lamp. An abnormality detection device for light inverter. An oscillation circuit that oscillates a rectangular wave;
A frequency and duty control unit for controlling the frequency and duty of the rectangular wave oscillated by the oscillation circuit;
A switching circuit having a plurality of switching elements that are turned on and off by a rectangular wave output from the oscillation circuit;
A DC power source connected to the input side of the switching circuit;
A piezoelectric transformer connected to the output side of the switching circuit and having an output voltage from the DC power supply applied to a primary terminal as an AC voltage via the switching circuit;
In an abnormality detection method for an inverter for a backlight having a fluorescent lamp connected to a secondary terminal of the piezoelectric transformer,
Detecting a zero-cross point of the output voltage waveform of the piezoelectric transformer, and outputting a pulse based on the zero-cross point;
Detecting a pulse time difference between the pulse output by the step of outputting a pulse based on the zero cross point and the rectangular wave pulse from the oscillation circuit;
An abnormality of the backlight inverter characterized by comprising: a step of determining an abnormality when the fluctuation value of the pulse time difference detected by the step of detecting the pulse time difference exceeds a preset reference range Detection method. The oscillation circuit outputs two types of rectangular waves whose phases are shifted,
A plurality of the piezoelectric transformers are provided, and an output voltage having a phase shift corresponding to the rectangular wave of the oscillation circuit is output from each piezoelectric transformer,
The step of detecting a zero-cross point of the output voltage waveform of the piezoelectric transformer and outputting a pulse based on the zero-cross point is to output a plurality of pulses.
Detecting the pulse time difference comprises:
A plurality of square-wave pulses with a phase shift from the oscillation circuit and a plurality of pulses with a phase shift output by the step of outputting a pulse with reference to the zero-cross point are detected. 6. The backlight inverter according to claim 5, wherein the time difference between the two is measured from the phase of the rectangular wave pulse output from the oscillation circuit and the phase of the pulse of the output voltage from the corresponding piezoelectric transformer. Anomaly detection method. Determining the abnormality comprises:
Calculating a short time average value of the time difference of the pulses detected by the step of detecting the pulse time difference; and
Calculating a long-time average value of the time difference of the pulses detected by the step of detecting the pulse time difference; and
The backlight unit according to claim 5, further comprising a step of detecting that a short-time average value and a long-time average value of a time difference of the pulses exceed a preset reference range. Inverter abnormality detection method. Determining the abnormality comprises:
Based on the pulse time difference detected by the step of detecting the pulse time difference and the time difference between the lower limit pulse and the upper limit pulse suitable for maintaining the lighting of the fluorescent lamp, the time difference between the pulses is determined as the lighting of the fluorescent lamp. The method for detecting an abnormality of an inverter for a backlight according to any one of claims 5 to 7, further comprising a step of detecting whether or not the time difference is within a range of a time difference appropriate for maintaining the voltage.

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