JP2009135060A - Discharge tube lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge tube lighting device that reliably operates arc discharge protection and overvoltage protection with a single high voltage capacitor in an LCD inverter power supply.
SOLUTION: Capacitors C1 and C2 that perform voltage division on a high voltage side of a discharge tube lighting device, means for detecting a voltage at a voltage dividing point, and an arc discharge frequency connected to a low voltage side of the capacitor C2 are resonated. A resonance circuit comprising a capacitor C3 and a coil L1, means for detecting arc discharge from the resonance circuit, means for judging a signal from both detection means and stopping the control circuit, and the inverter is turned on when arc discharge or overvoltage occurs. It is possible to provide a protection circuit that can be safely stopped and that operates with a single high voltage capacitor.
[Selection] Figure 1

Description

    The present invention relates to a discharge tube lighting device that protects a discharge tube by detecting overvoltage and arc discharge on the high voltage side of an inverter during and during lighting.

    A conventional discharge tube lighting device includes a high-pass filter that detects an arc discharge frequency from a current detection circuit, a rectifying / smoothing circuit that smoothes a detection signal, and a latch circuit that holds the detection signal, thereby detecting arc discharge. It was. This is called a current detection method. (For example, refer to Patent Document 1.) In the current detection method, arc discharge generated at the high voltage terminal on the secondary side of the transformer is detected using the current at the GND terminal that has passed through the inductance on the secondary side of the transformer. The detection accuracy of discharge was low in principle. In order to improve this point, a method for detecting the voltage has been proposed.

    The method of detecting this voltage is to connect the secondary GND ends of the two output transformers via a diode, and when the arc discharge occurs, the voltage at that connection point (neutral point) rises and the neutral point is Arc discharge was detected by utilizing the deviation. This is called a neutral point detection method. (For example, refer to Patent Document 2.) However, the neutral point detection method has low detection accuracy with respect to minute arc discharge in which the voltage rise at the neutral point is small or arc discharge that occurs simultaneously on the left and right.

There is a voltage detection system that improves this point and detects arc discharge by resonating only the arc discharge frequency from the inverter output voltage via a detection capacitor and detecting the signal. (For example, refer to Patent Document 3.)
JP 2002-151287 A (FIG. 1) JP 2004-054294 A (FIG. 3) JP 2007-188659 A (FIG. 2)

    However, in the conventional configuration, in the current detection method and the neutral point detection method, a high-voltage capacitor for detection is not necessary for arc discharge protection, but the accuracy is inferior. In the voltage detection method, the high-voltage output terminal is inferior. Separate detection high voltage capacitors were required for arc discharge protection and overvoltage protection (OVP). (Fig. 4) The voltage detection method has a problem that the risk increases as the number of high-voltage components increases, the possibility of failure increases, and further, miniaturization of the device is hindered due to the safety distance. It was.

  The present invention solves these problems, and an object of the present invention is to provide a discharge tube lighting device that detects arc discharge protection and overvoltage protection (OVP) with only one high-voltage capacitor for voltage detection. (Figure 3)

  In the discharge tube lighting device according to claim 1 of the present invention, the inverter circuit is connected to the high voltage side, and the voltage dividing capacitor composed of the first capacitor and the second capacitor is connected to the high voltage side of the inverter circuit, A first voltage detecting means for detecting a voltage at a voltage dividing point; a first voltage comparing means for comparing the detected voltage with a first predetermined voltage range; and a lower voltage side than the voltage dividing point of the second capacitor. A resonance circuit in which a third capacitor and a coil are connected in parallel between the ground, a second voltage detection means for detecting the voltage of the resonance circuit, and a second voltage detection means for comparing the detection voltage with a second predetermined voltage range. Two voltage comparison means, and the voltage detected by the first voltage detection means is outside the first predetermined voltage range and the voltage detected by the second voltage detection means is the second voltage detection means. If the voltage is outside the specified voltage range If the either also characterized by comprising a control means for stopping the inverter circuit.

  In the discharge tube lighting device according to claim 2 of the present invention, the inverter circuit is connected to the high voltage side, and a voltage dividing capacitor comprising a first capacitor and a second capacitor is connected to the high voltage side of the inverter circuit, A smoothing circuit in which a diode and a resistor are connected in parallel between the grounds is connected to the voltage dividing point, and the first voltage detecting means for detecting the smoothed voltage is compared with the first predetermined voltage range. A first voltage comparison means; a resonance circuit in which a third capacitor and a coil are connected in parallel between the ground and a voltage lower than the voltage dividing point of the second capacitor; and a second circuit for detecting a voltage of the resonance circuit. Voltage detection means, and second voltage comparison means for comparing the detected voltage with a second predetermined voltage range, wherein the voltage detected by the first voltage detection means is outside the first predetermined voltage range. And the second voltage detection In at least one of when the voltage detected by the stage is out of the second predetermined voltage range, the discharge tube lighting apparatus characterized by comprising a control means for stopping the inverter circuit.

  According to a third aspect of the present invention, in the discharge tube lighting device according to the first or second aspect, the first voltage comparison means, the second voltage comparison means, and the control means are a microcomputer. .

  According to the discharge tube lighting device of the present invention, it is possible to reduce dangerous high-voltage components. Particularly, the single high-voltage capacitor reduces the size of the device while improving safety and reducing the failure rate. Can be realized.

  Embodiments of a discharge tube lighting device according to the present invention will be described below in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 shows a configuration diagram of a discharge tube lighting device according to a first embodiment of the present invention.

  In FIG. 1, a high voltage capacitor C1 is connected to the high voltage side of an inverter circuit that generates an AC voltage, and an overvoltage detection circuit 1 and an arc discharge detection circuit 2 are connected to the other. The microcomputer is connected to the overvoltage detection circuit 1, the arc discharge detection circuit 2, and a control circuit. When a malfunction occurs, the microcomputer detects a detection signal and sends a stop signal to the control circuit to stop the inverter output and turn off the discharge tube. .

  The overvoltage detection circuit 1 receives as input the signal obtained by dividing the AC voltage by the detection capacitor C1 and the capacitor C2, and half-wave rectifies the signal by the diode D1 and the resistor R7, and further smoothes the signal by the resistor R8 and the capacitor C7. ing. The overvoltage detection circuit 1 serves as a smoothing circuit that smoothes the input signal, and outputs the smoothed DC signal to the microcomputer. When an overvoltage occurs, the output signal becomes large, and the amount of change is detected by a microcomputer, thereby enabling overvoltage detection.

  For example, when an overvoltage is generated on the high voltage side of the capacitor C1, the voltage at the connection point between the capacitors C1 and C2 that divides the voltage rises, and a positive half-cycle voltage signal is applied to the resistor R7 by the diode D1. The amount of current is determined by R7, and the electric current is charged to the capacitor C7 through the resistor R8, and the charged voltage is detected by the microcomputer.

  The arc discharge detection circuit 2 receives the AC voltage via the detection capacitor C1 and the capacitor C2, and performs a resonance operation in the resonance circuit 3 including the coil L1 and the capacitor C3. The resonance signal is transmitted to the transistor Q1 via the capacitor C4. The signal is held by a holding circuit using a transistor Q2, smoothed by a smoothing circuit using a resistor 6 and a capacitor 6, and the DC signal is output to a microcomputer. When arc discharge occurs, the DC output signal becomes large, and the amount of change is detected by a microcomputer, thereby enabling detection of arc discharge.

  For example, when arc discharge occurs on the high voltage side of the capacitor C1, a voltage signal including a high frequency is applied to the resonance circuit 3 via the capacitors C1 and C2. In the resonance circuit 3, the signal in the arc discharge frequency band is amplified by the capacitor C3 and the coil L1, and the resonance signal is input to the gate terminal of the transistor Q1 biased by the resistors R1, R2, and R3 via the capacitor C4. The transistor Q1 is turned on by the resonance signal when arc discharge occurs, Vcc is input to the gate terminal of the transistor Q2 during the ON operation, the transistor Q2 is turned off, and the capacitor C6 is connected to the capacitor C6 through the resistors R5 and R6. Are charged, and the charged voltage signal is detected by the microcomputer.

  As described above, in the first embodiment, both arc discharge detection and overvoltage detection can be detected from the same input signal, and a single high-voltage capacitor can be connected to the high-voltage output of the inverter. Thus, cost reduction and reliability improvement can be achieved.

  Further, in the first embodiment, by detecting only the discharge frequency of arc discharge by the resonance circuit, the influence of other noise components is reduced, and malfunction can be prevented.

  Further, in the first embodiment, when the discharge tube is turned on by PWM dimming, a malfunction detection operation during dimming can be prevented by performing a protection detection operation in synchronization with the PWM operating frequency by a microcomputer.

(Embodiment 2)
FIG. 2 shows a configuration diagram of a discharge tube lighting device according to the second embodiment of the present invention.

  FIG. 1 shows a protection method in a single-side lamp drive method, and FIG. 2 shows a protection method in a double-side lamp drive method.

  In the double-sided lamp drive system, the arc protection circuit only needs to be inserted on one side as shown in FIG. 1, but arc protection is inserted on both sides in order to increase the accuracy of arc detection at the opposite end of the lamp with the detection circuit. Sometimes.

  In FIG. 2, the overvoltage detection circuit 5 operates in the same manner as the overvoltage detection circuit 1, and sends a detection signal to the microcomputer. The arc discharge detection circuit 6 performs the same operation as that of the arc discharge detection circuit 2, but a part of the arc discharge detection circuit is shared by inputting the combined signal of the transistor Q1 and the transistor Q10 to the transistor Q2, and the circuit Simplify.

  The discharge tube lighting device according to the present invention can provide low-cost arc discharge protection and overvoltage protection in a backlight power supply for an LCD display.

Configuration diagram of discharge tube lighting device according to Embodiment 1 of the present invention The block diagram of the discharge tube lighting device in Embodiment 2 of this invention Schematic of the discharge tube lighting device of the present invention Schematic diagram of a conventional discharge tube lighting device

Explanation of symbols

1, 5 Overvoltage detection circuit 2, 6 Arc discharge detection circuit 3 Resonance circuit 4 Discharge tube 7 High voltage capacitor

Claims (3)

In a discharge tube lighting device in which a discharge tube is connected to the high voltage side of the inverter circuit, a voltage dividing capacitor consisting of a first capacitor and a second capacitor is connected to the high voltage side of the inverter circuit to detect the voltage at the voltage dividing point. First voltage detecting means, first voltage comparing means for comparing the detected voltage with a first predetermined voltage range, a third capacitor and a coil on a lower voltage side than the voltage dividing point of the second capacitor. A resonant circuit connected in parallel between the ground, a second voltage detecting means for detecting the voltage of the resonant circuit, and a second voltage comparing means for comparing the detected voltage with a second predetermined voltage range. And the voltage detected by the first voltage detection means is outside the first predetermined voltage range and the voltage detected by the second voltage detection means is outside the second predetermined voltage range. At least any of the cases The case, the discharge tube lighting apparatus characterized by comprising a control means for stopping the inverter circuit. In a discharge tube lighting device in which a discharge tube is connected to the high voltage side of the inverter circuit, a voltage dividing capacitor comprising a first capacitor and a second capacitor is connected to the high voltage side of the inverter circuit, and a diode and a resistor are connected to the voltage dividing point. A first voltage detecting means for detecting a smoothed voltage, and a first voltage comparing means for comparing the detected voltage with a first predetermined voltage range. A resonance circuit in which a third capacitor and a coil are connected in parallel between the ground on the low voltage side of the voltage dividing point of the second capacitor, a second voltage detection means for detecting the voltage of the resonance circuit, and the detection And a second voltage comparison means for comparing the voltage with a second predetermined voltage range, wherein the voltage detected by the first voltage detection means is outside the first predetermined voltage range and the second voltage range. Detected by voltage detection means Wherein the voltage when at least either of the second case is outside the predetermined voltage range, the discharge tube lighting apparatus characterized by comprising a control means for stopping the inverter circuit. The discharge tube lighting device according to claim 1 or 2, wherein the first voltage comparison means, the second voltage comparison means, and the control means are microcomputers.