JP2009032421A - Discharge lamp lighting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device precisely detecting current flowing into a discharge lamp without increasing the number of substrates for a current detection circuit. <P>SOLUTION: The discharge lamp lighting device has: an inverter having a transformer T1 with a primary winding P1, a first secondary winding S1, and a second secondary winding S2 and boosting high-frequency voltage converted from current voltage to high-frequency voltage by the transformer; a plurality of discharge lamps 1a, 1b connected between one end of the first secondary winding and the second secondary winding of the transformer; first current detection circuits D1, D2, and R1 with one end connected to the other end of the first secondary winding, with the other end connected to the ground and detecting the currents; and a first detection circuit 11a connected with both ends of the first secondary winding of the transformer and detecting the voltage generated in the first secondary winding of the transformer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a discharge lamp lighting device that lights a plurality of cold cathode discharge lamps (CCFLs), external electrode fluorescent lamps, fluorescent lamps and the like.

  In general, a cold cathode discharge lamp is lit when an inverter is applied with a voltage of several hundreds of volts to several hundreds of volts at a frequency of several tens of kHz. There is also a fluorescent tube called an external electrode fluorescent lamp (EEFL). The external electrode fluorescent lamp and the cold cathode discharge lamp have different electrode structures, there is almost no difference, and the light emission principle is the same as that of the cold cathode discharge lamp. For this reason, the inverter for lighting the external electrode fluorescent lamp and the cold cathode discharge lamp is the same in principle. For this reason, the following description will be made using a cold cathode discharge lamp (abbreviated as a discharge lamp).

  Discharge lamps and inverters are used in liquid crystal TVs, liquid crystal monitors, illumination devices, liquid crystal display devices, signboards, and the like. Inverters are often boosted by a transformer, and there are so-called “single-end high voltage” systems and “end-high voltage” systems. The single-sided high-voltage system is a system in which one side of the secondary winding (discharge lamp side) of the transformer has a low voltage with respect to the ground (GND). It is a system that becomes.

  FIG. 5 is a circuit diagram of a discharge lamp lighting device using a conventional one-end high-pressure system. This one-end high-voltage system includes an inverter unit 20 and a panel unit 30. The inverter unit 20 converts a DC voltage into a high-frequency voltage, boosts the high-frequency voltage with a transformer T3, and a secondary winding S1 ( One end is grounded)) and a high-frequency high-frequency voltage is generated. A high-frequency voltage generated in the secondary winding S1 causes a current to flow through the discharge lamp 1 in the panel unit 30, and the discharge lamp 1 is turned on. The current flowing through the discharge lamp 1 is detected by a current detection circuit including a current detection resistor R1 and diodes D1 and D2. A control circuit (not shown) performs control so that the detected current becomes a predetermined value.

  In this one-end high-pressure system, in addition to the current flowing through the discharge lamp 1 and circuit elements, there is also a current flowing through the parasitic capacitance. The current path that flows through the secondary winding S1 of the transformer T3 includes a current path (1) that flows through the voltage detection capacitors C1 and C2 for detecting the voltage of the secondary winding S1, wiring, etc. There are a current path (2) flowing through the parasitic capacitance C5 between the chassis and the like, and a current path (3) flowing through the discharge lamp 1.

  In general, since the chassis or the like is also at the ground potential, the leakage current flowing to the chassis or the like returns directly to the transformer T3. For this reason, in the example of FIG. 6, the currents in the path (1) and the path (2) do not flow through the current detection resistor R1, and only the path (3) flows through the current detection resistor R1. Only the flowing current can be detected. Using this detected current value, feedback control can be performed with high accuracy. In the example of FIG. 5, since both the voltage detection capacitor C2 and the current detection resistor R1 are connected to the ground, current detection with reference to the ground potential can be easily performed. FIG. 6 shows a configuration example in which the one-end high-pressure system shown in FIG. 5 is mounted on the panel portion. As shown in FIG. 5, a plurality of discharge lamps 1 are provided in the panel unit 30, and each discharge lamp 1 is connected to the inverter unit 20 by an electric wire 3, and the inverter unit 20 is configured by a single substrate.

  On the other hand, in the high voltage system at both ends, the ground potential of the secondary winding of the transformer cannot be determined, and both ends of the secondary winding are high voltage, so it is difficult to detect the current flowing through the discharge lamp and the voltage of the transformer. . For this reason, the double-sided high-voltage system shown in FIG. 7 uses the transformer T4 secondary side as the first secondary winding S1 and the second secondary winding S2, and connects one end of each winding to the ground. The ground potential on the secondary side of T4 is determined, and the current and voltage of each winding are detected with reference to the ground potential.

  In this case, the current path includes a current path (1) that flows through the voltage detection capacitors C1, C2, C3, and C4, a current path (2) that flows through parasitic capacitances C5 and C6 due to wiring and the like, and the discharge lamps 1a and 1b. And a current path (3) flowing therethrough. Since the current flowing through the current detection resistors R1 and R2 is only the path (3), only the current flowing through the discharge lamps 1a and 1b can be detected. Using this detected current value, feedback control can be performed with high accuracy. Further, since the voltage detection capacitors C2 and C4 and the current detection resistors R1 and R2 are all connected to the ground, current detection can be performed with reference to the ground potential.

  However, it is necessary to install a first current detection circuit including diodes D1 and D2 and a current detection resistor R1 and a second current detection circuit including diodes D3 and D4 and a current detection resistor R2 at one end of each discharge lamp 1a and 1b. There is. A configuration example in which the both-end high-pressure system shown in FIG. 7 is mounted on the panel portion is shown in FIG. As shown in FIG. 8, in addition to the substrate 20a for the inverter unit, a substrate 20b for the first current detection circuit and the second current detection circuit is added. Moreover, a connector, a harness, etc. which connect to the board | substrates 20a and 20b must be provided, and cost increases. Therefore, in order to reduce the cost, as shown in FIG. 9, current detection circuits such as current detection resistors R1 and R2 are installed in the inverter unit and configured by a single substrate.

  However, in the configuration example shown in FIG. 9, the current path that flows through the secondary windings S1 and S2 of the transformer T5 includes the current path (1) that flows through the voltage detection capacitors C1, C2, C3, and C4, and the parasitic due to wiring and the like. There are a current path (2) flowing through the capacitors C5 and C6 and a current path (3) flowing through the discharge lamps 1a and 1b. That is, there is a problem that the current of the path (1) flows through the current detection resistors R1 and R2.

  It is the current value of the path (3) that determines the brightness of the discharge lamp, and the current value of the path (1) does not contribute to the brightness. For this reason, when feedback control is applied with a detection value obtained by mixing the currents of the path (1), the discharge lamp current changes with time after the discharge lamp is turned on. In addition, a phenomenon occurs in which the discharge lamp current changes depending on the ambient temperature and the mounting state of the apparatus.

Specifically, since the impedance of the discharge lamp increases at low temperatures, it is necessary to generate a high voltage in the secondary windings S1 and S2. As a result, the current in the path (1) increases and the current flowing through the current detection resistors R1 and R2 increases. As a result, the current flowing through the discharge lamps 1a and 1b decreases. When the temperature is high, the current in the path (1) decreases and the current flowing through the current detection resistors R1 and R2 decreases. As a result, the current flowing through the discharge lamps 1a and 1b increases. That is, the discharge lamp is dark at a low temperature, bright at a high temperature, and the luminance changes.
6-19299

  As described above, the circuit shown in FIG. 9 has an advantage that it can be configured by a single substrate, but the current flowing through the discharge lamp varies due to a temperature change or the like.

  An object of the present invention is to provide a discharge lamp lighting device that can accurately detect a current flowing in a discharge lamp without increasing the number of substrates for a current detection circuit.

  In order to solve the above problems, the invention of claim 1 includes a transformer having a primary winding, a first secondary winding, and a second secondary winding, and converts a DC voltage into a high-frequency voltage. An inverter that boosts the high-frequency voltage by the transformer, and one or more discharge lamps connected between one end of the first secondary winding and one end of the second secondary winding of the transformer; One end connected to the other end of the first secondary winding of the transformer, the other end connected to the ground, and a first current detection circuit for detecting a current, and the first secondary winding of the transformer. And a first detection circuit which is connected to both ends of the wire and detects a voltage generated in the first secondary winding of the transformer.

  According to a second aspect of the present invention, in the discharge lamp lighting device according to the first aspect, the first detection circuit is connected to both ends of the first secondary winding of the transformer, and a first capacitor, a second capacitor, Are connected in series, and a first voltage detection circuit that detects a voltage across the first capacitor or the second capacitor.

  According to a third aspect of the present invention, in the discharge lamp lighting device according to the first aspect, the first detection circuit is connected to both ends of the first secondary winding of the transformer, and a first capacitor, a second capacitor, Have a first series circuit connected in series, and a voltage between a connection point between the first capacitor and the second capacitor and the ground is used as a detection voltage.

  According to a fourth aspect of the present invention, in the discharge lamp lighting device according to any one of the first to third aspects, the second secondary winding of the transformer is connected to both ends of the second secondary winding of the transformer. And a second detection circuit for detecting a voltage generated in the secondary winding.

  According to a fifth aspect of the present invention, in the discharge lamp lighting device according to any one of the first to third aspects, one end is connected to the other end of the second secondary winding of the transformer, and the other end is A second current detection circuit that is connected to ground and detects a current, and is connected to both ends of the second secondary winding of the transformer and detects a voltage generated at the second secondary winding of the transformer. And a second detection circuit.

  According to a sixth aspect of the present invention, in the discharge lamp lighting device according to the fourth or fifth aspect, the second detection circuit is connected to both ends of the second secondary winding of the transformer, A second series circuit having a fourth capacitor connected in series and a second voltage detection circuit for detecting a voltage across the third capacitor or the fourth capacitor are provided.

  A seventh aspect of the invention is the discharge lamp lighting device according to the fifth aspect, wherein the second detection circuit is connected to both ends of the second secondary winding of the transformer, and a third capacitor, a fourth capacitor, Has a second series circuit connected in series, and a voltage between a connection point between the third capacitor and the fourth capacitor and the ground is used as a detection voltage.

  According to the first aspect of the present invention, a current flows through the first detection circuit due to the voltage generated across the first secondary winding of the transformer, but this current does not flow through the first current detection circuit. That is, since the first current detection circuit detects a current obtained by removing the current flowing through the first detection circuit from the current flowing through the first secondary winding of the transformer, it is possible to suppress a change in the feedback amount due to a change in the impedance of the discharge lamp. . Therefore, the current flowing through the discharge lamp can be accurately detected without increasing the number of substrates for the current detection circuit.

  According to the invention of claim 2 and the invention of claim 3, the first detection circuit detects the voltage generated in the first secondary winding of the transformer, and uses the voltage detection value for protection in the event of an abnormality. it can.

  According to the invention of claim 4, the second detection circuit can detect the voltage generated in the second secondary winding of the transformer, and can be used for protection at the time of abnormality by the voltage detection value.

  According to the fifth aspect of the present invention, a current flows through the second detection circuit due to the voltage generated across the second secondary winding of the transformer, but this current does not flow through the second current detection circuit. That is, since the second current detection circuit detects a current obtained by removing the current flowing through the second detection circuit from the current flowing through the second secondary winding of the transformer, it is possible to suppress a change in the feedback amount due to a change in the impedance of the discharge lamp. . Therefore, the current flowing through the discharge lamp can be accurately detected without increasing the number of substrates for the current detection circuit.

  According to the invention of claim 6 and the invention of claim 7, the second detection circuit detects the voltage generated in the second secondary winding of the transformer, and uses the voltage detection value for protection in case of abnormality. it can.

  Hereinafter, embodiments of a discharge lamp lighting device of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of a discharge lamp lighting device according to Embodiment 1 of the present invention. In FIG. 1, a transformer T1 has a primary winding P1, a first secondary winding S1, and a second secondary winding S2, and constitutes an inverter. The inverter converts a DC voltage into a high frequency voltage by turning on and off a switching element (not shown) by a control circuit (not shown), and boosts the high frequency voltage by a transformer T1 to produce a first secondary winding. Output to S1 and the second secondary winding S2. A discharge lamp 1a and a discharge lamp 1b are connected in series between one end of the first secondary winding S1 of the transformer T1 and one end of the second secondary winding S2.

  The discharge lamps 1a and 1b are composed of, for example, a cold cathode discharge lamp, an external electrode fluorescent lamp, or a fluorescent lamp. Here, a cold cathode discharge lamp is used.

  A parasitic capacitance C5 is connected between the connection point between one end of the first secondary winding S1 of the transformer T1 and the discharge lamp 1a and the ground. A series circuit of a voltage detection capacitor C1 (first capacitor) and a voltage detection capacitor C2 (second capacitor) is connected to both ends of the first secondary winding S1 of the transformer T1.

  A parasitic capacitance C6 is connected between the connection point between the one end of the second secondary winding S2 of the transformer T1 and the discharge lamp 1b and the ground. A series circuit of a voltage detection capacitor C3 (third capacitor) and a voltage detection capacitor C4 (fourth capacitor) is connected to both ends of the second secondary winding S2 of the transformer T1.

  A series circuit of a diode D2 and a resistor R1 and a diode D1 connected in parallel to the series circuit are connected between the other end of the first secondary winding S1 of the transformer T1 and the ground. D1, D2 and resistor R1 constitute a first current detection circuit.

  Between the other end of the second secondary winding S2 of the transformer T1 and the ground, a series circuit of a diode D3 and a resistor R2 and a diode D4 connected in parallel to the series circuit are connected. D3, D4 and resistor R2 constitute a second current detection circuit.

  The control circuit obtains an average value current between the first current detection value detected by the first current detection circuit and the second current detection value detected by the second current detection circuit, and the average current value becomes a predetermined value. Thus, PWM control for turning on and off the switching element is performed.

  The voltage detection circuit (first voltage detection circuit) 11a detects the voltage across the voltage detection capacitor C2, and outputs the detected voltage to the control circuit. The voltage detection circuit (second voltage detection circuit) 11b detects the voltage across the voltage detection capacitor C4 and outputs the detected voltage to the control circuit. The control circuit determines whether or not an average voltage obtained by averaging the first voltage detection value from the voltage detection circuit 11a and the second voltage detection value from the voltage detection circuit 11b exceeds a predetermined voltage value. That is, the voltage detection circuits 11a and 11b are used to determine whether or not the voltage of the secondary winding S1 and the voltage of the secondary winding S2 are overvoltage.

  According to the discharge lamp lighting device of the first embodiment configured as described above, S1 → C1 → C2 → S1, S1 → C2 → C1 due to the voltage generated at both ends of the first secondary winding S1 of the transformer T1. → Current flows through the current path (1) of S1. The current in the current path (1) does not flow through the first current detection circuit including the diodes D1 and D2 and the resistor R1. That is, the first current detection circuit detects a current obtained by subtracting the current flowing through the first voltage detection circuit including the voltage detection capacitor C1 and the capacitor C2 from the current flowing through the first secondary winding S1 of the transformer T1.

  Further, due to the voltage generated at both ends of the first secondary winding S2 of the transformer T1, a current flows through a current path (1) of S2-> C4-> C3-> S2 and S2-> C3-> C4-> S2. The current in the current path (1) does not flow through the second current detection circuit including the diodes D3 and D4 and the resistor R2. That is, the second current detection circuit detects a current obtained by subtracting the current flowing through the second voltage detection circuit including the voltage detection capacitor C3 and the capacitor C4 from the current flowing through the second secondary winding S2 of the transformer T1.

  For this reason, the change of the feedback amount by the impedance change of discharge lamp 1a, 1b can be suppressed. Therefore, it is possible to detect the current flowing through the discharge lamps 1a and 1b with high accuracy without increasing the number of substrates for the current detection circuit.

  The voltage detection circuit 11a detects the voltage across the voltage detection capacitor C2, and the voltage detection circuit 11b detects the voltage across the voltage detection capacitor C4. When the average voltage obtained by averaging the first voltage detection value from the voltage detection circuit 11a and the second voltage detection value from the voltage detection circuit 11b exceeds a predetermined voltage value, the control circuit It can be determined that the voltage of S1 has become an overvoltage, that is, an abnormal voltage.

  FIG. 2 is a diagram showing a configuration of a discharge lamp lighting device according to Embodiment 2 of the present invention. In the second embodiment shown in FIG. 2, in contrast to the first embodiment shown in FIG. 1, the voltage between the connection point between the voltage detection capacitor C1 and the voltage detection capacitor C2 and the ground is used as the first voltage detection value in the control circuit. The voltage between the connection point of the voltage detection capacitor C3 and the voltage detection capacitor C4 and the ground is output to the control circuit as the second voltage detection value. In short, the first detection circuit detects the first voltage detection value via the first current detection circuit including the diodes D1 and D2 and the resistor R1. The second detection circuit detects the second voltage detection value via the second current detection circuit including the diodes D3 and D4 and the resistor R2.

  According to such a configuration, substantially the same effect as the effect of the first embodiment can be obtained, and the voltage detection circuits 11a and 11b can be eliminated, so that the cost is further reduced.

  FIG. 3 is a diagram showing a configuration of a discharge lamp lighting device according to Embodiment 3 of the present invention. The third embodiment shown in FIG. 3 is characterized in that the second current detection circuit including the diodes D3 and D4 and the resistor R2 is deleted from the configuration of the second embodiment shown in FIG.

  That is, depending on the set mounting state and application, current detection may be performed only by the first current detection circuit including the diodes D1 and D2 and the resistor R1. Therefore, the effect similar to the effect of Example 2 is acquired also by Example 3.

  FIG. 4 is a diagram showing a configuration of a discharge lamp lighting device according to Embodiment 4 of the present invention. The fourth embodiment shown in FIG. 4 is characterized in that the second voltage detection circuit including the voltage detection capacitor C3 and the voltage detection capacitor C4 is deleted from the configuration of the third embodiment shown in FIG.

  That is, depending on the set mounting state and application, voltage detection may be performed only by the first voltage detection circuit including the voltage detection capacitor C1 and the voltage detection capacitor C2. Therefore, the effect similar to the effect of Example 3 is acquired also by Example 4.

  In addition, this invention is not limited to the discharge lamp lighting device of the said Examples 1 thru | or 4. In Examples 1 to 4 of FIGS. 1 to 4, the number of discharge lamps is two, but the number of discharge lamps may be one. Moreover, you may combine each structure of Example 1 thru | or Example 4. FIG. For example, in FIGS. 3 and 4, a voltage detection circuit 11a that detects the voltage across the voltage detection capacitor C1 or the voltage detection capacitor C2 may be provided. Further, for example, in FIG. 3, a voltage detection circuit 11b that detects the voltage across the voltage detection capacitor C3 or the voltage detection capacitor C4 may be provided.

It is a figure which shows the structure of the discharge lamp lighting device of Example 1 of this invention. It is a figure which shows the structure of the discharge lamp lighting device of Example 2 of this invention. It is a figure which shows the structure of the discharge lamp lighting device of Example 3 of this invention. It is a figure which shows the structure of the discharge lamp lighting device of Example 4 of this invention. It is a circuit diagram of the discharge lamp lighting device using the conventional one end high pressure system. It is a figure which shows the structural example which mounted the one end high voltage | pressure system shown in FIG. 5 in the panel part. It is a circuit diagram of the discharge lamp lighting device using the conventional both-ends high pressure system. It is a figure which shows the structural example which mounted the both-ends high voltage | pressure system shown in FIG. 7 in the panel part. It is a circuit diagram of the discharge lamp lighting device using the conventional both-ends high-pressure system which installed the electric current detection part in the inverter part, and comprised with one board | substrate.

Explanation of symbols

T1, T3, T4, T5 Transformer P1 Primary winding S1 First secondary winding S2 Second secondary winding C1 to C4 Voltage detection capacitors C5 and C6 Parasitic capacitances R1 and R2 Current detection resistors D1 to D4 Diodes 1, 1a, 1b Discharge lamp 3 Electric wires 11a, 11b Voltage detection circuit 20 Inverter portions 20a, 20b Board 30 Panel portion

Claims (7)

An inverter comprising a transformer having a primary winding, a first secondary winding, and a second secondary winding, converting a DC voltage into a high-frequency voltage and boosting the high-frequency voltage by the transformer;
One or more discharge lamps connected between one end of the first secondary winding of the transformer and one end of the second secondary winding;
One end connected to the other end of the first secondary winding of the transformer, the other end connected to the ground, and a first current detection circuit for detecting a current;
A first detection circuit connected to both ends of the first secondary winding of the transformer and detecting a voltage generated in the first secondary winding of the transformer;
A discharge lamp lighting device comprising: The first detection circuit is connected to both ends of the first secondary winding of the transformer, and a first series circuit in which a first capacitor and a second capacitor are connected in series;
A first voltage detection circuit for detecting a voltage across the first capacitor or the second capacitor;
The discharge lamp lighting device according to claim 1, comprising:   The first detection circuit includes a first series circuit that is connected to both ends of the first secondary winding of the transformer and in which a first capacitor and a second capacitor are connected in series, and the first capacitor The discharge lamp lighting device according to claim 1, wherein a voltage between a connection point between the first capacitor and the second capacitor and the ground is used as a detection voltage.   2. A second detection circuit that is connected to both ends of the second secondary winding of the transformer and detects a voltage generated in the second secondary winding of the transformer. The discharge lamp lighting device according to claim 3. One end connected to the other end of the second secondary winding of the transformer, the other end connected to the ground, a second current detection circuit for detecting current;
A second detection circuit that is connected to both ends of the second secondary winding of the transformer and detects a voltage generated in the second secondary winding of the transformer;
The discharge lamp lighting device according to any one of claims 1 to 3, wherein the discharge lamp lighting device includes: The second detection circuit is connected to both ends of the second secondary winding of the transformer, and a second series circuit in which a third capacitor and a fourth capacitor are connected in series;
A second voltage detection circuit for detecting a voltage across the third capacitor or the fourth capacitor;
The discharge lamp lighting device according to claim 4 or 5, characterized by comprising:   The second detection circuit includes a second series circuit that is connected to both ends of the second secondary winding of the transformer and in which a third capacitor and a fourth capacitor are connected in series, and the third capacitor 6. The discharge lamp lighting device according to claim 5, wherein a voltage between a connection point between the first capacitor and the fourth capacitor and the ground is used as a detection voltage.

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