JP4342688B2 - Discharge lamp lighting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a discharge lamp lighting device for lighting a discharge lamp by outputting a high frequency voltage from an inverter.
[0002]
[Prior art]
Conventionally, a discharge lamp lighting device shown in FIGS. 4 and 5 is known. The discharge lamp lighting device shown in FIG. 4 has an inverter circuit 1 that outputs a high-frequency voltage, a discharge lamp 2 that is lit by the high-frequency voltage output from the inverter circuit 1, and a breakage of the filament F1 or F2 of the discharge lamp 2. And a disconnection detection circuit 3 for detecting. The output terminal 1a of the inverter 1 is connected to one terminal of the filament F1 through the current limiting element L, and the disconnection detection circuit 3 is connected to one terminal of the filament F2. In addition, a capacitor Cb and a resistor Rb connected in parallel are connected between the other terminals of the filaments F1 and F2.
[0003]
The disconnection detection circuit 3 includes resistors Rc and Rd connected in series, and a capacitor Cc and a diode D connected in parallel to the resistor Rd. Ca is a capacitor for cutting direct current, and resistors Ra and Rb are resistors for allowing a weak direct current to flow through the filaments F1 and F2 in order to detect disconnection of the filament F1 or F2. Cb is a capacitor for supplying a large preheating current to the filaments F1 and F2 before the start of discharge.
[0004]
In such a discharge lamp lighting device, a current flows in the direction of the arrow by the DC power source Vdc and a voltage is generated across the resistor Rd. However, when the filament F1 or F2 is disconnected or no load is applied, no current flows through the resistor Rd. No voltage is generated across the resistor Rd. The disconnection detection circuit 3 detects the voltage across the resistor Rd to detect disconnection or no load of the filament F1 or F2.
[0005]
However, when the discharge lamp 2 is lit, a rectangular high frequency voltage Vdc is output from the output terminal 1a of the inverter circuit 1 as shown in FIG. 6, and a DC voltage component of Vdc / 2 is included. As a result, a DC voltage (Vdc / 2) is generated at both ends of the capacitor Ca. Therefore, when the voltage applied to the discharge lamp 2 is high, a voltage is generated at both ends of the resistor Rd even if the filament F1 or F2 is disconnected. The disconnection detection circuit 3 has a problem that it cannot detect the disconnection of the filaments F1 and F2.
[0006]
In the discharge lamp lighting device shown in FIG. 5, the discharge lamp 2 is connected to the secondary winding Ta of the output transformer T, and the discharge lamp 2 is turned on by the voltage output from the secondary winding Ta. Since the voltage generated in the secondary winding Ta is directly applied to the discharge lamp 2, it is not necessary to use the DC cutting capacitor Ca, so the above problem does not occur.
[0007]
[Problems to be solved by the invention]
However, since any of the discharge lamp lighting devices detects the disconnection of the filaments F1 and F2 by passing a direct current through the filaments F1 and F2 of the discharge lamp 2, a resistance is applied between the filaments F1 and F2 of the discharge lamp 2. Rb must be connected. For this reason, the number of parts increases, and furthermore, since a high voltage similar to that at both ends of the discharge lamp 2 is applied to the resistor Rb, the capacity of the resistor Rb increases, resulting in an increase in size and cost. there were.
[0008]
The present invention has been made in view of the above problems, and an object thereof is to provide a discharge lamp lighting device capable of reducing the number of parts and preventing an increase in size and cost.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is directed to an inverter circuit that outputs a high frequency voltage and applies it to a primary winding of an output transformer, and a discharge lamp that discharges by a secondary voltage generated in the secondary winding of the output transformer. And one terminal of one filament of the discharge lamp is connected to the anode of the DC power source through a resistor, the other terminal of the filament is connected to one terminal of the secondary winding, and the other A discharge lamp lighting device in which one terminal of the filament is connected to the cathode of the DC power supply and the other terminal of the other filament is connected to the other terminal of the secondary winding,
A disconnection detection circuit for detecting disconnection of the filament is connected between one terminal of the one filament and one terminal of the other filament.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a discharge lamp lighting device according to the present invention will be described below with reference to the drawings.
[0011]
In FIG. 1, reference numeral 20 denotes an inverter circuit that outputs a high-frequency voltage having a predetermined frequency by the voltage V0 of the DC power supply E. It is connected. Both terminals of the secondary winding 21B of the output transformer 21 are connected to one terminal of the filaments 22F1 and 22F2 of the discharge lamp 22, respectively, and the other terminal of the filament 22F1 is connected to the anode of the DC power source E through the resistor R1. ing. The other terminal of the filament 22F2 is connected to the other terminal of the filament 22F1 through the capacitor C2 and grounded.
[0012]
Further, a disconnection detection circuit 30 for detecting disconnection of the filament 22F1 or 22F2 is connected to the other terminal of the filament 22F1 of the discharge lamp 22.
[0013]
The disconnection detection circuit 30 includes resistors R2 and R3 connected in series, and a capacitor C3 and a diode 31 connected in parallel to the resistor R3. One terminal of the resistor R2 is connected to the other terminal of the filament 22F1 of the discharge lamp 22, and the other terminal of the resistor R3 is grounded.
[0014]
Next, the operation of the discharge lamp lighting device will be described.
[0015]
First, when a power switch (not shown) is turned on, a high frequency voltage of a predetermined frequency is output from the inverter circuit 20 and applied to the primary winding 21A of the output transformer 21. A high-frequency voltage generated in the secondary winding 21B of the output transformer 21 is applied between the filaments 22F1 and 22F2 of the discharge lamp 22.
[0016]
Before the discharge of the discharge lamp 22 starts, a current flows in a closed circuit formed by the secondary winding 21B of the output transformer 21, the filaments 22F1, 22F2, and the capacitor C2, and the filaments 22F1, 22F2 are pre-heated. When the discharge is started, a current flows through a closed circuit formed by the discharge lamp 22 and the secondary winding 21B.
[0017]
On the other hand, if the discharge lamp 22 is normal, the voltage Va detected by the disconnection detection circuit 30 can be obtained by the equivalent circuit shown in FIG.
[0018]
That is, the voltage V0 of the DC power supply E is divided by the resistors R1 and 2Rf, and further divided by the resistors R2 and R3. Here, Rf (<< R1) is the resistance of the filaments 22F1 and 22F2, and the resistance of the secondary winding 21B of the output transformer 21 is ignored.
[0019]
Since the resistance Rf is Rf << R1, the voltage Va detected by the disconnection detection circuit 30 becomes a very small value.
[0020]
On the other hand, when the filament 22F1 or 22F2 is disconnected, the voltage Vb detected by the disconnection detection circuit 30 can be obtained by the equivalent circuit shown in FIG.
[0021]
That is, since the connection of the resistor Rf is lost due to the disconnection of the filament 22F1 or 22F2, the voltage V0 is divided by the resistor R1 + R2 and the resistor R3, and Vb has a larger value than Va. For this reason, the disconnection detection circuit 30 can detect disconnection or no load of the filament 22F1 or 22F2.
[0022]
Thus, even if the resistor Rb (see FIGS. 4 and 5) is not connected between the secondary windings 21B of the output transformer 21, the disconnection detection circuit 30 detects the disconnection or no load of the filaments 22F1, 22F2. Therefore, the number of parts can be reduced. In addition, since the resistor Rb having a large capacity is not necessary, the cost and size can be reduced.
[0023]
【The invention's effect】
As described above, according to the present invention, an inverter that outputs a high-frequency voltage and applies it to the primary winding of the transformer, and a discharge lamp that discharges by the secondary voltage generated in the secondary winding of the transformer, One terminal of one filament of the discharge lamp is connected to the anode of the DC power source through a resistor, the other terminal of the filament is connected to one terminal of the secondary winding, and the other filament is one terminal Is connected to the other terminal of the secondary winding, and the other terminal of the other filament is connected to the cathode of the DC power supply, wherein the other terminal of the one filament and the other Since the disconnection detection circuit that detects the disconnection of the filament is connected between the other terminal of the filament, the number of parts can be reduced and a resistor with a large capacity is not required. By becoming, it is possible to reduce the cost and size reduction.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a specific configuration of a discharge lamp lighting device according to the present invention.
FIG. 2 is an explanatory diagram showing an equivalent circuit when the discharge lamp of FIG. 1 is operating normally.
3 is an explanatory diagram showing an equivalent circuit when a filament of the discharge lamp of FIG. 1 is disconnected. FIG.
FIG. 4 is a circuit diagram showing a configuration of a conventional discharge lamp lighting device.
FIG. 5 is a circuit diagram showing a configuration of another conventional discharge lamp lighting device.
FIG. 6 is an explanatory diagram showing a waveform of an output voltage output from an inverter circuit.
[Explanation of symbols]
20 Inverter 21 Output transformer 21A Primary winding 21B Secondary winding 22 Discharge lamp 22F1 Filament 22F2 Filament 30 Disconnection detection circuit E DC power supply

Claims (1)

An inverter circuit that outputs a high-frequency voltage and applies it to the primary winding of the output transformer, and a discharge lamp that discharges by a secondary voltage generated in the secondary winding of the output transformer, and includes one of the filaments of the discharge lamp. The terminal is connected to the anode of the DC power source through a resistor, the other terminal of the filament is connected to one terminal of the secondary winding, and the other terminal of the other filament is connected to the cathode of the DC power source. A discharge lamp lighting device in which the other terminal of the other filament is connected to the other terminal of the secondary winding,
A discharge lamp lighting device, wherein a breakage detection circuit for detecting breakage of a filament is connected between one terminal of the one filament and one terminal of the other filament.

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