JP4470319B2 - Lighting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lighting device for lighting a discharge lamp at a high frequency.
[0002]
[Prior art]
2. Description of the Related Art A high-frequency inverter illumination device is widely used that includes a reactor connected in series to a discharge lamp having a preheating capacitor and a switching element that alternately applies a DC voltage and a zero voltage to these load circuits.
FIG. 6 shows a circuit diagram of a conventional illumination device. A DC power supply V and a series circuit of two transistors FET1 and FET2 are connected in parallel to the DC power supply V. A series circuit composed of two capacitors C1 and C2 is connected in parallel to the DC power supply V. A series circuit of the reactor L1 and the fluorescent tube K is connected between the connection portion of the two transistors FET1 and FET2 and the connection portion of the two capacitors C1 and C2. A condenser Cpre for preheating is connected to the fluorescent tube K. The transistors FET1 and FET2 are controlled so as to be alternately turned on and off by a control circuit (not shown), and a high frequency voltage is applied to the fluorescent tube K to light it.
[0003]
[Problems to be solved by the invention]
When the fluorescent tube K reaches the end of its life, it becomes a one-emitterless state. If the lighting operation is further continued in this one-emitter-less state, the filament will melt. If a voltage continues to be applied between the filaments in a state where the filaments are blown (melted open), a discharge is generated between the filaments, and the glass of the fluorescent tube K may be melted due to a temperature rise due to the discharge. In particular, fluorescent tubes with high brightness and a thin tube diameter of 16 mm have recently been used. In the fluorescent tube having a tube diameter of 16 mm, there is a higher possibility that the glass of the fluorescent tube is melted due to a temperature rise due to discharge. Therefore, it is important and required to reliably detect the life of the fluorescent tube.
Conventionally, as a method for detecting a single emitterless state of a discharge lamp including a fluorescent tube, there are a method for detecting a temperature of a switching element, a method for detecting a voltage of a filament, a method of detecting a voltage of a fluorescent tube, and the like. . However, the method for detecting the temperature of the switching element has a problem that the detection speed is slow and the detection accuracy is poor. In addition, in the method of detecting the voltage of the filament or the fluorescent tube, there is a problem that it becomes difficult to detect it by a circuit when one of the two filaments of the fluorescent tube is in a single emitterless state.
The present invention provides an illuminating device including detection means that can reliably detect the disconnection of a filament on one side of a discharge lamp and emit an output signal.
[0004]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a lighting device including a high-frequency inverter circuit that converts a DC voltage and supplies an AC voltage to a reactor connected in series with a discharge lamp. It is assumed that there is provided detection means for emitting an output signal when the generated voltage is less than a predetermined value and the terminal voltage of the filament on one side of the discharge lamp is detected.
[0005]
Further, the detecting means connects the auxiliary winding of the reactor to the input part of the switching element through a rectifying and smoothing circuit, and connects one terminal of the first resistor connected in parallel to both ends of the filament to the switching element. The output voltage of the auxiliary winding of the reactor is a voltage that does not turn on the switching element, and the output signal is emitted from the output part of the switching element when the terminal voltage of the filament is detected. Good.
Further, the detecting means connects a second resistor between one terminal of the first resistor and the output portion of the switching element, and a third resistor in parallel with the output portion of the switching element. Good.
With such a configuration, the disconnection of the filament on one side of the discharge lamp is detected and an output signal is output. Then, the control circuit that has received the output signal from the detection means can avoid the abnormal state of the lighting device by stopping the high-frequency inverter.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
As an embodiment of the present invention, FIG. 1 shows a circuit diagram of a lighting device. FIG. 2 shows a circuit diagram of the detection circuit of FIG. Symbols shown in the waveform diagrams described below are as follows, Vds2 is a drain-source voltage waveform of the switching element FET2, IL is a current waveform flowing in the primary side winding of the reactor L2, and VL is a reactor L2 Is a voltage waveform generated in the auxiliary winding, Ilamp is a current waveform flowing in the fluorescent tube K, and VR is a voltage waveform of the tube dropout resistance (resistor R5 + R6). Parts identical to those of the conventional example shown in FIG.
As shown in FIG. 1, the difference from the conventional example (FIG. 6) is that an auxiliary winding is provided in the reactor L2, and the output voltage VL of this auxiliary winding and the terminal voltage of the filament of the fluorescent tube K are respectively input. In these voltage relationships, an output signal is output when the output voltage VL of the auxiliary winding is not more than a predetermined voltage value (for example, substantially zero voltage) and the terminal voltage of one of the filaments of the fluorescent tube K is detected. This is a point provided with a detection circuit M.
FIG. 2 shows a circuit diagram of the detection circuit M. One of the auxiliary windings of the reactor L2 is connected to the anode of the diode D, and the other is grounded. A series connection circuit of resistors R1, R2, and R3 is connected between the cathode of the diode D and the ground. Connect capacitor C3 between the connection of resistors R1 and R2 and ground. The connection between the resistors R2 and R3 is connected to the base of the transistor TR. A resistor R4 is connected in parallel to both filament terminals of the fluorescent tube K, and a resistor R5 is connected between one of the resistors R4 (in this case, the filament terminal connected to the connection between the capacitors C1 and C2) and the ground. And connect a series circuit of R6. The collector of the transistor TR is connected to the connection between the resistors R5 and R6, and the emitter is connected to the ground side of the resistor R6. The output signal of the detection circuit M is output from the collector of the transistor (the connection portion between the resistors R5 and R6). Upon receiving this output signal, the control circuit stops the high frequency inverter circuit and avoids an abnormal state of the lighting device. Here, the resistors R4, R5, and R6 are all high resistances, and the current flowing through these resistors is almost negligible, so the voltage generated in the reactor L2 is not affected.
The operation of the detection circuit M will be described. The detection circuit M applies the voltage VL generated in the auxiliary winding of the reactor L2 to a circuit composed of a capacitor C3 rectified by a diode D and connected in parallel to a series circuit of resistors R2 and R3 via a resistor R1. When the voltage at the connection between the resistors R2 and R3 exceeds the base layer-emitter layer voltage (approximately 0.7 V) of the transistor TR, the transistor TR is turned on. On the other hand, when the voltage VL generated in the auxiliary winding of the reactor L2 is equal to or lower than the base layer-emitter voltage of the transistor TR, the transistor TR is turned off.
Next, the operation of the detection circuit M when the filament of the fluorescent tube K is normal on both sides, when one side of the filament of the fluorescent tube K is blown (disconnected), and when the fluorescent tube K is disconnected is described. To do.
(1) When the filament of the fluorescent tube K is normal FIG. 3 shows waveform diagrams of voltage and current at each part when the filament of the fluorescent tube K is normal on both sides. In this case, normal currents flow through the reactor L2 and the fluorescent tube K, respectively, so that the generated voltage VL is generated in the auxiliary winding of the reactor L2. The voltage VL generated by the auxiliary winding is rectified by the diode D and added to the series circuit of the resistors R1, R2, and R3. Smoothing is performed by connecting a capacitor C3 in parallel with the resistors R2 and R3. Since the connection between the resistors R2 and R3 is connected to the base of the transistor TR, and the divided voltage of the resistor R3 is set to exceed the base layer-emitter voltage (approximately 0.7V), The transistor TR is turned on. On the other hand, the divided voltage of the resistor R6 among the series resistors R5 and R6 connected to the resistor R4 connected in parallel to both filaments of the fluorescent tube K is applied to the transistor TR, but the transistor TR is turned on. The collector potential becomes equal to the ground potential, and therefore the detection circuit M does not emit an output signal.
(2) When one side of the filament of the fluorescent tube K is melted FIG. 4 shows waveform diagrams of voltage and current at each part when the filament on one side (reactor side) of the fluorescent tube is disconnected. In this case, since almost no current flows through the primary side winding of the reactor L2, the generated voltage VL of the auxiliary winding of the reactor L2 becomes almost zero voltage (the whisker-like voltage at the time of switching can be ignored). Then, the voltage VL generated in the auxiliary winding also becomes almost zero voltage (the beard-like voltage at the time of switching can be ignored), so that the transistor TR is turned off. On the other hand, among the filaments of the fluorescent tube K, the filament connected to the reactor L2 is melted, and this filament is open, but the filament connected to the connection between the capacitors C1 and C2 Is not blown, the terminal voltage of the filament on this side can be applied to the collector of the transistor TR as a divided voltage of the resistor R6 via the resistor R5. Thus, since the transistor TR is in an off state, this collector voltage becomes an output signal of the detection circuit M. In response to this output signal, for example, the control circuit stops the operation of the high-frequency inverter.
Although not shown, when one of the filaments of the fluorescent tube K that is connected to the connection part between the capacitors C1 and C2 is melted, the filament is opened but connected to the reactor L2. Since the side filament is not blown, the terminal voltage of this side filament can be detected, and the divided voltage of resistor R6 can be applied to the collector of transistor TR via resistors R4 and R5. The voltage becomes an output signal of the detection circuit M.
(3) When the fluorescent tube is disconnected FIG. 5 shows waveform diagrams of voltage and current of each part when the fluorescent tube is disconnected. In this case, since almost no current flows through the reactor L2, the voltage generated at the primary side winding of the reactor L2 is almost zero voltage (the voltage at the time of switching can be ignored). As a result, the generated voltage VL of the auxiliary winding also becomes almost zero voltage (the beard-like voltage at the time of switching can be ignored), and the transistor TR is turned off. On the other hand, since the fluorescent tube K is disconnected, no voltage is applied to any end of the resistor R4, and the voltage VR of the tube disconnection detection resistor (R5 + R6) does not detect the voltage. Then, the collector of the transistor TR becomes equal to the ground potential via the resistor R6, and therefore the detection circuit M does not emit an output signal.
As described above, the detection circuit M outputs an output signal when only one side of the filament of the fluorescent tube K is disconnected due to melting or the like. The control circuit that has received this signal can avoid an abnormal state of the lighting device by stopping the high-frequency inverter circuit. It is possible to prevent the filament of the fluorescent tube K from being melted and further the glass of the fluorescent tube K from being melted.
Although an example of a half-bridge circuit is shown here as an inverter circuit, a full-bridge circuit or other circuits may be used and are not particularly limited. Further, although a bipolar transistor is used as a switching element in the detection circuit, for example, a MOSFET may be used as long as it has a function similar to this, and there is no particular limitation.
[0007]
【The invention's effect】
The present invention includes a detecting means for generating an output signal when the generated voltage of the auxiliary winding of the reactor is equal to or lower than a predetermined value and the terminal voltage of the filament on one side of the discharge lamp is detected. The disconnection of the filament can be reliably detected. The control circuit that has received the output signal can stop the high-frequency inverter to prevent the filament from fusing and the glass of the discharge lamp from melting, thereby improving the reliability.
[Brief description of the drawings]
1 is a circuit diagram of an illuminating device showing an embodiment of the present invention. FIG. 2 is a circuit diagram of a detection circuit of FIG. 1. FIG. 3 is a waveform of voltage and current of each part in the case of a normal fluorescent tube in FIG. FIG. 4 is a waveform diagram of voltage and current of each part when the fluorescent tube is one-emitterless in FIG. 1. FIG. 5 is a waveform diagram of voltage and current of each part when the fluorescent tube is disconnected in FIG. 】 Circuit diagram of conventional lighting device 【Explanation of symbols】
FET1, FET2: FET transistors
L1, L2: Reactor K: Fluorescent tube
C1, C2, C3: Capacitors
Cpre: Preheating capacitor
D: Diode
TR: Transistor
R1, R2, R3, R4, R5, R6: Resistance
M: Detection circuit V: DC power supply

Claims (3)

In a lighting device including a high-frequency inverter circuit that converts a DC voltage to supply an AC voltage to a reactor connected in series with a discharge lamp, a voltage generated in an auxiliary winding of the reactor is equal to or lower than a predetermined value and the discharge An illuminating device comprising: a detecting means for generating an output signal when a terminal voltage of a filament on one side of an electric lamp is detected. The detecting means connects the auxiliary winding of the reactor to the input part of the switching element via a rectifying and smoothing circuit, and outputs one terminal of a first resistor connected in parallel to both ends of the filament to the output of the switching element. The output voltage of the auxiliary winding of the reactor is a voltage that does not turn on the switching element, and when the terminal voltage of the filament is detected, the output signal is emitted from the output part of the switching element. The lighting device according to claim 1. The detection means includes a second resistor connected between one terminal of the first resistor and the output portion of the switching element, and a third resistor connected in parallel to the output portion of the switching element. The lighting device according to claim 2.

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