JPH0266897A - Discharge lamp lightup device - Google Patents

Abstract

PURPOSE:To prevent dark lighting-up automatically by furnishing a leakage transformer, turning off a switching means when the dimming level becomes below the specified value, and shutting off the preheating current for the filament. CONSTITUTION:At first a switch 13 is closed, and an AC power supply preheats a discharge lamp 7 through a preheating transformer 16. At this time, a leakage transformer 6 takes out a voltage proportional to the output voltage of a lightup circuit from a sensor coil N4. Whole-wave rectification is made by a diode bridge 9, and the resultant is fed into a sensing control circuit 11 as the sensing voltage. When the dimming level sinks, the sensing voltage becomes smaller than the specified value, and the circuit 11 opens the switch 13 to shut off the preheating current for the filament of discharge lamp 7. Heating of the filament is stopped in the dimming darkness condition, and dark lighting up of the discharge lamp 7 is precluded automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a discharge lamp lighting device, and particularly to a lighting device that eliminates dark lighting of electrodes when the dimming level is low.

[Prior Art] Conventionally, in order to dim a discharge lamp, a thyristor was connected to the main circuit of the power supply, and phase control was performed by adjusting the conduction angle of the power supplied to the lamp load by the thyristor. . In such conventional lighting devices, a preheating transformer is connected before the thyristor circuit and the filament of the discharge lamp is preheated by this transformer, so that a constant preheating voltage is supplied even in the dimming state. It was configured so that

[Problems to be Solved by the Invention] However, in such conventional discharge lamp lighting devices, a constant preheating power is not supplied to the filament of the discharge lamp during dimming, especially when the dimming level is low. Therefore, there is a problem in that so-called dark lighting of the electrodes occurs particularly when the dimming level is low. Additionally, in order to prevent this phenomenon, there was a method of cutting off the main power supply when the dimming level was low, but this had the disadvantage of requiring a large-scale device.

SUMMARY OF THE INVENTION An object of the present invention is to provide a discharge lamp lighting device that can automatically prevent dark lighting of electrodes in a dark state during dimming using a simple circuit, in view of the problems with the conventional devices described above. It is in.

[Means for Solving the Problems] A discharge lamp lighting device according to the present invention includes a thyristor means that is inserted into the main circuit of a power source to adjust the lamp current, and an output of the thyristor means that is boosted and supplied to the lamp load. a leakage transformer, a preheating circuit for supplying a preheating current to the filament of the lamp load from a stage preceding the thyristor means, a switch means for conducting or cutting off the preheating circuit, and a switch means for conducting the preheating circuit when the output of the leakage transformer becomes below a predetermined value. It is characterized by comprising a control circuit that shuts off the switch means.

[Operation] In the above-described configuration, power whose flow angle is adjusted according to the dimming level by the operation of the thyristor means is supplied to the lamp load via the leakage transformer. Furthermore, the filament is heated by the preheating circuit with constant preheating power regardless of the dimming level. Thereby, the lamp load can be lit at a desired dimming level and the dimming level can be adjusted by controlling the thyristor means.

In such a dimming operation, when the dimming level becomes lower than a predetermined value, the output of the leakage transformer also becomes lower than the predetermined value, and therefore the control circuit turns off the switch means to cut off the filament preheating current. Therefore, when the dimming level is below a predetermined value, dark lighting or dim lighting of the electrodes is automatically prevented.

[Example] Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows a schematic configuration of a discharge lamp lighting device according to an embodiment of the present invention. The device shown in the figure includes a thyristor 1 inserted into the main circuit of a power supply through which AC power supply AC flows, a phase control circuit 3, a saw gauge 1 to a lance 5, a discharge lamp 7, a diode bridge 9, a detection control circuit 11, a switch 13, and a preheating circuit. It is composed of a transformer 15, a capacitor C for pulse generation, a resistor R, and the like. As is well known, the phase control circuit includes a circuit necessary for adjusting the trigger timing of the thyristor 1 according to the setting of a variable resistor, for example, and adjusting the flow angle of the power supply. Further, the preheating transformer 15 is connected via the switch 13 to the front stage of the circuit to which the thyristor 1 is connected. Note that the switch 13 is actually composed of a relay, a semiconductor switch, or the like.

FIG. 2 shows a specific example of the leakage transformer 5. As shown in the figure, the leakage transformer 5 includes an I-type core 21
, U-shaped core 23, 25. Primary coil (Nl) 27. Secondary coil (N2.N5) 29, bus core 31.33, and detection coil (N4) 35 provided in the bus core 33, for example.
It is composed of etc. Note that a slit is usually provided between the I-shaped core 21 and the U-shaped core 23, 25, or inside the I-shaped core 21.

In the lighting device having the above configuration, when the alternating current power supply AC is applied, since the switch 13 is initially closed, the discharge lamp 7 is preheated via the preheating transformer 15. Further, by the function of the phase control circuit 3, the flow angle of the thyristor 1 is controlled according to the setting of a variable resistor, for example, for adjusting the dimming level. In this case, during the period when the thyristor 1 is cut off, the AC power source AC is disconnected from the primary coil N1 and secondary coil N3 of the cage transformer 5.
, resistor R, and capacitor C, current flows and capacitor C is charged. In addition, during the period when the thyristor 1 is conducting, the electric charge charged in the capacitor C is discharged through the path of the resistor R1, the secondary coil N3, the thyristor 1, and the capacitor C, and is transferred to the discharge lamp 7 via the secondary coil N2 to a high voltage. A pulse is applied.

As a result, the discharge lamp 7 is lit at a dimming level set by an adjusting means such as a variable resistor provided in the phase control circuit 3.

In the above-described operation, a voltage proportional to the output voltage of the lighting circuit is extracted from the detection coil N4 of the leakage transformer 5, full-wave rectified by the diode bridge 9, and then inputted to the detection control circuit 11 as a detection voltage. . The detection control circuit 11 keeps the switch 13 closed if the magnitude of the detected voltage is greater than or equal to a predetermined value. On the other hand, when the detected voltage becomes smaller than a predetermined value, the detection control circuit 11 opens the switch 13 and stops heating the filament of the discharge lamp 7. That is, the detection control circuit 11 stops heating the filament when the brightness of the lamp reaches a predetermined value or lower, for example, 5% or lower, thereby preventing dim lighting of the electrodes in a dark state during dimming.

In addition, by providing the detection coil N4 of the leakage transformer 5 in the bus core part, pulses will not be generated in the detection voltage, making it easier to detect the voltage across the lamp or the lamp current. It becomes possible to safely detect a signal corresponding to the lamp current using a circuit.

[Effects of the Invention] As described above, according to the present invention, dim lighting of the electrode in a dark state during dimming, that is, dark lighting, is automatically prevented using an extremely simple circuit.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram schematically showing a discharge lamp lighting device according to an embodiment of the present invention, and FIG. 2 shows a specific configuration of a gauge transformer used in the device shown in FIG. FIG. 1... Thyristor, 3... Phase control circuit, 5...
Leakage transformer, 7... Discharge lamp, 9... Diode bridge, 11... Detection control circuit, 13... Switch, 15... Preheating transformer, 21... I-type core, 23° 25 ...U-shaped core, 27...primary coil, 29...secondary coil, 31.33...bass core,
35...Detection coil.

Claims (1)

[Scope of Claims] Thyristor means inserted into the main circuit of a power supply to adjust the lamp current, a leakage transformer that boosts the output of the thyristor means and supplies it to the lamp load, a filament of the lamp load from a stage preceding the thyristor means A preheating circuit that supplies a preheating current to a preheating circuit, a switch means that conducts or cuts off the preheating circuit, and a control circuit that cuts off the switch means when the output of the leakage transformer becomes equal to or less than a predetermined value. Discharge lamp lighting device.