JPH11204284A - Discharge lamp lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharge lamp lighting device allowing the use of an inexpensive saturation type current feedback transformer and allowing a protective action when an abnormality is detected even if the saturation type current feedback transformer is used. SOLUTION: This discharge lamp lighting device is provided with a step-up chopper circuit 1 including a chopper switching element 21, a self-excited inverter circuit 2 operated by receiving the DC output voltage of the step-up chopper circuit 1 and including a saturation type current feedback transformer 7, a discharge lamp lighting circuit 90 operated by receiving the oscillation output of the self-excited inverter circuit 2 and including a discharge lamp 9 and a ballast inductor 8 provided in series to it, and an abnormality protective circuit 19 detecting the abnormality of the discharge lamp 9, stopping the operation of the chopper switching element 21 when the abnormality is detected, changing its DC output voltage to the lowest level, changing the oscillation output frequency of the self-excited inverter circuit 2 to a higher level, and limiting the oscillation output of the self-excited inverter circuit 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes a boost chopper circuit, a self-excited inverter circuit that operates by receiving a DC output voltage of the boost chopper circuit, and a self-excited inverter circuit that operates by receiving an oscillation output of the self-excited inverter circuit. The present invention relates to a discharge lamp lighting device having a configuration including an electric lamp lighting circuit.

[0002]

2. Description of the Related Art A conventional discharge lamp lighting device shown in FIG. 2 will be described. FIG. 2 shows a switching element 2 for a chopper.
1 is provided. An inverter that operates by receiving a DC output voltage of the boost chopper circuit 1 and includes a self-excited inverter circuit 2 including a non-saturated current feedback transformer 7. A lighting circuit that operates by receiving the oscillation output of the self-excited inverter circuit 2 and includes a discharge lamp 9 and a discharge lamp lighting circuit 90 including a ballast inductor 8 in series with the discharge lamp 9. An abnormality protection circuit 19 is provided which detects an abnormality of the discharge lamp 9 and changes the oscillation output frequency of the self-excited inverter circuit 2 to a higher level when the abnormality is detected, thereby limiting the oscillation output of the self-excited inverter circuit 2. The boost chopper circuit 1 and the like will be supplemented. The chopper switching element 21 is a transistor, and includes a control circuit 20 for appropriately turning on and off the transistor. 29 is an AC power supply, 2
8 is a rectifier circuit, and 27 is a chopper inductor. 2
6 is a diode and 22 is a smoothing capacitor. The supplementary explanation about the self-excited inverter circuit 2 will be given. Reference numerals 3 and 4 denote inverter switching elements connected in series, 5.6 and flywheel diodes connected in antiparallel to the inverter switching elements 3.4, and 11 and 12 denote arm capacitors. A control circuit for alternately turning on and off each of the inverter switching elements 3 and 4 is provided. The components of the control circuit are the unsaturated current feedback transformer 7, auxiliary capacitors 13, 14, and 15, 16 and auxiliary transistors 17, 18, and the like. The discharge lamp lighting circuit 90 will be supplemented. The discharge lamp 9 is a fluorescent lamp. Reference numeral 10 denotes a preheating capacitor connected between the non-power supply terminals. The discharge lamp lighting circuit 90 becomes an inverter load. The load current flows through the primary winding of the unsaturated current feedback transformer 7. The supplementary description of the abnormal-time protection circuit 19 will be given. The abnormality protection circuit 19 monitors the voltage of the discharge lamp 10. Discharge lamp 1
When 0 is at the end of life and the tube voltage becomes excessive, it is determined to be abnormal. Then, when an abnormality is detected, the auxiliary transistor 17 (18) is turned off, and the circuit of the auxiliary capacitor 15 (16) connected thereto is opened. Then it looks like this: Auxiliary capacitor 13.15 (14.16)
The overall combined capacity is reduced. Self-excited inverter circuit 2
Oscillation output frequency increases. Ballast inductor 8
Impedance increases. Self-excited inverter circuit 2
Oscillation output decreases.

[0003]

When the abnormality is detected,
It is necessary to sufficiently increase the oscillation output frequency of the self-excited inverter circuit 2 and sufficiently limit the oscillation output.
The self-excited inverter circuit 2 must be capable of greatly varying the oscillation frequency. In this connection, an expensive current feedback transformer 7 is used. It is an object of the invention to enable the use of inexpensive saturated current feedback transformers. Another object of the present invention is to provide a discharge lamp lighting device capable of performing a protection operation when an abnormality is detected, even if the discharge lamp lighting device is a saturated current feedback transformer type.

[0004]

The device of the present invention detects an abnormality of a discharge lamp, and when the abnormality is detected, stops the operation of the chopper switching element and changes the DC output voltage of the step-up chopper circuit to the lowest level. At the same time, an abnormality protection circuit is provided which changes the oscillation output frequency of the self-excited inverter circuit to a higher level, thereby limiting the oscillation output of the self-excited inverter circuit. At the time of abnormality detection, the former and the latter are used together. Due to the former contribution, the latter burden is relatively small. The latter change in the level of the oscillation output frequency need not be significant.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. In this description, the part numbers in FIG. 2 are diverted as much as possible, and redundant description is omitted as appropriate. 1 detects an abnormality of the discharge lamp 9, stops the operation of the chopper switching element 21 when the abnormality is detected, changes its DC output voltage to the lowest level, and simultaneously outputs the oscillation output of the self-excited inverter circuit 2. An abnormal state protection circuit 19 is provided for changing the frequency to a higher level, thereby limiting the oscillation output of the self-excited inverter circuit 2. The output line from the abnormality protection circuit 19 is connected to the auxiliary transistors 17 and 18.
Leads to. This is the same as in the past. Error protection circuit 1
The other output line 9 is connected to the control circuit 20. Then, the oscillation operation of the control circuit 20 is appropriately stopped, and the operation of the chopper switching element 21 is stopped. Supplementary information on the operation at the time of abnormality detection is provided. When an abnormality is detected, the DC output voltage of the boost chopper circuit 1 is changed to the lowest level. This is the ground state of the boost chopper circuit 1. Thereafter, there is no switching loss of the chopper switching element 21. When an abnormality is detected, the level change of the DC output voltage and the level change of the oscillation output frequency are used together. With the change in the level of the DC output voltage, the oscillation output of the self-excited inverter circuit 2 is limited. Also, it is limited by the change of the level of the oscillation output frequency. In the present invention having the DC output voltage level change, the width of the change in the level of the oscillation output frequency is relatively smaller than that in the related art in which the level of the DC output voltage is not changed.
Therefore, a saturable current feedback transformer 7 can be used. The saturable-side current feedback transformer 7 has no burden of maintaining the non-saturation characteristic, and is accordingly small and inexpensive. Although the present invention uses the saturable current feedback transformer 7, it saturates at an appropriate timing during operation and prompts the inverter switching elements 3 and 4 to turn off. Such switching operations are known.

[0006]

According to the present invention, the abnormality of the discharge lamp is detected, and when the abnormality is detected, the operation of the chopper switching element is stopped to change the DC output voltage of the step-up chopper circuit to the lowest level. The main feature is to provide an abnormal time protection circuit for changing the oscillation output frequency of the circuit to a higher level, thereby limiting the oscillation output of the self-excited inverter circuit. According to this,
Inexpensive saturated current feedback transformers can be used. In addition, although the self-excited inverter circuit incorporates a saturated current feedback transformer, the oscillation output of the self-excited inverter circuit can be effectively limited when an abnormality is detected. Therefore, a discharge lamp lighting device excellent in cost and protection operation can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of the device of the present invention.

FIG. 2 is a circuit diagram of a conventional device.

[Explanation of symbols]

 1: Step-up chopper circuit 2: Self-excited inverter circuit 7: Unsaturated current feedback transformer 8: Ballast inductor 9: Discharge lamp 19: Abnormal protection circuit 21: Chopper switching element 90: Discharge lamp lighting circuit

Claims (1)

[Claims] A step-up chopper circuit including a chopper switching element; an inverter operable to receive a DC output voltage of the step-up chopper circuit, the self-excited inverter circuit including a saturable current feedback transformer; A lighting circuit that operates by receiving an oscillation output of a self-excited inverter circuit, the lighting circuit including a discharge lamp and a discharge lamp lighting circuit including a ballast inductor in series with the discharge lamp. The operation of the switching element is stopped to change the DC output voltage of the boost chopper circuit to the lowest level, and at the same time, to change the oscillation output frequency of the self-excited inverter circuit to a higher level, whereby the self-excited inverter circuit is changed. A discharge lamp lighting device comprising an abnormal-state protection circuit for limiting an oscillation output of the discharge lamp.