JPH04319294A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To surely detect a lifetime termination of a discharge lamp by utilizing a difference between a normal collector current and a collector current of the discharge lamp at the lifetime termination. CONSTITUTION:In a discharge lamp lighting device where a switching element 8 is turned on or off and a discharge lamp 9 is pre-heated with application of a current to a pre-heating capacitor 10 when the switching element 8 is operative, before the discharge lamp 9 is lit with application of a lamp current thereto, a part of an iron core of an inductance 7 is such constituted that its Curie point is lower than those of other iron cores. Upon detection of a large current flowing in the switching element 8, the on or off operation of the switching element 8 is stopped by a current detection circuit 33.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device for lighting a discharge lamp such as a fluorescent lamp using high frequency waves.

0002

[Prior art] By lighting a discharge lamp at high frequency,
It has been known that lighting devices can be made smaller and lighter, and that the luminous efficiency of discharge lamps can be improved. A conventional discharge lamp lighting device of this type is shown in FIG. In the figure, 1 is a DC power supply circuit, which includes a rectifier 3 connected to a commercial power source 2, a rush current prevention resistor 4, and a smoothing capacitor 5. 6 is a resonance capacitor, 7
8 is a resonant inductance, and 8 is a transistor, which constitute an automatic inverter circuit. 9
1 is a discharge lamp such as a fluorescent lamp, 10 is a preheating capacitor, and 11 is a current limiting inductance. A current transformer 12 includes a primary winding 12a and a secondary winding 12b. 1
4 is a bias circuit, which includes a starting resistor 15, a diode 16,
A resistor 17 and a bias capacitor 18 are provided. 19 is a surge absorber, and 20 is a noise prevention capacitor.

Next, the operation will be explained. The voltage of the AC power source 2 is rectified by a rectifier 3, and a smoothing capacitor 5 is charged via an inrush current prevention resistor 4. In the operation of the self-commutated inverter circuit at startup, a small amount of current flows through the starting resistor 15 to the base of the transistor 8, so that the transistor 8 tries to turn on. As a result, a current Il flows from the positive side of the power supply circuit 1 to the collector of the transistor 8 through the resonance inductance 7, the current limiting inductance 11, and the discharge lamp 9.
one filament, the preheating capacitor 10, the other filament, and the primary winding 12a of the current transformer 12.
A collector current Ic corresponds to the sum of the current Ia flowing through the collector current Ic.

At this time, the primary winding 12 of the current transformer 12
The feedback current generated in the secondary winding 12b of the current transformer 12, ie, the base current Ib of the transistor 8, flows due to the current Ia flowing through the transistor 8, and the transistor 8 is completely turned on. Thereafter, the base current Ib resonates in series with the inductance of the secondary winding 12b and the capacitor 18. That is, after the base current flows in the forward direction for a certain period of time, the base current flows in the reverse direction. As a result, transistor 8 is turned off.

When the transistor 8 is turned off, the resonant inductance 7 is reduced during the on period of the transistor 8.
, the energy stored in the current limiting inductance 11 is transferred to the resonance capacitor 6 and the preheating capacitor 10.
causes resonance between the As a result, the polarity of the current flowing through the primary winding 12a changes as it resonates, turning on the transistor 8 again. In this state, the filament of the discharge lamp 9 is preheated, and the voltage of the capacitor 10 is applied to both ends of the discharge lamp 9.

When the discharge lamp 9 is turned on, the impedance of the discharge lamp 9 decreases, and the current limiting inductance 11
A tube current Ia flows through the discharge lamp 9 and the primary winding 12a of the current transformer 12. Since the impedance of the discharge lamp 9 during lighting is sufficiently smaller than the impedance of the capacitor 10, substantially all of the current flowing through the current limiting inductance 11 flows through the discharge lamp 9. The on period of the transistor 8 during lighting is determined so that the rated tube current flows.

To give a specific example, the AC power supply 2 is a commercial voltage of 100V, and the capacity of the smoothing capacitor 5 is 100μF.
, the resonance inductance 7 is 10mH, the current limiting inductance 11 is 1mH, the capacity of the resonance capacitor 6 is 4700PF, and the capacity of the preheating capacitor 10 is 11
000 PF, the discharge lamp 9 is FCL30, and when the transistor 8 turns on and off at about 40kHz, the discharge lamp 9
A current of approximately 600mA flows through the At this time, the current flowing through the current limiting inductance 11 is approximately the same as the current flowing through the discharge lamp 9, which is 600 mA, and the current flowing through the resonance inductance 7 is approximately 200 mA.

[0008]

[Problem to be solved by the invention] When the discharge lamp 9 reaches the end of its life and current no longer flows in only one direction, there is a problem in that the current in the resonance inductance 7 becomes two to three times the normal value. . For example, when one emitter of the discharge lamp 9 disappears, and the discharge lamp current flows only in the direction of the arrow a as shown in FIG. become.

When the discharge lamp 9 is normal, the current flowing through the resonance inductance 7 is small, so there is no problem if the resonance inductance 7 is a small inductance, but at the end of the life of the discharge lamp 9, the current increases and the resonance The temperature rise of the inductance 7 may become high and cause a failure. This is well known, and as a countermeasure, there is an example in which a temperature switch 23 using bimetal is provided in the resonant inductance 7 to turn off the power when the temperature rises, as shown in FIG. Furthermore, as shown in FIG. 7, there is a device in which a current detection resistor 24 is inserted in series with a resonance inductance 7, and a photocoupler 25 is used to turn off the power when the current becomes large.

However, when the current in the discharge lamp 9 becomes unidirectional and the current in the resonant inductance 7 becomes large, the collector current Ic of the transistor 8 is not much different from that during normal lighting, and due to the magnitude of the collector current Ic. Detection at the end of life was difficult. In view of the above problems, the present invention intentionally sets the current of the resonance inductance 7 to a large value when the current of the resonance inductance 7 becomes large and the temperature of the resonance inductance 7 becomes high. The end of the life of the discharge lamp 9 is reliably detected by utilizing the difference between the collector current Ic at the end of the life of the discharge lamp 9 and the end of the life of the discharge lamp 9.

[0011]

[Means for Solving the Problem] The technical means of the present invention for solving this technical problem consists of a DC power supply circuit 1,
A parallel circuit of a resonant capacitor 6 and a resonant inductance 7 and a switching element 8 are connected in series, and a discharge lamp 9 is connected to both ends of the resonant inductance 7 through a current limiting inductance 11 to form a discharge lamp. A preheating capacitor 10 is connected in parallel to 9, and the switching element 8 is turned on and off by the resonance of the capacitors 6, 10 and inductances 7, 11, and when the switching element 8 is turned on, a current is passed through the preheating capacitor 10 to generate a discharge lamp. In a discharge lamp lighting device in which a tube current is applied to the discharge lamp 9 after preheating the discharge lamp 9 to light the discharge lamp 9 , a part of the iron core 47 of the resonance inductance 7 is smaller than other iron cores. The switching element 8 is configured to have a low Curie point, and is provided with a current detection circuit 33 that detects that the current flowing through the switching element 8 has become large and stops the on/off operation of the switching element 8. .

0012

[Operation] When the discharge lamp 9 reaches the end of its life, the current flowing through the resonant inductance 7 becomes large and the temperature of the resonant inductance 7 rises. As a result, the inductance value of a part of the iron core 47 of the resonance inductance 7 becomes low, and the current flowing through the switching element 8 becomes large. Therefore, when the temperature of the resonant inductance 7 becomes high, the current of the resonant inductance 7 can be intentionally set to a large value, and the current flowing through the switching element 8 creates a large difference between the normal state and the end of its life. The detection circuit 32 reliably detects that the discharge lamp 9 is at the end of its life and stops the on/off operation of the switching element 8.

[0013]

[Embodiment] The present invention will be explained below according to the illustrated embodiment. In FIG. 1, a current detection circuit 33 having a detection element 31 and a detection resistor 32 is provided. The configuration is such that the on/off operation of the transistor 8 is stopped upon detecting that the transistor 8 has become large. Further, the transistor 35,
36, resistor 37, 38, 39, Zener diode 4
0 and a capacitor 41 is provided, and since the collector current Ic of the transistor 8 increases for 0 to 0.5 seconds when the discharge lamp 9 is started, the timer circuit 42 operates to increase the collector current Ic of the transistor 8 for 0 to 0.5 seconds when the discharge lamp 9 is started. For a second, the detection signal of the detection circuit 33 is set to 0, thereby preventing the detection circuit 33 from malfunctioning.

As shown in FIG. 2, the resonance inductance 7 is constructed by combining a pair of E-type iron cores 45 and 46 to form a sun-shaped iron core 47, and winding a coil around the central magnetic path of this iron core 47. The one E-type iron core 45
is made of, for example, manganese-based ferrite, so as to have a Curie point of 150°C, and the other E-type iron core 46 is made of, for example, nickel-based ferrite, so as to have a Curie point of 100 to 120°C. death,
When the temperature of the iron core 47 reaches or exceeds the Curie point, the inductance value L of the resonance inductance 7 suddenly becomes small.
Collector current Ic flowing through transistor 8 is made to increase.

That is, if the entire iron core of the resonant inductance 7 is constructed so that the Curie point is 100 to 120°C, the inductance value L of the resonant inductance 7 is
suddenly becomes 0 mH, the collector current Ic of the switching element 8 becomes an abnormally large value, and if detection is delayed, there is a risk that the transistor 8 will fail. Therefore, in the configuration of the above embodiment, only one of the E-type iron cores 45 of the iron cores 47 is configured so that the Curie point is 100 to 120°C, and as a result, the collector current Ic becomes abnormally large and the transistor 8 In order to prevent any failure of the resonant inductance 7, only a part of the iron core 47 of the resonance inductance 7 has a lower Curie point than the other iron cores. Then, by changing the ratio of the iron core whose Curie point is 120°C to the whole iron core of the resonant inductance 7, the collector current Ic at the end of the life is made to be 1.5 to 2.5 times the normal value, and the discharge is carried out. Electric light 9
The end of life of the product can be easily detected.

3 to 5 respectively show other embodiments. In the case of FIG. 3, a leaky core 49 is provided between a pair of E-type cores 45 and 46 of the core 47 of the resonance inductance 7, and the E-type core 45 , 46 are made of, for example, manganese-based ferrite so that the Curie point is 150°C,
The leaky core 49 is formed of nickel-based ferrite,
The structure is such that the Curie point is 100 to 120°C. In the case of FIG. 4, the iron core 47 is constructed by combining an E-type iron core 51 and an I-type iron core 52 in a Japanese character shape, and the E-type iron core 51 is made of, for example, manganese-based ferrite, so that the Curie point is 150°C. The I-type iron core 52 is made of, for example, manganese ferrite, and the Curie point is
The temperature is set to 120°C. In the case of FIG. 5, the iron core 47 is constructed by combining a U-shaped core 54 and a T-shaped core 55 in a Japanese-shaped configuration, and the U-shaped core 54 is made of, for example, manganese ferrite, and has a Curie point of 150. ℃, and the T-shaped core 55 is made of, for example, nickel-based ferrite, so that the Curie point is 100 to 120.
It is configured so that the temperature is ℃.

Although the transistor 8 is used as a switching element in the above embodiment, a thyristor or other switching element may be used in place of the transistor 8.

[0018]

According to the present invention, a part of the iron core 47 of the resonance inductance 7 is configured to have a lower Curie point than the other iron cores, and the switching element 8
A current detection circuit 33 is provided that detects when the current flowing through the resonant inductance 7 becomes large and stops the on/off operation of the switching element 8. Therefore, when the discharge lamp 9 reaches the end of its life, the current flowing through the resonance inductance 7 becomes large. , the temperature of the resonant inductance 7 becomes high, and the inductance value L of a part of the iron core 47 of the resonant inductance 7 whose Curie point is low becomes small.
The current flowing through becomes large. Therefore, the current detection circuit 33 can reliably detect that the discharge lamp 9 has reached the end of its lifespan, and the on/off operation of the switching element 8 can be reliably stopped without malfunction, thereby preventing failures due to the discharge lamp 9 reaching the end of its lifespan. It is possible.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a plan view of an iron core of a resonance inductance.

FIG. 3 is a plan view of the iron core of the resonance inductance.

FIG. 4 is a plan view of the iron core of the resonance inductance.

FIG. 5 is a plan view of the iron core of the resonance inductance.

FIG. 6 is a circuit diagram showing a conventional example.

FIG. 7 is a circuit diagram showing a conventional example.

[Explanation of symbols]

1 DC power supply circuit 6 Resonance capacitor 7 Resonance inductance 8 Transistor (switching element) 9 Discharge lamp 10 Preheating capacitor 11 Current limiting inductance 33 Current detection circuit

Claims (1)

[Claims] 1. A DC power supply circuit (1), a parallel circuit of a resonant capacitor (6) and a resonant inductance (7), and a switching element (8) are connected in series, and the resonant inductance (7) A discharge lamp (9) is connected to both ends of the lamp via a current limiting inductance (11), and a preheating capacitor (10) is connected to the discharge lamp (9).
are connected in parallel, the switching element (8), the capacitors (6), (10) and the inductance (7)
(11) is turned on and off by resonance, and when the switching element (8) is turned on, a current flows through the preheating capacitor (10) to preheat the discharge lamp (9).
In a discharge lamp lighting device that lights the discharge lamp (9) by passing a tube current through it, a part of the iron core (47) of the resonance inductance (7) has a Curie point lower than that of the other iron cores. A current detection circuit (33) is provided, which is configured such that the current flowing through the switching element (8) becomes large and stops the on/off operation of the switching element (8). A discharge lamp lighting device characterized by: