JPH06310292A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To enable the lighting of a discharge lamp to be continued, even, if any of capacitors goes wrong, so as to prevent the breakage of a semiconductor switching element by connecting in series a plurality of ballast capacitors of a self-excited inverter. CONSTITUTION:A high-frequency power supply operated by a self-excited inverter 6 discharges electricity to light a fluorescent lamp 15 through a capacitor 14 being a stabilizer. In this case, since the ballast capacitors 10 and 11 of the inverter 6 are set to double the required capacitance, even if one tails, the inverter 6 continues its oscillation, and the lamp 15 maintains its lighting. Hereby, any breakdown by overcurrents of switching transistors 7 and 8 can be prevented without providing any emergency protective circuit, so the reduction of the number of parts becomes possible, consequently the cost up can be prevented.

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 by a self-excited inverter.

[0002]

2. Description of the Related Art As a lighting device for a discharge lamp, for example, a fluorescent lamp, a direct current power source is converted into a high frequency power source by a self-excited inverter composed of a transistor which is a semiconductor switching element, a high frequency transformer and a ballast capacitor.
The thing which supplied this to the fluorescent lamp is provided.

In this case, when the ballast capacitor of the inverter is short-circuited, not only the inverter stops oscillating and the lighting of the fluorescent lamp is stopped, but also the transistor is damaged due to overcurrent.

In order to solve such a problem, the technique disclosed in Japanese Patent Laid-Open No. 63-284798 has been disclosed. That is, in this conventional example, a lamp abnormal time protection circuit that detects that an abnormal voltage is generated in the secondary example of the high frequency transformer when the component elements of the inverter, for example, the ballast capacitor has a short circuit failure, turns off the fluorescent lamp is provided. It is provided.

[0005]

In this conventional example, the transistor of the inverter can be prevented from being damaged, but there is a problem that the fluorescent lamp is in the off state, and the lamp abnormality protection circuit is composed of many circuit parts. Because
There is a problem of cost increase.

The present invention has been made in view of the above circumstances, and an object thereof is to enable a discharge lamp to be lit even when a short-circuit failure occurs in a ballast capacitor, and to save circuit components. It is an object of the present invention to provide a lighting device for a discharge lamp that does not increase the cost.

[0007]

According to the present invention, a self-excited inverter comprising a semiconductor switching element, a high frequency transformer and a ballast capacitor is provided, and a DC power supply is converted into a high frequency power supply by this inverter and supplied to a discharge lamp. In the discharge lamp lighting device described above, the ballast capacitor of the inverter is configured by connecting a plurality of capacitors in series.

[0008]

According to the discharge lamp lighting device of the present invention, even if one of the ballast capacitors of the inverter is short-circuited, the rest can be supplemented and the lighting of the discharge lamp can be continued.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. The DC power supply terminals 1 and 2 are for applying a power supply voltage of a DC power supply obtained by rectifying and smoothing a commercial AC power supply by a rectifying circuit or a power supply voltage V of a DC power supply such as a storage battery. The DC power supply terminal 1 is connected to the DC bus bar 4 via the reactor 3, and the other DC power supply terminal 2 is connected to the DC bus line 5.

The self-excited inverter 6 includes transistors 7 and 8 which are semiconductor switching elements and a primary coil 9P.
1, 9P2 and secondary coils 9S1 and 9S2, and a high frequency transformer 9 and ballast capacitors 10 and 11.

That is, the collectors of the transistors 7 and 8 are connected to one terminals of the primary coils 9P1 and 9P2, respectively, and the other terminals of the primary coils 9P1 and 9P2 are connected to the DC bus 4. Further, the bases of the transistors 7 and 8 are connected to the DC bus 4 via resistors 12 and 13, ballast capacitors 10 and 11 are connected in series between the collectors of the transistors, and the emitters of the transistors 7 and 8 are connected to the DC bus 5. It is connected.

The secondary coil 9 of the high frequency transformer 9
A capacitor 14 and a fluorescent lamp 15 as a discharge lamp are connected in series between both terminals of S1, and both terminals of the secondary coil 9S2 are connected to the bases of the transistors 7 and 8, respectively.

Next, the operation of this embodiment will be described. When a DC power supply voltage V is applied between the DC power supply terminals 1 and 2,
For example, a base current flows in one of the transistors 7 and 8 and the transistor 7 becomes conductive. As a result, the DC bus bar 4, the primary coil 9P1,
A current flows through the path of the transistor 7 and the DC bus 5, and an induced voltage (positive feedback voltage) is generated in the secondary coil 9S2 of the high frequency transformer 9, and this is given to the base of the transistor 7.

Therefore, the transistor 7 rapidly becomes conductive, and the current flowing through the primary coil 9P1 of the high frequency transformer 9, that is, the collector current of the transistor 7 increases. After that, the high frequency transformer 9 becomes magnetically saturated, and the collector current of the transistor 7 becomes zero. At this time, an induced voltage (negative feedback voltage) in the opposite direction to that described above is generated in the secondary coil 9S2 of the high frequency transformer 9, and this is applied to the bases of both transistors 7 and 8. Due to the negative feedback voltage generated in the secondary coil 9S2, the transistor 7 becomes non-conductive, the transistor 8 becomes conductive, and the current flows in the primary coil 9P2.

The operation thereafter is the same as that described above, the inductances of the primary coils 9P1 and 9P2 of the high frequency transformer 9 are set to L, and the series capacitance of the ballast capacitors 10 and 11 is C (the capacitance of each of the capacitors 10 and 11 is required). 2C), which is twice as much as
The oscillation frequency f of the self-excited inverter 6 is

[0016]

[Equation 1] Becomes Then, the high-frequency power source of the self-excited inverter 6 is connected to the fluorescent lamp 15 via the condenser 14 serving as a stabilizer.
Then, the fluorescent lamp 15 is discharged and turned on.

In this case, since the ballast capacitors 10 and 11 of the self-excited inverter 6 are set to 2C, which is twice the required capacitance, the inverter 6 continues to oscillate even if one short-circuits. The fluorescent lamp 15 will continue to light.

As described above, according to the present embodiment, the ballast capacitor of the self-excited inverter 6 is constituted by the series circuit of the two capacitors 10 and 11, so that one of them is short-circuited to cause a failure. Inverter 6 on the other hand
Can continue to oscillate, and the lighting of the fluorescent lamp 15 can be continued.

As a result, damage to the transistors 7 and 8 due to overcurrent can be prevented without providing a conventional lamp abnormality protection circuit using a large number of circuit components, and the cost is increased. Nothing.

In the above embodiment, as the ballast capacitor of the inverter 6, the capacitors 10 and 11 having twice the required capacitance are provided in series, but instead, the required capacitance of 3 is provided. It is also possible to connect in series three or more capacitors having a capacitance more than double.

Besides, the present invention is not limited to the above-mentioned embodiments, and it is needless to say that the present invention can be appropriately modified and implemented without departing from the scope of the invention.

[0022]

According to the discharge lamp lighting device of the present invention, the ballast capacitor of the self-excited inverter is formed by connecting a plurality of capacitors in series. The lamp can continue to be lit, damage to the semiconductor switching element can be prevented, and moreover, the number of parts can be reduced and the cost can be prevented from increasing, which is an excellent effect. is there.

[Brief description of drawings]

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

[Explanation of symbols]

In the drawings, 6 is an inverter, 7 and 8 are transistors (semiconductor switching elements), 9 is a high frequency transformer, 10 and 11 are ballast capacitors, and 15 is a fluorescent lamp (discharge lamp).

Claims (1)

[Claims] 1. A lighting apparatus for a discharge lamp, comprising a self-excited inverter comprising a semiconductor switching element, a high frequency transformer and a ballast capacitor, wherein the inverter converts a direct current power source into a high frequency power source and supplies it to a discharge lamp. A lighting device for a discharge lamp, wherein the ballast capacitor of the inverter is formed by connecting a plurality of capacitors in series.