JPS6029197B2 - discharge lamp lighting device - Google Patents

Description

[Detailed description of the invention] The present invention relates to a discharge lamp lighting device.

In a discharge lamp lighting device, an accident may occur in which a circuit connecting the discharge lamp is short-circuited.

Such an accident may occur due to a short circuit between lead wires, or a short circuit due to failure of a noise prevention capacitor connected between both ends of the discharge lamp. If such a short-circuit accident occurs, excessive current may flow through the ballast, causing it to burn out. Furthermore, the flow of such an excessive current is extremely dangerous as electric shock and other accidents are likely to occur. It is an object of the present invention to suppress excessive current due to the occurrence of a short-circuit accident, enable the suppression circuit to also be used for dimming a discharge lamp, and simplify the circuit configuration for this purpose.

Embodiments of this invention will be described with reference to figures. IA, IB
2 is a power supply line, 2 is a ballast consisting of a primary coil 3 and a secondary coil 4, 5 is a discharge lamp, and 6 is a phase advancing capacitor.

These configurations are not much different from ordinary discharge lamp lighting devices of this type. According to the invention, a bidirectional thyristor, for example a triax 8, is connected between the power line IB and one end of the discharge lamp 5.
and an impedance element 9 for short-circuit current suppression (in the example shown, capacitor 1
0 and inductance coil 11). Further, a gate signal extraction circuit 12 is connected in parallel to the discharge lamp 5. In the example shown in the figure, it is constituted by a series circuit of a primary coil 14 of a transformer 13 and an impedance element 15 for current limiting. A secondary coil 16 of the transformer 13 is connected between the anode A and the gate G of the triac 8. Gate signal extraction circuit 1 by using transformer 13
2 and the anode A and gate G of the triac 8 can be electrically insulated. Note that instead of the transformer 13, a signal transmission element that insulates input and output, such as a photocoupler, may be used. Further, a switch element 18 is connected between the line 17 drawn out from the gate G of the try hook 8 and the power supply line IB. In the above configuration, when the switch element 18 is assumed to be in the OFF state and the power supply terminals IA and IB are connected to a commercial AC power source, the secondary voltage of the ballast 2 generated thereby is transferred to the impedance element 9 and the gate signal extraction circuit 12. This induces a voltage in the secondary coil 16 of the transformer 13.

Since the triax 8 is turned on by this induced voltage, the secondary voltage of the ballast 2 is applied to the discharge lamp 5, and the discharge lamp 5
lights up. After lighting the discharge lamp 5, the gate signal output circuit 1
2 is applied with a lamp voltage, and a voltage is subsequently induced in the secondary coil 16. As a result, the triac 8 also continues to remain on, so the discharge lamp 5 continues to remain lit. Here, it is assumed that certain points a and b at both ends of the discharge lamp 5 are short-circuited due to some kind of accident.

Then, the discharge lamp 5 cannot be lit, and the gate signal extraction circuit 12
There is no voltage across both ends of the circuit, so the triax 8 is turned off. As a result, the short-circuit current from the ballast 2 flows through the impedance element 9 and the short-circuited points a and b. At this time, since this short circuit current is suppressed by the impedance element 9, it does not become excessive, thereby preventing burnout of the ballast 2 and preventing the occurrence of electric shock and other dangers. Next, assume that the switch element 18 is turned on while the discharge lamp 5 is normally lit.

Then, since the anode A and gate G of the triac 8 are short-circuited, the triac 8 is turned off even if the discharge lamp 5 is lit. Then, the lamp current begins to flow into the discharge lamp 5 via the impedance element 9. Therefore, the lamp current becomes lower than before the switch element 15 was turned on, and thereby the discharge lamp 5 is dimmed. It will be easily understood that this dimming is achieved by the impedance element 9 used for suppressing short-circuit current. In this case, the capacitor 10 serves as a phase advance capacitor. By the way, according to the above configuration, the line 17 is connected to the gate G of the triac 8, and the line 14 and the anode A of the triac 8 are connected to each other.
, a switch element 18 is connected between the power supply line IB and the power supply line IB connected to the power supply line IB.

That is, the power supply line IB is also used as a line for turning on and off between the anode A and gate G of the triax 8, and it is only necessary to pull out one of the lines 17, which simplifies the circuit configuration. Furthermore, manufacturing or installation work becomes easier. If the triax 8 is connected so that its anode A faces the discharge lamp 5 side, a line from the anode A and a line from the gate G must be prepared separately. It is clear that this will happen. Note that as the switch element 18, a type that can be opened and closed manually may be used, but automatic dimming becomes possible by using a switch element that responds to external light, such as a phototransistor or a photoconductive element, instead. .

As described in detail above, according to the present invention, it is possible to prevent the burnout of the ballast due to short-circuit current, and the impedance element for suppressing short-circuit current can also be used for dimming. Since the power supply line can also be used as the connection circuit for the switch element, the connection configuration can be simplified.

[Brief explanation of drawings]

The figure is a circuit diagram showing an embodiment of the invention.

Claims (1)

[Scope of Claims] 1. It has a primary coil and a secondary coil that are connected in series with each other, and one end of the primary coil on the side of the secondary coil and the other end of the primary coil on the side opposite to the end. A ballast whose other end is connected to a power source for lighting, and a discharge lamp connected between output terminals of the ballast so that a secondary voltage of the ballast is applied. In the discharge lamp lighting device, a bidirectional thyristor is connected between the other end of the primary coil and the discharge lamp, and an impedance element for dimming and short-circuit current suppression is connected in parallel to the bidirectional thyristor. and applying a gate signal extracted from a gate signal extraction circuit connected in parallel to the discharge lamp between the anode and gate of the bidirectional thyristor on the other end side of the primary coil. A discharge lamp lighting device further comprising: a switch element connected between the gate of the bidirectional thyristor and a power supply line connected to the other end of the primary coil. A discharge lamp lighting device.