JPH03297096A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To protect an inverter circuit in the last stage of lifetime of a discharge lamp using simple configuration and at a low cost by furnishing a heat emitting body in a location close to ferrite, and allowing it to make heat emission when a sensing means has sensed that the lamp is in its last stage of lifetime. CONSTITUTION:A switching element 7 of an inverter circuit 4 is put on to convert the DC power from a DC power supply 3 into high frequency output, while the output of the inverter circuit 4 is fed back to the switching element 7 by a current transformer 11 and then the switching element 7 is operated. If it is sensed that a discharge lamp concerned 12 has launched into its last stage of lifetime, a heat emitting body 16 is put in its work for heat emission to raise the ferrite temp. of the current transformer 11 to the Curie point, and thereby the magnetic permeability is lessened, and feed to the switching element 7 is stopped to stop the feed to the inverter circuit 4. Thereby the inverter circuit 4 can be protected simply and uncostly at the last stage of lifetime of the discharge lamp 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a discharge lamp lighting device that lights a discharge lamp using high frequency waves.

(Prior Art) As a conventional discharge lamp lighting device, the configuration shown in FIG. 5, for example, is known.

A rectifying and smoothing circuit 2 is connected to a commercial AC power source 1, and the commercial AC power source 1 and the rectifying and smoothing circuit 2 rectify it into a DC power source 3.

The output terminal of the rectifying and smoothing circuit 2 is connected in series with the input winding 5a of the output transformer 5 of the inverter circuit 4 and the parallel circuit of the resonance capacitor 6, and the collector and emitter of the transistor 7. On the base,
A bias resistor 8 and a control circuit 9 are connected.

Further, the output winding 5b of the output transformer 5 is the primary winding 11 of the current transformer 11! The capacitor 1 for starting is connected to the filaments 12a and 12b of the discharge lamp 12 through the filaments 12* and 12b.
3 is connected.

Further, a control circuit 9 is connected to the secondary winding 11b of the current transformer 11.

Further, the output transformer 5 has a detection winding 5C, and this detection winding 5C has a protection circuit 14 connected to the control circuit 9.
is connected.

Then, the DC power from the DC power supply 3 is converted into high frequency power by the inverter circuit 4, and the discharge lamp 12 is turned on.

Further, when the discharge lamp 12 reaches the end of its life, for example, the filament on one side burns out and discharge occurs in only one direction.
In other words, it has characteristics similar to those of a diode, and the output transformer 5 may be heated due to direct current bias, or the transistor 7 may be heated and destroyed due to abnormal oscillation.

Therefore, at the end of the life of the discharge lamp 12, the abnormal voltage of the discharge lamp 12 is detected by the detection winding 5C, and the protection circuit 14 detects the abnormal voltage of the discharge lamp 12.
The output of the control circuit 9 is controlled to lower the output of the transistor 7, thereby lowering the output of the inverter circuit 4 or stopping oscillation, thereby protecting the inverter circuit 4.

(Problem to be Solved by the Invention) However, the device shown in FIG. 5 requires a protection circuit 14 to control the output to the transistor 7 of the detection winding 5C1 control circuit 9 for detecting the end of the life of the discharge lamp 12. ,
This has the problem that the circuit configuration becomes complicated and the device becomes expensive.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a discharge lamp lighting device that has a simple configuration and is inexpensive, and that can protect an inverter circuit at the end of the life of a discharge lamp.

[Structure of the invention]

(Means for Solving the Problems) A discharge lamp lighting device of the present invention includes: an inverter circuit that converts DC power from a DC power source into high-frequency output via a switching element; a discharge lamp lit by the inverter circuit; A current transformer connected to the output side of the inverter circuit and having a ferrite that is fed back to the switching element; a heating element installed close to the ferrite of the current transformer; and a detection means that causes the heating element to generate heat when detecting the terminal stage.

(Function) The present invention operates a switching element of an inverter circuit to convert DC power from a DC power source into high frequency output. Further, the output of the inverter circuit is fed back to the switching element using a current transformer to operate the switching element. When it detects that the discharge lamp is at the end of its life, it makes the heating element generate heat to raise the temperature of the ferrite in the current transformer to the cue temperature, lowering the magnetic permeability.
The output to the switching element is stopped, and the output of the inverter circuit is stopped.

(Example) Hereinafter, an example of the discharge lamp lighting device of the present invention will be described with reference to the drawings.

Note that parts corresponding to those in the conventional example shown in FIG. 5 will be described with the same reference numerals.

As shown in Figure 1, a commercial AC power supply 1 has a rectifying and smoothing circuit 2.
are connected, and the commercial AC power supply 1 and the rectifying and smoothing circuit 2 constitute a DC power supply 3.

A parallel circuit of an inverter circuit 4, an input winding 5a of an output transformer 5, a resonance capacitor 6, and a collector-emitter of a transistor 7 as a switching element are connected in series to the output end of the rectifying and smoothing circuit 2. is,
A bias resistor 8 and a control circuit 9 are connected to the terminal of the transistor 7 .

Further, the output winding 5b of the output transformer 5 includes a capacitor 15 for DC cut as a means for detecting the end of life, and
Through the primary winding 11a of the feedback current transformer 11,
Filament 12a of discharge lamp 12.

12b, these filaments 12g,
A starting capacitor 13 is connected between the terminals 12b and 12b.

Furthermore, the control circuit 9 is connected to the secondary winding 11b of the current transformer 11, and the -order winding 11a and the capacitor 1
A heating element 16 is connected in parallel to 5.

Further, as shown in FIGS. 2 and 3, this heating element 16 has a secondary winding 1.1g and a secondary winding 11b that are electrically insulated from each other, and have a circular shape such as a ferrite Il.
c and is attached to the substrate 17. and,
A heating element 16 is attached close to this ferrite lle.

Furthermore, as shown in Fig. 4, the magnetic permeability of ferrite LLC increases as the temperature rises according to the Keuri law, and when the cue temperature is reached, the magnetic permeability suddenly drops to almost 0 at the cue point.
become.

The heat generated by the heating element 16 is set so that the temperature of the ferrite llc reaches the Curie temperature when the discharge lamp 12 reaches the end of its life and the transistor 7 exceeds the range in which it can operate normally.

Next, the operation of the above embodiment will be explained.

First, an AC output from a commercial AC power supply 1 is rectified and smoothed by a rectification and smoothing circuit 2, and then outputted as DC by a DC power supply 3. In this state, a base current is supplied to the transistor 7 via the bias resistor 8 to turn on the transistor 7 and cause it to resonate, so that the inverter circuit 4 outputs a high frequency signal and lights up the discharge lamp 12. At this time, the current transformer 11 provides positive feedback to the control circuit 9 to control the on/off of the transistor 70.

Then, when the discharge lamp 12 reaches the end of its life, the voltage of the discharge lamp 12 increases and a half-wave discharge phenomenon occurs, exhibiting diode characteristics. The resulting DC component is cut by the capacitor 15, and this DC component is bypassed to the heating element 16, which generates heat. This heat generation raises the temperature of the ferrite Ilc, and when the temperature of the ferrite 11c reaches the cue temperature shown in FIG. 4, the magnetic permeability of the ferrite 11 rapidly approaches 0, and the current transformer
The coupling ratio between the primary winding 11a and the secondary winding 11b of the secondary winding 11. Almost no voltage is induced in b, and the control circuit 9 stops the oscillation of the transistor 7.

In addition, when the temperature of ferrite llc decreases to below the cue temperature, the magnetic permeability of ferrite lie increases,
Primary winding 11M of current transformer 11 and secondary winding 11b
Since the coupling rate with the secondary winding 11b increases and the voltage induced in the secondary winding 11b increases, the control circuit 9 outputs again and the inverter circuit 4 oscillates again.

Note that the heating element 16 is not limited to a resistor and may be a semiconductor heating element or the like, and the method of attaching the heating element 16 to the ferrite 11c is not limited to that shown in FIGS. 2 and 3.

Further, the detection means 15 is not limited to the one shown in the above embodiment,
It may be a device that detects the voltage across both ends of the battery-powered lamp 12.

〔Effect of the invention〕

According to the present invention, a heating element is provided adjacent to the ferrite,
When the detection means detects the end of the life of the discharge lamp, the heating element is made to generate heat, raising the temperature of the ferrite until it reaches the cue temperature, reducing or stopping the output of the switching element, and reducing the output of the inverter circuit. Therefore, the inverter circuit can be protected at the end of the life of the discharge lamp with a simple configuration and at low cost.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the discharge lamp lighting device of the present invention, Fig. 2 is a front view showing the connection between the ferrite and the heating element, Fig. 3 is a side view of the above, and Fig. 4 is the ferrite. FIG. 5, which is a diagram showing the relationship between temperature and magnetic permeability, is a circuit showing a conventional example. 3. DC power supply, 4. Inverter circuit, 7. Transistor as a switching element, 11. Current transformer,
11c - ferrite, 12 - discharge lamp, 15 - capacitor as a detection means, 16 - heating element. Concentration [°]

Claims (1)

[Claims] (1) An inverter circuit that converts DC power from a DC power supply into high-frequency output via a switching element, a discharge lamp that is lit by this inverter circuit, and a discharge lamp connected to the output side of the inverter circuit and fed back to the switching element. The current transformer includes a current transformer having a ferrite, a heating element mounted close to the ferrite of the current transformer, and a detection means for detecting the end of the life of the discharge lamp and causing the heating element to generate heat when the end of the life is detected. A discharge lamp lighting device characterized by: