JPH0331038Y2 - - Google Patents

Description

[Detailed explanation of the idea] This invention relates to a high frequency discharge lamp lighting device.

In this type of lighting device, a configuration is known in which a high-frequency inverter is used and a discharge lamp is lit by the high-frequency output of the high-frequency inverter. In this case, it has been considered to preheat the filament of the discharge lamp using direct current. Incidentally, discharge lamps used in copying machines, facsimile machines, etc. are required to have a short starting time. For this purpose, it is sufficient to shorten the preheating time, so it is usually considered to increase the preheating current. However, if the preheating current is designed to increase in this way, for example, if the power supply voltage fluctuates and increases, the voltage across the filament, that is, the filament voltage, will also increase.
If the lamp is kept in a continuous preheating state, the discharge lamp will darken early and its life will be shortened. Therefore, it has not been possible to increase the preheating current unnecessarily.

The purpose of this invention is to reduce the direct current resistance of the preheating circuit to increase the preheating current at the initial stage of preheating, without impairing the life of the discharge lamp even in this case.

An embodiment of this invention will be described with reference to the drawings. 1 is a positive power supply terminal of a DC power supply, 2 is a switching element for starting, and 3 is a high frequency inverter, which is mainly composed of a pair of transistors 4 and an oscillation transformer 5, and a primary coil 6 of the oscillation transformer 5.
The center tap of the transistor 4 is connected to the power supply terminal 1, and the emitters of both transistors 4 are connected to the negative terminal (ground) of the DC power supply. Reference numerals 7 and 8 denote secondary coils of the oscillation transformer 5, which are wound with the same polarity and connected with opposite polarity when viewed from the terminal 9 of the preheating DC power supply.
10 is a discharge lamp, 11 and 12 are its filaments,
13 is a switching element for preheating.

When the switching element 13 is turned on, a series circuit (preheating circuit) of the filament 11, the secondary coil 8, the filament 12, the secondary coil 7, and the switching element 13 is completed between the terminal 9 and the ground. The direct current flowing thereby preheats each filament 11, 12. At this time, since the directions of the direct currents flowing through the secondary coils 7 and 8 are opposite, the oscillation transformer is not biased. Then, when switching element 2 is turned on, high frequency inverter 3 operates in oscillation. 2 due to this
The discharge lamp 1 is caused by the high frequency output induced in the next coil 8.
0 starts and lights up. Furthermore, if the capacitor 14 is connected, the secondary coil 7 is also connected to the discharge lamp 10 in a high frequency manner. Capacitor 14 is filament 11
may be connected to the opposite end.

According to this idea, each filament 11,1
A constant voltage element 15, 16 such as a Zener diode is connected between each end of the filament 2 so that the filament voltage is applied as a reverse voltage. Then, the DC resistance of the preheating circuit described above is reduced. Specifically, the preheating resistor that is conventionally required is omitted, or a preheating resistor with a smaller resistance value is used.

When the above-mentioned preheating circuit is completed by turning on the switching element 13, a preheating current flows through each filament 11 and 12, but since this preheating current is larger than that in the conventional configuration, the preheating circuit is quickly preheated. become. Since the filament temperature rises based on this preheating, its resistance value gradually increases and the filament voltage increases. When this filament voltage reaches a specified voltage, constant voltage elements 15 and 16 which use this specified voltage as a constant voltage operating voltage (Zena voltage) operate,
No higher voltage is applied to the filaments 11, 12. FIG. 2 shows characteristic curves of filament current and filament voltage in this configuration. Note that the curve indicated by a dotted line indicates a conventional configuration.

In the state of continuous preheating, the filament voltage does not exceed a specified voltage due to the action of constant voltage elements 15 and 16. Therefore, early blackening of the discharge lamp is prevented. Conversely, even if the power supply voltage for preheating fluctuates and decreases, the filament voltage will not become so low due to the constant voltage elements 15 and 16. Therefore, the filament continues to be preheated as specified, so the life of the flashing discharge lamp is good.

As described in detail above, this invention has the advantage that even if the preheating current is increased to shorten the starting time, the life of the discharge lamp in the continuous preheating state is not impaired in any way.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing an embodiment of this invention, Figure 2 is a circuit diagram showing an embodiment of this invention.
The figure shows the operating characteristic curve of this invention. 1, 9... DC power supply terminal, 3... High frequency inverter, 5... Oscillation transformer, 7, 8... Secondary coil, 10... Discharge lamp, 11, 12... Filament, 13... For preheating Switching element, 1
5, 16... Constant voltage element.

Claims (1)

[Claims for Utility Model Registration] It has a pair of transistors 4 and an oscillation transformer 5, and the oscillation transformer 5 has first and second second transistors.
High frequency inverter 3 provided with secondary coils 7 and 8
a discharge lamp 10 comprising a pair of filaments 11 and 12; and a preheating DC power source for DC preheating the filaments 11 and 12, with the one filament connected between terminals of the preheating DC power source. 11. A switching element 13 that is turned on during preheating is connected in series to a series circuit in which the first secondary coil 8, the other filament 12, and the second coil 7 are connected in series, and the first and second coils are connected in series. The secondary coils 7 and 8 are connected so that the direct currents flowing in them are in opposite directions, and the filaments 11 and 12 are connected so that the voltage between both ends of each of the filaments 11 and 12 is applied as a reverse voltage. A high frequency discharge lamp lighting device is constructed by connecting constant voltage elements 15 and 16 to each other.