JPH0364894A - Discharge tube lighting device - Google Patents

Abstract

PURPOSE:To reduce heat generation of a transformer and a ballast impedance element by controlling the ratio of coil wires of the transformer by a timer circuit operated on the basis of a lighting command signal. CONSTITUTION:Since a transformation ratio control circuit 9 is connected to a transformer 5' on the side where a ratio of coil wires is increased, an output voltage of the transformer 5', on the secondary side becomes high so that a discharge tube 6 starts lighting with the application of a voltage higher than a lighting start voltage. Upon turning-on of a lighting command signal CNT, a timer circuit 8 is operated to output a signal into the transformation ratio control circuit 9 after a predetermined elapse, thereby switching the transformer 5' in such a manner as to make the transformation coil wires small. When the ratio of coil wires of the transformer 5' becomes small, the output voltage of the transformer 5' is decreased. Therefore, the output voltage of the transformer 5' is small when the discharge tube 6 is lit so that the impedance of a ballast impedance element 7 can be decreased and an electric power to be consumed by the transformer 5' can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a discharge tube lighting device used as a reading light source for facsimiles, scanners, and the like.

[Conventional technology]

Generally, fluorescent lamps are widely used as light sources for facsimiles and scanners. Fluorescent lamps make full use of rare gas discharge to produce HP
It is widely known that a high voltage is applied at the start of lighting, and after lighting, a low voltage sufficient to maintain discharge is applied to light the battery.

In addition, it is well known that this type of fluorescent lamp obtains high voltage by rapidly releasing the energy stored in the inductor to generate high voltage at the start of lighting. As soon as a magnetic disturbance occurs, low-power devices such as facsimile machines that use ICs that operate at low voltages may require electrical/magnetic shielding.

As a countermeasure against this problem, a method has conventionally been used in which a necessary voltage (lighting voltage) is constantly generated when the discharge tube starts lighting, and after lighting, the balance is maintained using a ballast impedance element.

FIG. 3 is a block diagram showing a conventional discharge tube lighting device. In the figure, a power supply voltage V supplied to a power supply input terminal 1 is turned on/off by a switching element 3 composed of a transistor, a relay, etc. according to a lighting command signal CNT inputted to a lighting command signal input terminal 2. Supplied to oscillator 4. A transformer 5 is connected to the output end of the oscillator 4, and a voltage as high as the lighting voltage of the discharge tube 6 is generated at the output of the transformer 5. After the discharge tube 6 lights up, the voltage applied to both ends of the discharge tube 6 may be low, so the ballast impedance element T causes a voltage drop in the current flowing through the discharge tube 6, and the output voltage of the transformer 5 and the discharge A balance is maintained with the voltage required after the tube 6 is turned on.

[Problem to be solved by the invention]

However, in the conventional discharge tube lighting device, the transformer 5
Since the output voltage of the transformer 5 is higher than the lighting start voltage of the discharge tube 6, the power consumption of the transformer 5 is large and a lot of heat is generated. The casing, the output end of the transformer 5 and the discharge tube 6
ballast impedance element 7 inserted between
There was a problem that the power consumption was large.

Therefore, the present invention has been made in order to solve the above-mentioned conventional problems, and its purpose is to provide a discharge tube lighting device in which heat generated by a transformer and a ballast impedance element is reduced.

[Means to solve the problem]

A discharge tube lighting device according to the present invention includes an oscillator that generates an alternating current voltage, a transformer that boosts the output voltage of the oscillator, and a transformation ratio control circuit that controls the transformation ratio of the transformer.
It has a timer circuit that operates based on a lighting command signal.

[Effect]

In the discharge tube lighting device according to the present invention, the transformation ratio of the transformer is switched according to the output voltage of the timer circuit.

〔Example〕

Hereinafter, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, and the same parts as in the previous figures are given the same reference numerals. In the same figure, the switching element 3 receives a signal CN that commands lighting.
T controls on/off the power supply voltage V supplied to the oscillator 4 and timer circuit 8. Transformer 5' is oscillator 4
The output is boosted according to the winding ratio set by the transformation ratio control circuit 9, and the discharge tube 6 is driven via the ballast impedance element T.

With this configuration, when the switching element 3 is first turned off, that is, when the discharge tube 6 is dimmed, the oscillator 4 stops oscillating because the power supply voltage V is not supplied to the oscillator 4. The output of the timer circuit 8 is then input to a transformation ratio control circuit 9 to control the turns ratio of the transformer 5' to be increased. When the signal CNT that instructs lighting is turned on, the switching element 3 is connected and the power supply voltage V is turned on.

is applied to the oscillator 4 and the timer circuit 8 through the switching element 3. An oscillator 4 to which a power supply voltage V is applied.
starts oscillation, and an output voltage is applied to the discharge tube 6 through the transformation ratio control circuit 9, the transformer 5', and the ballast impedance element 7. At this time, since the transformation ratio control circuit 9 is connected to the side of the transformer 5' where the winding ratio increases, the secondary output voltage of the transformer 5' is not a high voltage, and the discharge tube 6 starts lighting. A higher voltage is applied, and the discharge tube 6 starts lighting. When the lighting command signal CNT is turned on, the timer circuit 8 also starts operating, and when a certain set time is reached, a signal is output to the transformation ratio control circuit 9 when the time is up, and the turns ratio of the transformer 5' becomes smaller. As the winding ratio of the transformer 5' to be switched becomes smaller, the output voltage of the transformer 5' decreases.

When the discharge tube 6 is lit, the output voltage of the transformer 5' becomes smaller, so the impedance of the ballast impedance element 7 can be made smaller than in the conventional discharge tube lighting device. The power consumption of ' is also reduced because the output voltage amplitude becomes smaller.

Note that the timer circuit 8 described above may be modified in various ways.
FIG. 1 shows an example of this. FIG. 2 shows the configuration of a timer circuit 8' according to another embodiment. In the figure, when the lighting command signal CNT is turned on, the switching element 3 is connected, and the power supply voltage vl is applied to the switching element 3.
f: Through the resistor R of the timer circuit 8' and the capacitor C
Start charging. When the charging voltage of the capacitor C reaches the comparison voltage Vref of the comparator 10, the output of the comparator 10 is inverted, and the transformer 5' is switched off so as to reduce the winding ratio, as shown in the transformation ratio control circuit 9 of FIG. Change. The transistor Q quickly discharges the charge stored in the capacitor C when the lighting command signal CNT is turned off.

〔Effect of the invention〕

As explained above, according to the discharge tube lighting device according to the present invention, since the winding ratio of the transformer is controlled by the timer circuit operated by the lighting command signal, the heat generation of the transformer and the parasitic impedance element can be reduced. As a result, an extremely excellent effect can be obtained in that a transformer and a parasitic impedance element can be realized at low cost.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing one embodiment of the discharge tube lighting device according to the present invention, Fig. 2 is a circuit diagram showing another embodiment of the timer circuit, and Fig. 3 shows the configuration of a conventional discharge tube lighting device. It is a block diagram. 1... Power input terminal, 2... Lighting command signal input terminal, 3... Switching element, 4... Oscillator, 5'... Transformer, 6... Discharge tube ,7.・0
．． Parast impedance element, 81B''...Timer circuit, 9...Transformation ratio control circuit, 10...Comparator, R...Resistor, C...Capacitor, Q...
...transistor.

Claims (1)

[Claims] In a discharge tube lighting device comprising an oscillator that generates an alternating current voltage, a transformer that boosts the output voltage of the oscillator, and a discharge tube connected to the secondary side of the transformer, a timer that starts operation in response to a lighting command signal. 1. A discharge tube lighting device comprising: a circuit; and a transformation ratio control circuit for controlling the transformation ratio of the transformer.