JPH0448594A - Direct current lighting circuit of discharge tube - Google Patents

Abstract

PURPOSE:To continue stable electric discharging by installing a starting circuit which has a simple structure and is able to start safely and re-start even in the case of starting failure. CONSTITUTION:A serial circuit of a chock coil CH2, a switching circuit, and heaters F1, F2 of a discharging tube is connected with the output side of a rectifying circuit BR and at the same time a chock coil CH1 is connected with the input side of the rectifying circuit. Owing to the chock coil installed in an a. c. circuit side, d.c. voltage can be controlled at the time of starting and lighting and thus stable starting and lighting is carried out. Also, the chock coil installed in the d.c. side generates spike voltage at the time of starting and stabilizes discharging current as a d.c. resistor at the time of lighting.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a lighting circuit for a discharge tube, particularly a discharge tube having a heater, using a DC power source.

(Prior Art) Light sources using discharge tubes, such as fluorescent lamps and mercury lamps, are usually turned on using AC power as a power source, but it is well known that the amount of light flickers. This flicker has an unfavorable effect on the eyes even when used for general lighting. Furthermore, when used as a light source for image processing, for example, a light source using a COD as an image detector, the scanning speed is synchronized with the frequency of the power supply, and the period during which the light intensity decreases due to flickering, C
A complicated circuit had to be used, such as not performing detection from the CD. In this case, it is impossible to deal with flicker using the synchronization method described above in high-resolution TVs that require high scanning speed, so fluorescent lamps, which have excellent optical characteristics, are used as light sources for illumination. etc. could not be used for illumination during imaging.

As a countermeasure against flickering, there is a method of using multiple fluorescent tubes and staggering the timing of their lighting, but this method was not able to avoid fluctuations in the amount of light due to the influence of social gatherings.

It is clear that if a fluorescent tube or the like is lit using a DC power source, the problem of flickering will not occur. However, a lighting circuit using a DC power source is not only complicated, but also difficult to start stably.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned circumstances, and has a simple configuration, can perform stable startup, and can restart even if startup fails. It is an object of the present invention to provide a DC lighting circuit for a discharge tube such as a fluorescent tube, which is equipped with a starting circuit capable of providing stable discharge and which can sustain stable discharge.

(Means for Solving the Problems) In the first aspect of the present invention, in a DC lighting circuit for a discharge tube, a series circuit of a choke coil, a switching circuit, and a heater for the discharge tube is connected to the output side of the rectifier circuit. In addition, a choke coil is connected to the input side of the rectifier circuit, and in the second invention, in the DC lighting circuit for a discharge tube, the choke coil and the rectifier circuit are connected to the output side of the rectifier circuit. The present invention is characterized in that a series circuit of an output circuit of a voltage responsive relay circuit responsive to an output voltage and a heater of a discharge tube is connected, and a choke coil is connected to the input side of the rectifier circuit.

A manual bushing switch can be used as the switching circuit.

A lighting tube can be used as the switching circuit.

In order to provide appropriate delay characteristics to the voltage responsive relay circuit,
A time constant circuit can be added.

(Embodiment) FIG. 1 is a circuit diagram for explaining an embodiment of the present invention. In the figure, AC is an alternating current power supply, SWl is a power switch,
F is fuse, BR is rectifier circuit, C is capacitor, CH
I and CH2 are choke coils, SW2 is a start switch, Fl and F2 are heaters for fluorescent tubes, and SW3 is a changeover switch.

When the power switch SWl is turned on, the output of the rectifier circuit BR charges the capacitor C. At the beginning of charging, the impedance of choke coil CHI is large due to the leakage effect, and the surge current of charging capacitor 〇 is suppressed. As charging progresses, the charging current decreases and the output voltage of the rectifier circuit BR increases, and at the end of charging, the charging voltage becomes a voltage close to the peak value (for example,
140V). When the start switch SW2 is turned on for a short time, the heater Fl is turned on in the on state.

A current flows that heats F2, and electromagnetic energy is accumulated in choke coil CH2. Due to the leakage effect of the choke coil CHI due to the heating current of the heater (for example, about IA), the potential of the capacitor C decreases considerably. When the start switch SW2 is turned off, the transient voltage of the electromagnetic energy accumulated in the choke coil CH2 causes a small discharge in the fluorescent tube using the heaters Fl and F2 as discharge electrodes, and then the capacitor C is charged. A main discharge can be generated by the energy accompanying the discharge.

Due to the discharge current in the main discharge (for example, a continuous current of about 600 mA), the impedance of the choke coil CHI, which has leakage characteristics, is large, and the output voltage of the rectifier circuit BR decreases due to the voltage drop (for example, 70 V
Stable discharge can be maintained by the current limiting effect due to the resistance of the choke coil CH2.

If the discharge fails to start, the start switch may be operated again.

Since this discharge is a direct current discharge, blackening occurs near one heater electrode. In that case, selector switch SW3
By reversing , the direction of discharge can be reversed and blackening can be eliminated.

The starting switch SW2 may be a switch that is turned on for a predetermined period of time and then turned off by a timer operation, or may be a manual pushbutton switch.

The starting switch SW2 may be operated in conjunction with the power switch SW1, and may be turned on for a short time only at the initial stage of turning on the power switch SW1. For example, by using a lighting switch and a light-off switch, the power switch SW1 and the starting switch SW2 can be turned on when the lighting switch is pressed by hand, and the starting switch SW2 is turned off when the hand is released. Alternatively, a rotary switch operated by a pull string may be used as the power switch, and the starting switch SW2 may be turned on only while the string is being pulled when the power is turned on.

The heater heating current may be set to an appropriate value by inserting a resistor in series with the circuit of the starting switch SW2.

A lighting tube such as a glow lamp, a timer switch, or the like may be used instead of the starting switch SW2.

FIG. 2 is a circuit diagram of an embodiment using a glow lamp as a switch circuit. In the figure, the same parts as in Figure 1 are
The same reference numerals are used to omit the explanation.

GL is a glow lamp.

When the power switch SWI is turned on, the output of the rectifier circuit BR charges the capacitor C. When the charging voltage reaches the discharge start voltage of the glow lamp, the glow lamp is discharged, and the bimetal switch is turned on by the heat, causing a heating current to flow through the heaters Fl and F2 of the fluorescent tube. When the bimetal switch is turned off, the transient voltage of the accumulated electromagnetic energy causes a small discharge in the fluorescent tube using the heater as the discharge electrode, followed by a main discharge due to the energy associated with charging the capacitor C. What can be done is the same as in the case of FIG. 1 described above.

Due to the discharge current in the main discharge (for example, a continuous current of about 600 mA), the impedance of the choke coil CHI, which has leakage characteristics, is large, and the output voltage of the rectifier circuit BR decreases due to the voltage drop (for example, 70 V
degree), the glow lamp will not turn on.

If the discharge cannot be started, the capacitor C is charged up, and when the charging voltage reaches the discharge start voltage of the glow lamp, the glow lamp is discharged again, and the above-mentioned starting operation can be repeated.

FIG. 3 is a circuit diagram of an embodiment using a voltage-responsive switching circuit as the switch circuit.

In the figure, the same parts as in FIG. 1 are given the same reference numerals, and their explanation will be omitted. R1-R8 are resistors, VR is variable resistor, TR
I to TR4 are transistors, R5 is a switching transistor, ZD is a Zener diode, and D is a diode.

When the power switch SWI is turned on, the output of the rectifier circuit BR charges the capacitor C. The charging voltage is divided by the resistor R1 and the variable resistor VR.
When the operating voltage of the Schmitt circuit consisting of RI, TR2 and resistors R2 to R6 reaches (for example, 110V), the transistor TR2 is turned off due to its operation.
Zener diode ZD due to the increase in collector potential
becomes conductive, transistors TR3 and TR4 turn on,
The output transistor TR5 becomes conductive, and as described above,
A heating current is passed through the heaters Fl and F2, and electromagnetic energy is accumulated in the choke coil CH2. As mentioned above, the choke coil C due to the heating current of the heater
Due to the leakage effect of HI, the potential of capacitor C decreases, and the Schmitt circuit is restored. Due to the return of the Schmitt circuit, the output transistor TR5 is turned off.
Due to the transient voltage of the electromagnetic energy stored in the choke coil CH2, a small discharge occurs in the fluorescent tube using the heater Fl and F2 as the discharge electrode, and then the capacitor C
A main discharge can be caused by the energy associated with charging.

As described above, the output voltage of the rectifier circuit BR decreases due to the discharge current in the main discharge, so the Schmitt circuit does not operate while the discharge continues.

If the discharge fails to start, or if the discharge stops for some reason, the capacitor C will be charged up, and the Schmitt circuit will operate again.
The startup operation described above can be repeated.

Appropriate time constant characteristics may be given to the relay circuit by connecting a one-shot multivibrator to the output side of the Schmitt circuit or inserting an appropriate time constant circuit.

In addition, in each Example, it was experimentally confirmed that when the choke coil CH2 on the DC circuit side is provided on the negative side as shown in the figure, the spike voltage at the time of startup is larger.

(Effects) As is clear from the above explanation, according to the present invention, commercially available fluorescent tubes and mercury discharge tubes can be lit with a DC power supply, so there is no flickering, and a brighter light source can be obtained, making it suitable for general lighting. It is possible to obtain a light source that is particularly suitable for use in image processing, for example, a light source for fax machines, copying machines, illumination light sources for high-quality TV photography, light sources for high-speed cameras, backlights in liquid crystal devices, etc.

The choke coil provided on the AC circuit side can control the DC voltage at startup and lighting, allowing stable startup and lighting. Further, the choke coil provided on the DC side generates a spike voltage at startup and stabilizes the discharge current as a DC resistance during lighting, so a DC lighting circuit can be provided with a simple circuit configuration.

If the discharge fails to start, it can be easily restarted and stabilized. Figures 1 to 3 are circuit diagrams of different embodiments of the present invention.

AC...AC power supply, SWl...power switch, BR
... Rectifier circuit, C... Capacitor, CHI, CH
2... Choke coil, Fl, F2... Fluorescent tube heater SW3... Changeover switch, R1-R8...
Resistor, VR...variable resistance, TRI~TR4...transistor, ZD...zener diode, D...diode, SW2...start switch, GL...glow lamp, R5...switching transistor.

Claims (2)

[Claims] (1) DC lighting of a discharge tube characterized in that a series circuit of a choke coil, a switching circuit, and a discharge tube heater is connected to the output side of the rectifier circuit, and a choke coil is connected to the input side of the rectifier circuit. circuit. (2) Connecting a series circuit of a choke coil, an output circuit of a voltage-responsive relay circuit that responds to the output voltage of the rectifier circuit, and a heater of the discharge tube to the output side of the rectifier circuit;
A DC lighting circuit for a discharge tube, characterized in that a choke coil is connected to the input side of the rectifier circuit.