JPH0845686A - Ballast for fluorescent lamp - Google Patents

Abstract

PURPOSE:To decrease consumption of energy on a thermistor by actuating a thyristor which is controlled by a capacitor and diode AC switch when a fluorescent tube begins operating, and allowing the current to flow to a silicon rectifier. CONSTITUTION:Between an R/F circuit 10 and a high frequency switching circuit 30, a starting current limiting circuit 20 is installed through a loop including a thermistor 21 having a negative temp. coefficient. The thermistor 21 is connected parallel with a diode 25 installed facing oppositely to a thyristor 24, and the gate terminal of the thermistor is connected with a resistance 26 and a diode AC switch 23, to which a capacitor 22 is connected. The capacitor 22 is connected with the cathode of the thyristor 24 and a voltage dividing resistance 28 to constitute the starting current limiting circuit 20. When a fluorescent tube AB is going to start with a starter circuit 40, the current flowing through the filament of the fluorescent tube is controlled, and gradual increase is made by the thermistor 21. By the diode AC switch the thyristor is actuated to the capacitor 22, and the current flows through the thyristor 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ballast for a fluorescent lamp (inverter), which prolongs the life of the fluorescent lamp, prevents the user from receiving an electric shock, and further protects the fluorescent tube and the electronic ballast. It is for doing.

[0002]

BACKGROUND OF THE INVENTION Most fluorescent lamps today use conventional wound ballasts, but some new electronic ballasts have also been developed, which save electricity and operate without a starter. It is possible, there is little radio interference, the size is small, and the weight is light. Due to the advantages mentioned above, these new ballasts are replacing conventional ones at a considerable speed. FIG. 1 shows an electronic ballast that has recently been bustling the market. This operates like a half bridge converter, and a low frequency AC voltage for home use (60 Hz) is converted into a stable DC voltage by the rectifying / filtering circuit 10. The converted DC voltage is the high frequency switching circuit 2
Input to 0. After the high-frequency switching circuit 20 starts operating by the charging circuit 30, that is, when the charging capacitor is charged by the charging circuit 30 to the extent that the diac 32 starts operating, the high-frequency switching circuit 2
The drive transformers L1, L2, L3 wound on the same core first have the 0 conversion transistor Q1 activated.
Are mutually induced, and the conversion transistors Q1 and Q2 operate quickly. That is, only one of the transistors is activated, and the other is turned off at this time.

As a result of the transistors Q1 and Q2 operating at high speed, a current flows from left to right in the inductor 4 as the transistor Q1 operates, and the transistor Q1 also operates.
With the operation of 2, the current flows from right to left. Therefore, for the inductor 4 and the fluorescent tube 40, the current functions as an alternating current. Due to the fairly fast mutual operation of the transistors Q1, Q2, the current in the inductor L4 and the fluorescent tube can be treated as a high frequency alternating current. In other words, when the high frequency switching circuit 20 is swept and operates, a high frequency alternating current can be oscillated in the fluorescent tube 40. Inductor L4 acts as a current stabilizer and can limit overcurrent from flowing into fluorescent tube 40, preventing fluorescent tube 40 from burning due to overcurrent. As a result of this high-frequency alternating current being supplied, the inductor L4 and the capacitor C1 start to resonate, and a high resonance voltage is generated at both ends of the fluorescent tube, so that each filament 41 is rapidly heated, and electrons are emitted from the filament 41 to cause the resonance. The inert gas in the light tube is activated and turned on. When the fluorescent tube 40 is activated,
Since the impedance drops and the current in it increases, most of the current does not flow in the capacitor C1 but flows in the resonant circuit of the inductor L4 and the capacitor C2. Since the capacitance of the capacitor C2 is much larger than that of the capacitor C1, the capacitance is shifted to the lower frequency range of the natural resonance frequency. This shift in the natural resonance frequency changes the operating point Q of the circuit. As a result, the circuit is not in the optimal (ooptimal) resonance during the starting phase. Therefore, the output voltage and power from this circuit will drop substantially after the fluorescent lamp is activated. From this point on, the fluorescent tube 40 continues to light up with a stable output voltage and current until the power supply is stopped.

[0004]

The above-mentioned prior art electronic ballasts are characterized by their small size, light weight, fast lighting, power saving and operation without a starter, and operating frequency. The frequency is 25 KHz or more, so it does not flicker. However, the actual operation has the following drawbacks. 1. When each fluorescent lamp is started, a momentary inrush current is applied to the filament of the fluorescent tube, so if the fluorescent officer is frequently turned on and off, oxides on the filament will be removed. , Instantaneous inrush current
As a result of the high temperatures generated by, the filaments can wear out after a relatively short time and the filaments can burn out, which greatly shortens the life of the fluorescent tube. 2. If the fluorescent tube cannot be lit within the rated time or at all, the prior art ballast will be placed in resonance with the continuous high voltage developed across the fluorescent tube, and the fluorescent tube will However, it is exposed to high voltage continuously rather than momentarily, which easily causes failure. 3. Abnormal continuous high voltage and power, as described in 2 above, adversely affect the ballast circuitry, especially the conversion transistors, and the latter is easily burned out.

The inventor of the present invention has been aware of the above-mentioned drawbacks of the above circuit and has developed a safer improved version having a better performance.

[0006]

SUMMARY OF THE INVENTION Therefore, the main object of the present invention is to provide a fluorescent lamp ballast (inverter), which is a rectifier / filter circuit and
It is equipped with a starting current limiting circuit, a high frequency switching circuit, a protection circuit and a starting circuit. The rectifying / filtering circuit and the high frequency switching circuit are used for converting a low frequency AC voltage input into a high frequency AC voltage output. To be done. An inductor and a capacitor are used in the starting circuit, and the fluorescent tube is lit and continuously glows by interlocking with each other to generate resonance in the circuit. During operation of the fluorescent tube, the starting current limiting circuit limits the current flowing through the filament, gradually increasing the current to the extent that the oxide on the filament is slowly consumed, easing the heating process, This prolongs the life of the fluorescent tube.

Further, in the electronic ballast for a fluorescent lamp provided as the second object of the present invention, a protective circuit is used, and the fluorescent lamp cannot be turned on within the rated time or cannot be started at all. In addition to detecting, the oscillation of the conversion transistor of the high-frequency switching circuit is stopped to prevent it from staying at its optimum resonance stage for a long time, which prevents the fluorescent tube from deteriorating and also Prevents circuits from burning out and protects them.

In the electronic ballast for a fluorescent lamp provided as a further object of the present invention, since the fluorescent tube and the high frequency switching circuit are insulated by the insulating transformer, the fluorescent tube and the power source are not grounded together. Well-insulated, there is no fear of electric shock when the user replaces the fluorescent tube.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 2, a ballast (inverter) for a fluorescent lamp according to the present invention is connected to a rectifying / filtering circuit (hereinafter abbreviated as R / F circuit) 10 and an output terminal of the R / F circuit 10. The starting current limiting circuit 20, the high frequency switching circuit 30, the starting circuit 40 connected to the output terminal of the high frequency switching circuit 30, and the protection circuit 50 connected to the starting circuit 40. The R / F circuit 10 is used to convert a household AC power supply into a DC power supply by a bridge rectifier, and when the capacitor 31 is charged to such an extent that the DIAC 32 starts to operate, the entire high frequency switching circuit 30 is swept. The DC voltage is converted into a high frequency AC voltage, and the high frequency AC voltage is applied to the starting circuit 4
0 is supplied. At this time, the inductor 4 of the starting circuit 40
1 starts to resonate with the capacitor 42, and alternately activates the fluorescent tubes A and B by a high resonant voltage.
When the inductor operates, the inductor 41 resonates with the capacitor 44 having a larger capacitance, thereby moving to a frequency region where the natural resonance frequency is low, and by generating a lower output voltage and current, the fluorescence is reduced. The tube discharges,
When lit, the inductor 41 can effectively function as a current ballast, limiting overcurrent flow in the fluorescent tubes A and B.

If the fluorescent tubes A and B cannot be operated within the rated time, or cannot operate at all, the high current flowing in the fluorescent tubes causes the inductor 41 to react and thus the coupling coil of the protection circuit 50 to have a suitable voltage. , Which causes the capacitor 53 to charge until the voltage at which the diac 54 is activated is reached.
The thyristor 52 is then swept into the diac 54 to actuate and forward bias the diode 55, grounding the transistor gate voltage and stopping the resonance of the entire high frequency switching circuit. The supply of high-frequency alternating current is stopped.

Since the thermistor 21 of the starting current limiting circuit 20 has a negative temperature coefficient, when the fluorescent tubes A and B are activated, the current flowing through their filaments gradually increases (at the beginning of the thermistor 21). Since the initial resistance is large,
When a current passes through it, its temperature rises and its resistance decreases, so the current gradually increases as the resistance of the thermistor decreases), and the filament of the fluorescent tube is activated to activate the fluorescent tube. When the current increases to the extent that lights up, the capacitor 22 is charged enough to trigger the diac 23, and as a result, the thyristor 24 operates,
As a result, no further current flows through the thermistor 21 after the fluorescent tube has started, so that electrical energy is prevented from being consumed on the thermistor and the efficiency of the entire circuit is improved. In other words, at the moment when the fluorescent tube starts to operate, a large inrush current is generated due to the resistance of the thermistor 21.
(large inrush current) does not occur. Thus, the temperature rise of the filament is not so steep that the oxidant on it is well protected and the life of the fluorescent tube can be extended.

Still referring to the starting circuit 40, the fluorescent tube A
By connecting the isolated output transformer 44 to the high frequency switching circuit 30, B and B can obtain a high output voltage from the high frequency switching circuit 30. Moreover, since the ground of the fluorescent lamp is different from the ground of the power source, even if the user accidentally touches the circuit of the fluorescent tube, there is no electric shock.

The features of the improved ballast according to the present invention, as shown in FIG. 2, are as follows:
Is disposed between the R / F circuit 10 and the high frequency switching circuit 30 via a loop having a thermistor 21 having a negative temperature coefficient. The thermistor 21 includes a thyristor 24 and a thyristor (SCR). Is connected in parallel with a diode 25 arranged in the opposite direction to the gate terminal of the thyristor 24.
3 and the capacitor 22 is connected to the diac 23. The capacitor 22 is connected to the cathode of the thyristor 24, and the capacitor 22 is further connected to the voltage dividing resistor 28, and the voltage dividing resistor (voltage dev
ision resistor) 28 is a DC bus voltage
To constitute a starting current limiting circuit 20, whereby the current flowing through the filaments of the fluorescent tubes is controlled by the thermistor 21 at the moment when the fluorescent tubes A and B start to operate by the starting circuit 40. Gradually increase, and further
After the thyristor is activated by the capacitor 22 and the diac 23 and the fluorescent tube is activated, the current flows through the thyristor rather than the thermistor 21, which reduces the consumption of energy on the thermistor.

Furthermore, the starting circuit 40 comprises a capacitor and an inductor, which are connected to the primary winding of the isolation transformer, while the secondary winding of the transformer is a pair with the capacitors connected in parallel. Connected in series to the fluorescent tubes, one of which is connected in parallel to another capacitor, whereby both fluorescent tubes are connected to the primary and secondary windings of the transformer. As a result of being electrically connected to each other, electric power is obtained by the output of the high frequency switching circuit, and both the fluorescent tube and its power source have different grounds,
Prevent leakage of fluorescent tubes.

Further, according to FIG. 2, the coupling coil of the protection circuit is connected to the inductor on the common core so that an appropriate voltage is induced to charge the capacitor, which activates the diac. And the diac controls the operating state of the thyristor. The thyristor controls the operation of the diode connected to the gate of the conversion transistor of the high-frequency switching circuit, so that if the fluorescent tube does not operate within the rated time, the appropriate current and voltage on the coupling coil from the inductor. Is triggered, the capacitor is charged, the diac operates with the thyristor and the diode, the gate of the conversion transistor is grounded, and the oscillation of the high frequency switching circuit is stopped.

As is apparent from the above, the present invention improves the performance of the conventional electronic ballast and extends the life of the fluorescent tube by using the starting current limiting circuit 20, the starting circuit 40, and the protection circuit 50. Lengthen and protect the ballast's own circuitry to prevent electric shock to the user.

[Brief description of drawings]

FIG. 1 shows a circuit of an electronic ballast according to the prior art.

FIG. 2 shows a circuit of an electronic ballast according to the invention.

[Explanation of symbols]

 10 Rectifier / Filter Circuit 20 Starting Current Control Circuit 21 Thermistor 30 High Frequency Switching Circuit 40 Starting Circuit 50 Protection Circuit 52 Thyristor 53 Capacitor 54 Diac

Claims (3)

[Claims] 1. A rectifying / filtering circuit connected to an AC power supply, a starting current control circuit and a high frequency switching circuit connected to an output terminal of the rectifying / filtering circuit, and an output terminal of the high frequency switching circuit. In a ballast for a fluorescent lamp comprising a starting circuit and a protection circuit connected to the starting circuit, the starting current limiting circuit is a rectifier / filter circuit formed by a loop having a thermistor having a negative temperature coefficient. The thermistor is arranged between the high-frequency switching circuit and the thyristor (SCR) in parallel with a diode arranged in the opposite direction to the thyristor, and a gate terminal of the thyristor is a resistor. A capacitor is connected to the diac, and the capacitor is connected to the diac, and the capacitor is the cathode end of the thyristor. Connected, the capacitor is further connected to voltage dividing resistors,
The voltage divider resistor is then connected to a DC bus voltage to form the starting current limiting circuit, so that at the moment the fluorescent tube is activated by the starting circuit, the fluorescent lamp is activated. The current flowing through the filament of the light tube is controlled by the thermistor and gradually increases, and further, after the fluorescent tube has started to operate, the thyristor controlled by the capacitor and the diac is operated so that the current is not the thermistor. A ballast for a fluorescent lamp, characterized in that it flows through the silicon rectifier and reduces energy consumption on the thermistor. 2. The starting circuit includes a capacitor and an inductor, the capacitor and the inductor being connected to both ends of a primary winding or an insulating transformer, and the secondary winding of the transformer being connected to a pair of fluorescent tubes. A capacitor is connected in parallel to the fluorescent tube, and one of the fluorescent tubes is connected in parallel to yet another capacitor, whereby the primary winding and the secondary winding of the transformer are electrically connected. The result is that the fluorescent tube is powered by the high frequency switching circuit and the fluorescent tube and its power supply are separately grounded to prevent leakage of the fluorescent tube. Item 1. A ballast stabilizer for fluorescent lamp according to item 1. 3. A voltage is induced in a coupling coil of the protection circuit to charge a capacitor that controls the operating state of the diac, the diac controls the operating state of the thyristor, and the thyristor controls the operating state of the high frequency switching circuit. Controls the operation of a diode connected to the gate of the conversion transistor, which induces a suitable current and voltage on the coupling coil from the inductor if the fluorescent tube is not activated within a rated time, 2. The capacitor according to claim 1, wherein the capacitor is charged, the diac starts operating together with the thyristor and the diode, the gate of the conversion transistor is grounded, and the oscillation of the high frequency switching circuit is stopped. Ballast for fluorescent lamps.