JPH09213490A - Fluorescent lamp ballast - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably light a fluorescent lamp in starting by alternately turning on and off a switching element of bridge-connection with frequency higher than resonance frequency in starting, and moving from frequency higher than resonance frequency in which the lighting of the fluorescent lamp is easiest to resonance frequency in which the efficiency of the fluorescent lamp is highest. SOLUTION: A rectifier circuit 3 for converting an AC power source 2 into a DC power source 6, and a transformer 14 in which a primary winding 15 is connected to the DC power source 6 through switching elements 11, 12 are arranged. A control circuit 20 which moves frequency induced in the transformer 14 by turning on and off the switching elements 11, 12 from the high frequency in starting to low frequency in the stationary state is arranged. In a fluorescent lamp 16, the secondary winding 18 of the transformer 14 is connected to one end of each filament, and current flows between the filaments in lighting. A resonance capacitor 50 is connected to between other ends of the filament, and the secondary winding 18 forms a closed circuit together with the filament.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent lamp stabilizing device for shifting the frequency of an inverter for lighting a fluorescent lamp at a high frequency from a high value at startup to a low value at steady state.

[0002]

2. Description of the Related Art Nikkei Electronics, published on April 21, 1986, pp. 118-120, describes one of IC control methods.
A fluorescent lamp stand for lighting a fluorescent lamp at a high frequency (20 kHz or higher) with a stone inverter is disclosed. This fluorescent lamp stand has the advantages that the flicker is almost eliminated, the luminous efficiency is increased, and the weight is lighter, as compared with low frequency (50/60 Hz) lighting. However, as the inverter, for example, a push-pull type using two transistors is mainly used for large power consumption using a commercial power supply of 200 volts.

Further, JP-A-4-32198 and JP-A-4-163888 disclose an inverter using two power transistors of SEPP type. It has been shown that the excitation circuit that controls on / off of these power transistors shifts the oscillation frequency from a low value to a high resonance value in a normal state at startup, but the model number of the IC circuit is not specifically described. , Therefore its composition is unknown.

[0004]

Generally, in an inverter type fluorescent lamp stabilizer, the output voltage V of the secondary winding of the transformer is as shown in FIG. 1 when the fluorescent lamp is normally connected.
As shown by the curve A, as the oscillation frequency f increases, the oscillation frequency f gradually decreases, and there is a tendency that the oscillation frequency f gradually increases after passing the minimum resonance frequency. This resonance frequency is mainly determined by the characteristics of the inverter, and is the point at which the fluorescent lamp emits light best in a steady state.

On the other hand, since the filament of the fluorescent lamp is not sufficiently warmed at the time of start-up, it is possible to stably turn on the fluorescent lamp by exciting it at a frequency higher than the resonance frequency rather than exciting it at a frequency lower than the resonance frequency. It turned out to be possible. That is, as disclosed in JP-A-4-32198 and JP-A-4-163888, the fluorescent lamp cannot be stably turned on when excited at a frequency lower than the resonance frequency at the time of startup. .

On the other hand, under no load, that is, when the fluorescent lamp is removed, as shown by the curve B in FIG. 1, as the oscillation frequency f decreases from a predetermined value, the oscillation frequency f rises sharply and shows a substantially maximum value near the resonance frequency. Tend. This no-load state may deteriorate various components used in the inverter and shorten their lives. In the above publication, the oscillation frequency is shifted to a value lower than the resonance frequency to prevent an overload, but power is continuously supplied to the inverter circuit, and deterioration of various components cannot be avoided.

The present invention has been made in view of the above circumstances, and provides a lighting circuit for starting and lighting a fluorescent lamp at a frequency higher than the resonance frequency, and then lighting the fluorescent lamp at the resonance frequency with good luminous efficiency. Has an aim. Also,
When the no-load condition is reached, the power supply is stopped for a predetermined period, and then the power supply is restarted to detect the load condition.

[0008]

A fluorescent lamp stabilizer according to the present invention comprises a rectifier circuit for converting an AC power supply into a DC power supply,
A transformer whose primary winding is connected to the DC power supply via a switching element, and on / off control of the switching element to shift the frequency induced in the transformer from a higher frequency at startup to a lower frequency at steady state. A control circuit, a secondary winding of the transformer is connected to one end of each filament, and a fluorescent lamp in which a current flows between the filaments at the time of lighting, and a fluorescent lamp connected between the other ends of the filaments to connect the secondary winding and A resonant capacitor that cooperates with the filament to form a closed circuit.

The transformer is connected to a tertiary winding capable of supplying electric power to the control circuit, a quaternary winding capable of detecting the presence or absence of the fluorescent lamp or an abnormal state, or one filament of the fluorescent lamp. A preheat winding is provided.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a circuit diagram of a stabilizer 1 for a fluorescent lamp, which is an embodiment of the present invention. In this figure, for example, 200
The volt AC power source 2 is full-wave rectified by the bridge-connected rectifier 3, and then the smoothing capacitors 4 and 5 connected in series form a DC power source 6 of about 280 V between the positive line and the ground line. These smoothing capacitors 4 and 5 have approximately the same capacitance,
Form a 0 volt positive and negative power supply.

The DC power supply 6 has two N-channel MOSFETs controlled so that only one of them is turned on.
11, 12 are connected in series. That is, the MOSFET 11
Has a drain connected to the positive line of the DC power supply 6 and a source connected to the drain of the MOSFET 12
It forms the output 13 of the P connection, while the source of the MOSFET 12 is connected to the negative line, ie grounded. The primary winding 15 of the output transformer 14 is connected between the output terminal 13 and the connection point 7 of the smoothing capacitors 4 and 5.

The output transformer 14 is connected to one end of each filament 17 of the two fluorescent lamps 16.
The secondary winding 18, the preheating winding 19 connected to preheat the other filament 17, and the control circuit 2 in the steady state
And a low power supply winding 21 capable of feeding zero. In these fluorescent lamps 16, a resonance capacitor 50 is connected between the other ends of one filament 17 and the value thereof is set appropriately. Further, the output transformer 14 detects a no-load state when the fluorescent lamp 16 comes off, as will be described later.
A secondary winding 45 is provided.

On the other hand, the gates and sources of the MOSFETs 11 and 12 are connected to the non-inverting and inverting outputs of the control circuit 20 via an isolator, that is, a coupling transformer 22, respectively. The control circuit 20 includes a general-purpose PWM integrated circuit 24 such as TL494 manufactured by Texas Instruments Incorporated.
Including, two open collector outputs are combined transformer 2
It is connected to each end of a primary winding 25 having two center taps.

The oscillation frequency of the PWM integrated circuit 24 is determined by an external capacitor 26 and a resistor 27 which are connected to the CT and RT terminals, respectively. Of course, the other ends of the capacitor 26 and the resistor 27 are grounded. A time constant circuit in which another resistor 28 and a capacitor 29 are connected in series is connected in parallel to the resistor 27. Therefore, the combined resistance value connected to the RT terminal is
As the battery 9 charges, the resistors 27 and 28 at power-on
Is gradually changed to the value of the resistor 27.

This finally shifts the oscillation frequency of the PWM integrated circuit 24 from a high frequency at which the fluorescent lamp 16 easily lights up, for example, 49 kHz to a resonance frequency of 26 kHz at which the fluorescent lamp 16 emits light with high efficiency. On the other hand, the secondary windings 30 and 31 of the coupling transformer 22 are connected to the MOSFET 1
1 and 12 are respectively connected to the gate and the source. Instead of the coupling transformer 22, for example, two photo couplers may be used as the isolator.

At the time of startup, for example, about 280
12 from the high voltage power source of the volt via the starting circuit 32
A low voltage of volt is supplied to the control circuit 20. The starting circuit 32 includes a resistor 35 of which the one end is connected to the positive electrode line of the high voltage DC power supply 6 and which has a resistance of, for example, 150 kΩ. The other end of the resistor 35 is connected to the anode of the switching diode 38 via the diac 36 and the series protection resistor 37, and further to the electrolytic capacitor. Further, a constant voltage diode 39 having a Zener voltage of, for example, 12 V is connected to the anode of the switching diode 38, and these electrolytic capacitor and Zener diode are grounded.

Since the starting circuit 32 consumes about 22 times the electric power consumed by the control circuit 20, the starting circuit 32 is operated only for a while after the fluorescent lamp 16 is turned on after the power is turned on. Therefore, the half-wave rectifier circuit 33 is connected to the low power supply winding 21 of the output transformer 14, and supplies power to the control circuit 20 via the switching diode 34 in a steady state. A common cathode of these switching diodes 34 and 38 is connected to the control circuit 20 via a tube separation protection circuit 40.

In the tube separation protection circuit 40, the collector is connected to the cathode common and the emitter is the control circuit 20.
Of NPN transistors 41 connected to the hot side of. The base of the NPN transistor 41 is connected to the collector of the NPN transistor 42 whose emitter is grounded and the pull-up resistor 43. The base of the NPN transistor 42 is connected to the cathode of the thyristor 44 having a gate on the anode side, and the anode of the thyristor 44 is connected to the positive side of the half-wave rectifier circuit 33. Half-wave rectifier circuit 33
The negative side of is grounded. On the other hand, between the anode and the gate of the thyristor 44, a quaternary winding 45 for detecting a no-load state when the fluorescent lamp 16 is disconnected is connected via a zener diode and a rectifying diode connected in series. There is.

Therefore, when the peak value of the quaternary winding 45 sharply rises and exceeds a predetermined threshold value in the no-load state, the thyristor 44 holds itself in the ON state,
The NPN transistor 42 is turned on, the base voltage of the NPN transistor 41 is lowered to about zero volt, and the power supply to the control circuit 20 is cut off.

The operation of the fluorescent lamp stabilizer 1 according to the present invention will be described. When the power is turned on, the DC power supply 6 is supplied between the drain-source of the MOSFETs 11 and 12 connected in series and to the smoothing capacitors connected in series. On the other hand, the power of 12V is supplied to the control circuit 2 via the starting circuit 32.
0 is supplied. Since the capacitor 29 is not charged, the control circuit 20 starts transmitting at an oscillation frequency that depends on the parallel value of the resistors 27 and 28, for example, 48 kHz, and
The FETs 11 and 12 are alternately driven to the ON state. Therefore, a high-frequency alternating current having a frequency of 48 kHz is supplied to the primary winding 15 of the output transformer 14, and a high-voltage high-frequency alternating current is induced in the secondary winding.

Therefore, the fluorescent lamp 16 has the preheating winding 1
Even if the temperature of the filament is not raised by 9, the light is stably emitted. As the capacitor 29 is charged with electric charge, the influence of the resistor 28 becomes weaker, the combined resistance value of the resistors 27 and 29 rises, and the oscillation frequency falls to the resonance frequency of, for example, 24 kHz. Also, the filament warms up and the fluorescent lamp 1
6 lights efficiently and more stably. Therefore, high-voltage high-frequency alternating current with a frequency of 48 to 24 kHz is induced in the primary winding 15 of the output transformer 14, and low-voltage high-frequency alternating current is induced in the low power supply winding 21.

The winding ratio of the primary winding 15 and the low power supply winding 21 is such that a low-frequency high-frequency AC can obtain a voltage slightly higher than the output voltage of the starting circuit 32 after half-wave rectification, that is, 12V.
It is set in advance. Therefore, the power supply to the control circuit 20 is switched from the starting circuit 32 to the half-wave rectifier circuit, and the step-down resistor 5 is prevented from overheating.

Further, for example, when the fluorescent lamp 16 is cut off during lighting or has a poor contact, the output transformer becomes in a no-load state, the induced voltage of the secondary winding rises, and the quaternary winding The induced voltage also rises. When the induced voltage of the quaternary winding exceeds a predetermined threshold value, it is detected by the thyristor, the power supply to the control circuit is cut off for a certain period, and then self-recovers and shifts to the starting state. Since this abnormal state can be visually observed, if the fluorescent lamp 16 is replaced, the normal state is restored.

[0024]

As described above, in the fluorescent lamp stabilizing device of the present invention, the bridge-connected MOSFETs are alternately turned on and off at a frequency higher than the resonance frequency at the time of start-up, so that the resonance frequency at which the fluorescent lamp is most likely to light up. From higher frequencies,
Since the fluorescent light shifted to the most efficient resonance frequency,
While maintaining stable lighting at the time of starting the fluorescent lamp, it is possible to shift to a state of good luminous efficiency and continue lighting the hand.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an oscillation frequency and an output voltage of a stabilizer for a fluorescent lamp according to the present invention.

FIG. 2 is a circuit diagram showing an embodiment of a fluorescent lamp stabilizer according to the present invention.

[Explanation of symbols]

 1 Stabilizer for Fluorescent Lamp 2 AC Power Supply 3 Rectifier 6 DC Power Supply 11 Switching Element 12 Switching Element 14 Transformer 16 Fluorescent Lamp 20 Control Circuit 50 Capacitor

Claims (4)

[Claims] 1. A rectifier circuit for converting an AC power supply into a DC power supply, a transformer whose primary winding is connected to the DC power supply via a switching element, and an ON / OFF control of the switching element to induce the transformer. A control circuit that shifts the generated frequency from a higher one to a lower one in a steady state, and a fluorescent lamp in which a secondary winding of this transformer is connected to one end of each filament and a current flows between these filaments when lighting, A stabilizer for a fluorescent lamp, which is connected between the other ends of these filaments and comprises a resonance capacitor that cooperates with the secondary winding and the filament to form a closed circuit. 2. The stabilizer for a fluorescent lamp according to claim 1, wherein the transformer is provided with a tertiary winding capable of supplying electric power to the control circuit. 3. The stabilizing device for a fluorescent lamp according to claim 1, wherein the transformer is provided with a quaternary winding capable of detecting the presence or absence of the fluorescent lamp or an abnormal condition. 4. The preheating winding connected to one filament of the fluorescent lamp is provided in the transformer.
Alternatively, the fluorescent lamp stabilizing device according to the item 2.