JPH0432198A - Fluorescent lamp lighting circuit - Google Patents

Abstract

PURPOSE:To arbitrarily set oscillation frequency independently by providing an excitation circuit for driving a semiconductor element for switching. CONSTITUTION:A connecting point P1 in the middle of two FET transistors TR1, TR2, channels of which are connected in series to a DC power source DC, and another connecting point P2 in the middle of two capacitors C2, C3 are connected to each other via a coil L4 of an output transformer T2 provided with a coil L6 constituting an inside power source and a coil L5 connected to electrodes disposed at both ends of a fluorescent tube 3. The gate terminals of the FET transistors TR1, TR2 are connected to two outputs each having a phase reverse to that of an excitation circuit 4, respectively. The excitation circuit 4 comprises an IC circuit IC1, a transformer T1 wherein two outputs from the IC circuit IC1 are connected to a coil L1, outside attached adjusting resistor R1 and a capacitor C1 for determining oscillation frequency of the IC circuit IC.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a lighting circuit for a fluorescent lamp apparatus using a fluorescent tube, and more particularly to an improvement in excitation means for an inverter type lighting circuit.

[Prior art]

Inverter-based lighting circuits are used to light fluorescent tubes because they cause less flickering during use, are not affected by power supply frequencies that vary by region, and are highly power efficient. Such conventional inverter circuits for fluorescent lamps obtain high-frequency AC power by switching DC power obtained by rectifying and smoothing AC power using semiconductor elements, and use the switching elements as part of the oscillation circuit. It was an automatic method. An example of such a conventional automatic lighting circuit will be explained with reference to the drawings.

FIG. 4 is a circuit diagram showing the configuration of an automatic lighting circuit 30 for lighting this type of fluorescent tube 31. This is the rectifier and smoothing circuit 2, and the NPN transistor Q that performs oscillation operation.
1, Q2, a transformer T31 having windings L31 to L34 for commutation and power conversion, resistors R31 and R32 for biasing the transistors Q1 and Q2, a fluorescent tube 3, and a series-connected winding of the transformer T31. L31, L3
It consists of a capacitor C4 connected in parallel with 2. This lighting circuit 30 consists of constants of transistors Q1 and Q2 and a winding L3.
The inverter operates by oscillating at a frequency determined by the electrical constants of L1 to L33.

[Problems with conventional technology]

By the way, the above-mentioned conventional automatic oscillation type lighting circuit has problems in that it is difficult to increase the frequency (which leads to miniaturization) and it is difficult to increase the power. Furthermore, the oscillation frequency is influenced by the individual characteristics of the parts used and the fluorescent tubes, so there are large variations, and as a result, the circuit current (fluorescent tube current) varies, resulting in power consumption and brightness, which results in a lack of uniformity in the product. There was a problem.

In addition, the oscillation frequency changes depending on the power supply voltage, so the oscillation frequency changes from moment to moment according to the pulsations in the power supply voltage.As a result, the spectrum of the electromagnetic noise generated is not uniform, making it difficult to take noise countermeasures. There were also problems.

Furthermore, during a transition such as when the power is turned on, there is a possibility of abnormal oscillation, and in the worst case, there is a risk that the circuit will be damaged. Additionally, there were other problems, such as the inability to freely select a desired oscillation frequency due to component limitations, and the difficulty in designing circuit constants of transformers and the like.

By the way, in a general inverter type lighting circuit for fluorescent lamp equipment, the output voltage (voltage at both ends of the fluorescent tube) is determined by the relationship between the switching frequency f and the resonance frequency determined by the output transformer and the seven capacitors connected to it. changes depending on the load condition, and the relationship is as shown in the graph shown in FIG.

In other words, when the fluorescent tube is properly lit (song MA), the output voltage of the inverter circuit applied to both ends of the fluorescent tube is approximately constant (Vz
V: about 1), and at the resonance frequency of the output section 12, the output of the inverter circuit shows a minimum value 2. However, at this time, the output section is in a resonant state and the maximum power is supplied to the fluorescent tube, and the efficiency is high, so operation at this frequency f2 is desirable. However, under no load, that is, with the fluorescent tubes removed (curve B), the output of the inverter circuit increases to V at the resonance frequency f2 due to the resonance of the output section. For this reason, the conventional lighting circuit for fluorescent lamp equipment has the problem that the inverter circuit is destroyed by the resonance current at this time.

[Means for solving problems]

The purpose of the present invention is to provide a new lighting circuit that solves the problems of the conventional lighting circuits described above.For this purpose, the present invention provides a lighting circuit for inverter-type fluorescent lamps that uses switching. It is configured as a separately excited type, and is equipped with an excitation circuit that drives and switches the semiconductor element for use.

Further, in another invention of the present application, the excitation circuit first starts an oscillating operation using a starting power source based on the DC power source at startup, and continues the subsequent oscillating operation exclusively using an internal power source based on the resulting output of the high frequency AC power source. Configure the lighting circuit for fluorescent lamp fixtures so that:

In still another aspect of the invention, a lighting circuit for a fluorescent lamp is provided with an oscillation frequency control circuit that controls and changes the oscillation frequency of the excitation circuit in accordance with the voltage applied to both ends of the fluorescent tube.

[Embodiments of the invention]

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram of a lighting circuit 1 for fluorescent lamp equipment, which is an embodiment of the present invention. In the figure, 2 is a rectifying and smoothing circuit that is connected to the input AC power source AC and rectifies the AC to obtain the DC power source DC. TRI, TR2 are two FET transistors whose channels are connected in series to this DC power supply DC.
It is R2.

Similarly, two capacitors C2 and C3 connected in series are connected to the DC power supply DC. A connection point P1 between the two FET transistors TRI and TR2 and a connection point P2 between the two capacitors C2 and C3 are connected via a winding L4 of the output transformer T2. This transformer T2 also includes a winding L6 that constitutes an internal power source, which will be described later, and a winding L5 that is connected to both end electrodes of the fluorescent tube 3.

Both ends of the winding at both end portions of the winding L5 (i.e., the winding L
5 (ends and intermediate taps) are connected to the filament of the fluorescent tube 3, respectively. Further, a capacitor C4 is connected between the two intermediate taps (therefore, between the filaments).

Further, the gate terminals of the FET transistors TRI and TR2 are respectively connected to two outputs of the excitation circuit 4 having opposite phases. This excitation circuit 4 includes an IC circuit ICI, this IC
A transformer T with two outputs from I connected to winding L1
1. External components for determining the oscillation frequency of the ICI include adjustment resistors R1 and C1. The outputs from the other two windings L2 and L3 of the transformer T1 are connected to the above-mentioned excitation circuit 4.
The two outputs having opposite phases are connected to the gate terminals of the FET transistors TRI and TR2. This excitation circuit 4 is supplied with electric power from a low voltage power source which will be described later.

The above-described lighting circuit for fluorescent lamp equipment of the present invention includes an excitation circuit 4 for driving switching-like transistors TRI and TR2 independently from other parts, so the excitation frequency of this excitation circuit 4 ( Since the oscillation frequency (oscillation frequency) can be independently set arbitrarily, the overall design is simplified and the degree of freedom in selecting parts used is also expanded.

By the way, the voltage of the power supply required by the excitation circuit 4 is much lower than the voltage supplied to other parts,
The aforementioned DC power source DC cannot be used as is, and a separate power source is required.

Of course, a dedicated power supply circuit may be prepared, but the overall configuration becomes complicated and this is not preferable. Therefore, in this embodiment, a low voltage power supply produced from the above-mentioned DC power supply DC and a low-voltage power supply produced by the above-mentioned winding L6 of the transformer T2 are used. The structure is such that it can be used by skillfully switching between the voltage power source and the voltage source. Hereinafter, the power source portion for the excitation circuit 4, which is another invention of the present application, will be described in detail.

In FIG. 1, 5 is a starting power source that operates only at the initial stage (at startup) when the lighting circuit for fluorescent lamp equipment is energized.
It consists of a transistor TR3 whose collector terminal is connected to the DC power supply DC, a diode D2 whose anode terminal is connected to its emitter terminal, a series circuit of a resistor R2 and a constant voltage diode D1 connected to the DC power supply DC, An intermediate connection point between the resistor 2 and the diode D1 is connected to the base terminal of the transistor TR3. Note that the cathode side of the diode D2 is an output and is connected to the excitation circuit 4 as a power source.

The output voltage of this power supply circuit is determined depending on the characteristics of the voltage regulator diode DI, for example, a Zener voltage of 12V is applied to Dl.
If a constant voltage diode is used, the output voltage will be a little less than 12V. This starting power source 5 is essential at the time of starting up because it can supply power to the excitation circuit 4 even when the lighting circuit 1 for fluorescent lamp equipment is not yet in operation, but on the other hand, it is generally a high voltage DC power source Since the voltage is lowered to produce a lower voltage, the loss in this part is large and a large amount of heat is generated. Therefore, it is not possible to continue operation for a long time using small and small capacity parts, but in the present invention, small parts can be used in conjunction with the internal power supply 6 described below.

The internal power source 6 is also a power source for the excitation circuit 4, but is a power source that is continuously used while the lighting circuit 1 for fluorescent lamp equipment is in operation. This internal power supply 6 is connected to the transformer T
The AC voltage induced in the winding L6 of No. 2 due to inverter operation is used, and D4 and D5 rectify this AC voltage.
, a smoothing circuit consisting of a coil L7 and a capacitor C5 connected to these outputs, an IC regulator IC2 that makes the output of this smoothing circuit a predetermined voltage, and a diode D3 whose anode terminal is connected to this output.

The cathode terminal of this diode D30 is connected to the cathode terminal of the diode D2 mentioned above, and the excitation circuit 4
Used as a power source. That is, the cathode terminals of the two diodes D2 and D3 are connected to each other, and power is supplied to the excitation circuit 4 from this connection point.

Briefly explaining the operation of the lighting circuit 1 for fluorescent lamp equipment of this embodiment, when the rectifying and smoothing circuit 2 is energized, a DC power supply DC is obtained, and a voltage is applied to the series transistors TRI and TR2 and the starting power supply 5. be done. Therefore, the starting power supply 5 supplies the excitation circuit 4 with a power of about 12V, for example. Therefore, the excitation circuit 4 starts an oscillation operation and drives the transistors TRI and TR2 alternately.
An alternating current equal to the oscillation frequency of the excitation circuit 4 flows through the winding L4, and a high frequency alternating current is obtained through the winding L5, eventually lighting up the fluorescent tube 3. At the same time, an alternating current voltage is also obtained in the winding L6, so that a power supply voltage slightly higher than the output voltage (12V) of the starting power supply 5 is obtained from the diode D3.

In this case, since the diode D2 is reverse biased, power is no longer supplied from the starting power supply circuit 5, and therefore the power consumption in this circuit and the accompanying heat generation are extremely reduced, and as a result, the starting power supply circuit 5 Thermal damage is prevented.

In this way, the output voltage of the internal power supply circuit 6 is set to be slightly higher than the output voltage of the starting power supply circuit 5, so the diode switch makes the circuit simple and compact, but the loss is large, so it can be used for a long time. Startup power supply circuit 5 that cannot withstand
However, as soon as the internal power supply circuit 6 starts operating, the operation automatically stops, and the internal power supply circuit 6 with low loss continuously supplies power to the excitation circuit 4 during operation.

Note that the excitation circuit 4 only needs to supply power for driving the gate of the MOS transistor, and has a frequency of 100 kHz.
In the case of front and rear switching frequencies, about 30mW is sufficient.
The excitation circuit could also be configured with a simple CR/IC oscillation circuit.

Next, at the resonant frequency f2 found in the above-mentioned inverter-type fluorescent lamp lighting circuit, the output of the inverter circuit rises to ■1 due to the resonance of the output section, and the resonant current at this time destroys the inverter circuit. Further inventions of the present application for preventing storage will be described.

FIG. 2 shows a lighting circuit 10 for fluorescent lamp equipment to which this invention is applied.
FIG. 2 is a circuit diagram showing one embodiment of the present invention. Description of the same parts as in FIG. 1 will be omitted. In addition to the parts shown in the previous embodiment of FIG. 1, this embodiment adds voltage detection means 7 and oscillation frequency control means 8. The pressure detection means 7 includes a winding L8 newly installed in the transformer T2 of the output section, and electrical components connected to the output of this winding L8, namely a resistor R7 and a diode D6 connected in parallel, and a base terminal and an emitter terminal. It consists of an NPN (NPN) transistor TR4 connected to it and a resistor R6 connected in series thereto. The diode D
The anode terminal of the transistor TR4 is connected to the emitter terminal of the transistor TR4, and is also connected to the ground side terminal of the winding L8. Further, the collector terminal of the transistor TR4 becomes the output (P3) of the voltage detection means 7.

The oscillation frequency control means 8 includes a resistor R3 connected in series to the ground side terminal of the resistor R1 for configuring the excitation circuit 4 described above and determining the oscillation frequency, and an FET whose channel is connected in parallel to the resistor R1. A transistor TR5, a resistor R4 connected between the gate terminal of the transistor TR5 and the power supply, a capacitor C6 connected between the gate terminal of the transistor TR5 and the ground, one end connected to the gate terminal of the transistor TR5, and the other end connected to the input terminal ( P4).

In this lighting circuit 10 for fluorescent lamp equipment, when the power is turned on, T
Since R5 is in the OFF state, the oscillation frequency is determined by (R1+R3) and C1. This frequency f1 is set to a value different from the resonance frequency f2 of the output section. The lighting circuit 10 for fluorescent lamp equipment starts inverter operation at this frequency f. Then, after a time period determined by the time constants of resistors R4 and 06 has elapsed, transistor TR5 is turned on, and excitation circuit 4 now operates at a frequency determined by R1 and CI. The values of R1 and C1 are set so that the frequency at this time becomes the resonant frequency f2. Therefore, sufficient power is supplied to the fluorescent tube 3 in this state. at the same time,
The voltage applied to the fluorescent tube 3 is detected from the winding L8 of the transformer T2, and the corresponding voltage is applied to the transistor TR5 of the oscillation frequency control circuit 8. If this detected voltage is high, the transistor TR5 is turned off, and if this detected voltage is low, it is turned on.

That is, if the detected voltage is high, the oscillation frequency is f.

If it's low, go to f2.

Therefore, before the fluorescent tube 3 lights up when the power is turned on, the filament is not heated and there is almost no load, and the frequency of fl in the graph of FIG. voltage.

Eventually, when the filament is sufficiently heated and the fluorescent tube 3 lights up, the voltage drops to V4 (curve A).

Therefore, the output of the voltage detection means 7 changes and the oscillation frequency increases to f2.
change to If you set the detection voltage to ■8 between ■3 and ■4 in this way, when the fluorescent tube 3 lights up,
Turn on the transistor TR5 after a time determined by the constants of R4 and C6, excite it at the frequency f2 determined by R1 and C1 (move the operating point to f2 on the graph), and light the fluorescent tube 3 with regular power. I can do it. Even if a no-load condition occurs, such as when the fluorescent tube 3 is not installed or when the fluorescent tube 3 is removed for replacement without turning off the power, the operating frequency shifts to f, and the inverter is activated by suppressing the output voltage. This ensures that no load is placed on the circuit.

Furthermore, even if the fluorescent tube 3 gradually deteriorates during use and approaches a no-load state, the operating point moves to f, and the inverter circuit is protected.

Further, since the fluorescent tube 3 is turned on after preheating is completed when the power is turned on, the blackening phenomenon is minimized, which has the effect of significantly extending the life of the fluorescent tube 3. Another advantage is that even if there is a wiring error during construction, there will be no vibrations that could destroy the inverter circuit.

〔Effect of the invention〕

The above-described lighting circuit for fluorescent lamp equipment of the present invention includes an excitation circuit 4 for driving switching-like transistors TRI and TR2 independently from other parts, so the excitation frequency of this excitation circuit 4 ( Since the oscillation frequency (oscillation frequency) can be independently set arbitrarily, the overall design is simplified and the degree of freedom in selecting parts used is also expanded.

Furthermore, when the excitation circuit starts up, it first starts an oscillating operation using a starting power source based on the DC power source, and continues the subsequent oscillating operation exclusively using an internal power source based on the output of the high frequency AC power source obtained as a result. In this case, the entire lighting circuit for fluorescent lamp equipment is constructed in a small size because thermal damage is prevented even if the startup power supply circuit is configured with small-capacity components without power consumption and associated heat generation in the startup power supply circuit section. can.

Furthermore, since it is equipped with an oscillation frequency control circuit that controls and changes the oscillation frequency of the excitation circuit according to the voltage applied to both ends of the fluorescent tube, maximum power can be supplied when the fluorescent tube is normally lit. When there is no load or a light load, it is possible to change the oscillation frequency and lower the output voltage to prevent destruction of the lighting circuit for fluorescent lamp equipment.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a lighting circuit for fluorescent lamp equipment according to the present invention; FIG. 2 is a circuit diagram showing an embodiment of a lighting circuit for fluorescent lamp equipment according to another invention of the present application; The figure shows the relationship between the oscillation frequency and the output voltage of the lighting circuit for a fluorescent lamp according to the present invention, and FIG. 4 shows a circuit diagram of a conventional lighting circuit for a fluorescent lamp. 1.10...Lighting circuit for fluorescent lamp equipment, 3...Fluorescent tube, 4...Excitation circuit, 5...Starting circuit, 6...
Internal power supply, 8...Oscillation frequency control circuit.

Claims (1)

[Scope of Claims] [1] An inverter-type fluorescent lamp in which a high-frequency AC power source is obtained by switching a DC power source obtained by rectifying and smoothing an AC power source using semiconductor elements, and lighting a fluorescent tube with this high-frequency AC power source. What is claimed is: 1. A lighting circuit for separately excited fluorescent lamp fixtures, comprising: an excitation circuit for driving and switching the semiconductor element. [2] At startup, the excitation circuit first starts an oscillating operation using a starting power source based on the DC power source, and continues the subsequent oscillating operation exclusively using an internal power source based on the output of the high frequency AC power source obtained as a result. Claim 1
Lighting circuit for fluorescent light fixtures as described. [3] The fluorescence according to claim 1 or 2, further comprising an oscillation frequency control circuit that controls and changes the oscillation frequency of the excitation circuit in accordance with the voltage applied to both ends of the fluorescent tube. Lighting circuit for lighting equipment.