JP2756540B2 - Lighting circuit for fluorescent lamp - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a lighting circuit for a fluorescent lamp apparatus using a fluorescent tube, and more particularly to an improvement of an inverter type lighting circuit.

(Prior art)

In order to light the fluorescent tube, an inverter-type lighting circuit is used because flicker during use is small, the power supply frequency is not affected by a region, and power efficiency is good. Such a conventional inverter circuit for fluorescent lamps uses a semiconductor element to switch a DC power obtained by rectifying and smoothing an AC power to obtain a high-frequency AC power, and uses the switching element as a part of an oscillation circuit. It was self-excited. An example of such a conventional self-excited lighting circuit will be described with reference to the drawings.

FIG. 4 is a circuit diagram showing a configuration of a self-excited lighting circuit 30 for lighting this kind of fluorescent tube 31. This is a rectifying and smoothing circuit 2, NPN transistors Q1 and Q
2.Transformer T with windings L31-L34 for light current and power conversion
31. It comprises resistors R31 and R32 for biasing the transistors Q1 and Q2, the fluorescent tube 3, and a capacitor C4 connected in parallel to the series-connected windings L31 and L32 of the transformer T31. The lighting circuit 30 oscillates at a frequency determined by the constants of the transistors Q1 and Q2 and the electrical constants of the windings L31 to L33 and performs an inverter operation.

Such a self-oscillation type lighting circuit has a problem that it is difficult to increase the frequency (which leads to downsizing) and to increase the power. Furthermore, the oscillation frequency varies depending on the individual characteristics of the components used and the fluorescent tube, causing a large variation. The circuit current (fluorescent tube current) varies accordingly, resulting in a difference in power consumption and brightness, resulting in a lack of uniformity of the product. There are difficulties. In addition, the oscillation frequency changes depending on the power supply voltage, so the oscillation frequency changes every moment according to the pulsation of the power supply voltage, and the spectrum of the generated electromagnetic noise is not uniform, so it is difficult to take noise countermeasures. There are drawbacks. Furthermore, during a transition such as when the power is turned on, there is a possibility of abnormal oscillation. In the worst case, the circuit may be damaged. In addition, there are also disadvantages in that a target oscillation frequency cannot be freely selected due to the restriction of parts, and that it is difficult to design circuit constants such as a transformer.

FIG. 1 is a circuit diagram showing an example of a separately-excited inverter-type lighting circuit 1 for a fluorescent lamp appliance which has solved the above-mentioned problems.
This circuit has a configuration in which an excitation circuit is separately provided and the driving power supply is used both for the commercial power supply and for the output of the inverter. In the figure, reference numeral 2 denotes a rectifying and smoothing circuit which is connected to an input AC power supply AC and rectifies the AC to obtain a DC power supply DC. TR
Reference numerals 1 and TR2 denote two FET transistors TR1 and TR2 whose channels are connected in series to the DC power supply DC. Similarly, two capacitors C2 and C3 connected in series are connected to the DC power supply DC. An intermediate connection point P1 between the two FET transistors TR1 and TR2 and an intermediate connection point P2 between the two capacitors C2 and C3 are connected via a winding L4 of an output transformer T2. The transformer T2 is also provided with a winding L6 constituting an internal power supply to be described later and a winding L5 connected to both end electrodes of the fluorescent tube 3. Both ends of the winding at both ends of the winding L5 (that is, the end of the winding L5 and the intermediate tap) are respectively connected to the filament of the fluorescent tube 3. A capacitor C4 is connected between the two intermediate taps (and thus between the filaments).

Further, the gate terminals of the FET transistors TR1 and TR2 are connected to two outputs of the excitation circuit 4 having opposite phases. The excitation circuit 4 includes an IC circuit IC1, a transformer T1 having two outputs from the IC1 connected to a winding L1, and external adjustment resistors R1 and C1 for determining the oscillation frequency of the IC1. The outputs from the other two windings L2 and L3 of the transformer T1 are connected to the gate terminals of the FET transistors TR1 and TR2 as two outputs whose phases of the excitation circuit 4 are opposite to each other. Power is supplied to the excitation circuit 4 from a low-voltage power supply described later.

Since the fluorescent lamp lighting circuit includes the excitation circuit 4 for driving the switching transistors TR1 and TR2 independently of the other parts, the excitation frequency (oscillation frequency) of the excitation circuit 4 is independent. Can be set arbitrarily, so that the overall design is simplified and the degree of freedom in selecting the parts to be used is 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, and the above-described DC power supply DC cannot be used as it is, and requires a separate power supply. Become. Of course, a dedicated power supply circuit may be prepared, but since the entire configuration is complicated and not preferable, in this embodiment, the low-voltage power supply generated from the DC power supply DC and the low-voltage power supply generated by the winding L6 of the transformer T2 are used. The configuration is such that both the power supply and the voltage power supply are skillfully switched. Hereinafter, a power supply portion for the excitation circuit 4 according to another invention of the present application will be described in detail. In FIG. 1, reference numeral 5 denotes a start-up power supply which operates only at the initial stage (at the start-up) when the lighting circuit for a fluorescent lamp is energized. The transistor TR3 has a collector terminal connected to the DC power supply DC, and an anode is connected to the emitter terminal. A terminal D is connected, and a series circuit of a resistor R2 and a constant voltage diode D1 connected to a DC power supply DC, and an intermediate connection point between the resistor 2 and the diode D1 is connected to a base terminal of the transistor TR3. I have. The cathode side of the diode D2 is an output and is connected to the excitation circuit 4 as a power supply. The output voltage of this power supply circuit depends on the characteristics of the constant voltage diode D1. For example, if a constant voltage diode having a Zener voltage of 12V is used for D1, the output voltage will be slightly less than 12V. The starting power supply 5 is indispensable at the time of starting because it can supply power to the excitation circuit 4 even when the lighting circuit 1 for a fluorescent lamp apparatus is not operating yet. The breakage in this area is large and is accompanied by a large amount of heat generation, because a lower voltage is generated by lowering the voltage. Therefore, the operation cannot be continued for a long time using small and small-capacity components. However, in this circuit, small components can be used in combination with the internal power supply 6 described below.

The internal power supply 6 is also a power supply for the excitation circuit 4, but is a power supply that is continuously used while the lighting circuit for fluorescent lamp fixture 1 is operating. This internal power supply 6
The AC voltage induced by the inverter operation is used in the winding L6 of T2, and a smoothing circuit composed of D4 and D5 for rectifying the AC voltage, a coil L7 and a capacitor C5 connected to these outputs, IC that sets the output of a circuit to a specified voltage
It consists of a regulator IC2 and a diode D3 whose anode is connected to this output. The cathode circuit of the diode D3 is connected to the cathode terminal of the diode D2 and used as a power source of the excitation circuit 4. 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.

The operation of the lighting circuit 1 for a fluorescent lamp apparatus will be briefly described. 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 TR1 and TR2 and the starting power supply 5. Therefore, a power of, for example, about 12 V is supplied from the starting power supply 5 to the excitation circuit 4. Therefore, the exciting circuit 4 starts the oscillating operation and alternately drives the transistors TR1 and TR2. Therefore, an alternating current equal to the oscillating frequency of the exciting circuit 4 flows through the winding L4 of the transformer T2, and a high-frequency AC is obtained through the winding L5. As a result, the fluorescent tube 3 is turned on. Winding at the same time
Since an AC voltage is also obtained at L6, a power supply voltage slightly higher than the output voltage (12V) of the starting power supply 5 is obtained from the diode D3. When this happens, the diode
Since D2 is reverse-biased, no power is supplied from the start-up power supply circuit 5, so that the power consumption and the accompanying heat generation in this circuit portion are extremely reduced, thereby preventing the start-up power supply 5 from being thermally destroyed. You.

Since the output voltage of the internal power supply circuit 6 is set to be slightly higher than the output voltage of the start-up power supply circuit 5, the diode switch is simple and small, but has a large loss due to the diode switch. When the internal power supply circuit 6 operates, the operation of the start-up power supply circuit 5 which does not withstand the operation automatically stops immediately, and the power of the excitation circuit 4 is continuously supplied during operation by the internal power supply circuit 6 having a small loss.

The excitation circuit 4 only needs to be able to supply power for driving the gate of the MOS transistor. A switching frequency of about 100 kHz requires only about 30 mW, and the excitation circuit is also composed of a simple CR / IC oscillation circuit.

Circuits similar to those described above are described in, for example,
No. 99 (Japanese Utility Model Application No. 61-1000084; already proposed 1), a configuration in which an excitation circuit is separately provided and its driving power supply is generated by feedback from the main power supply of the inverter and the commercial frequency output of the load. Discharge lamp ballast is disclosed.

By the way, in a general inverter type lighting circuit for a fluorescent lamp fixture, the output voltage V (the voltage across the fluorescent tube) is
The relationship between the switching frequency f and the resonance frequency determined by the output transformer and the capacitor connected to the output transformer, and furthermore, the relationship changes according to the load condition, and the relationship is as shown in the graph of FIG.

That is, the state where the fluorescent tube is properly lit (curve A)
Then, the output voltage V of the inverter circuit applied to both ends of the fluorescent tube
Is substantially constant regardless of the oscillation frequency f of the inverter circuit (V ₂ −
The output of the inverter circuit at the resonant frequency f ₂ of are output section a V about ₃₎ shows a very small value V _2. However, this time is supplied maximum power to the fluorescent tube at the output resonant state, the operation for efficient at this frequency f ₂ is desirable.

[Problems of the prior art]

By the way, in the conventional inverter-type fluorescent lamp lighting circuit as described above, a constant high voltage sufficient to cause a discharge phenomenon consistently when energized is applied to both ends of the fluorescent tube, and the residual heat current is applied to the filament. Is flowing. That is, immediately after the power is turned on, the filament is not sufficiently heated, and the high voltage for discharge is applied from the time when the thermoelectrons are not supplied into the fluorescent tube, and the thermoelectrons generated by heating the filament are reduced to the discharge critical amount. Upon reaching, discharge is started immediately at this point. This is considered to be an advantage of the inverter type fluorescent lamp that lights immediately after energization, but the discharge is forcibly started between the electrodes (filaments) in the atmosphere of the amount of thermionic electrons which is not enough. As a result, the filament surface deteriorates and accelerates the thinning of the filament.As a result, the life of the filament is shortened, and the blackening phenomenon is promoted.As a result, the life of the fluorescent tube is shortened. Has shortened the service life. In addition, even if the filament does not break, the thermoelectron supply capacity of the filament deteriorates,
At the above-mentioned fixed high voltage, discharge cannot be started and the lamp is not lit, so that the fluorescent tube cannot be used. As described above, in the general inverter-type fluorescent lamp lighting circuit, there is a first problem that the fluorescent tube is easily deteriorated due to the fixed frequency.

As a configuration corresponding to this point, for example, JP-A-63-17
No. 5389 (hereinafter also referred to as Proposal 2) discloses a configuration in which the residual heat of a fluorescent tube is started, and after a certain period of time, the output frequency of a high-frequency AC power supply is shifted to a frequency that increases the output. In particular, the proposal discloses a technique in which the oscillation frequency smoothly changes to the lighting frequency with the lapse of time after the completion of the preheating, whereby a sufficient preheating current can be obtained during the preheating time. In particular, the proposal proposes that a large stress is not applied to the switching element of the inverter circuit at the time of starting. That is, in the existing proposal, by having the timer circuit, sufficient preheating is performed at a constant frequency lower than the resonance point of the drive circuit for a fixed time after the power is turned on. After a certain period of time, the oscillation frequency gradually changes as intended by the CR circuit, and the discharge lamp is turned on during the change of the frequency during this period.
Then, even after lighting, the frequency continues to shift, and operation is continued at one fixed oscillation frequency that is higher than the resonance point of the drive circuit finally determined by the fixed resistance. In this way, the purpose of eliminating a sudden change in frequency and preventing an excessive stress from being applied to the switch element is achieved.

As a second drawback of the conventional circuit, for example, in the conventional circuit and the like in FIG. 4 the first-mentioned, the in state lighting circuit is off a no-load or fluorescent tubes (curve B) of the resonance frequency f ₂ inverter the output of the circuit rises to V ₁ for the resonance of the output unit. Therefore, there is a phenomenon that the inverter circuit is broken by the resonance current at this time. This point is the same in the above-mentioned proposal 2 (Japanese Patent Application Laid-Open No. 63-175389). The fixed time after power-on is fixed at a constant frequency lower than the resonance point of the drive circuit depending on the timer circuit. Although the temperature changes smoothly after sufficient heat is applied for a long time, the light-emitting device continues the lighting operation by shifting to the oscillation frequency higher than the resonance point through the resonance point frequency of the drive circuit. In other words, the output always passes through the resonance point,
If the lighting circuit has no load, the resonance current may cause an excessive load or damage to the inverter circuit.

To avoid the second difficulty, it is effective to limit the output when no load is applied. For example, Japanese Unexamined Patent Publication No. 63-175394 (hereinafter also referred to as "proposed 3") discloses a non-load detecting circuit and an end-of-life detecting circuit for a discharge lamp lighting device using a separately excited current resonance type inverter circuit. An oscillation control circuit that reduces the oscillation output of the inverter circuit by a signal from the circuit, and an inverter stop circuit that stops the operation of the inverter circuit when an overcurrent flows when the output is reduced. This allows
It does not function at all under normal conditions.It detects the connection / replacement of the discharge lamp at no load or at the end of the life of the discharge lamp without using the switch on the non-power supply side of the discharge lamp used before, and limits the output of the inverter circuit. Alternatively, it is disclosed to cancel. The output limitation of the inverter circuit in the above proposal is performed by setting two separate oscillation frequencies and completely switching between them.

[Problems to be solved by the invention]

The present invention has been made in consideration of the actual situation of the conventional inverter-type fluorescent lamp lighting circuit as described above, and has a simple configuration, but has been described in the aforementioned conventional circuit. A fluorescent tube and a lighting device that simultaneously solves the first and second difficulties, that is, the problem that the fluorescent tube filament is easily damaged and the service life is shortened, and also has a no-load protection function. It is an object of the present invention to newly propose a lighting circuit for a fluorescent lamp which has excellent protection performance of the circuit itself and further improved reliability.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, a DC power supply obtained by rectifying and smoothing an AC power supply is switched by a semiconductor element driven by an excitation circuit to obtain a high-frequency AC power supply, and the fluorescent tube is lit by the high-frequency AC power supply. In a lighting circuit for a fluorescent lamp appliance of a separately excited inverter type, a voltage detection unit that outputs an analog signal corresponding to a voltage value applied to both ends of the fluorescent tube; and an oscillation frequency of the excitation circuit, Controlling and changing according to the output, before powering on the fluorescent tube and before turning on the fluorescent tube, set the frequency to suppress the output voltage of the high-frequency AC power supply low according to the output of the voltage detection means, and start the preheating of the fluorescent tube. After a lapse of a certain period of time, the output voltage of the high-frequency AC power supply is shifted to a higher frequency, and the output of the voltage detector is changed in response to lighting of the fluorescent tube. And an oscillating frequency control circuit for changing the output voltage to a frequency corresponding to the specified voltage.

Further, at the time of startup, the excitation circuit starts an oscillating operation by a starting power supply based on the DC power supply, and the subsequent oscillating operation is continued exclusively by an internal power supply based on an output of the high-frequency AC power supply obtained as a result. Is also good.

As a preferred configuration example of the voltage detecting means 7, a winding L8 newly provided in the transformer T2 of the output section, and a winding L8
Each resistor connected in parallel with the output of the
R7 and the cathode terminal were connected to the resistor R6, the anode terminal side was grounded to the diode D6, the base terminal was connected to the resistor R6, and the emitter terminal was connected to the anode terminal of the diode D6.
NPN transistor TR4 and said transistor
The collector terminal of TR4 is set as an output (P3), and the oscillation frequency control means 8 includes a resistor R3 connected in series to a ground terminal of a resistor R1 for configuring the excitation circuit 4 and determining an oscillation frequency; FET transistor TR5 whose channel is connected in parallel with this resistor R1, resistor R4 connected between the gate terminal of this transistor TR5 and the power supply, capacitor C6 connected between the gate terminal of transistor TR5 and ground, and the gate terminal of transistor TR5 And a resistor R5 connected at one end to the output of the voltage detecting means 7 at the other end.

(Example of the invention)

 Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 2 shows a lighting circuit 10 for a fluorescent lamp apparatus to which the present invention is applied.
FIG. 3 is a circuit diagram showing one embodiment. The description of the same parts as in FIG. 1 is omitted. In this circuit, elevated at this time at the resonant frequency f ₂ as seen in the fluorescent lamp fixture for lighting circuit of the inverter system in addition to suppressing the degradation of the fluorescent tube and V ₁ for the resonance of the output the output of the inverter circuit This prevents the inverter circuit from being destroyed by the resonance current.

In the embodiment, in addition to the parts shown in FIG. 1, a voltage detecting means 7 and an oscillation frequency controlling means 8 are added. The voltage detecting means 7 is a winding newly provided in the transformer T2 of the output section.
L8 and electrical components connected to the output of the winding L8, namely, a resistor R7 and a diode D6 connected in parallel, an NPN transistor TR4 connected to a base terminal-emitter terminal, and a resistor R6 connected in series to these. Become. The anode terminal of the diode D6 is connected to the emitter terminal of the transistor TR4 and to the ground terminal of the winding L8. The collector terminal of the transistor TR4 becomes the output (P3) of the voltage detecting means 7. With the voltage detecting means 7 having such a configuration, an analog signal corresponding to the voltage value applied to both ends of the fluorescent tube can be obtained (voltage detection).

The oscillating frequency control means 8 comprises a resistor R3 connected to the ground terminal of the resistor R1 for determining the oscillation frequency, which constitutes the excitation circuit 4 described above, and an FET having a channel connected in parallel to the resistor R1. One end is connected to the transistor TR5, the resistor R4 connected between the gate terminal of the transistor TR5 and the power supply, the capacitor C6 connected between the gate terminal of the transistor TR5 and the ground, and the other end is connected to the input terminal ( P4).

The circuit is configured to be driven in a direction in which the transistor TR5 is turned off when the analog signal (detection voltage) obtained from the voltage detection means 7 is sufficiently high, and in a direction in which the transistor TR5 is turned on when the analog signal is low. That is, if the detection voltage is high, the oscillation frequency is f1
If the output voltage is low, the operation is directed to f2, and the operation is balanced at an operating point where the output voltage is constant (output voltage VX: frequency fx). When the detection voltage is sufficiently low, the transistor TR4 does not operate and hardly functions. Supplementary explanation of the operation of the voltage detecting means 7 is as follows. The charge stored in the capacitor C6 is discharged via the resistor R5 every half cycle of the output to make the transistor
It operates to lower the potential of the gate terminal of TR5.

In the lighting circuit 10 for a fluorescent lamp device, when the power is turned on, the TR
Since 5 is in the OFF state, the oscillation frequency is determined by (R1 + R3) and C1. This frequency f1 is the resonance frequency f2 of the output part.
The output voltage is set to be lower at a value different from. Fluorescent lighting fixtures for lighting circuit 10 is preheated starts inverter operating at this frequency f ₁ is started. The voltage applied to the fluorescent tube 3 is detected from the winding L8 of the transformer T2, and the corresponding output is connected to the transistor TR5 of the oscillation frequency control circuit 8. At this time, the detection voltage of the voltage detection means 7 is low and the output terminal is low. Does not affect the oscillation frequency. After all, the initial output is f ₁ frequency, voltage V ₃ in Figure 3 graph. After the operation starts, the transistor TR5 turns on at a speed determined by the time constant of the high resistance R4 and C6, and the output voltage becomes V
_X If the output voltage after starting to rise to (frequency f _X) elapses a predetermined time is V _Y discharge firing voltage filament is sufficiently fluorescent tube 3 which is heated is turned. Corresponding to the output voltage from V ₄ (up curve A) decreases. The change in the voltage applied to the fluorescent tube 3 is in a further decreasing direction, and the voltage detecting means 7 does not affect the oscillation frequency. Note that if there is no lighting, the oscillation frequency is balanced at a constant operating point (f _X : V _X ) that is sufficiently lower than f ₂ (the output voltage is low) as described later (protection operation). Normally, since the fluorescent tube is lit, the oscillation frequency continues to rise, and the transistor TR5 is completely turned on (saturated).
The excitation circuit 4 will operate at the frequency determined by R1 and C1. Setting the values of R1 and C1, as the frequency at this time is the resonance frequency f _2. Therefore, in this state, sufficient power is supplied to the fluorescent tube 3.

The detection voltage of the voltage detecting means 7 in this manner in the V ₃ and V ₁ of the intermediate
If it is set to V _X (frequency f _X ), the discharge of the fluorescent tube 3 is started at V _Y during the transition of the transistor TR5 from V ₃ to V ₁ at a speed determined by the constants of R4 and C6. is allowed, (waiting for output change corresponding to the fluorescent tube lighting from the voltage detecting means) by which the fluorescent tube 3 is lit, perform excitation at frequency f ₂ determined by R1 · C1 (the operating point of the graph f ₂ ), and the fluorescent tube 3 can be continuously lit with normal power. The arrow line in FIG. 2 indicates the locus of the operating point for lighting.

On the other hand, the output AC power supply voltage detecting means 7 even if such output unlighted or dismounted of the fluorescent tube does not occur discharge even beyond the V _Y would increase output exceeds the detection voltage V _X changes in the direction of suppressing the output (collector potential of the transistor TR5 turns) sufficiently lower than the oscillation frequency f _2, so that the output voltage is low operating point: acting to balance at (f _X V _X) AC power supply output is to f ₂ of the high output voltage to prevent destruction of the circuit without shifting.

As described above, when the power is turned on, the fluorescent tube 3 is preheated for a certain period of time and is turned on after sufficient preheating is completed, so that the filament is not damaged. As a result, the blackening phenomenon is minimized and the life of the fluorescent tube 3 is shortened. The effect of dramatically extending is obtained. It has been confirmed that it can be used more than 10 times by the number of times of lighting.

At the same time, the oscillation frequency control circuit controls and changes the oscillation frequency of the excitation circuit according to the voltage applied to both ends of the fluorescent tube. At the time of load or light load, the oscillation frequency is changed to lower the output voltage, thereby preventing the lighting circuit for the fluorescent lamp device from being broken. That is, the operating frequency shifts to f _X (V _X ) even when a no-load condition occurs, such as when the fluorescent tube 3 is not attached or when the fluorescent tube 3 is removed without turning off the power for replacement. A known function that suppresses the load on the inverter circuit by suppressing the voltage is also realized at the same time. Further, it becomes possible operating point is protected moved inverter circuit f _X when the fluorescent tube 3 is close gradually deteriorated unloaded condition during use. There is also an advantage that there is no danger of breaking the inverter circuit even if there is erroneous wiring during construction.

The resonance frequency f has been described an example in which an output suppression operation region lower f ₁ side _2, any frequency range which is also unloaded output is low voltage exceeding the resonance frequency as the output suppression operation area side equivalent Circuit can be configured.

In addition, since the above-described lighting circuit for a fluorescent lamp apparatus includes the excitation circuit 4 for driving the switching transistors TR1 and TR2 independently of other parts, the excitation frequency of the excitation circuit 4 ( Since the oscillation frequency can be set arbitrarily by itself, the overall design is simplified and the degree of freedom in selecting the parts to be used is increased.

Further, at the time of start-up, the excitation circuit starts an oscillating operation by a starting power supply based on the DC power supply, and continues a subsequent oscillating operation exclusively by an internal power supply based on an output of the high-frequency AC power supply obtained as a result. In this case, even if the starting power supply is composed of small-capacity components without causing power consumption and heat generation in the starting power supply circuit portion, thermal destruction is prevented beforehand, so that the entire lighting circuit for a fluorescent lamp apparatus is reduced in size. ing.

〔The invention's effect〕

As described above, the lighting circuit for a fluorescent lamp apparatus of the present invention is configured such that a DC power supply obtained by rectifying and smoothing an AC power supply is switched by a semiconductor element driven by an excitation circuit to obtain a high-frequency AC power supply. A separately-excited inverter system for lighting a fluorescent tube with a power supply, in particular, a voltage detecting unit that outputs an analog signal corresponding to a voltage value applied to both ends of the fluorescent tube, and an oscillation frequency of the excitation circuit. It is controlled and changed in accordance with the output of the voltage detecting means, and at the time of power-on and before the fluorescent lamp is turned on, the frequency is set to a frequency which suppresses the main voltage of the high-frequency AC power supply in accordance with the output of the voltage detecting means, and the fluorescent lamp Start preheating, and after a certain period of time, shift to a frequency that increases the output voltage of the high-frequency AC power supply,
Oscillation frequency control circuit for changing the output voltage of the high-frequency AC power supply to the frequency corresponding to the specified voltage after waiting for the output change corresponding to the fluorescent tube lighting from the voltage detection means. In the conventional inverter-type fluorescent lamp lighting circuit, the filament is deteriorated at the time of lighting (at the start of discharge) due to the means and the operation of the oscillation frequency control circuit, and the useful life of the fluorescent tube is shortened. With the practical effect that the same fluorescent tube can be used for a longer period of time by solving the difficulties and at the same time, most of the configuration is shared and the known no-load circuit protection function is combined As a result, a highly functional and highly reliable lighting circuit can be realized with a simple configuration, and its usefulness is extremely high.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an example of a known fluorescent lamp lighting circuit (separately excited type), FIG. 2 is a circuit diagram showing an embodiment of a fluorescent lamp lighting circuit according to the present invention, and FIG. FIG. 4 is a diagram showing a relationship between an oscillation frequency and an output voltage in a fluorescent lamp lighting circuit according to the present invention, and FIG. 4 is a circuit diagram of a conventional fluorescent lamp lighting circuit (self-excited type). 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 (3)

(57) [Claims] 1. A separately excited inverter system in which a DC power supply obtained by rectifying and smoothing an AC power supply is switched by a semiconductor element driven by an excitation circuit to obtain a high-frequency AC power supply, and a fluorescent tube is lit by the high-frequency AC power supply. In a lighting circuit for a fluorescent lamp device, a voltage detection unit that outputs an analog signal corresponding to a voltage value applied to both ends of the fluorescent tube, and an oscillation frequency of the excitation circuit is controlled according to an output of the voltage detection unit. Before powering on the fluorescent tube at power-on, set the frequency to suppress the output voltage of the high-frequency AC power supply low to correspond to the output of the voltage detecting means, start the residual heat of the fluorescent tube, and after a certain time elapses The output voltage of the high-frequency AC power supply is shifted to a higher frequency, and the output voltage of the high-frequency AC power supply is further regulated to the specified voltage after the output change corresponding to the fluorescent tube lighting from the voltage detection means. Fluorescent lighting fixtures for lighting circuit, characterized by comprising an oscillation frequency control circuit for changing to a frequency corresponding to the. 2. An excitation circuit according to claim 1, wherein said excitation circuit starts an oscillating operation by a starting power supply based on said DC power supply at the time of starting, and continues an oscillating operation exclusively by an internal power supply based on an output of said high-frequency AC power supply obtained as a result. The lighting circuit for a fluorescent lamp device according to claim 1, wherein: 3. The power supply according to claim 1, wherein said voltage detecting means comprises a transformer in an output section.
A winding L8 newly provided in T2, and a diode D6 in which the output of the winding L8 is connected in series and in parallel via a resistor R6 to a resistor R7 and a cathode terminal connected to the resistor R6 and the anode terminal side is grounded. An NPN transistor TR4 having a base terminal connected to a resistor R6 and an emitter terminal connected to the anode terminal of the diode D6, and the collector terminal of the transistor TR4 serving as an output (P3). A resistor R3 connected in series to the ground terminal of the resistor R1 for forming the excitation circuit 4 and determining the oscillation frequency, an FET transistor TR5 having a channel connected in parallel to the resistor R1,
A resistor R4 connected between the gate terminal of TR5 and the power supply, a capacitor C6 connected between the gate terminal of the transistor TR5 and ground, and one end connected to the gate terminal of the transistor TR5 and the other end connected to the output of the voltage detecting means 7. Connected resistor
The lighting circuit for a fluorescent lamp device according to claim 1, wherein the lighting circuit comprises R5.