JPH0719665B2 - Electrodeless discharge lamp lighting device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrodeless discharge lamp lighting device for dimming and lighting an electrodeless discharge lamp in which a rare gas and a metal vapor are enclosed in a translucent bulb. is there.

[Background technology]

A method for controlling an electrodeless discharge lamp by time division dimming is conventionally disclosed in US Pat. No. 4,219,760 and JP-A-55-39135.

FIG. 5 shows such an electrodeless discharge lamp lighting device. In FIG. 5, 3 is a radio frequency oscillator
Is an intermediate amplifier that amplifies a small-amplitude high-frequency signal of the oscillation circuit 3, 5 is a power amplifier that receives the output signal of the intermediate amplifier 4 and amplifies the power, and 6 is an output power of the power amplifier 5 that matches the load. Matching circuit 6 for performing (matching)
Are configured respectively.

An electromagnetic wave radiator 2 composed of a coil is wound around the electrodeless discharge lamp 1, and the electromagnetic wave radiator 2 is connected to the output terminal of the matching circuit 6.

Reference numeral 7 denotes a dimming control circuit for generating the dimming signal shown in FIG. 6 (b) for performing time division dimming, and by adjusting the adjuster 8 of the variable resistor, FIG. The ON period T ₂ in the constant period T _{1 of} b) is changed and the ratio T ₂ / T ₁ is changed to perform dimming.

As described above, the regulator 8 such as the variable resistor of the dimming control circuit 7
In addition to the case where the light amount is manually adjusted, a light amount detector 9 arranged in the vicinity of the electrodeless discharge lamp 1 detects a light amount, and a feedback control circuit 10 for feedback control so that the light amount is always set by the detection signal is added. There is also one as a conventional example.

Hereinafter, the circuit operation of FIG. 5 will be described in detail with reference to FIG.

High frequency voltage (10 MHz) suitable for electrodeless discharge by the oscillator circuit 3.
z order), and the oscillation voltage waveform is amplified by the intermediate amplifier 4 to obtain the high frequency voltage waveform shown in FIG. 6 (a).

The dimming control circuit 7, freely varied by adjusting the regulator 8 such as a variable resistor fundamental oscillation period T ON period T ₂ is long enough during a certain period T ₁ of the from ₀ oscillation circuit 3, T ₂ The ON-OFF waveform of FIG. 6 (b) is created by changing the dimming ratio of / T ₁ .

The ON-OFF waveform shown in FIG. 6 (b) obtained by the dimming control circuit 7 is added to the intermediate amplifier 4 to turn on / off the amplifying action so that the high frequency voltage waveform shown in FIG. 6 (a) is time-divided intermittently. A voltage waveform as shown in FIG. 6C is output from the intermediate amplifier 4.

When the waveform of FIG. 6 (c) is input to the power amplifier 5, it becomes a power-amplified high-frequency high-frequency intermittent voltage waveform, which is input to the matching circuit 6.

Here, the operation of the matching circuit 6 will be briefly described. In a high-frequency circuit, when applying the high-frequency voltage output from the amplifier to the load, if the output impedance of the amplifier and the input impedance of the load are matched with the characteristic impedance of the line, the output voltage from the amplifier will be as if it were on an infinite line. As it propagates, there is no reflection at each coupling point between the amplifier and the line and between the line and the load, and power is efficiently supplied from the amplifier to the load. However, in general, the output impedance of the amplifier and the input impedance of the load do not match, so a four-terminal circuit network composed of a capacitor, a coil, etc. is inserted between the output terminal of the amplifier and the input terminal of the load to perform impedance conversion. Align. This 4-terminal network is called a matching circuit.

Then, the output end of the matching circuit 6 is connected to the electromagnetic wave radiator 2 wound around the electrodeless discharge lamp 1, and the output power from the amplifier 6 is efficiently supplied to the electrodeless discharge lamp 1 of the load. The electrode discharge lamp 1 emits light. In this case, the electromagnetic waves emitted from the electromagnetic wave radiator 2 excite mercury in the electrodeless discharge lamp 1 to generate ultraviolet rays. This ultraviolet ray is converted into visible light by, for example, a fluorescent body and is emitted to the outside.

By adjusting the adjuster 8 to shorten the ON period T ₂ in FIG. 6 (b), the emission of the electrodeless discharge lamp 1 becomes weaker, and conversely, the ON period T ₂ should be lengthened to approach T _1. As a result, the light emission of the electrodeless discharge lamp 1 becomes stronger and dimming can be performed.

In the conventional example of FIG. 5, if the ON period T ₂ is simply determined by the adjuster 8, the amount of light emission during dimming is not constant due to changes in the power supply voltage, characteristic changes due to temperature rise of the electrodeless discharge lamp 1, and the like. There is a problem such as. Therefore, the light quantity detector 9 is provided in the vicinity of the electrodeless discharge lamp 1, and the light quantity detector 9 is provided.
By applying the detection signal of 1 to the dimming control circuit 7 via the feedback control circuit 10, when the light emission amount of the electrodeless discharge lamp 1 increases due to a rise in the power supply voltage, the detection amount of the light amount detector 9 increases, The dimming control circuit 7 can be automatically adjusted so that the ON period T ₁ is shortened, and dimming control can always be performed with a constant light amount.

However, the conventional example shown in FIG. 5 has the following drawbacks. In FIG. 6, when the ON period T ₂ in the cycle T ₁ is sufficiently shortened and the dimming ratio is reduced to narrow down the amount of light emission, the electrodeless discharge lamp 1 causes an arc discharge at a certain period or less. It cannot be maintained and goes out. That is, T ₂ / T ₁
The dimming ratio of is not dimmable below a certain value, and there is a limit to the dimming ratio.

The limit of this dimming ratio depends on the structure of the electrodeless discharge lamp 1, the type of internal gas, the gas pressure, the structure of the coil that is the electromagnetic wave radiator 2, the cycle T _1, etc., but T ₂ / T ₁ Is 25 to 3
About 0% has been observed.

Therefore, for the purpose of expanding the lower limit of the dimming ratio and lowering the dimming ratio so that the electrodeless discharge lamp 1 can maintain the arc discharge as much as possible even when the light emission amount is narrowed down, the following means. Is proposed. FIG. 7 is a waveform diagram for explaining the means proposed for achieving this object.

7 (a) is an output signal of the dimming control circuit 7 similar to that of FIG. 6 (b), and during the ON period T ₂ , arc discharge is performed with a high voltage amplitude A _{1 as} shown in FIG. 7 (b). , In the OFF period T ₃ of the remaining period of the cycle T ₁ , the output voltage waveform is not set to zero as shown in FIG. 6 (c), but the voltage amplitude is set to A ₂ as shown in FIG. 7 (b). By using the dropped high-frequency voltage waveform, the electrodeless discharge lamp 1 is caused to perform glow discharge instead of arc discharge during the OFF period T ₃ . By doing so, during the OFF period T ₃ , the gas ions of the electrodeless discharge lamp 1 remain without disappearing, and the conductivity of the enclosed gas remains in a good state, resulting in arc discharge.
Restriking is greatly facilitated by the first part of the ON period T _2, therefore as a result, can reduce the ON period T _2, the dimming ratio T ₂ / T
The lower limit of ₁ can be reduced. Therefore, it is possible to maintain lighting of the electrodeless discharge lamp 1 even if the dimming ratio is lowered and the light emission amount is greatly narrowed down.

However, as shown in FIG. 7, the setting of the amplitude A ₂ during the OFF period T ₃ is severe, and the ambient temperature of the electrodeless discharge lamp 1
Due to the temperature rise due to heat generation of the electrodeless discharge lamp 1 itself, variations among the electrodeless discharge lamps 1, arc discharge instead of glow discharge occurs in the OFF period T ₃ , the dimming level is greatly changed, and glow discharge also occurs. It becomes too weak, and the gas ions of the electrodeless discharge lamp 1 are extinguished, which makes it difficult to expand the target lower limit of dimming. As described above, with the means shown in FIG. 7, it is not easy to expand the lower limit of the dimming ratio.

[Object of the Invention]

An object of the present invention is to provide an electrodeless discharge lamp lighting device capable of easily and surely expanding the lower limit of the dimming ratio without causing the dimming level to fluctuate.

[Disclosure of Invention]

An electrodeless discharge lamp lighting device of the present invention is a high frequency power source capable of switching an output frequency, an electrodeless discharge lamp, and the high frequency power source connected to the output end of the high frequency power source and arranged near the electrodeless discharge lamp. An electromagnetic wave radiator that radiates high-frequency power supplied from a power source to the electrodeless discharge lamp as an electromagnetic wave, a matching circuit provided between the high-frequency power source and the electromagnetic wave radiator, and an output cycle longer than the high-frequency power source. A dimming control circuit for switching and controlling the output frequency of the high frequency power source so that the output frequency of the high frequency power source is the matching frequency for a part of the predetermined period and the output frequency of the high frequency power source is the non-matching frequency for the remaining time. It has and.

According to the configuration of the present invention, the dimming control circuit controls the switching of the output frequency of the high frequency power source, so that the output frequency of the high frequency power source is the matching frequency for a part of the predetermined period and the output of the high frequency power source is for the remaining time. Since the frequency is a non-matching frequency, reflection does not occur in a part of the predetermined period, the high frequency power of the high frequency power source is efficiently applied to the electrodeless discharge lamp, and the remaining time in the predetermined period is reflected Occurs and is added to the electrodeless discharge lamp with low efficiency, and the electrodeless discharge lamp can be dimmed by adjusting the ratio of a part of time to a predetermined cycle.

Moreover, since the high frequency power of the non-matching frequency is applied to the electrodeless discharge lamp during the remaining time of the predetermined period, the arc discharge that contributes to the light emission is stopped but the glow discharge that does not contribute to the light emission continues during the remaining time. As a result, the ions in the electrodeless discharge lamp do not disappear and the conductivity of the enclosed gas remains good, facilitating re-ignition at the beginning of a part of the next predetermined cycle. Therefore, even if the dimming ratio is lowered and the light emission amount of the electrodeless discharge lamp is narrowed down, the arc discharge of the electrodeless discharge lamp can be continued, and the lower limit of the dimming ratio can be expanded.

Furthermore, the glow discharge of the electrodeless discharge lamp is maintained during the remaining time of the predetermined cycle by switching the output frequency of the high frequency power supply to a non-matching frequency, and therefore the range of the output frequency of the high frequency power supply is Since it is not as severe as in the case of the adjustment, it is possible to easily and surely expand the lower limit of the dimming ratio without causing the dimming level to fluctuate.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 to 3. As shown in FIG. 1, this electrodeless discharge lamp lighting device is connected to a high-frequency power source I whose output frequency can be switched, an electrodeless discharge lamp 1, and an output end of the high-frequency power source I, and the electrodeless discharge lamp. An electromagnetic wave radiator 2 including a coil arranged near the discharge lamp 1 and radiating high-frequency power supplied from the high-frequency power source I to the electrodeless discharge lamp 1 as an electromagnetic wave; the high-frequency power source I and a front electromagnetic wave radiator 2;
And a matching circuit 6 provided between the high frequency power supply I and a predetermined period longer than the output cycle of the high frequency power supply I, the output frequency of the high frequency power supply I is used as a matching frequency for part of the time, and the remaining time is the output frequency of the high frequency power supply. And a dimming control circuit 7 for switching and controlling the output frequency of the high-frequency power source I so that the frequency is a non-matching frequency. In this case, the high frequency power supply I is composed of a main oscillation circuit 3, a sub oscillation circuit 3 ', an intermediate amplifier 4, a power amplifier 5 and a changeover switch circuit 11.

The main point of this electrodeless discharge lamp lighting device is that, as shown in the waveform diagram of FIG. _2, during the ON period T _{2 of the} electrodeless discharge lamp 1, the high frequency AC voltage of the main oscillation frequency f ₁ is applied to the intermediate amplifier 4 Then, a constant is set in the matching circuit 6 so that it is transmitted through the power amplifier 5 and is transmitted to the electrodeless discharge lamp 1 during arc discharge with the maximum efficiency with respect to the main oscillation frequency f ₁ . , among OFF period T ₃ is that it has to switch to the sub-oscillation frequency f ₂ with reasonably difference between the main oscillation frequency f ₁ of the oscillation frequency as shown in FIG. 2 (b). In the matching circuit 6, since the high frequency AC voltage having the sub-oscillation frequency f ₂ cannot be matched during the OFF period T ₃ , most of the electric power is reflected and the electrodeless discharge lamp 1 is in this period. Although no arc discharge occurs, by appropriately selecting the sub-oscillation frequency f ₂ , it is possible to apply some voltage to the electrodeless discharge lamp 1 for glow discharge. For this reason, the ions in the electrodeless discharge lamp 1 do not disappear even during the OFF period T ₃ that does not contribute to light emission, and thus the conductivity of the enclosed gas remains in a good state, and the purpose can be achieved.

The configuration and operation of the circuit block shown in FIG. 1 will be described in detail below.

In FIG. 1, the intermediate amplifier 4, the power amplifier 5, the matching circuit
6, the electrodeless discharge lamp 1, the electromagnetic wave radiator 2, the dimming control circuit 7, the adjuster 8 such as a variable resistor, the light amount detector 9 and the feedback control circuit 10 of the additional configuration are the same as in the conventional example of FIG. is there.

The main oscillation circuit 3 oscillates at the main oscillation frequency f ₁ . The sub oscillation circuit 3 'is made to oscillate at a secondary oscillation frequency f _2. The output end of the main oscillation circuit 3 is connected to the normally open terminal a of the changeover switch 12 of the changeover switch circuit 11, and the output end of the suboscillation circuit 3'is connected to the normally closed terminal b of the changeover switch 12 and this changeover is performed. The common terminal c of the switch 12 is connected to the input terminal of the intermediate amplifier 4.

Further, the time division ON / OFF signal of the dimming control circuit 7 is input to the changeover switch circuit 11 and used as the changeover signal of the changeover switch 12.

Next, the operation will be described.

By adjusting the adjuster 8 such as the variable resistor in FIG. ₁ to set the ON period T ₂ in the constant cycle T ₁ so as to obtain a desired dimming ratio, the time division shown in FIG. An on / off signal is generated at the output terminal of the dimming control circuit 7 and used as a switching signal for the changeover switch circuit 11.

For this reason, the voltage becomes ON during the ON period T ₂ in FIG. 2 (a), the changeover switch 12 operates and the terminals a and c are connected, and the oscillation waveform of the main oscillation frequency f ₁ becomes a voltage at the intermediate amplifier 4. Amplified,
Since the power is amplified by the voltage amplifier 5 and the oscillation frequency is f _1, it is matched by the matching circuit 6 and the high frequency voltage is efficiently supplied to the electrodeless discharge lamp 1 of the load, and the electrodeless discharge lamp 1 is in the ON period. During T ₂ , it will be arc-discharged and emit light.

Then, the output signal of the light control circuit 7 enters the OFF period T ₃ turns off, the changeover switch circuit 11 becomes inoperative, the changeover switch 12 is reversed to the normally closed terminal b side, the sub-oscillation circuit 3 '
The sub-oscillation frequency f ₂ is amplified by the intermediate amplifier 4 and the power amplifier 5, and is added to the electrodeless discharge lamp 1 via the matching circuit 6. Therefore, as described above, the sub-oscillation frequency f ₂ cannot be matched and is reflected, so that the electrodeless discharge lamp 1
Shows a glow discharge state in which almost no emitted light is generated without reaching arc discharge. Therefore, the lower limit value of the dimming control can be expanded as described above.

FIG. 3 shows a specific circuit example of the circuit block shown in FIG. 1, and the same blocks and parts are designated by the same reference numerals. In FIG. 3, 1 is an electrodeless discharge lamp, 2 is an electromagnetic wave radiator consisting of a coil, 26 is a DC power supply, and 27 is a power switch.

The main oscillator circuit 3 is composed of a bias resistor 28, a crystal oscillator 29, a transistor 31, an emitter resistor 32, a bypass capacitor 33, and a load transformer 30, and a secondary winding of the load transformer 30 has a high-frequency oscillation voltage of a main oscillation frequency f _1. Is getting

The sub-oscillation circuit 3 ′ is configured similarly to the main oscillation circuit 3, and includes a bias resistor 34, a crystal oscillator 35, a transistor 37, an emitter resistor 38, a bypass capacitor 39, and a load transformer 36, and a secondary winding of the load transformer 36. A high-frequency oscillation voltage with the sub-oscillation frequency f ₂ is obtained on the line.

The intermediate amplifier 4 is composed of a high frequency choke coil 40, a transistor 41 and a coupling capacitor 42, amplifies a small signal high frequency oscillation voltage and supplies it to the power amplifier 5.

The power amplifier 5 changes the unbalanced high frequency voltage supplied from the intermediate amplifier 4 into an AC voltage balanced with respect to the ground potential by the two coils 43 and 44 wound around the same core. Then, the power transistors 49 and 50 composed of MOS-FETs form a push-pull amplifier circuit configuration, and a balanced AC voltage is supplied to each gate terminal of the power transistors 49 and 50 via both coupling capacitors 45 and 46. It The resistors 47 and 48 and the capacitor 51 form a gate bias circuit. Coil 53, 54, coil 55, 56, capacitor 57, 58 and coil 59, 60 wound on the same core and capacitor 52 are connected to the drains of both power transistors 49, 50, and power amplifier 5 is connected by these circuits. Of the coil 59, 60 and generates an amplified high frequency voltage at the output terminals of the coils 59, 60.

The matching circuit 6 is composed of a series-parallel four-terminal circuit of a coil 61, a capacitor 62, and a capacitor 63, and is adjusted to the main oscillation frequency f ₁ by adjusting the capacitance of the capacitors 62 and 63. The output terminal of the matching circuit 6 is connected to the electromagnetic wave radiator 2 including a coil.

The dimming control circuit 7 shows an example in which IR3M02 (manufactured by Sharp Corp.) is used as an integrated circuit IC, and resistors 66, 6 are used.
7, 68, 69, 72, 73, 74, a capacitor 71, a semi-fixed resistor 70, and a variable resistor 8 are added as external parts. This integrated circuit IC adjusts the semi-fixed resistance 70 to set the cycle T ₁ to, for example, 100
Set to μs or the like. Further, by adjusting the adjuster 8 including a variable resistor, the ON period T ₂ can be adjusted to change the dimming ratio, and the average power supplied to the electrodeless discharge lamp 1 can be changed to perform dimming. It has become. Integrated circuit
The same output voltage waveform as in Fig. 2 (a) is obtained from the 11th terminal of the IC.

The changeover switch circuit 11 is composed of two transistors 77 and 78 and resistors 79 and 80 which are symmetrically arranged. The emitter terminal of the transistor 77 is connected to the ground terminal, the collector terminal is connected to one end of the secondary terminal of the load transformer 36 of the sub-oscillation circuit 3 ', and the other end of the secondary terminal is connected to the ground terminal. The base of the transistor 77 is connected to the 11th terminal of the integrated circuit IC via the resistor 73.

The emitter terminal of the transistor 78 is connected to the ground terminal, the collector terminal is connected to one end of the secondary terminal of the load transformer 30 of the main oscillation circuit 3, and the other end of the secondary terminal is also connected to the ground terminal. . The base terminal of the transistor 78 is a resistor
It is connected to terminal 9 of the integrated circuit IC via 74.

The potential of the 9th terminal of the integrated circuit IC operates so as to be in the opposite phase to the potential of the 11th terminal. That is, contrary to the waveform of FIG. 2A, the T ₂ period is low and the T ₃ period is high.

Since the 11th terminal of the integrated circuit IC has the same signal as in FIG. 2 (a), it is at the high level in the period T ₂ , and the resistance 73
Current flows through the base of transistor 77 via
The transistor 77 becomes conductive and the output terminal of the oscillation circuit 3'is short-circuited. During the same period, the 9th terminal of the integrated circuit IC is at the low level, the base current of the transistor 78 does not flow,
The transistor 78 is in the cutoff state, and the output voltage of the main oscillation circuit 3 is applied to the input terminal of the intermediate amplifier 4 via the resistor 80. As a result, a high frequency voltage of the main oscillation frequency f ₁ comes to a period T ₂ of the second view is amplified (b) during the period T _2.

Becomes the period T _3, and the signal is reversed, 11 Pin low level of the integrated circuit IC, the ninth pin is at high level. Therefore, the base current of the transistor 77 disappears and the transistor 77 is cut off, the base current flows to the transistor 78, the transistor 78 becomes conductive, and the secondary winding output terminal of the load transformer 30 of the main oscillation circuit 3 is short-circuited. Sub oscillator circuit 3 '
The secondary winding output of the load transformer 36 is applied to the input terminal of the intermediate amplifier 4 via the resistor 79. As a result, in a period T _3, the auxiliary oscillating frequency f ₂ frequency current is amplified, would be a period T ₃ in FIG. 2 (b), operating as described in the description of the circuit blocks of FIG. 1 Is realized.

As described above, the electrodeless discharge lamp lighting device according to this embodiment has the power amplifier 5 to the matching circuit 6 at the radio frequency.
When high frequency power is supplied to the electrodeless discharge lamp 1 which is a load via the power supply, due to the property that reflection occurs when the matching state shifts and power is not sufficiently supplied to the load, the ON period T of the constant cycle T ₁ is used. _During the period ₂ , the frequency of the high frequency power applied to the electrodeless discharge lamp 1 is set to the main oscillation frequency f ₁ and the matching circuit 6 is adjusted to the matching state, power is efficiently supplied to the electrodeless discharge lamp 1, and the remaining OFF period At T ₃ , by appropriately shifting the frequency of the high-frequency power, the matching state is removed, and the electrodeless discharge lamp 1 is glow-discharged to generate gas ions in the electrodeless discharge lamp 1 even in a low light emission state. It keeps the filled gas to have good conductivity, which shortens ON period T ₂ and dimming ratio (T ₂ / T ₁ ).
Since it is difficult to cause disappearance or the like when the aperture is narrowed down, it is possible to widen the lower limit value of dimming and widen the dimming width.

FIG. 4 shows another embodiment of the oscillation frequency switching method of the oscillation circuit 3. The oscillator circuit 3 of FIG. 4 is a well-known Clap oscillator circuit, which is connected as shown in the figure with a transistor 15, a coil 16, a transformer 19, capacitors 17, 18, 20, 21, resistors 22, 23, etc. Therefore, a terminal f is provided from the base terminal of the transistor 15 via the capacitor 17 and is connected to the normally open terminal a of the changeover switch 12 from the terminal f side via the capacitor 18. The common terminal c of the changeover switch 12 is connected to the transformer.
It is connected to the collector terminal of the transistor 15 through the primary winding 19 and the capacitor 18 is connected between the normally closed terminal b and the terminal f of the changeover switch 12 by a capacitor 18 'whose capacity is appropriately changed. ing. By setting the capacitances of capacitors 18 and 18 'so that the oscillation frequency when using capacitor 18 is f ₁ and the oscillation frequency when using capacitor 18' is f ₂ Similarly, the frequency can be switched by the changeover switch 12. The oscillation output is obtained from the secondary output terminals j and k provided on the secondary winding of the transformer 19 and is input to the intermediate amplifier 4.

Although FIG. 2B shows the case where the frequency f ₂ is lower than the frequency f ₁ , the matching can be similarly shifted even when the frequency f ₂ is high, and the effect of the present invention can be achieved.

Further, in the circuit diagram of the embodiment of FIG. 3, a MOS-FET is used as the power transistor of the power amplifier 5,
A high frequency bipolar transistor or a static induction transistor may be used.

The configuration for switching the oscillation frequency can also be realized by using a voltage variable capacitance diode as the oscillation capacitor of the oscillation circuit and switching the bias voltage applied to this voltage variable capacitance diode.

〔The invention's effect〕

According to the electrodeless discharge lamp lighting device of the present invention, the output frequency of the high frequency power supply is switched and controlled by the dimming control circuit, so that the output frequency of the high frequency power supply is used as the matching frequency for the remaining time for a part of the predetermined period. Since the output frequency of the high frequency power supply is a non-matching frequency, reflection does not occur at a part of the predetermined cycle, and the high frequency power of the high frequency power supply is efficiently added to the electrodeless discharge lamp. The remaining time is reflected and is added to the electrodeless discharge lamp with low efficiency, and the electrodeless discharge lamp can be dimmed by adjusting the ratio of a part of time to a predetermined cycle. Moreover, since the high frequency power of the non-matching frequency is applied to the electrodeless discharge lamp during the remaining time of the predetermined period, the arc discharge that contributes to the light emission is stopped but the glow discharge that does not contribute to the light emission continues during the remaining time. As a result, the ions in the electrodeless discharge lamp do not disappear and the conductivity of the enclosed gas remains good, facilitating re-ignition at the beginning of a part of the next predetermined cycle. Therefore, even if the dimming ratio is lowered and the light emission amount of the electrodeless discharge lamp is narrowed down, the arc discharge of the electrodeless discharge lamp can be continued, and the lower limit of the dimming ratio can be expanded.

Furthermore, the glow discharge of the electrodeless discharge lamp is maintained during the remaining time of the predetermined cycle by switching the output frequency of the high frequency power supply to a non-matching frequency, and therefore the range of the output frequency of the high frequency power supply is Since the adjustment is not as severe as in the case of the adjustment, it is possible to easily and surely increase the lower limit of the dimming ratio without causing the dimming level to fluctuate.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing its operation, FIG. 3 is a circuit diagram showing its concrete configuration, and FIG. 4 is another embodiment of the present invention. FIG. 5 is a block diagram showing a conventional example, FIG. 6 is a waveform diagram showing its operation, and FIG. 7 is a waveform diagram showing the operation of the proposed example. I: high frequency power supply, 1 ... electrodeless discharge lamp, 2 ... electromagnetic wave radiator, 6 ... matching circuit, 7 ... dimming control circuit

Claims (1)

[Claims] 1. A high frequency power source capable of switching an output frequency, an electrodeless discharge lamp, and a high frequency power source which is connected to an output end of the high frequency power source and is arranged near the electrodeless discharge lamp. An electromagnetic wave radiator that radiates electric power to the electrodeless discharge lamp as an electromagnetic wave, a matching circuit provided between the high frequency power source and the electromagnetic wave radiator, and a part of a predetermined period longer than the output period of the high frequency power source. No electrode provided with a dimming control circuit for switching and controlling the output frequency of the high frequency power source so that the output frequency of the high frequency power source is a matching frequency and the remaining time is an output frequency of the high frequency power source is a non-matching frequency. Discharge lamp lighting device.