JP2000125566A - Lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform stable high-frequency operation. SOLUTION: Resonance means Lr and Cd, where a discharge tube is connected and a capacitor Cf for generating a voltage in synchronization with a current that flows to a resonance means are connected in series to the connection point S of first and second semiconductor switching elements being connected in series complementarily, and a capacitor voltage is applied to a control terminal G of the first and second semiconductor switching elements via a phase shift means Lg for shifting phase according to the frequency change in the resonance means. In this manner, stable high-frequency operation in synchronization with a resonance current is enabled also, when resonance conditions are changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lighting device for a discharge tube.

[0002]

2. Description of the Related Art In recent years, in a discharge tube (for example, a fluorescent lamp),
2. Description of the Related Art A method of converting a DC voltage into a high-frequency AC voltage by a lighting circuit using an inverter and applying the converted DC voltage to a resonance load circuit including a discharge tube is increasing. The resonance load circuit includes a resonance inductor and a resonance capacitor for setting a resonance frequency. Such a lighting circuit is a lighting circuit including two power semiconductor switching elements connected in a half-bridge structure between the positive and negative electrodes of a DC power supply, and applies the high-frequency AC voltage to both ends of a resonance load circuit. The waveform of the current flowing through the resonance load circuit (hereinafter referred to as resonance current) resonates with the inductor and the capacitor, and becomes a sine wave. This resonance current is controlled by changing the operating frequency of the lighting circuit. In recent years, there is a lighting device equipped with a dimming function capable of arbitrarily adjusting brightness in lighting equipment. Adjusting the brightness of the discharge tube can be achieved by changing the magnitude of the current flowing through the discharge tube. Here, if the operating frequency at which the two power semiconductor elements are turned on and off alternately is fs, and the resonance frequency determined by the resonance inductor and the capacitor is fo, f
When fs is changed with respect to o, the lamp current also changes, and dimming becomes possible. Based on this principle, the lighting circuit controls the operating frequency fs to perform dimming.

As a conventional example for stabilizing the operating frequency of a switching element, there is a lighting circuit disclosed in Japanese Patent Application Laid-Open No. 8-45685. This circuit has a half-bridge circuit that supplies an AC voltage to a resonance load circuit including a discharge lamp, shunts a part of the resonance current to a capacitance and a feedback transformer, and performs a half-bridge according to the secondary voltage of the feedback transformer. A control signal is supplied to the high-side and low-side switching elements of the circuit to perform a self-excited operation.

Further, as a conventional example of a lighting circuit for realizing dimming, there is a driving device as disclosed in Japanese Patent Application Laid-Open No. 8-37092. This driving device includes: 1) a timer circuit that generates a square wave having a desired frequency; 2) a high-side and low-side driving circuit that respectively drives two power semiconductor switching elements of an inverter according to a driving signal from the timer circuit;
3) a high-side dead time delay circuit and a low-side dead time delay circuit for preventing simultaneous conduction of two power semiconductor switching elements; and 4) a signal based on the low-side common potential based on the high-side common potential. And a level shift circuit for transmitting the drive signal from the timer circuit to the high side. These circuits are incorporated in one integrated circuit. In the above conventional example, it is possible to perform dimming by changing the operating frequency fs by controlling the frequency of the timer circuit.

[0005]

In the conventional example of JP-A-8-45685, a control signal having the same frequency as the resonance current is supplied to a half bridge circuit by a feedback transformer. In other words, the circuit is a self-excited circuit in which the operation of the half-bridge circuit continues even when no signal is externally supplied, and is particularly suitable for high-frequency operation. However, since the feedback transformer has a self-inductance, a phase difference occurs between the control signal and the resonance current, and the frequency of the control signal may deviate from an appropriate value. The operating environment of the lighting circuit built in the base of the bulb becomes high due to the heat generated from the discharge tube. The characteristics of the magnetic core used in the feedback transformer change at high temperatures, causing a change in inductance. Due to these fluctuations, the phase difference and the frequency may deviate from appropriate values, and a through current may flow through the half-bridge circuit, causing an increase in loss. It is desired to reduce the size of the lighting circuit of a bulb-type fluorescent lamp with a built-in lighting circuit in the base.The smoothing capacitor used in the converter that converts AC to DC is made smaller by reducing the capacitance. I'm trying.
The reduction in the capacity of the smoothing capacitor causes an increase in DC voltage fluctuation, and the operation of the lighting circuit becomes unstable.

Therefore, the first problem to be solved by the present invention is as follows:
An object of the present invention is to provide a lighting circuit that stably performs high-frequency operation even when a DC voltage fluctuates.

The conventional example of Japanese Patent Application Laid-Open No. 8-37092, which realizes dimming, is applied to a lighting device that operates at a high frequency, and the leakage current of a level shift circuit for transmitting a driving signal from a timer circuit to the high side is applied. Is a problem. There are various types of level shift circuits, and all of them include at least one semiconductor switching element between the low side and the high side. The semiconductor switching element has a parasitic capacitance between its input and output terminals, and the parasitic capacitance is charged or discharged every time the output voltage of the lighting circuit changes. If the high frequency lighting circuit is controlled by the conventional method, the leakage current will increase,
A problem such as an increase in loss or malfunction of noise occurs.

A second problem to be solved by the present invention is to provide a lighting device for a discharge tube in which high-frequency operation is taken into consideration, wherein the operating frequency of a lighting circuit is changed to enable dimming of the discharge tube. It is in.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and a lighting device according to the present invention has the following configuration. That is, in the lighting device according to the present invention, the alternating current is applied to the discharge tube connected to the resonance means in accordance with the switching of the first and second semiconductor switching elements connected in series between the positive electrode and the negative electrode of the DC power supply. A current is supplied, and a control terminal and a reference terminal of the first and second semiconductor switching elements are connected to each other at a common point, and a connection point where the reference terminal of the first and second semiconductor switching elements is connected to each other. Between at least one pole of the DC power supply, a resonance unit connected to a discharge tube, a first capacitor that generates a voltage synchronized with a current flowing through the resonance unit,
Are connected in series, and the voltage of the first capacitor is applied to the control terminals of the first and second semiconductor switching elements via the phase shift means for shifting the phase according to the frequency change of the resonance means.

[0010]

FIG. 1 shows a lighting circuit for supplying an alternating current to a discharge tube 1. The discharge tube 1 is intended for an ordinary fluorescent lamp having a filament or an electrodeless fluorescent lamp having no filament and generating plasma with lines of magnetic force emitted from an excitation coil. AC power supply AC
Is rectified by a rectifier circuit DB composed of a diode bridge, and a DC voltage is supplied to a lighting circuit of the discharge tube 1 after smoothing by a capacitor C1. The switching elements Q1 and Q2 connected in series are complementary. For example, the switch Q1 is an n-channel MOSFET, and although not shown, a free-wheeling diode (hereinafter referred to as QD1) is provided between a source terminal and a drain terminal. Built-in. Switch Q2
Is a p-channel MOSFET, and has a freewheeling diode (hereinafter referred to as QD2) between the drain terminal and the source terminal. The drain terminal of switch Q1 is a capacitor C
1, and the drain terminal of the switch Q2 is connected to the negative electrode of the capacitor C1. The source terminals of the switches Q1 and Q2 are connected at a common connection point S, and the gate terminals are connected at a connection point G. Q1,
The current flowing between the drain and the source of Q2 is controlled by the same voltage between the connection point G and the connection point S. A resonance load circuit including a capacitor Cf, a resonance inductor Lr, and resonance capacitors Cd and Cr is connected between the connection point S and the negative electrode of the capacitor C1, and a discharge tube (or fluorescent lamp) 1 is connected in parallel with Cr. Is provided. The capacitor Cd of the resonance load circuit may be omitted. Also, the resonance load circuit
A configuration connected between the connection point S and the positive electrode of the capacitor C1 may be used. The frequency of the current flowing through these resonant load circuits is determined by each value. Switching element Q
A bidirectional current is caused to flow through the resonant load circuit by the alternating switching operation of 1 and Q2 to light the discharge tube. Capacitor C2 connected between the drain and source of switch Q1
Adjusts the voltage change time between the drain and the source of both switches. Capacitor C2 plays a similar role when connected between the drain and source of Q2.

The gate drive circuit for controlling the conduction state of the switches Q1 and Q2 includes a capacitor Cf connected on a resonance load circuit. The capacitor Cf obtains a drive voltage from a current flowing through the resonance load circuit in order to operate the gate drive circuit. One end of the capacitor Cf is set to a point F, and an inductor Lg is connected between the connection points G and F. The inductor Lg gives a phase difference between the current flowing through the resonance load circuit and the voltage between the gate and the source. Zener diodes ZD1 and ZD2 coupled in series in opposite directions are provided in parallel between the gate and the source. These function to prevent the destruction of the switching elements when an overvoltage is applied between the gate and the source of the switching elements Q1 and Q2. MO
Some SFETs already have a built-in Zener diode for gate overvoltage protection. When such a switching element is selected, the above-mentioned Zener diode may be removed. Further, a capacitor Cgs is provided between the gate and the source to adjust the voltage change time between the gate and the source. That is, in the alternate switching operation of the switches Q1 and Q2, it plays a role of compensating for a dead time from when one switch is turned off and the other switch is turned on.

In FIG. 1, when the DC voltage of the capacitor C1 increases due to a rise in the voltage of the AC power supply AC at the time of starting, the voltage at the node F, ie, the voltage of the capacitor Cf, gradually decreases with respect to the node S. At this time, a voltage equivalent to the voltage of the capacitor Cf is applied between the gate and the source. When the voltage between the gate and the source falls below the threshold voltage of the switching element Q2, Q2 turns on and a current flows from the connection point F to the connection point S, so that the voltage at the connection point F increases. As a result, the voltage between the gate and the source becomes
Q2 turns off because it immediately exceeds the threshold voltage of Q2. Here, since the capacitor Cf, the capacitor Cgs, and the inductor Lg connected between the connection point F and the connection point S constitute an LC resonance circuit, a slight voltage change of the capacitor Cf causes a current flowing in the LC resonance circuit. And the voltage swing between the gate and the source increases. Due to such an oscillation phenomenon, the switches Q1 and Q2 start switching operations alternately.

Next, the operation of the circuit of FIG. 1 will be described. The discharge tube 1 is supplied with a high-frequency current by a resonance load circuit using Q1, Q2 and Lr, Cr, Cd. Assuming that the current of the load resonance circuit is iL and the direction flowing from the connection point S to F in FIG. 1 is defined as positive, there are four operation modes during one cycle of the current iL. Hereinafter, each operation mode will be described.

Mode 1: When Q1 turns on, capacitor 1
, A current iL flows through a path of Q1, Cf, Lr, Cd, and Cr. The current iL charges the Cr and partially flows to the discharge tube 1 to flow. Also, the capacitor Cf is charged by iL, but the voltage at the connection point F with respect to the connection point S decreases. The decrease in the voltage at the node F reduces the gate voltage.
1 turns off. On the other hand, the gate voltage of Q2 is higher than the threshold value of Q2, and is in an off state.

Mode 2: When Q1 is turned off, current i
L has a value with a positive polarity, and this current is Lr, C
The flow continues along the routes of d, Cr, QD2, and Cf. Note that a part of the current iL flows by being shunted to the discharge tube 16. The current iL charges Cf, and the voltage at the node F further decreases, so that the gate voltage also decreases. When the gate voltage falls below the threshold value of Q2, Q2 turns on. The current polarity during the mode 2 is Q
2, the current continues to flow through QD2 as long as the polarity of the current does not change even if Q2 turns on. Current i
Mode 2 is a period until the polarity of L changes to negative.

Mode 3: When the polarity of the current iL changes from positive to negative, since Q2 is on in Mode 2, iL becomes Q2
Flows through. That is, iL is Q2, Cr, Cd, Lr, Cf
And Cf is charged by iL. The voltage at the connection point F increases due to iL, and when the gate voltage exceeds the threshold value of Q2, Q2 turns off. On the other hand, Q1 is in an off state because the gate voltage is equal to or lower than the threshold value of Q1.

Mode 4: When Q2 is turned off, current i
L has a value with negative polarity, and the current iL is changed to Lr, Cf, QD1,
The current continues to flow through the paths of the capacitors C1, Cr, and Cd. still,
Part of the current iL flows to the discharge tube 16 in a divided manner. Current i
L charges Cf, and the voltage at node F further increases.
The gate voltage also increases. When the gate voltage exceeds the threshold value of Q1, Q1 turns on. In addition, the current polarity during the mode 4 is opposite to that of Q1, and the current continues to flow through QD1 even if Q1 is turned on, as long as the polarity of the current does not change. Mode 2 is a period until the polarity of the current iL changes to positive.

As described above, the operations from mode 1 to mode 4 are performed during one cycle of the current iL, and thereafter, this operation is repeated.

Next, the gate circuit will be described in detail.
The gate circuits are distinguished by the conduction states of the Zener diodes connected to the respective switching elements. FIG. 2 shows a circuit when the Zener diode is turned on, and has a configuration in which the Zener diode and the inductor Lg are connected in series. In FIG. 2, the combined impedance Zg of the Zener diode and the inductor Lg becomes inductive due to the large reactance of the inductor Lg.
Here, assuming that the voltage of the capacitor Cf based on the connection point S is Vcf, the gate current flowing through the paths of Lg, ZD2, and ZD1 is ig, and the voltage between the gate and the source is Vgs, ig has a lag phase with respect to Vcf. And Vgs is also delayed.

On the other hand, when the Zener diode is off, the gate circuit is a circuit as shown in FIG. 3, and the capacitor Cgs is connected in series with the inductor Lg. In FIG. 3, the combined impedance of Cgs and Lg is only the resistance when the capacitance or the inductiveness or the reactance of Cgs and Lg becomes the same value from the relationship between the magnitude and frequency of Cgs and Lg. Therefore,
The gate current ig flowing through the impedance Zg composed of Cgs and Lg is equal to the voltage Vcf of Cf with respect to the connection point S.
In advance or lag, or in phase. Here, when the reactance of the capacitor Cgs is larger than the reactance of Lg, that is, in the case of a capacitance, the gate current ig advances with respect to the voltage Vcf of the Cf with respect to the connection point S, and the gate which is the voltage across Cgs. The voltage Vgs between the sources also advances.

Here, the operation of the gate circuit when the DC voltage applied to the lighting circuit fluctuates as shown in FIG. 4 will be described. For example, in the ordinary fluorescent lamp in which the discharge tube 1 of FIG. 1 includes a filament, when the DC voltage increases, the equivalent resistance RL of the fluorescent lamp decreases, and the combined capacitance on the resonant load circuit of FIG. The resonance frequency fo determined by the capacitance and the resonance inductor Lr decreases as shown in FIG. FIG. 5 shows the frequency characteristics of the gate circuit of FIG. FIG.
Is the phase difference φg of the gate voltage Vgs with respect to the resonance current iL when the resonance frequency fo changes, and the voltage V at the connection point S
s, that is, the phase difference φ of the resonance current iL with respect to the output voltage of the inverter and the operating frequency fs. FIG. 6 shows waveforms of the gate voltage Vgs, the resonance current iL, and the voltage Vs at the connection point S. From FIG. 5, as the resonance frequency fo increases, the phase difference φg decreases from φg1 to φg2. This is because when the impedance Zg of the series circuit composed of Cgs and Lg in FIG. 3 is capacitive, the impedance of the gate approaches inductive due to an increase in the resonance frequency fo. Thereby, the gate current ig flowing in the series circuit
The voltage Vgs between the gate and the source, which is the voltage across Cgs, is also delayed from the waveform shown by the broken line in FIG. 6 to the waveform shown by the solid line, and the phase difference φg becomes smaller. Also, as shown in FIG. 6, the voltage Vs at the connection point S is delayed from the waveform shown by the broken line to the waveform shown by the solid line, and the phase difference φ becomes smaller from φ1 to φ2 in FIG.

On the other hand, in the case of the self-excited lighting circuit as shown in FIG. 1, the operating frequency fs increases as the load resonance frequency increases as shown in FIG. However, since the phase difference φ is reduced from φ1 to φ2 as described above, fs is changed from fs1 to fs from the relationship between the phase difference φ and the operating frequency fs shown in FIG.
2, the increase of the operating frequency fs is suppressed. That is, the phase difference φg is automatically adjusted so as to reduce the change Δfs in the operating frequency with respect to the change Δfo in the resonance frequency. The capacitance of the capacitor C1 is set so that the change in the DC voltage is as small as possible. However, since the capacitor C1 has a relatively large shape among components used in the lighting circuit, it is desirable to reduce the capacitance and reduce the size. It is. When the capacitance of the capacitor C1 is reduced as described above, the change in the DC voltage increases, but the self-excited operation can be stably continued in accordance with the DC voltage and the load fluctuation by the above operation.

Next, a method for adjusting the brightness of the discharge tube will be described. In recent years, there is a lighting device equipped with a dimming function capable of arbitrarily adjusting brightness in lighting equipment. Adjusting the brightness of the discharge tube can be achieved by changing the magnitude of the current flowing through the discharge tube. In the resonance load circuit, the relationship between the operating frequency fs of the lighting circuit and the resonance current iL is as shown in FIG. 8, and as the operating frequency fs is increased with respect to the resonance frequency fo determined by the resonance inductor and the capacitor, the current of the discharge tube increases. Decrease. Based on this principle, the lighting circuit controls the operating frequency fs to perform dimming. The dimming of the incandescent lamp is performed by controlling the flow angle of the AC power supply AC by a dimmer using a triac and adjusting the power supplied to the light bulb. According to the present invention, in a lighting circuit using an inverter, for example, when a converter that outputs a DC voltage in accordance with AC whose flow angle is controlled by a dimmer is used, a discharge tube corresponding to a change in the DC voltage is used. Brightness can be adjusted. When the DC voltage changes, the resonance frequency of the load also changes as shown in FIG. In the above description, the phase difference φg of the gate voltage was adjusted so as to reduce the change in the operating frequency with respect to the change in the resonance frequency, and the self-excited operation was continued. In the lighting circuit described here for dimming, the dimming of the discharge tube is performed by increasing the change in the operating frequency fs with respect to the change in the resonance frequency fo.

FIG. 9 shows a configuration of a gate circuit for implementing dimming. FIG. 9 shows a configuration of a gate circuit in which a capacitor Cg is provided in parallel with the inductor Lg in FIG. 3, and shows a case where the Zener diode is off. 3 and 9,
Similar components have been described above with reference to FIG. 3, and description thereof will be omitted. In FIG. 9, capacitors Cgs, C
g and the inductor Lg have a combined reactance of Cgs,
From the relationship between the magnitudes and frequencies of Cg and Lg, only capacitance or inductive or resistance is required. Therefore, the current ig flowing through the gate circuit is advanced or delayed or in phase with respect to the voltage Vcf of Cf based on the connection point S. Here, as the resonance frequency increases, the capacitor C
The reactance Xc of g decreases and the reactance XL of inductor Lg increases. When the reactance Xc becomes smaller than XL, the combined impedance of the gate circuit becomes capacitive, and the voltage Vc of Cf with respect to the connection point S
The current iL flowing through the gate circuit advances with respect to f. As a result, the voltage Vgs between the gate and the source, which is the voltage across Cgs, also has an advanced phase, and the phase difference φg with respect to the resonance current iL increases. By connecting the capacitor Cg in parallel with the inductor Lg as described above, when the resonance frequency increases, as shown in FIG.
And the phase difference φ can be increased. That is, since the increase in the phase difference φ increases the operating frequency fs, the change Δfs in the operating frequency with respect to the change Δfo in the resonance frequency can be increased. FIG. 9 of the present invention.
When the resonance frequency increases, the reactance of the capacitor Cf decreases and the voltage Vcf of the Cf also decreases when the gate drive circuit uses the voltage of the capacitor Cf connected to the resonance load circuit. Vcf and gate voltage Vg
s is in a proportional relationship, and Vgs decreases as Vcf decreases. FIG. 11 shows operation waveforms when the amplitude of the gate voltage increases and decreases when the resonance frequency fo changes. In FIG. 11, the operation waveform when the resonance frequency fo is low is shown by a broken line, and the gate voltage Vgs
Becomes larger. When Vgs is large, the phase difference φ between the voltage Vs at the connection point S and the resonance current iL becomes small. On the other hand, when the resonance frequency fo increases, the operation waveform becomes as shown by the solid line, and the amplitude of the gate voltage Vgs decreases. As Vgs decreases, the phase difference φ increases. The present invention that performs the gate drive by feeding back the voltage of the capacitor Cf on the resonance load circuit is different from the gate drive using the conventional feedback transformer,
When the resonance frequency fo increases, the gate voltage is reduced to increase the phase difference φ, thereby increasing the operating frequency fs. Summarizing the above, the gate circuit as shown in FIG. 9 adjusts the phase difference φg of the gate voltage, and further adjusts the amplitude of the gate voltage Vgs using the capacitor Cf, thereby reducing the change Δfo in the resonance frequency. On the other hand, dimming is performed by increasing the change Δfs in the operating frequency.

The starting in the above-described embodiment has a circuit configuration in which the capacitor Cf connected to the resonance load circuit is charged according to the DC voltage to start the operation. On the other hand, a lighting circuit using a starting capacitor other than the capacitor Cf is shown in FIG. FIG. 12 shows the starting capacitor Cs in FIG.
1 and FIG. 12, the same components have been described above with reference to FIG. 1, and description thereof will be omitted. The starting capacitor Cs is connected between the connection point G and the connection point F in series with the inductor Lg. A resistor R1 is connected between the positive electrode of the capacitor C1 and the connection point G, and a resistor R2 is connected between the connection point S and the negative electrode of the capacitor C1. or,
A resistor Rd is connected in parallel to the capacitor Cf. At the time of starting, the starting capacitor Cs is charged via the resistors R1, R2, and Rd as the DC voltage increases, and a voltage substantially equal to the voltage of the starting capacitor Cs is applied between the gate and the source. When the voltage between the gate and the source exceeds the threshold voltage of the switching element Q1, Q1 turns on, current flows from the connection point S to the connection point F, and the voltage at the connection point F, that is, the voltage of the capacitor Cf decreases. Here, since the capacitor Cf, the starting capacitor Cs, the capacitor Cgs, and the inductor Lg connected between the connection point F and the connection point S constitute an LC resonance circuit, the capacitors Cs and Cf
Due to the slight voltage change, the current flowing through the LC resonance circuit increases, and the voltage amplitude between the gate and the source increases. Due to such an oscillation phenomenon, the switches Q1 and Q2 start switching operations alternately. After the start of the operation, the resistor Rd connected in parallel to the capacitor Cf has an effect of reducing the DC component of the voltage generated in the capacitor Cf, and does not adversely affect the operation. That is, Rd equalizes the positive and negative voltage amplitudes generated in Cf, makes the conduction period of the upper and lower switching elements equal, and stably maintains the operation of the lighting circuit. The embodiment using the starting capacitor can be modified other than the above-described configuration, and a configuration in which Cs is connected in series with a resistor between the connection points G and S in FIG. 12 may be used.

FIG. 13 shows a lighting circuit in which a starting inductor Ls is connected in series with a capacitor Cf between a connection point S and a connection point F. In the above description, a slight voltage change of the capacitor Cf or the starting capacitor Cs is used as a starting pulse to increase the voltage amplitude between the gate and the source. However, by using the starting inductor Ls as shown in FIG. A large induced voltage can be obtained with a small current, and reliable starting can be performed. After the start of the operation, the self-excited operation is not adversely affected by selecting the reactance of the capacitor Cf to be much larger than the reactance of the starting inductor Ls.

[0027]

According to the present invention, the high frequency operation of the lighting device is stabilized.

[Brief description of the drawings]

FIG. 1 shows a first embodiment of a lighting circuit according to the present invention.

FIG. 2 is a gate circuit when the Zener diode of FIG. 1 is in a conductive state.

FIG. 3 is a gate circuit when the zener diode of FIG. 1 is not in a conductive state;

FIG. 4 is a graph showing a relationship between a DC voltage change of FIG. 1 and an equivalent resistance and a resonance frequency of a discharge tube.

5 is a graph showing a relationship between a resonance current versus a gate voltage and a phase difference between an inverter output voltage and a resonance current and an operation frequency with respect to a resonance frequency of the gate circuit of FIG. 1;

FIG. 6 is an operation explanatory diagram of the embodiment in FIG. 1;

FIG. 7 is a graph showing a relationship between an inverter output voltage and a phase difference of a resonance current with respect to an operating frequency in the embodiment of FIG. 1;

FIG. 8 is a graph showing a relationship between an operating frequency of a lighting circuit and a resonance current in a resonance load circuit.

FIG. 9 shows a gate circuit for dimming according to the present invention.

10 is a graph showing the relationship between the phase difference between the resonance current and the gate voltage and the phase difference between the inverter output voltage and the resonance current and the operating frequency with respect to the resonance frequency of the gate circuit of FIG.

FIG. 11 is an explanatory diagram of the operation of the gate circuit in FIG. 9;

FIG. 12 shows a second embodiment of the lighting circuit according to the present invention.

FIG. 13 shows a third embodiment of the lighting circuit according to the present invention.

[Explanation of symbols]

1: discharge tube, AC: AC power supply, DB: rectifier circuit, Q1,
Q2: Power MOSFET, ZD1, ZD2: Zener diode, Zg: Impedance, C1, C2, Cd, C
r, Cf, Cgs, Cg, Cs: capacitor, Lg, L
r, Ls: inductor, R1, R2, Rd: resistance.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 41/282 H05B 41/29 A (72) Inventor Yuichi Minamimura 888 Fujibashi, Ome-shi, Tokyo Hitachi, Ltd. Heater Lighting Division F term (reference) 3K072 AA02 AA16 BA03 BB01 BC01 BC03 DD04 GA03 GB12 GC01 HA06 5H007 AA03 BB03 CA02 CB03 CB12 CB22 CC03 DA03 DB03

Claims (10)

[Claims] 1. A lighting device for supplying an alternating current to a discharge tube connected to a resonance means in accordance with switching of first and second semiconductor switching elements connected in series between a positive electrode and a negative electrode of a DC power supply. A control terminal and a reference terminal of the first and second semiconductor switching elements are connected to each other at a common point, and a connection point where the reference terminals of the first and second semiconductor switching elements are connected to each other. Connecting at least one of the poles of the DC power supply, a resonance unit to which the discharge tube is connected, and a first capacitor that generates a voltage synchronized with a current flowing through the resonance unit, in series, A voltage of a capacitor is applied to control terminals of the first and second semiconductor switching elements via a phase shift unit that shifts a phase according to a frequency change of the resonance unit. That lighting device. 2. A lighting device according to claim 1, wherein said phase shift means is a first inductor, and comprises a gate drive circuit comprising said first inductor and said first capacitor. . 3. The device according to claim 2, further comprising a second capacitor for limiting a voltage change of the control terminal between the control terminal and the reference terminal of the first and second semiconductor switching elements. A lighting device, comprising: a gate drive circuit including the capacitor and the first inductor. 4. The device according to claim 3, further comprising a clamp between a control terminal and a reference terminal of the first and second semiconductor switching elements, the clamp means restricting a voltage of the control terminal to an allowable value or less.
A lighting device comprising: a gate drive circuit comprising the clamp means, first and second capacitors, and the first inductor. 5. The lighting device according to claim 4, wherein a third capacitor is provided between a common connection point of the reference terminals of the first and second semiconductor switching elements and at least one pole of the DC power supply. apparatus. 6. The lighting device according to claim 5, further comprising starting means for applying a starting voltage to said first capacitor. 7. The semiconductor device according to claim 2, further comprising a fourth capacitor in parallel with said first inductor, and a gate drive circuit comprising said first and fourth capacitors and said first inductor. Characteristic lighting device. 8. The semiconductor device according to claim 2, further comprising: a starting capacitor connected between a positive electrode and a negative electrode of the DC power supply via a resistor, wherein the voltage of the starting capacitor is adjusted by the first and second semiconductor switching elements. A lighting device for applying a voltage between a control terminal and a reference terminal. 9. A circuit according to claim 2, further comprising a second starting inductor in series with said first capacitor, and a gate drive circuit comprising said first and second inductors and said first capacitor. A lighting device, characterized in that: 10. A lighting apparatus comprising: the lighting device according to claim 1; and an electrodeless fluorescent lamp as the discharge tube.