JPH0330291A - Inverter device - Google Patents

Abstract

PURPOSE:To reduce the switching loss by alternating the high frequency operating period when switching elements are mutually turned on/off to supply the high frequency power to a load and the direct current operating period when one of the switching elements is turned on/off to supply the direct current power to the load at the time of no-load in a load circuit. CONSTITUTION:A load circuit in which capacitors C3, C4 are connected to a load H in parallel and an inductor L1 is connected to the load H in series is comprised. At the time of no-load in this load circuit, the high frequency operating period when a first and a second switching elements Q1, Q2 are mutually turned on/off to supply the high frequency power to the load H and the direct current operating period when one of the first and the second switching elements Q1, Q2 is turned on/off to supply the direct current power to the load H are alternated in a cycle lower than the on/off cycle of the switching elements Q1, Q2. Consequently, In the case that the load H is not started in the high frequency operating period, the direct current operating period following to the high frequency operating period becomes the dormant period practically after conclusion of charge of a capacitor connected to the load H in parallel. The reactive current flowing to the switching elements Q1, Q2 at the time of start is thereby reduced to reduce the switching loss.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter device using semiconductor switching elements, and is particularly suitable for, for example, starting and lighting a high-pressure discharge lamp.

[Prior Art] Figure 14 is a circuit diagram of a conventional inverter device. The circuit configuration will be explained below. The DC power supply E includes a transistor Q. , Q2 are connected in parallel. Transistor Q. , Q2 has a diode D +
, D2 are connected in antiparallel. An LC series resonant circuit consisting of an inductor L and a capacitor C1 is connected to both ends of the transistor Q1 via a coupling capacitor C2. The capacitance value of the coupling capacitor C2 is set to a sufficiently larger value than that of the resonance capacitor C1, and is charged to approximately half the voltage of the DC power supply E during steady state, and does not contribute to resonance. Capacitor C
A discharge lamp H is connected in parallel to both ends of I.

Figure 15(a) shows the voltage across the discharge lamp H at startup.
This is a waveform diagram of No. 2. In the figure, T1 is the first operation period, and transistor Q. ．． Q2 performs on/off operations alternately. When transistor Q, is on and transistor Q2 is off, the charging voltage of capacitor C, is used as the power source,
From capacitor C2 to transistor Q1, capacitor C,
, a current flows through the inductor L1. Next, when transistors QQ2 are both turned off, the inductor and r
Due to efit energy, current flows through capacitor C2, DC power supply E, diode D2, and capacitor CI. Next, transistor Q. is off and transistor Q
2 is on, the capacitor C2,
A current flows through the inductor L1, the capacitor C+, and the transistor Q2. Next, when transistors Q, Q2 are both turned off, current flows through capacitor C diode D1 and capacitor C2 due to the energy stored in inductor L1. Since the discharge lamp H is in a no-load state, almost no current flows below 9. The same process is repeated until the inductor L. A high frequency current flows through the LC series resonant circuit consisting of the capacitor C and the capacitor C. The frequency of this high-frequency current is determined by the switching frequency of the transistors Q, , Q2, and is usually several tens of K}{z.

In the first operating period T1 shown in FIG. 15(a), the switching frequency is set close to the resonant frequency of the LC series resonant circuit, and the voltage across the capacitor C1 increases due to resonance, so the discharge lamp H The voltage V2 across the terminal gradually increases. When this voltage V2 reaches a predetermined value Vp, the second operation period T2 begins.

Also in the second operating period T2, transistors Q, . Q2 is turned on and off alternately, but the switching frequency is set to a frequency that is different from the resonant frequency of the LC series resonant circuit. Therefore, the resonance effect weakens and the voltage across the capacitor C decreases, so the voltage v2 across the discharge lamp H decreases. The discharge lamp H is operated during the first operation period T. It is started by the high voltage Vp and shifts to a glow discharge state. Then, the high-frequency power supplied during the second operation period T2 causes a transition to an arc discharge state. However, in this conventional example, the transistor Q remains in an unloaded state until the discharge lamp H starts. ,Q. must continue to operate on and off, and reactive current must continue to flow through the LC series resonant circuit. This reactive current becomes a large current even in a no-load state, so the transistor Q. , Q2 and diode D + ,
D There is a problem of putting too much stress on 2. In particular, when the high voltage Vp is generated by the resonance effect, the current intermittent by the transistors Q 1 and Q 2 is large, which increases switching loss and heats the element. For this reason, an element with a large current withstand capacity is required, resulting in an increase in cost and an increase in the size of the device. Therefore, when starting the discharge lamp H, the transistor Q. It is conceivable to turn on and off transistors Q2 and to pause transistors Q, , Q2 during the second operation period T2. The operating waveform in this case is
This is shown in Figure 5 (b). In this method, transistor Q. ，
Since Q2 operates intermittently, the stress applied to the element is reduced. However, in this method, even if the discharge lamp H enters the glow discharge state due to the high voltage Vp, after that,
It is not possible to supply the energy to transition to the arc discharge state. Therefore, it is necessary to provide a circuit to detect the glow discharge state, and when the start of glow discharge is detected, to switch to continuous supply of power to transition to arc discharge, which complicates the configuration of the control circuit. There is a problem with doing so.

Figure 16 shows another conventional inverter device (Japanese Unexamined Patent Publication No. 62-2
6791).

This inverter device is suitable for lighting a high pressure discharge lamp H because it can supply square wave electric power to the negative reed. Because,
This is because when the high-pressure discharge lamp H is lit with high-frequency power, the arc becomes unstable due to an acoustic resonance phenomenon, but when the high-pressure discharge lamp H is lit with rectangular wave power, the acoustic resonance phenomenon can be avoided.

The circuit and configuration of the inverter device will be explained below. The DC power supply E includes a series circuit of transistors Q, , Q2 and a transistor Q. ,Q. series circuits are connected in parallel. Diodes D and D4 are connected in antiparallel to the transistors Q and Q4, respectively. Transistor Q, . Q2 connection point and the transistor Q. ．． Q.
An inductor L and a pulse transformer P are connected between the connection points of
A high pressure discharge lamp H is connected via the secondary winding of T.

A capacitor C is connected in parallel to a series circuit between the secondary winding of the pulse transformer PT and the high pressure discharge lamp H, and an igniter IG is connected in parallel. Transistor Q,,
Q, is switched at a high frequency of several tens of KHz, and transistors Q2 and Q4 are switched at a low frequency of several hundred KHz. Figure 17 shows the waveform of the voltage V2 across the high-pressure discharge lamp H in the above circuit at the time of starting. During the operating period Ta in which the voltage 2 is positive, the transistor Q is turned on, and the transistor Q2 . With Q3 turned off, transistor Q
, is turned on and off at high frequency. Further, during the operation period Tb in which the voltage V2 is negative, the transistor Q2 is turned on, and the transistors Q, . Q. While turning off transistor Q
3 is turned on and off using high frequency. Each operating period T a ,
At Tb, high voltage Vp generated by igniter IQ is applied to high pressure discharge lamp H via pulse transformer PT and capacitor CI. As a result, the high-pressure discharge lamp H enters a glow discharge state. The energy of the DC voltage Va following the high voltage Vp causes the high pressure discharge lamp H to
transitions from a glow discharge state to an arc discharge state. In this conventional example, a high voltage Vp for starting the high pressure discharge lamp H is generated by an igniter IG and a pulse transformer PT. However, the igniter IG and pulse transformer PT are unnecessary circuits after starting, and the provision of such starting-only circuit components poses the problem of increasing the size and cost of the lighting device. [Problems to be Solved by the Invention] As shown in FIG. 15(a), in an inverter device that does not include circuit components dedicated to starting, such as an igniter or a pulse transformer, as in the conventional example shown in FIG. When the LC resonance effect is used to generate a high voltage for starting and to supply energy after starting, there is a problem in that stress on the switching elements increases. Furthermore, if only the high voltage for starting is generated intermittently to reduce the stress on the switching elements, as shown in Figure 15(b), there is a problem that energy cannot be supplied after starting. , it is necessary to detect the start and quickly switch the operation, which poses a problem in that the configuration of the control circuit becomes complicated. On the other hand, as shown in FIG.
Although this does not cause the problems of increased stress on the switching elements or increased complexity of the control circuit, it does require circuit components dedicated to starting, which causes the problem of an increase in the size and cost of the lighting device. The present invention has been made in view of these points, and its purpose is to drive a load such as a high-pressure discharge lamp that requires high voltage at startup and energy supply after startup. The object of the present invention is to realize a small and inexpensive inverter device suitable for.

[Means for Solving the Problems] In the present invention, in order to solve the above problems, the first
As shown in FIG. 2 and FIG. 2, the load circuit includes a load (for example, a discharge lamp H), a capacitor C1 connected in parallel and an inductor L1 connected in series, and at least first and second switching elements (for example, a transistor Q, . . . Q2) connected in series is connected in parallel to a DC power supply E, and in an inverter device that supplies power to a load circuit by the switching operation of the switching element, when the load circuit is not loaded, the first and second A high-frequency operation period T,,T, in which the switching elements of the switching elements alternately turn on and off to supply high-frequency power to the load, and one of the first or second switching elements turns on and off to supply DC power to the load. DC operation period T2, T. The present invention is characterized by comprising a control means for alternating the on-off period of the switching element at a lower period than the on-off period of the switching element.

[Function] In the present invention, when the load circuit is not loaded, the first and second switching elements alternately turn on and off to supply high frequency power to the load. ,T. and the first
Or a DC operation period T. in which one of the second switching elements turns on and off to supply DC power to the load. ,T. and,
Since the alternation is performed at a cycle lower than the on/off cycle of the switching element, the high frequency operation period T + , T
By setting the switching frequency at T.s near the resonant frequency of the load circuit, the load can be started by applying a high voltage Vp to the load, and the DC operating period T.s.
,T. can supply energy to the load after startup. If the load does not start at the high voltage Vp during the high frequency operation period T + , T s, the load is in a no-load state (
Since the high impedance state remains, no current flows through the load circuit after the capacitor C1 connected in parallel with the load is charged.

That is, in the present invention, the high frequency operation periods T1, T,
If the load does not start at the high voltage Vp of T. is substantially the rest period of the switching element. Thereby, it is possible to reduce the reactive current flowing through the switching element at the time of starting, and it is possible to reduce switching loss. Moreover, the high frequency operation period T. , T, when the load is started at high voltage Vp,
Subsequent DC operating periods T2, T. Since energy can be supplied to the load in the conventional example, there is no need to provide special detection means or control means for switching the switching operation from intermittent operation to continuous operation, which simplifies the configuration.

[Example 1] FIG. 1 is a circuit diagram of a first embodiment of the present invention.

The circuit structure will be explained below. The DC power supply E includes transistors Q, . Series circuit of Q2 and capacitor C
,,C. The series circuits are connected in parallel. Each transistor Q, . Q t has a diode D +
, D2 are connected in antiparallel. Each capacitor C,,C. is charged with approximately half the voltage of DC power supply E. Transistor QI. A discharge lamp H is connected through an inductor L1 between the connection point of Q2 and the connection point of capacitors Cs and C4.

A capacitor C is connected in parallel to the discharge lamp H.

Each transistor Q. , Q2 are supplied with control signals as shown in FIG. 2, respectively.

During the operation period T + , T 3 shown in FIG. 2, the transistors Q, , Q. performs on/off operations alternately. As a result, a high frequency voltage is applied to the discharge lamp H. next,
During the operation period T2, a positive DC voltage is applied to the discharge lamp H by turning on and off the transistor Q1 at high frequency while the transistor Q2 remains off. Further, during the operation period T4, a negative DC voltage is applied to the discharge lamp H by turning on and off the transistor Q2 at a high frequency while the transistor Q remains off. Therefore, the voltage V2 across the discharge lamp H becomes as shown in FIG.

Here, the operation period T. , T, will be explained in detail. During this period, transistor Q
．． ．． Q2 is turned on and off alternately after a predetermined dead-off time.
It will be turned off. First, when transistor Q is on and transistor Q2 is off, capacitors C and J are connected to transistor Q. , inductor L, and capacitor C1 to discharge capacitor C, while current flows from DC power source E to transistor Q1 through inductor L1 and capacitor C to charge capacitor C. Ru. Since discharge lamp H is in a no-load state,
Almost no current flows. After that, transistor Q. ，
When Q2 are both turned off, the stored energy in inductor L causes inductor L. A current flows from the capacitor CI, the capacitor C4, and the diode D2. next,
When the transistor Q1 is off and the transistor Q2 is on, current flows from the capacitor C through the inductor and the transistor Q2, discharging the capacitor C, and also discharging the capacitor C from the DC power supply E.
, capacitor C1, inductor, transistor Q
Current flows through C2 to charge capacitor C3.

Then transistors Q, . When both Q2 are turned off, the stored energy in inductor L1 causes the inductor to
A current flows from the diode D through the capacitor C, and the capacitor C. Thereafter, the above process is repeated, and a high frequency current flows through the series resonant circuit of inductor L1 and capacitor C1. The frequency of this high frequency current is determined by the frequency of the transistors Q, ,Q. determined by the switching frequency of Therefore, if the switching frequency is set to a frequency close to the resonant frequency of the series resonant circuit (usually a frequency slightly higher than the resonant frequency), a high frequency and high voltage will be generated across the capacitor C1 due to the resonance effect, and the discharge lamp H is applied to The amplitude of this high frequency high voltage can be freely set depending on the relationship between the resonant frequency of the series resonant circuit consisting of inductor L and capacitor C1 and the switching frequency of transistors Q1 and Q2. If you change the circuit constants of inductor L1 and capacitor C1 and the design values of switching frequency according to the lighting conditions,
It becomes possible to obtain desired starting performance.

Figure 6 shows the transistor Q during the operating period T, , T, l.
,,Q. 3 is a graph showing the relationship between the switching frequency f of , and the high voltage Vp obtained by the switching frequency. In the diagram, ``. is the resonant frequency of the load circuit under no load, that is, the resonant frequency of the series resonant circuit consisting of the inductor and capacitor C1. Operating period T + , T
The switching frequency r of the transistor QQ2 at z is set in the frequency range fa to rb, which is slightly higher than the resonance frequency f0, as shown by the shaded area in FIG. In this frequency range, since the resonance frequency is close to 10, the amplitude of the high voltage Vp can be increased, and since a slow phase current flows, the circuit operation is stabilized.

FIG. 7 shows that during the operating period T1, the switching frequency f
The waveform of voltage V2 is shown when V2 is decreased from rb to fa. In this case, the resonance effect gradually becomes stronger, so
The voltage V2 applied to the discharge lamp H gradually increases. Note that even when the switching frequency f is not changed, the resonance effect gradually becomes stronger, so that an operating waveform as shown in FIG. 7 is obtained.

FIG. 8(a) shows the waveform of voltage V2 when the switching frequency r is varied in the range fa to rb during the operating period T,,T, and FIG. 8(b) shows the waveform of the voltage V2 during the operating period T,,T.
．． ,T. , the switching frequency f is changed from fa to '
The waveform of the voltage v2 is shown when the voltage v2 is increased to b. In this way, the operating period T. , T3, by changing the switching frequency ', the peak high current FE-V
The timing of giving p can be changed. In FIG. 7, the operating period T. At the end of FIG. 8(a), the operating period T
．． , T, and in FIG. 8(b), the operating period T. ,T
, a peak high voltage Vp is applied at the beginning of each. Which of these operating waveforms to select may be determined depending on the starting characteristics of the discharge lamp H, the circuit configuration, etc.
Next, the circuit operation when a positive DC voltage is generated during the operation period T2 will be described. During this period, transistor Q2 remains off and transistors Q,
only performs on/off operations at high frequencies. First, when the transistor Q1 is on, a current flows from the capacitor C through the transistor Q1, the inductor L1, and the capacitor C, discharging the capacitor C. ．． Current flows through capacitor C, and capacitor C4 is charged. Since discharge lamp H is in a no-load state,
Almost no current flows. Next, when transistor Q is turned off, current flows from inductor L1 through capacitor CI, capacitor C, and diode D2 due to the energy stored in inductor L. Thereafter, the above process is repeated to create a chopper circuit with inductor L1 and capacitor C as smoothing elements and diode D2 as a feedback current path, and capacitor C1 is charged with DC voltage. Next, a description will be given of the circuit operation when a negative DC voltage is generated during the operation period T. During this period, transistor Q, remains off and transistor Q2
only performs on/off operations at high frequencies. First, when the transistor Q2 is on, a current flows from the capacitor C4 through the capacitor C1 inductor L1 and the transistor Q2, discharging the capacitor C, and also from the DC power supply E to the capacitor C3, the capacitor CI, the inductor L1, and the transistor Q2. Current flows through the capacitor C, charging it. Next, when transistor Q2 turns off, the energy stored in inductor L1 causes inductor L. from diode D. Current flows through capacitors C and CI. Hereafter, repeat the above process, use the inductor L and capacitor C1 as smoothing elements,
A chopper circuit with diode D as a feedback current path is installed, and capacitor C1 is charged with a DC voltage of opposite polarity to the operating period T2. Note that during the operating period T2, T, when the discharge lamp H is in a no-load state, charging of the capacitor C1 is completed in the first few cycles, and no current flows thereafter. Therefore, the operating period T. ,T. If the discharge lamp H does not start at the high voltage Vp of T. is essentially a hiatus period. In addition, when the discharge lamp H is started at the high voltage Vp during the operation period T,,T,, the following operation period T2T4 is a period for supplying energy to transition the discharge lamp H from the glow discharge state to the arc discharge state. becomes. When the discharge lamp H is a high-pressure discharge lamp, it is preferable that after starting, the operation periods T 2 and T 4 are periodically repeated for rectangular wave lighting. Further, when the discharge lamp H is a fluorescent lamp, after starting, the operation period TT may be continued and high-frequency lighting may be performed.

[Example 2] FIG. 3 is a circuit diagram of a second embodiment of the present invention.

In this embodiment, the capacitor C.
,C. In place of transistor Q. ．． Q. This is a connection of . Each transistor Q. ,Q. has a diode D. ,D. are connected in antiparallel. In this embodiment, transistor Q. ．． The control signal supplied to Q2 is the same as the control signal shown in FIG. Further, the control signal supplied to transistor Q is the same as the control signal supplied to transistor Q2, and the control signal supplied to transistor Q4 is the same as the control signal supplied to transistor Q.

First, during the operating period T + , T s , the transistor Q. A first state in which Q4 is on and transistors Q2, Q, are off, a second state in which transistors Q, -Q, are all off, and a second state in which transistors Q, . is off and transistor Q2. Q. A high frequency voltage is applied to the discharge lamp H by repeating the third state in which the transistors are on and the fourth state in which all the transistors Q1 to Q are off in the same order. Next, the operation period T. Now, transistor Q2.
Q, remains off and transistors Q, . Q. is turned on and off at high frequency, and a DC voltage is applied to the discharge lamp H.
Further, during the operation period T4, the transistors Q, . Q. remains off, transistor Q2. Q, is turned on and off at a high frequency, and a DC voltage of opposite polarity to the operating period T2 is applied to the discharge lamp H. Therefore, in this embodiment, the voltage V2 applied to the discharge lamp H has the waveform shown in FIG. 4, as in the first embodiment.

However, since Example 1 has a half-bridge configuration,
The magnitude of the DC voltage Va is approximately half of the voltage V1 of the DC power supply E, but since this embodiment has a full bridge configuration,
The magnitude of the DC voltage Va is approximately the same as the voltage V of the DC power supply E.

Therefore, this embodiment is particularly suitable when the tube voltage during lighting of the discharge lamp H is high. FIG. 5 is an explanatory diagram of the operation of Examples 1 and 2. Figure (a)
shows the configuration of the load circuit in Example 1.2.

In Example 1.2, the input voltage VAB of the load circuit changes as shown in FIG. In the second embodiment, it is approximately equal to the voltage V of the DC power supply E. By the way, in each of the above embodiments, the discharge lamp H has an operating period of T. , T, but the inventors of the present invention attempted a starting test under various conditions and found that the operation period T2, T. It was discovered that the magnitude of the DC voltage Va applied at the engine is also deeply related to the starting performance.
FIG. 9 shows the results of investigating the relationship between the magnitude of the DC voltage Va applied to the discharge lamp H during the operating period T2, T, and the starting probability of the discharge lamp H. The discharge lamp H used in the starting test was
Metal halide lamp 70W (made by Osram) IQI-I
This is a random item (S70W/WDL). This discharge lamp H
The rated value is tube voltage = 95V (+10V to -15V),
Tube current = 0.92A, tube power = 75W. As is clear from FIG. 9, when the DC voltage Va applied to the discharge lamp H during the operating periods T2 and T4 becomes less than 1.5 times the tube voltage, the starting probability decreases significantly, and the DC voltage Va Voltage 2
It was found that good starting performance can be obtained when the temperature is increased by ~3 times. Also, if the DC voltage Va is made too high, it is necessary to increase the voltage withstand capacity of switching elements, etc.
The DC voltage Va is limited to three times the tube voltage or less, as this will lead to an increase in cost and an increase in the size of the device. Therefore, the operating periods T2, T. It is preferable that the DC voltage Va applied to the discharge lamp H be set in a range of 1.5 to 3 times the tube voltage during lighting.

FIG. 10 is a waveform diagram showing the voltage v2 across the discharge lamp H during the starting test. In the figure, the operating period T + .
The switching frequency at T:l is about 80KHz, and the high voltage Vp generated during the same period is about 4400KHz.
It is V. In addition, the pulse width at 3600V (voltage value is 3
The time during which the voltage exceeds 600V is approximately 2 μsec. The length of the operating periods T + and T 3 is approximately 100 Jjsec
However, good starting performance was obtained in the range of several tens of microseconds to several 118 ee. Operating period T2, T. The length of is about 1
0IIsec, but good starting performance was obtained in the range of several msec to several + msec. Operating period T. ,T. The high voltage Vp at is necessary to transition the discharge lamp H from the no-load state to the glow discharge state, and the DC voltage Vp during the operating periods T 2 and T 4 is
a is necessary to shift the discharge lamp H from the glow discharge state to the arc discharge state. If this DC voltage Va is too low, although the discharge lamp H enters the glow discharge state, sufficient current does not flow through the discharge lamp H, and the lamp cannot shift to the arc discharge state. Therefore, to start the discharge lamp H, the operating period T,
,T. Not only the high voltage Vp but also the operating period T 2 ,
The DC voltage Va of T4 is also required. [Embodiment 3] Figure 11 is a circuit diagram of a third embodiment of the present invention. This embodiment differs from the embodiment shown in FIG. 1 in that a step-up chopper circuit X is connected to the output side of the DC power supply E. The configuration of this boost chopper circuit X will be explained below. One end of an inductor L is connected to the positive pole of the DC power supply E. The other end of the inductor L is connected to the negative pole of the DC power supply E via the transistor Q. The connection point between inductor L and transistor Q is connected via diode D to one end of a series circuit of capacitors C3 and C4. The other end of the series circuit of capacitors C s and C 4 is connected to the negative pole of DC power supply E. The operation of this boost chopper circuit X will be explained below. When the transistor Q is on, the DC current from the DC power supply E flows through the inductor L through the transistor Q5.
, and energy is stored in the inductor L. Next, when the transistor Q5 is turned off, the inductor L generates a voltage across it, and the voltage obtained by adding the voltage across the inductor L3 to the voltage V of the DC power supply E is applied to the capacitor C via the diode D. ．． , C is applied to the series circuit of 4. Similarly, transistors Q,
By switching the voltage v1 of the DC power supply E
A voltage higher than that of capacitors C , , C . can be obtained in a series circuit. Also, the on-state of transistor Q,
By changing the duty (ratio of on-time to the switching period), the voltage obtained in the series circuit of capacitors C3 and C4 can be freely set. As already mentioned, the operating periods T2, T. The DC voltage Va applied to the discharge lamp H is determined by the charging voltage of the capacitors Cs and C. Therefore, at startup, the discharge lamp H
DC voltage Va about 1.5 to 3 times the tube voltage when lighting
Good starting performance can be obtained by controlling the on-duty of the transistor Qs in the boost chopper circuit X so that . On the other hand, after the discharge lamp H is started, the DC voltage Va does not need to be approximately 1.5 to 3 times the tube voltage, and may be set to a voltage suitable for the load conditions. Therefore, it is preferable to switch the on-duty of the transistor Q in the boost chopper circuit X before and after starting the discharge lamp H. Note that the chopper circuit connected to the output side of the DC power supply E is not limited to a step-up type, but may be a step-down type. However, the voltage obtained by rectifying and smoothing the AC power supply is the DC voltage V required for starting.
Since it is generally lower than a, it is preferable to use a boost chopper circuit X as in this embodiment. [Embodiment 4] FIG. 12 is a circuit diagram of a fourth embodiment of the present invention. This embodiment uses transistors Q, .
A control signal as shown in Fig. 2 is given to Q2 to control the discharge lamp H.
A voltage (2) as shown in FIG. 4 is obtained across both ends of the line.

In the conventional example shown in FIG. 14, the load circuit is connected in parallel to the transistor Q1 on the high potential side via the coupling capacitor C2, and in the present embodiment, the load circuit is connected in parallel to the transistor Q2 measuring the low potential. However, it is not a substantial difference. If a capacitance value of several tens of μF to several hundred μF is used as the coupling capacitor C2, in a steady state, a voltage approximately half of the voltage V1 of the DC power source E will be charged to the capacitor C. Ru. Therefore, in this embodiment, the operating period T 2 . The magnitude of the DC voltage Va applied to the discharge lamp H at T4 is approximately half of the voltage V1 of the DC power supply E. [Embodiment 5] FIG. 13 is a circuit diagram of a fifth embodiment of the present invention.

In this embodiment, in the embodiment shown in FIG. 1, the secondary winding of the pulse transformer PT is connected in series with the discharge lamp H in the load circuit. Additionally, a resonant circuit for generating starting voltage is connected in parallel with the load circuit. The structure of this resonant circuit for generating starting voltage will be explained below. Transistor Q. ,Q. One end of capacitor C2 is connected to the connection point of capacitors C 3 , C
One end of the capacitor C0 is connected to the connection point 4,
An inductor L2 is connected between the other end of the capacitor C2 and the other end of the capacitor Co. The primary winding of a pulse transformer PT is connected to both ends of the capacitor C0. Capacitor C0 and inductor L2 form a series resonant circuit, and due to their resonance, a voltage generated across capacitor C0 is applied to discharge lamp H via pulse transformer PT and capacitor CI. In this embodiment, the high voltage for starting is boosted by a pulse transformer PT, and the discharge lamp H
, the current flowing through the switching element during the operation period TT can be reduced.

In this embodiment, transistors Q, . Q. The control signal given to is the same as the control signal shown in Figure 2. The switching frequency during the operating periods T + and T s may be set slightly higher than the resonant frequency of the series resonant circuit of the inductor L2 and the capacitor co. In addition, the inductor Ll and capacitor C may be designed based on operation during steady lighting. The inductor has an operating period T, ,T,
The coupling capacitor C2 is designed to block high frequencies during the operating period T, , T. The design should be designed to block the direct current at . Note that in each of the above embodiments, the operation period T. ,T. Although the polarity of the DC voltage at is inverted, the operating period T t
, the polarity of the DC voltage at T4 may be the same. In this case, the waveform diagram of the voltage (2) across the discharge lamp H becomes as shown by the broken line in FIG.

[Effects of the Invention] The present invention includes a load circuit in which a capacitor is connected in parallel to a load and an inductor is connected in series, and when the load circuit is not loaded, the first and second switching elements are alternately turned on and off. The high-frequency operation period when the switching element is turned off and supplies high-frequency power to the load, and the DC operation period when one of the first or second switching elements is turned on and off and supplies DC power to the load are determined by turning the switching element on and off. Since the alternation is performed at a lower frequency than the current cycle, if the load does not start during the high-frequency operation period, the subsequent DC operation period will essentially become a rest period after the capacitor connected in parallel with the load has completed charging. This has the effect of being able to reduce the reactive current flowing through the switching element during startup, and reducing switching loss. Moreover, if the load starts during the high-frequency operation period, energy can be supplied to the load during the following DC operation period, so a special There is no need to provide detection means or control means, and the effect is that elliptical precepts are simplified. If the high voltage for starting is generated by the inductor and capacitor in the load circuit, there will be no need for circuit parts dedicated to starting, which will have the effect of reducing costs and making the device smaller and lighter. ．． In addition, when the load is a discharge lamp, good starting performance can be obtained by setting the DC voltage during the DC operation period to a range of 1.5 to 3 times the tube voltage when the discharge lamp is lit. effective,

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention, FIG. 2 is an operating waveform diagram of the same as above, FIG. 3 is a circuit diagram of a second embodiment of the present invention, and FIG. 4 is an operating waveform diagram of the same as above. 5(a) and 5(b) are a circuit diagram and a waveform diagram for explaining the operation of the present invention, respectively.
8 are explanatory diagrams of the operation during the high frequency operation period of the present invention, FIGS. 9 and 10 are explanatory diagrams of the operation during the DC operation period of the present invention, and FIG. 11 is a circuit diagram of the third embodiment of the present invention. , FIG. 12 is a circuit diagram of a fourth embodiment of the present invention, FIG. 13 is a circuit diagram of a fifth embodiment of the present invention, FIG. 14 is a circuit diagram of a conventional example, and FIG. 15 is an operation waveform diagram of the same as above. , FIG. 16 is a circuit diagram of another conventional example, and FIG. 17 is an operating waveform diagram of the same. E is a DC power supply, Q, , Q2 are transistors, C1 is a capacitor, L1 is an inductor, H is a discharge lamp, TT3 is a high frequency operation period, T2, T. is the DC operating period. Figure 1

Claims (3)

[Claims] (1) A load circuit including a capacitor connected in parallel to a load and an inductor connected in series, a circuit in which at least a first and a second switching element are connected in series is connected in parallel to a DC power supply, and the switching element is In an inverter device that supplies power to a load circuit through a switching operation, a high-frequency operation period in which the first and second switching elements alternately turn on and off to supply high-frequency power to the load when the load circuit is not loaded; It is characterized by comprising a control means for alternating the DC operation period in which one of the first and second switching elements is turned on and off to supply DC power to the load, at a cycle lower than the on-off cycle of the switching element. inverter device. (2) Claim 1 characterized in that the switching frequencies of the first and second switching elements during the high frequency operation period are set near the resonant frequency of the load circuit when no load is applied.
The inverter device described. (3) The load is a discharge lamp, and the DC voltage applied to the load during the DC operation period is 1.5% of the tube voltage when the discharge lamp is lit.
The inverter device according to claim 1, wherein the inverter device is set in a range of 5 times to 3 times.