JPH05176550A - Inverter apparatus - Google Patents

Abstract

PURPOSE:To facilitate the secure inverter operation of an inverter apparatus which is constituted by the combination of a chopper circuit having an inductor for energy storage and an inverter circuit having a load circuit including a resonance circuit even if the terminal voltage of a switching device varies following the voltage of a smoothing capacitor. CONSTITUTION:The terminal voltage of a switching device 52 and the voltage of a smoothing capacitor 41 are respectively divided by resistors 61-64 and compared with each other by a comparator 65. The output of the comparator 65 is supplied to a single-shot multivibrator circuit 73 for driving as its synchronizing timing signal. With this constitution, even at the time of start when the voltage of the smoothing capacitor 41 is not yet high enough and during the period of voltage rising while the voltage of the smoothing capacitor 41 varies, the synchronizing timing signal can be obtained securely, so that an inverter circuit can perform an oscillating operation steadily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device in which a chopper circuit for obtaining DC power from an AC power source and an inverter circuit for converting this DC power into high frequency power are combined.

[0002]

2. Description of the Related Art FIG. 4 shows a conventional inverter device (Japanese Patent Application No.
1-335332)). The circuit configuration will be described below. The AC input terminal of the diode bridge DB is connected to the AC power source E via a filter circuit including capacitors C ₁ and C ₂ and a transformer T ₁ . The DC output terminal of the diode bridge DB has an inductor L ₁ , a diode D ₁ and a MOS transistor Q _1.
Two series circuits are connected. MOS transistor Q
_A capacitor C ₃ is connected to both ends of ₂ through a diode D _2.
Are connected. A series circuit of a bipolar transistor Q ₁ and a MOS transistor Q ₂ is connected to both ends of the capacitor C ₃ . At both ends of the transistor Q ₁ ,
The discharge lamp FL is connected via the DC cut capacitor C ₄ and the primary winding of the inductor T ₂ . Discharge lamp FL
A resonance capacitor C ₅ is connected in parallel between the non-power supply side terminals of the filament. The secondary winding of the inductor T ₂ is connected to the base of the transistor Q ₁ via the resistor R _13.
It is connected between the emitters. MOS transistor Q ₂
A series circuit of resistors R ₁₁ and R ₁₂ is connected in parallel to both ends of. The connection point of the resistors R ₁₁ and R ₁₂ is input to the drive circuit C. The output of the drive circuit C is the MOS transistor Q ₂
Has been entered into the gate.

In this device, a MOS transistor
Q₂The switching of chopper circuit and inverter circuit
It is shared as an element. Bipolar transistor Q
₁Is the inductor T₂From the secondary winding of the load circuit resonance current
Is fed back for self-excited driving, and MOS transistor Q
₂Is a voltage dividing resistor R₁₁，
R ₁₂Detected by, and control the ON section by drive circuit C
is doing. In this case, the load circuit capacitor C_Four, C_Five
And inductor T₂Switch than natural vibration frequency by
Ringing frequency is set higher than the excitation voltage of the resonant circuit.
The resonance current is driven in the lag mode in which the lag phase occurs. this
The drive system of the device is disclosed in Japanese Patent Application No. 63-297276.
Has been done.

The operation of the circuit shown in FIG. 4 in the steady state will be described with reference to the operation waveform diagram of FIG. Figure 5 (A)
The waveform of the voltage across the transistor Q _1, FIG. 5 (B) is a waveform of the current flowing through the diode D ₂ and the transistor to Q ₁ when considering only the inverter circuit, FIG. 5 (C) is considered only chopper circuit 7 is a waveform of a current flowing through the diode D _{2 at} that time. Actually, a current obtained by combining the currents of FIGS. 5B and 5C flows through the diode D ₂ and the transistor Q ₁ as shown in FIG. 5D. The ON section of the transistor Q ₁ has the capacitors C ₄ and C ₅ and the discharge lamp F.
It is determined by the resonant current waveform determined by L and the inductor T ₂ . Similarly, FIG. 5 (E) shows a MOS transistor Q.
₂ shows the waveform of the voltage across both ends, FIG. 5 (F) shows the waveform of the current flowing in the MOS transistor Q ₂ when only the inverter circuit is considered, and FIG. 5 (G) shows the transistor Q ₂ when only the chopper circuit is considered. It is the waveform of the current flowing through. Actually, a current obtained by combining the currents of FIGS. 5F and 5G flows in the MOS transistor Q ₂ as shown in FIG. 5H. Here, the ON period of the transistor Q _{2 formed} of the power MOSFET is determined by the drive circuit C by detecting that a current flows through the antiparallel diode parasitic on the transistor Q ₂ and the voltage across the diode has fallen. ..

FIG. 6 is a circuit configuration in which the inverter device of FIG. 4 is further embodied (see Japanese Patent Application No. 01-335334).
Indicates. The inverter circuit 5 includes a transistor 51 and a MOSFET 52 as main switching elements. A diode 53 is connected in antiparallel to the transistor 51, and a MOSFET 52 includes a parasitic diode 54 in the reverse direction. At both ends of the transistor 51,
Capacitor 5 through DC cut capacitor 57
8 and the primary circuit 55a of the transformer 55 are connected in series. Further, the secondary winding 55b of the transformer 55 is used as a feedback means, and the oscillating current of the inverter circuit 5 is fed back to the base terminal of the transistor 51, which is one of the switching elements, via the resistor 56.

Next, the smoothing circuit 4 includes an inductor 42,
MOSFET 52 and diode 5 of the inverter circuit 5
3 and a smoothing capacitor 41.
That is, the MOSFET 52 and the diode 53 of the inverter circuit 5 are also used as the switching means for the chopper of the smoothing circuit 4. The output of the rectifier circuit 3 is applied to the MOSFET 52 via the inductor 42, and when the MOSFET 52 is turned on, the inductor 42 is turned on.
When electromagnetic energy is accumulated in the MOSFET and the MOSFET 52 is turned off, this electromagnetic energy is released to the smoothing capacitor 41 via the diode 53. The DC voltage charged in the smoothing capacitor 41 is supplied to the inverter circuit 5
Becomes the input voltage of.

Next, the inverter starting circuit 6 comprises a series circuit of resistors 61 and 62 connected in parallel to both ends of the MOSFET 52 in order to detect the off state of the transistor 51. In the series circuit of the resistors 61 and 62, the inductor 4
The rectification output of the rectification circuit 3 is applied via 2, and the rectification signal of the commercial power supply 1 is applied at the time of startup. Upon receiving the output of the inverter starting circuit 6, the control circuit 7 generates a signal for controlling the on / off of the MOSFET 52. Here, the control circuit 7 is composed of a monostable multivibrator circuit 73, a resistor 71 and a capacitor 72 for determining the output pulse width thereof.
The monostable multivibrator circuit 73 is composed of a general-purpose integrated circuit (for example, μPD4538 manufactured by NEC Corporation), and after the falling trigger input terminal B changes from High level to Low level, the output terminal Q is High for a certain period of time. The level and the output terminal Q'become Low level.
In this embodiment, the output signal of the inverter starting circuit 6 is the trigger signal of the monostable multivibrator circuit 73. The time when the output terminal Q of the monostable multivibrator circuit 73 becomes High level (the output terminal Q'is L
The time when it becomes the ow level) is the resistance 71 and the capacitor 72.
It is determined by the time constant of. The output terminal Q is connected to the gate terminal of the MOSFET 52 via the drive circuit 8 including an integrated circuit for buffer (eg, μPD4050 manufactured by NEC Corporation). The drive circuit 8 is for amplifying the output current of the output terminal Q of the monostable multivibrator circuit 73. Therefore, the monostable multivibrator circuit 73
Operates as a timer circuit for determining the ON period of the MOSFET 52. The commercial power supply 1 and the rectifier circuit 3
A filter circuit 2 including capacitors 21 and 24 and transformers 22 and 23 is inserted between the AC input terminals. The filter circuit 2 is designed to have a low impedance with respect to the commercial AC frequency from the commercial power source 1 and a high impedance with respect to the switching frequency of the chopper type smoothing circuit 4, and the smoothing circuit 4
The switching current flowing through is smoothed so that the input current has a waveform close to a sine wave.

The operation of the above circuit will be described separately when the inverter circuit is started (before the inverter circuit starts oscillation) and after the inverter circuit is started (after the inverter circuit starts oscillation).

(A) Operation at Startup of Inverter Circuit First, when the commercial power supply 1 is turned on, the output voltage of the rectifier circuit 3 and the capacitors 41, 57 and 58 and the resistors 61 and 62 are provided across the MOSFET 52. A combined voltage of the voltages generated by discharging via is applied.
A voltage waveform diagram obtained by dividing this voltage by the resistors 61 and 62 is shown in FIG. At this time, the relationship between the voltage V ₆ divided by the resistors 61 and 62 and the threshold voltage value Vth of the trigger input terminal B of the monostable multivibrator circuit 73 is set as shown in FIG. ing. Now, when the voltage V ₆ across the resistor 62 changes from a state higher than the threshold voltage value Vth of the trigger input terminal B of the monostable multivibrator circuit 73 to a state lower than the threshold voltage value Vth, the output terminal Q of the monostable multivibrator circuit 73.
Becomes high level for a certain period of time, as shown in FIG. The time when the output terminal Q becomes High level is determined by the resistor 71 and the capacitor 72. As a result, the MOSFET 52 is turned on, a current flows from the smoothing capacitor 41 through the capacitor 57, the capacitor 58, and the primary winding 55a of the transformer 55, and the capacitor 57 is charged. At this time, the transistor 51
Is reverse-biased by the secondary winding 55b of the transformer 55, and is turned off. Eventually, the output terminal Q of the monostable multivibrator circuit 73 becomes low level, and M
The OSFET 52 is turned off. At this time, since the current flowing through the primary winding 55a of the transformer 55 becomes zero, a reverse voltage is induced in the secondary winding 55b, the transistor 51 is turned on, the discharge of the capacitor 57 is started, and eventually. When the current becomes zero, the transistor 51 turns off. When the transistor 51 is turned off, the output voltage of the rectifier circuit 3 is applied again via the inductor 42, and the MOSFET 52 is turned on again as described above. As described above, the inverter circuit is activated and eventually shifts to the oscillation mode.

(B) Operation after startup of inverter circuit FIG. 8 is an operation waveform diagram showing a high frequency operation of the above circuit. FIG. 8A shows a voltage Vd ₂ across the MOSFET 52,
The figure (b) shows the voltage across the resistor 62, and the figure (c) shows the output voltage of the secondary winding 55 b of the transformer 55. Further, FIG. 8D shows the forward current Ic _{2 of the} MOSFET 52.
And the reverse current Id ₂ , and the figure (e) shows the forward current Ic ₁ of the transistor 51 and the current Id ₁ flowing in the diode 53.
Is shown. In FIG. 8, the period t ₁ is MOSF.
This is a period in which the ET 52 is off and the transistor 51 is on. During the period t _2, the transistor 51 is off and the MOSF is on.
This is the period when the ET 52 is on. Here, the inverter circuit 5 is operated by the operation at the time of start-up described in (a) above.
When an oscillating current starts to flow into the secondary winding 55 of the transformer 55,
The transistor 51 is biased by b, and the electric charge accumulated in the capacitor 57 is used as a power source to supply a current I to the transistor 51.
c ₁ flows (see FIG. 8 (e)). At this time, the core of the transformer 55 is linearly magnetized toward the saturation magnetic flux.
Eventually, when the core reaches saturation flux, the inductance rapidly goes to zero, resulting in transistor 5
The time variation of the collector current of 1 becomes infinite. The collector current Ic _{1 of the} transistor 51 is the base current hfe
When it reaches double, the transistor 51 becomes unsaturated,
Since the induced voltage in each winding 55a, 55b of the transformer 55 decreases, the base current fed back also decreases, and the transistor 51 is turned off. Even after the transistor 51 turns off,
Since the oscillating current flowing in the primary winding 55a of the transformer 55 tries to flow in the same direction, the parasitic diode 54 of the MOSFET 52 becomes conductive, and the current Id ₂ passes through the load 9 including a discharge lamp, the capacitor 57, and the capacitor 41. Flowing. When the parasitic diode 54 becomes conductive, the MOSFET 5
Since the drain voltage Vd ₂ of ₂ becomes zero, the falling trigger input terminal B of the monostable multivibrator circuit 73 changes from the high level to the low level, and the output terminal Q of the monostable multivibrator circuit 73 becomes the high level, The gate terminal of MOSFET 52 is forward biased. After the oscillating current Id ₂ flowing in the parasitic diode 54 of the MOSFET 52 becomes zero, the capacitor 4
A combined current Ic _{2 of the} oscillating current flowing from 1 through the inverter circuit and the current flowing from the rectifying circuit 3 through the inductor 42 flows. At this time, electromagnetic energy due to the current flowing is accumulated in the inductor 42. Eventually, after a lapse of a predetermined time determined by the resistor 71 and the capacitor 72, the output terminal Q of the monostable multivibrator circuit 73.
Goes low and the MOSFET 52 is turned off. The electromagnetic energy stored in the inductor 42 when the MOSFET 52 is turned on is released to the smoothing capacitor 41 via the diode 53 and the diode bridge of the rectifier circuit 3 when the MOSFET 52 is turned off.
The smoothing capacitor 41 is charged. In this case, the current flowing through the diode 53 is a combined current of the oscillating current from the inverter circuit 5 and the output current of the rectifying circuit 3.

[0011]

In the above-mentioned conventional example, an inverter starting circuit 6 for starting the inverter circuit 5 by inputting the rectified output of the commercial power source 1 to the control circuit 7 of one MOSFET 52, and an inverter circuit. 5 MOSFE
Since the circuit for detecting the OFF of T52 is also used, an inexpensive inverter device can be provided. However, when the inverter circuit 5 is activated, the threshold voltage Vth of the trigger input terminal B of the monostable multivibrator circuit 73 is set between the maximum value V ₁ and the minimum value V ₂ of the voltage V ₆ across the resistor 62. There is a need.
However, since the maximum value V ₁ and the minimum value V ₂ of the voltage V ₆ across the resistor 62 change depending on the input voltage, there is a problem that it cannot handle the input voltage in a wide range. further,
After the inverter starts operating, the voltage of the smoothing capacitor 41 increases due to the boosting action of the chopper circuit, the voltage applied across the MOSFET 52 increases, and the voltage across the resistor 62 changes to the threshold voltage Vt.
There is a problem in that the ON drive signal in the forward direction is not given to the MOSFET 52 without being lower than h.

For example, as shown in FIG.
When the flywheel current If flowing in the reverse parasitic diode of the FET 52 is large, the flywheel current If is large.
The voltage V ₆ across the resistor 62 becomes equal to or lower than the threshold voltage Vth while the MOSFET 52 is flowing.
A positive ON drive signal is applied to. However,
When the flywheel current If decreases due to a decrease in the power supply voltage or the like, as shown in FIG. 9B, the voltage V ₆ across the resistor 62 is maintained during the flywheel current If is flowing.
However, when the flywheel current If disappears, the voltage V ₆ across the resistor 62 starts to increase.
Therefore, the threshold voltage is V in FIG.
If it is set high like th ₁ , the MOSFET 5 is turned off when the voltage V ₆ across the resistor 62 becomes Vth ₁ or less.
2 is given a positive ON drive signal and the inverter operation continues, but the threshold voltage is shown in FIG.
If it is set to a low value like Vth _2, the voltage V ₆ across the resistor 62 does not become Vth ₂ or less, so that the MOSF
The forward drive signal is not given to the ET 52, and the inverter operation does not continue. Therefore, it is preferable to set the threshold voltage as low as possible near the maximum value of the voltage V ₆ across the resistor 62. However, as described above, when the inverter circuit is started or when the boosted voltage is still low, on the contrary, the threshold voltage may be higher than the maximum value of the voltage V ₆ across the resistor 62. In this case, the threshold voltage Vth is always higher than the voltage V ₆ across the resistor 62, and even in this case, the MOSFET 52 is not supplied with the ON drive signal in the positive direction and the inverter does not operate. ..

The present invention has been made in view of the above circumstances, and an object thereof is to combine a chopper circuit having an inductor for energy storage and an inverter circuit having a load circuit including a resonance circuit. In the inverter device, it operates reliably even at startup or when the boost voltage of the chopper circuit is low, and when the flywheel current decreases due to momentary power failure or power fluctuation after reaching normal stable operation, It is to ensure that the inverter operation can be performed.

[0014]

According to the present invention, in order to solve the above problems, as shown in FIG. 1, a first switching element (bipolar transistor 51 and diode 53) that does not block a reverse current is provided. ) And a second switching element (MOSFET 52) in series with a smoothing power source (capacitor 41) connected in parallel, and includes a resonance circuit by alternately turning on and off the first and second switching elements. When an inverter circuit that supplies high-frequency power to the load circuit and one switching element (MOSFET 52) in the inverter circuit are turned on, a current flows from the AC power supply 1 to the energy storage inductor 42 through the switching element, and the inductor 42 is energized. Is stored, and when one of the above switching elements is off, the other switching A chopper circuit for releasing the stored energy in the inductor 42 to the smooth power through the reverse current current path of the child (diode 53), in synchronization with the falling of the voltage across one of the switching elements described above,
In an inverter device provided with a drive circuit (monostable multivibrator 73) that turns on one of the switching elements for a certain period of time, the voltage across the switching element is compared with a reference voltage that changes according to the voltage of the smoothing power supply. The output signal of the comparison circuit 65 is a synchronization timing signal of the drive circuit.

[0015]

In the circuit of FIG. 1, the threshold level (threshold voltage) for detecting the fall of the voltage across the MOSFET 52 is changed according to the power supply voltage of the smoothing capacitor 41 boosted by the chopper circuit. Therefore, it operates reliably even at startup or when the boost voltage of the chopper circuit is low, and after reaching normal stable operation,
Even if the flywheel current decreases due to momentary power failure or power fluctuation, the inverter can be operated reliably.

[0016]

1 is a circuit diagram of a first embodiment of the present invention.
The configuration and basic operation of the inverter device are the same as those of the conventional circuit of FIG. 4, but the voltage obtained by dividing the voltage across the MOSFET 52 by the resistors 61 and 62 and the voltage across the smoothing capacitor 41 by the resistors 63 and 64. The characteristic is that the divided voltage is compared by a comparison circuit 65 composed of an IC for operational amplifier, and the output signal is applied to the falling trigger input terminal B of the monostable multivibrator circuit 73. That is, in the conventional circuit, as shown in FIG.
The voltage V _{6 obtained} by dividing the voltage across the FET 52 by the resistors 61 and 62 was compared with the constant threshold voltage Vth determined by the monostable multivibrator circuit 73. Therefore, when the flywheel current is small,
As shown in FIG. 2B, the voltage drop across the MOSFET 52 is small, and the voltage drop across the MOSFET 52 may not be detected. On the other hand, in the present embodiment, the reference voltage Vt to be compared with the above voltage V ₆ according to the increase or decrease of the voltage across the smoothing capacitor 41.
h'will change. With this configuration, there are the following advantages.

First, since the chopper is not operating at startup, the smoothing capacitor 41 can obtain a pulsating current voltage obtained by rectifying and smoothing the input voltage. This pulsating voltage is applied to the resistor 6
Assuming that the voltage across the resistor 64 obtained by dividing by 3 and 64 is the reference voltage Vth 'of the comparison circuit 65, it is set such that V ₁ >Vth'> V ₂ as shown in FIG. Then, as shown in FIG. 2D, the comparison circuit 65 detects that the voltage V ₆ is lower than the reference voltage Vth ′, the activation is started, and the inverter circuit starts the oscillation operation. As a result, the chopper circuit operates and the voltage across the smoothing capacitor 41 is boosted.
The voltage applied to both ends of T52 rises and the resistances 61 and 6
Although the voltage V ₆ across the resistor 62 divided by 2 increases,
Accordingly, the voltage Vth ′ of the resistor 64 obtained by dividing the smoothing capacitor 41 by the resistors 63 and 64 also becomes high. That is,
No matter how the boosted voltage of the chopper circuit changes, both the reference voltage Vth ′ and the detection voltage V ₆ change, and they compensate each other. Therefore, the transistor 51 in the upper stage is affected by the influence of the power supply fluctuation, the momentary power failure, etc. described above.
Even when the voltage drop across the lower MOSFET 52 is small when the transistor is turned off, the transistor 51 can be reliably detected to be turned off and the oscillation operation can be continued.

FIG. 3 is a circuit diagram of the second embodiment of the present invention. The circuit configuration will be described below. The inverter circuit has a half-bridge structure, and power MOSFE
A series circuit of transistors Q ₁ and Q _{2 formed} of T and a series circuit of capacitors C ₅ and C ₆ are capacitors C ₃ for smoothing.
LC connected in parallel between the transistor Q ₁ and Q ₂ and between the connection points of the capacitors C ₅ and C ₆ and including an inductor L ₂ , a capacitor C ₇ and a discharge lamp FL.
The resonance circuit is connected as a load circuit. Here, the capacitances of the capacitors C ₅ and C ₆ are the capacitors C ₇ for resonance.
The capacitance is sufficiently larger than that of the capacitors C ₅ and C ₆ and does not contribute to resonance.

Transistor Q of the inverter circuit₁, Q₂
The control electrode of the transistor Q₁, Q₂Turn on alternately
-The drive signals that turn off are drive circuits I, respectively.
C₁, IC₂Sourced from. AC power supply E
C Densa C₁, C₂And trance T ₁Consisting of
AC input terminal of the diode bridge DB is connected via
The DC output terminal of the diode bridge DB is connected to
Inductor L₁And diode D₁And transistor Q₂Directly
The column circuit is connected. This inductor L₁Is a die
Aether D₁And transistor Q₁Reverse parasitic diode
And smoothing capacitor C₃And diode bridge DB
It forms a closed circuit with the DC output terminal of.

The chopper circuit in this embodiment comprises a transistor Q ₂ , a diode D ₁ , a reverse parasitic diode of the transistor Q ₁ , a smoothing capacitor C ₃ and an inductor L ₁ . When the transistor Q ₂ is on, a current flows from the diode bridge DB through the inductor L ₁ , the diode D ₁ and the transistor Q ₂ , and energy is stored in the inductor L ₁ .
Then, when the transistor Q ₂ turns off, the inductor L
Stored energy diode D ₁ of the _1, the transistor Q
It is discharged through the reverse parasitic diode of ₁ , the capacitor C ₃ , and the capacitor C ₃ is charged. As a result, the AC power source E can be switched to obtain a smooth DC voltage in the capacitor C ₃ .

Next, the transistor Q₁Drive circuit IC₁
The configuration of will be described. Drive circuit IC₁Is a general security
Constant multivibrator circuit (for example, NEC Corporation)
Manufactured by μPD4538), the power supply terminal Vdd,
Low voltage DC power supply E for Vss₁DC voltage is applied
It In addition, this monostable multivibrator circuit IC₁of
Time constant setting terminal T₁, T₂Is the capacitor C₈Connected
Has been done. This capacitor C₈Is the resistance R₃Through
Be charged. Therefore, the monostable multivibrator times
Road IC₁Pulse width of one-shot pulse output from
Is the resistance R₃And capacitor C₈Determined by the time constant of
It Also, the transistor Q₁The voltage across the_Five，
R₆Detected by the operational amplifier.
Comparing circuit IC consisting of IC for use_FiveApplied to the non-inverting input terminal of
Has been done. This comparison circuit IC_FiveThe inverting input terminal of
Smoothing capacitor C₃The voltage across both ends of the resistor R₉, R_TenIn minutes
The applied voltage is diode D₂Marked as reference voltage via
Has been added. This comparison circuit IC_FiveOutput signal of the drive
Circuit IC₁Sync signal to the falling trigger input terminal B of
Has been entered as. Drive circuit IC₁Inversion output terminal of
The output signal obtained at Q'is an inverting circuit IC.₃By phase
After being reversed, the resistance R₁Through transistor Q₁of
It is input to the control pole. Transistor Q₂Drive circuit
IC₂Is the transistor Q₁Drive circuit IC₁alike
It is configured. The diode D ₂The Transis
Q₂When R is off, the resistance R_TenThe voltage across both ends of the comparison circuit I
C_FiveGround level (transistor Q₁, Q₂Connection
Voltage level of the point), the comparison circuit IC_Five
Prevents high negative voltage from being applied to the inverting input terminal of
It has been inserted in order to do.

[0022]

According to the present invention, a chopper circuit including an inductor for energy storage and an inverter circuit including a load circuit including a resonance circuit are combined, and switching common to the chopper circuit and the inverter circuit is performed. In an inverter device configured to operate the drive circuit of the switching element by detecting the fall of the voltage across the element, in response to the voltage across the switching element changing according to the voltage of the smoothing power source, Since the reference voltage for detecting the fall of the voltage across the switching element is also changed in the same way, when the smoothing power supply is not completely boosted, such as when starting, or the voltage of the smoothing power supply changes during the boosting process. Even if it does, the sync timing signal of the drive circuit is surely obtained and the inverter circuit stabilizes. There is an effect that it is possible to perform the oscillation operation.

[Brief description of drawings]

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

FIG. 2 is a waveform diagram for explaining an operation of the present invention and a conventional example.

FIG. 3 is a circuit diagram of a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a first conventional example.

FIG. 5 is a waveform diagram for explaining the operation of the first conventional example.

FIG. 6 is a circuit diagram of a second conventional example.

FIG. 7 is a waveform diagram for explaining a low frequency operation of a second conventional example.

FIG. 8 is a waveform diagram for explaining a high frequency operation of a second conventional example.

FIG. 9 is a waveform diagram for explaining a problem of the second conventional example.

[Explanation of symbols]

 41 smoothing capacitor 42 chopper inductor 51 bipolar transistor 52 MOS transistor 53 diode 55 transformer 57 capacitor for cutting DC component 58 resonance capacitor 61 resistor 62 resistor 63 resistor 64 resistor 65 comparator circuit 73 monostable multivibrator circuit

Claims (1)

[Claims] 1. A first and a second which do not block a reverse current.
An inverter circuit that supplies high-frequency power to a load circuit including a resonance circuit by connecting a series circuit of switching elements in parallel to both ends of a smoothing power source and alternately turning on and off the first and second switching elements. , When one of the switching elements in the inverter circuit is turned on, a current is passed from the AC power supply to the energy storage inductor through the switching element to store energy in the inductor, and when one of the switching elements is turned off, the other switching element A chopper circuit that discharges the energy stored in the inductor to the smoothing power supply via the reverse current conduction path, and the one switching element is turned on for a fixed time in synchronization with the fall of the voltage across the one switching element. And a drive circuit for The voltage across the switching element, an inverter apparatus according to claim output signal of the comparator circuit for comparing a reference voltage which changes in accordance with the voltage of the smoothing power supply that has a synchronization timing signal of the driving circuit.