JPH0834698B2 - Inverter device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter device, and more particularly to a MOS (Metal Oxide Semiconductor) transistor, more broadly MIS (Metal Insulator Semiconductor) between a DC voltage input point and a load. The present invention relates to an inverter device which converts a DC voltage into an AC voltage corresponding to the single frequency by interposing a transistor in series and driving the MOS transistor with a signal having a single frequency. The device according to the invention may be, for example, an RF (radio frequency) excited CO
₂ (Carbon dioxide) Can be used as a high frequency power source for laser devices.

[Conventional technology]

FIG. 2 shows an example of a conventional configuration of the above-mentioned inverter device. In the figure, Q21, Q22, Q23 and Q24 are N
A channel type MOS transistor is shown, in which transistors Q21 and Q22 are connected in series and transistors Q23 and Q24 are connected in series between the input points of the DC voltage E _S. Load 20 is connected between the connection point of transistors Q21 and Q22 and the connection point of transistors Q23 and Q24. Further, drive signals V _GS1 , V _GS2 , V _GS3 , and V _{GS4 of} single frequency are applied to the gate terminals of the transistors Q21 to Q24, respectively. Here, the drive signals V _GS1 and V _GS4 are the same signal, V _GS2 and V _GS3 are also the same signal, and the former and the latter are in a phase opposite to each other. Therefore, the transistor pairs Q21 and Q24 and Q22 and Q23 alternately perform on / off operations according to the frequency of the drive signal V _GS1 . This allows the load to be applied when transistors Q21 and Q24 are on.
The voltage of E _S is applied to 20, and when the transistors Q22 and Q23 are in the ON state, the negative voltage of −E _S is applied to the load 20.

The capacitors C _S1 ′, C _S2 ′ C _S3 ′ and C _S4 ′ shown in broken lines in FIG.
Indicates the output capacitance between the drain and source of 21, Q22, Q23, Q24. Such output capacitance is determined by the size and impurity concentration of the drain region and the source region of the MOS transistor, the formation position between the drain and the source, and the existence thereof is generally known to those skilled in the art.

[Problems to be solved by the invention]

In the conventional inverter device described above, since the output capacitance (capacitor) exists between the drain and source of the switching MOS transistor, the switching operation is not performed promptly due to the charge / discharge characteristics of the capacitor. There was a problem. Therefore, for example, when the transistors (Q21, Q22, Q23, Q24) are switched from the (on, off, off, on) state to the (off, on, on, off) state, the capacitors are connected through the transistors Q21 and Q22. C _S1 'charging current and capacitor C _S2 of' the discharge current flows, at the same time, since the same charge and discharge current through transistors Q23 and Q24 flows, each of the on-resistance and the capacitor C _S1 of the transistor Q21 to Q24 '-C There is a problem that power loss occurs based on the value of _S4 '.

Further, as the frequency of the drive signals V _{GS1 to} V _GS4 becomes higher, the reactance of the capacitors C _S1 ′ to C _S4 ′ decreases and the current easily flows, so that the power loss further increases and the switching operation described above is further performed. However, there is also a problem that the speedup, that is, the higher frequency of the power source is impaired, because the speed inferiority of the above appears more conspicuously.

The present invention has been made in view of the above-mentioned problems in the conventional technology, and it is an object of the present invention to provide an inverter device capable of reducing power loss in the device to increase efficiency and increasing the frequency as a power supply. Has an aim.

[Means for solving problems]

According to the present invention, at least one MI is interposed in series between the DC voltage input point and the load and performs a switching operation according to the single frequency in response to the drive signal of the single frequency.
The S-transistor, the first inductance element that is inserted in series at the above-mentioned DC voltage input point and that makes the output current of the MIS transistor constant at the above-mentioned single frequency, and the above-mentioned load are connected in parallel. There is provided an inverter device including an equivalent total capacitance when looking at the input side and a second inductance element that resonates in parallel.

[Action]

In the inverter device according to the present invention, since the second inductance element that resonates with the equivalent total capacitance (equivalent capacitor) when the input side is viewed from the load is connected in parallel with the load, the drain / source of the MIS transistor is connected. The influence of the capacitance of the entire device including the output capacitance (capacitor) between is canceled by the second inductance element. This is equivalent to the absence of capacitors. Therefore, the power loss caused by the charging / discharging current of the capacitor flowing at the time of switching the MIS transistor can be eliminated, and the efficiency of the inverter device can be improved.

Further, since there is no influence of the capacitor, it is possible to solve the problem that the switching speed of the MIS transistor is impaired as the frequency of the drive signal increases in the conventional type. This means that there is no restriction on the upper limit of the frequency, in other words, that the device of the present invention can be used as a power source at high frequencies.

〔Example〕

FIG. 1 shows a circuit configuration of an inverter device as an embodiment of the present invention. The example shown in FIG. 1 is RF-excited CO ₂
The case where this device is incorporated as a high frequency power source of a laser device is shown.

In Fig. 1, RFC indicates a high frequency choke coil,
The coil is for keeping the current flowing through the circuit constant. Q1 to Q4 each represent an N-channel type MOS transistor, in which the transistors Q1 and Q2 are connected in series and the transistors Q3 and Q4 are connected in series via the high frequency choke coil RFC between the input points of the DC voltage E _S. . Also, the capacitors C _S1 , C _S2 , C _S3 , C shown in broken lines
_S4 represents the output capacitance between the drain and source of the transistors Q1, Q2, Q3, Q4, respectively. Reference numeral 10 denotes a laser tube as a load, which is a high frequency inverter output voltage V
_A pair of electrodes 10a, 10b to which _OUT is applied, and a quartz tube for discharge
It consists of 10c. A coil L is connected between the pair of electrodes 10a and 10b. 11 is a coaxial cable for electrically connecting the inverter circuit and the laser tube,
It has a central conductor 11a and an outer conductor 11b. Note that the capacitor C _O indicated by a broken line represents the equivalent capacitance of the cable 11. Laser tube 10 through the center conductor 11a of this cable
The one electrode 10a is connected to the connection point of the transistors Q1 and Q2, and the other electrode 10b of the laser tube 10 is connected to the connection point of the transistors Q3 and Q4 via the outer conductor 11b.

Drive signals V _GS1 , V _GS2 , V _GS3 , and V _GS4 having a single frequency f ₀ are applied to the gates of the MOS transistors Q1 to Q4, respectively. Here, the drive signals V _GS1 and V _GS4 are the same signal, V _GS2 and V _GS3 are also the same signal, and the former and the latter are in a phase opposite to each other. Therefore, the transistors Q1 and Q4 and Q2 and Q3 alternately perform on / off operations according to the frequency f _{0 of the} drive signal. As a result, a high frequency voltage of amplitude E _S corresponding to the frequency f ₀ is applied between the electrodes of the laser tube 10.

The coil L connected in parallel with the laser tube 10 is selected to have a value that causes parallel resonance with the equivalent total capacitance (equivalent capacitor) when the input side, that is, the inverter circuit side is viewed from both electrode ends of the laser tube. That is, between the value of each element and the frequency f _{0 of the} drive signal, There is a relationship. Here, the capacitor C _K is represented by (C _S2 + C _S3 ) or (C _S1 + C _S4 ). The former corresponds to the case where the transistors (Q1, Q2, Q3, Q4) are switched from the (ON, OFF, OFF, ON) state to the (OFF, ON, ON, OFF) state, and the latter, each transistor has its This corresponds to switching to the opposite state. Therefore, considering that the inductance of the coil L has a fixed value, the output capacitance of each of the transistors Q1 to Q4 is (C _S2 + C _S3 ) = (C _S1
It is necessary to select each transistor to satisfy the relationship of + C _S4 ).

As described above, the coil L and the equivalent capacitor (C _O +
Since C _K ) causes parallel resonance, the input impedance when looking at the inverter circuit side from both electrode ends of the laser tube becomes extremely large. That is, each output capacitance C _S1 to C of the transistor
The effect of the capacity of the entire device including _S4 is canceled by the action of the coil L. Therefore, the power loss caused by the charging / discharging current of each output capacitance flowing through the transistor at the time of switching the transistor is eliminated, and the power conversion efficiency of the entire device is increased. Especially the frequency of the drive signal
The higher f ₀ , the more pronounced this effect.
This is because when the coil L is not connected, the reactances of the output capacitors (capacitors) C _{S1 to} C _S4 of the transistors Q1 to Q4 decrease as the frequency increases, which facilitates the flow of current, thus reducing the power consumption. This is because the loss will increase further.

In addition, since there is no influence by the capacitors C _{S1 to} C _S4 of each transistor, in other words, the state in which there is no equivalent frequency-dependent element is realized, and each transistor is switched by the drive signal of frequency f _0. When operating, it is not necessary to place a restriction on the upper limit of the frequency f ₀ . As a result, the device shown in FIG. 1 can be used as a power source and can have a high frequency, and further, the switching of the MOS transistors Q1 to Q4 can be promptly performed regardless of the magnitude of the frequency f ₀ .

Therefore, the inverter device of this embodiment is extremely advantageous for a load such as the laser tube 10 used in this embodiment whose efficiency increases as the applied voltage frequency increases.

Although the CO ₂ laser is described as an example in the present embodiment, the present invention is not limited to this, and is applicable to all other gas lasers such as He-Ne, CO, and excimer.

〔The invention's effect〕

As described above, according to the present invention, it is possible to reduce the power loss in the inverter device, increase the power conversion efficiency, and increase the frequency of the power source.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an inverter device as an embodiment of the present invention, and FIG. 2 is a circuit configuration diagram showing an inverter device as an example of a conventional type. (Explanation of symbols) 10… Load (laser tube), 11… Coaxial cable, Q1 to Q4… MO
S transistor, RFC ... High frequency choke coil, L ... Coil, C _{S1 to} C _S4 ... Output capacitance (capacitor), C _O ... Cable capacitance, E _S ... DC voltage, V _{GS1 to} V _GS4 ... Drive signal, V _OUT ... Inverter Output voltage.

Claims (1)

[Claims] 1. A at least one MIS transistor interposed in series between a DC voltage input point and a load for performing a switching operation in response to a drive signal of a single frequency in accordance with the single frequency. A first inductance element that is inserted in series with the DC voltage input point and that keeps the output current of the MIS transistor constant at the single frequency, and is connected in parallel with the load, and when the input side is viewed from the load. An inverter device comprising: a second inductance element that resonates in parallel with the equivalent total capacitance.