JP7184485B2 - Voltage converter, high frequency power supply for plasma generation - Google Patents

Description

The present invention relates to a voltage converter and a high frequency power supply for plasma generation.

A voltage converter such as a DCDC converter is sometimes provided with a constant resistance between output terminals in order to stabilize the operation of the switching power supply when the output voltage is low.

FIG. 5 shows an example (prior art) of a voltage conversion device 50 having a constant resistance between output terminals. The voltage conversion device 50 of FIG. 5 includes a DC power supply unit 11, a second semiconductor switch 12 (hereinafter referred to as a second FET 12), a diode 13, an inductor 14, a smoothing capacitor 15, and a second FET control unit 21 that controls the second FET 12. It is an asynchronous rectification step-down DCDC converter that steps down the DC voltage applied from the DC power supply unit 11 and supplies the stepped-down DC output voltage to the load S3'.

The voltage conversion device 50 further includes a first semiconductor switch 51 (hereinafter referred to as a first FET 51), a resistor 52, a voltage detection unit 17 that detects the voltage value (output voltage value) of the output voltage of the voltage conversion device 50, and the control of the first FET 51. is provided with a first FET control unit 53 for performing For example, Japanese Patent Application Laid-Open No. 2002-300002 describes a technique in which a semiconductor switch and a resistor are provided between output terminals as in the voltage conversion device 50 of FIG. 5 .

In the voltage converter 50 of FIG. 5, when the output voltage is low and the impedance of the load S3' is high, the output current becomes small and the operation becomes difficult to stabilize. Therefore, when the output voltage is low, the first FET 51 is turned on so that the current also flows through the resistor 52 . This ensures stable operation of the voltage conversion device 50 .

JP 2014-054027 A

However, in the voltage converter 50 of FIG. 5, the resistance value of the resistor 52 is a fixed value. Moreover, the on-resistance value of the first FET 51 is also a substantially constant value. Therefore, in the region where the first FET 51 is turned on, the power loss increases as the output voltage of the voltage conversion device 50 increases. Moreover, the resistance value changes abruptly before and after the black value of the output voltage which determines whether the first FET 51 is turned on. That is, the impedance of the load S3' viewed from the voltage conversion device 50 changes suddenly, causing a problem in terms of stability.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a voltage converter or the like having a variable resistor between output terminals having a resistance value corresponding to an output voltage.

A voltage conversion device according to an aspect of the present disclosure is a voltage conversion device that converts an input voltage into a predetermined output voltage, and is connected between output terminals to which the output voltage is output, and the output voltage is applied. a semiconductor switch, a voltage detection unit for detecting an output voltage value between the output terminals, a current detection unit for detecting a current value flowing through the semiconductor switch, and a target current corresponding to the output voltage value detected by the voltage detection unit a target current value setting unit for deriving a value; and a semiconductor switch control unit for controlling the on-resistance of the semiconductor switch so that the current value detected by the current detection unit approaches the target current value. do.

In this aspect, the semiconductor switch connected between the output terminals and to which the output voltage is applied can function as a variable resistor having a resistance value corresponding to the output voltage.

The voltage conversion device according to one aspect of the present disclosure further includes a storage unit that stores a target resistance value corresponding to the output voltage value detected by the voltage detection unit, and the target current value setting unit stores the storage unit. By referencing, a target resistance value corresponding to the output voltage value detected by the voltage detection unit is derived, and a target current value is derived using the output voltage value detected by the voltage detection unit and the target resistance value. characterized by

In this aspect, since the storage unit is provided in which the target resistance value corresponding to the output voltage value detected by the voltage detection unit is stored, the resistance value between the output terminals of the voltage conversion device is stored as the output voltage of the voltage conversion device. It can be adjusted according to the voltage value. Moreover, since the resistance value can be freely determined, it is possible to set the resistance value suitable for the output voltage value of the voltage converter.

The voltage conversion device according to one aspect of the present disclosure further includes a storage unit that stores a target current value corresponding to the output voltage value detected by the voltage detection unit, and the target current value setting unit stores the storage unit. By referencing, a target current value corresponding to the output voltage value detected by the voltage detection unit is derived.

In this aspect, since the storage unit is provided in which the target current value corresponding to the output voltage value detected by the voltage detection unit is stored, the resistance value between the output terminals of the voltage conversion device is stored in the output of the voltage conversion device. It can be adjusted according to the voltage value. At this time, the process of deriving the target current value using the output voltage value and the target resistance value can be omitted compared to the case where the target resistance value corresponding to the output voltage value is stored in the storage unit.

A high-frequency power supply for plasma generation according to one aspect of the present disclosure includes a voltage conversion device according to one aspect of the present disclosure, and an RF output device that converts a DC voltage output from the voltage conversion device into an AC voltage and outputs the and

In this aspect, the high-frequency power supply (high-frequency power supply for plasma generation) includes a voltage conversion device according to one aspect of the present disclosure and an RF that converts a DC voltage output from the voltage conversion device into an AC voltage and outputs it. and an output device. Therefore, by causing the current control section to function as a variable resistor having a resistance value appropriate to the output voltage, it is possible to provide a high-frequency power supply for plasma generation that can reduce loss, for example.

In the present invention, the semiconductor switch connected between the output terminals and to which the output voltage is applied can function as a variable resistor having a resistance value corresponding to the output voltage.

1 is a schematic diagram showing one configuration example of a plasma control system according to Embodiment 1. FIG. 1 is a schematic circuit configuration diagram showing one configuration example of a voltage converter according to Embodiment 1. FIG. 4 is a flow chart showing a processing procedure by a current control unit; FIG. 4 is an explanatory diagram of a resistance table stored in a storage unit; 1 is a schematic circuit configuration diagram showing one configuration example (prior art) of a voltage conversion device in which a constant resistance is provided between output terminals; FIG.

A voltage conversion device 1 according to the present invention is used as one component of a high-voltage power supply device such as a plasma control system S, for example. For the sake of simplification, elements that are the same or similar to those of the prior art are given the same reference numerals.

(Embodiment 1)
FIG. 1 is a schematic diagram showing one configuration example of a plasma control system S according to the first embodiment. The plasma control system S is used when performing plasma processing such as etching in a semiconductor matching process, and includes, for example, a plasma load S3, a matching box S2, and a high frequency power supply S1.

The plasma load S3 includes a plasma chamber (not shown) in which plasma is generated, and generates plasma in the plasma chamber with high-frequency power supplied from the high-frequency power supply S1 to perform plasma processing such as etching in a semiconductor matching process. I do.

The matching box S2 is interposed between the high frequency power supply S1 and the plasma load S3. The matching box S2 is, for example, the output impedance of the high-frequency power supply S1, and the load-side impedance when the plasma load S3 side is viewed from the output end of the high-frequency power supply S1 or the input end of the matching box S2, which is equivalent to the output end of the high-frequency power supply S1. It is a device that adjusts the capacitance value of an internal variable capacitor (not shown) so that the The function of the matching box S2 can suppress the reflected power from the plasma load S3. Note that the matching box S2 is not an essential component, and the plasma load S3 and the high-frequency power supply S1 may be directly connected.

The high-frequency power supply S1 is, for example, an AC power supply that outputs a high-frequency voltage (high-frequency power) in an RF band (Radio Frequency) such as 2 MHz, 13.56 MHz, 27 MHz, or 60 MHz. set to a value. This high-frequency power supply S1 includes a voltage conversion device 1 that converts an input DC voltage into a predetermined DC voltage and outputs it, and an inverter circuit (not shown) that converts the output voltage output from the voltage conversion device 1 into a predetermined and an RF output device S11 (RF power supply) that converts and outputs a high-frequency alternating voltage (RF voltage).
In such a high-frequency power supply S1, for example, the power value at the output end is controlled to a desired power value, so in the following description, power is described as a controlled variable instead of voltage.

FIG. 2 is a schematic circuit configuration diagram showing one configuration example of the voltage converter 1 according to the first embodiment. The voltage converter 1 includes a DC power supply unit 11, a second semiconductor switch 12 (hereinafter referred to as a second FET 12), a diode 13, an inductor 14, a smoothing capacitor 15, and a second FFT control unit 21 that controls the second FET 12. 11, and supplies the stepped-down DC output voltage to the load S3'. 2, the RF output device S11 and the matching device S2 shown in FIG. 1 are omitted. That is, in FIG. 2, the configuration downstream of the voltage converter 1 is the load S3'.

The voltage conversion device 1 further includes a first semiconductor switch 16 (hereinafter referred to as a first FET 16) connected between output terminals (between the positive electrode side output terminal 101 and the negative electrode side output terminal 102), the output voltage of the voltage conversion device 1 , a current detection unit 18 for detecting the current flowing through the first FET 16, and a current control unit 30 for controlling the first FET 16.

The DC power supply unit 11 is, for example, a DC power supply obtained by transforming a commercial AC power supply, followed by full-wave rectification and smoothing, or a large-capacity storage battery.

The second FET 12 is, for example, an n-channel MOSFET, and receives a control-related signal from the second FFT control section 21 at its gate terminal. The second FET 12 is interposed between the positive electrode side of the DC power supply unit 11 and the inductor 14 with the drain facing the positive electrode side of the DC power supply unit 11 and connected in series with the inductor 14 .

The diode 13 is branched from the connection contact between the second FET 12 and the inductor 14 and connected in parallel with the inductor 14 with its anode facing the positive electrode side of the DC power supply section 11 .

The smoothing capacitor 15 is interposed between the load terminal of the inductor 14 and the negative output terminal of the DC power supply section 11 , and is connected in parallel with the diode 13 via the inductor 14 . The smoothing capacitor 15 is connected in parallel with the load S3 and outputs a smoothed DC voltage to the load S3'.

The first FET 16 is, for example, an n-channel MOSFET, and a gate terminal receives a control-related signal from the current control section 30 (first FET control section 33). The first FET 16 is connected between the output terminals of the voltage converter with the drain facing the positive electrode side of the DC power supply section 11 . Moreover, since the first FET 16 can be used mainly in the linear region by controlling the voltage value input to the gate terminal, the on-resistance value can be adjusted.

The voltage detection unit 17 includes voltage detection means or a voltmeter such as a shunt resistor or a Hall element, detects the voltage value of the output voltage smoothed by the smoothing capacitor 15 (output voltage value), and detects the current control unit 30 (target Output to the current value setting unit 31). Note that the output voltage value detected by the voltage detection section 17 may be output to the second FFT control section 21 . Also, the voltage detection unit 17 may include a low-pass filter.

The current detection unit 18 includes, for example, a shunt resistor, an all-element current detection means, or an ammeter. The current value of the drain current flowing through is detected and output to the current control unit 30 .

Further, in FIG. 2, the power detection unit 24 detects the power value supplied to the load S3′ (for example, the plasma load S3), and the detected power value (detected power value) is input to the second FFT control unit 21. exemplified.
When the power value to be detected is the power value of the high-frequency power supplied to the plasma load S3, normally, the traveling-wave power output from the high-frequency power supply S1 and directed toward the plasma load S3 is to be detected. Alternatively, the load side power obtained by subtracting the reflected wave power from the forward wave power may be detected. In such a case, the power detector 24 is provided near the plasma load S3, for example, but is not limited to this. For example, it may be provided near the output end of the RF output device S11, the input end of the matching device S2, or the output end of the matching device S2.

The second FFT control unit 21 performs, for example, feedback control such as PID control so that the power value detected by the power detection unit 24 approaches the target power value set by the target power value setting unit 22. On/off control of 2FET12 is performed.
Specifically, when the detected power value is smaller than the target power value, the on/off control of the second FET 12 is performed so that the voltage value of the voltage output from the voltage converter 1 increases. For example, the percentage of ON time of the second FET 12 in PWM control is increased.
Conversely, when the detected power value (detected power value) is greater than the target power value, the voltage value of the voltage output from the voltage converter 1 is decreased. For example, the ratio of ON time of the second FET 12 in PWM control is reduced.
When applying the voltage conversion device 1 to the plasma control system S shown in FIG. Therefore, by controlling the output voltage value of the voltage converter 1, the power value of the high frequency power supplied to the plasma load S3 can be controlled to a desired value.
In addition, the control method of 2nd FET12 in the voltage converter 1 is not limited above. For example, the on/off control of the second FET 12 is performed so that the voltage value at the output terminal of the voltage conversion device 1 detected by the voltage detection unit 17 becomes equal to the target voltage value set by the target voltage value setting unit 23. may The target power value setting unit 22 and the target voltage value setting unit 23 may be provided in the high frequency power supply S1 or may be provided in an external device.

The current control section 30 includes a target current value setting section 31 , a storage section 32 and a first FET control section 33 . The target current value setting unit 31 receives the voltage value (output voltage value) detected by the voltage detection unit 17, reads the target current value corresponding to the output voltage value from the storage unit 32, and calculates the target current value. Output. The target current value is a target drain current value and can be calculated by output voltage value/target resistance value according to Ohm's law.

The first FET control unit 33 includes an MPU (Micro-processing unit), a system LSI (Large-Scale Integration), or an FPGA (field-programmable gate array), and performs various control processing, arithmetic processing, and the like. The first FET control unit 33 inputs the target current value output from the target current value setting unit 31 and the detected current value output from the current detection unit 18, and controls the detected current value so that the detected current value approaches the target current value. The gate voltage applied to the gate terminal of the 1FET 16 is increased or decreased.
For example, when the detected current value is smaller than the target current value, the voltage is applied to the gate terminal of the first FET 16 so as to increase the detected current value, that is, so that the resistance value between the output terminals of the voltage conversion device 1 becomes low. increase the gate voltage to
On the contrary, when the detected current value is larger than the target current value, the gate terminal of the first FET 16 is connected to the gate terminal of the first FET 16 so as to decrease the detected current value, that is, to increase the resistance value between the output terminals of the voltage converter 1 . Reduce the applied gate voltage.
By controlling as described above, the first FET 16 can function as a variable resistor having a resistance value corresponding to the output voltage value of the voltage converter 1 .

FIG. 3 is a flow chart showing a processing procedure by the current control section 30. As shown in FIG. The current control unit 30 starts the following processing by executing a program stored in its own storage area (storage unit 32), for example.

The first FET control section 33 of the current control section 30 starts controlling the first FET 16 (S11). The first FET control unit 33 turns on the first FET 16 by applying, for example, a predetermined gate voltage, which is predetermined as an initial value, to the gate terminal in controlling the on/off of the first FET 16 . Alternatively, the first FET control unit 33 acquires the target voltage value of the output terminal of the voltage conversion device 1 determined based on the target power value to be supplied to the load S3′ by communicating with the second FFT control unit 21, etc. The gate voltage may be determined based on the target voltage value. A drain current flows through the first FET 16 when the first FET control unit 33 turns on the first FET 16 .

The target current value setting unit 31 inputs the output voltage value detected by the voltage detection unit 17 (S12). The target current value setting unit 31 refers to the resistance table stored in the storage unit 32 and derives the target resistance value corresponding to the input output voltage value (S13).

The target current value setting unit 31 derives the target current value based on the derived target resistance value and the input output voltage value (S14). The resistance table defines the relationship between the output voltage value and the target resistance value corresponding to the output voltage value, as shown in FIG. 4A, which will be described later. The target current value may be derived from the output voltage value using a table that defines the relationship between the output voltage value and the target current value.

The first FET control unit 33 inputs the target current value derived by the target current value setting unit 31 and the drain current value detected by the current detection unit 18, and derives the deviation between them (S15). The deviation is derived, for example, by subtracting the drain current value from the target current value.

The first FET control unit 33 determines whether or not the deviation is 0 (S16). If the deviation is 0 (S16: YES), the first FET control unit 33 performs loop processing to execute the processing of S12 again.

If the deviation is not 0 (S16: NO), the first FET control section 33 determines whether or not the drain current value is smaller than the target current value (S17). If the drain current value is smaller than the target current value (S17: YES), the first FET controller 33 increases the gate voltage applied to the first FET 16 (S171). As a result, the resistance value of the first FET 16 decreases and the drain current value increases.

If the drain current value is not smaller than the target current value (S17: NO), that is, if the drain current value is larger than the target current value, the first FET control section 33 reduces the gate voltage applied to the first FET 16 (S172 ). As a result, the resistance value of the first FET 16 increases and the drain current value decreases.

After performing the processing of S171 or S172, the current control unit 30 performs loop processing to perform the processing of S12 again.

Next, with reference to FIG. 4, functions of the current control section 30 will be described. FIG. 4 is an explanatory diagram of a resistance table stored in the storage unit 32. As shown in FIG. FIG. 4A is an example of resistance values (vertical axis) corresponding to output voltage values (horizontal axis). FIG. 4B is an example of the drain current value (vertical axis) corresponding to the output voltage value (horizontal axis), which is obtained by converting FIG. 4A. FIG. 4C is an example of the power loss value (vertical axis) corresponding to the output voltage value (horizontal axis), which is obtained by converting FIG. 4A.

The storage unit 32 is composed of a RAM (random access memory), a ROM (read only memory), or the like. The storage unit 32 stores a resistance value (hereinafter referred to as , target resistance) are stored as a resistance table.

The resistance table has characteristics as shown in FIG. 4A, for example. can be represented in graph form as As shown in FIG. 4A, the target resistance value corresponding to the output voltage value increases as the output voltage value increases. The relationship between the output voltage value and the corresponding target resistance value is appropriately determined based on the circuit configuration of the voltage converter 1, the characteristics of each element that constitutes the circuit, and the like. Therefore, it is possible to determine the relationship between the output voltage value suitable for the circuit configuration of the voltage converter 1 and the corresponding target resistance value, and to efficiently reduce the loss. This will be described with reference also to FIGS. 4B and 4C.

As shown in FIG. 4A, for example, the target resistance value when the output voltage value is 200 [V] is 1,200 [Ω]. Therefore, if the resistance value between the output terminals of the voltage converter 1 can be adjusted to the target resistance value of 1,200 [Ω], the drain current value will be 0.17 [A] according to Ohm's law. .
Also, the target resistance value when the output voltage value is 800 [V] is 80,000 [Ω]. Therefore, if the resistance value between the output terminals of the voltage converter 1 can be adjusted to the target resistance value of 800 [Ω], the drain current value will be 0.01 [A] according to Ohm's law.
Therefore, the characteristic of the drain current value with respect to the output voltage value as shown in FIG. 4B is obtained.

In the above example, when the output voltage value increases by approximately four times (800/200=4), the target resistance value becomes 100 times (80000/800=100).
That is, as the output voltage value increases, the target resistance value increases significantly. As a result, as shown in FIG. 4B, the characteristic is such that as the output voltage value increases, the drain current decreases significantly. The loss W of the first FET 16 at this time is represented by V2/R, where V is the output voltage value and R is the target resistance value. be done. That is, it can be seen that the loss can be adjusted by appropriately setting the target resistance value for the output voltage value.

As described above, when the increase rate of the target resistance value is larger than the square of the increase rate of the output voltage value, the loss becomes smaller as the output voltage value increases.
In the example shown in FIG. 4C, the target resistance value is determined so that the loss is substantially constant in the region where the output voltage value is from about 50 to 300 V, and the loss gradually increases in the region where the output voltage value is about 300 V or higher. The target resistance value is set so that

If the region in which the loss is approximately constant is defined as the “constant loss region”, the “constant loss region” may be within a predetermined range (for example, plus or minus 5 W) as long as the loss is substantially constant. All you have to do is
In addition, in the example shown in FIG. 4C, it can be divided into a “constant loss region” and a “non-constant loss region”, but the present invention is not limited to this.
That is, in the configuration of this embodiment, the resistance value between the output terminals of the voltage conversion device can be freely determined, so the resistance value between the output terminals of the voltage conversion device can be determined from the viewpoint of loss.
For example, in a region where the output voltage value of the voltage conversion device is low, even if more drain current flows than in the example shown in FIG. In such a case, in order to improve the responsiveness of the control, it is possible to intentionally increase the loss for operation.

As can be seen from the above description, if the target resistance value for the output voltage value stored in the resistance table is known, the target drain current value (target current value) can be calculated according to Ohm's law. The target current value setting unit 31 performs this process and outputs the target current value.

Note that the resistance table (FIG. 4A) stored in the storage unit 32 contains discrete values, so there are cases where the target resistance value corresponding to the output voltage value detected by the voltage detection unit 17 is not stored. In such a case, interpolation calculation is performed using the stored target resistance value, and after deriving the target resistance value corresponding to the output voltage value detected by the voltage detection unit 17, the target current value can be derived. .
Of course, when using the characteristic of the drain current corresponding to the output voltage value as shown in FIG. A target resistance value corresponding to is derived.
Alternatively, the non-stored target resistance value or target current value may be derived using a function instead of the interpolation calculation.

Next, the effects of the current control section 30 of this embodiment will be described.
(1) By using the current control unit 30 of the present embodiment, the resistance value between the output terminals of the voltage conversion device can be adjusted according to the output voltage value of the voltage conversion device 1 . Moreover, since the resistance value can be freely determined, the resistance value suitable for the output voltage value of the voltage converter 1 can be set. Further, in this embodiment, a table showing the correspondence between the output voltage value and the target resistance value or target current value can be used. Therefore, the target resistance value or target current value corresponding to the output voltage value can be derived by a simple method of referring to the table. As a result, the resistance value between the output terminals of the voltage conversion device 1 can be adjusted according to the output voltage value of the voltage conversion device 1 by a simple method.

(2) By using the current control unit 30 of the present embodiment, the target resistance value can be increased as the output voltage value of the voltage converter 1 increases. Therefore, in a region where the output voltage value of the voltage conversion device 1 is low, the target resistance value can be determined so that the loss does not increase even if the output voltage value of the voltage conversion device 1 increases.

(3) If the current control unit 30 of the present embodiment is used, the drain current changes rapidly ( suddenly become 0, etc.). Therefore, it is possible to reduce the possibility that the load will suddenly change due to the control of the first FET 16 . On the other hand, in the prior art, the drain current becomes 0 when the first FET 51 is turned off. Therefore, the present invention is superior to the prior art in terms of stability.

(4) By using the current control unit 30 of the present embodiment, even in a region where the output voltage of the voltage converter 1 is high, a drain current corresponding to the output voltage flows. The lower the output voltage, the larger the drain current. Therefore, when the output voltage of the voltage conversion device 1 fluctuates from a high voltage to a low voltage, it is possible to shorten the time for the charge of the capacitor of the voltage conversion device 1 to discharge compared to the conventional technology. Therefore, the responsiveness is better than that of the prior art.

The voltage conversion device 1 is an asynchronous rectification step-down DCDC converter, but is not limited to this. The voltage conversion device 1 includes a converter that needs to ensure a predetermined current when the output voltage is low. It can be applied to converters, flyback converters, half-bridge converters, full-bridge converters, interleaved or multi-phase circuits.

Also, in the above embodiment, the first FET 16 that functions as a variable resistor is provided between the output terminals, but the configuration is not limited to this. For example, a resistor may be connected in series with the first FET 16 . In that case, the first FET 16 may be controlled so that the combined resistance value of the resistor connected in series with the first FET 16 becomes a desired resistance value.

The embodiments disclosed this time are illustrative in all respects and should be considered not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the meaning described above, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

S plasma control system, S1 high-frequency power supply, S11 RF output device, S2 matching box, S3 plasma load (load), S3' load, 1 voltage conversion device (DCDC converter), 11 DC power supply, 12 second FET (second semiconductor switch), 13 diode, 14 inductor, 15 smoothing capacitor, 16 first FET (first semiconductor switch), 17 voltage detection section, 18 current detection section, 21 second FET control section, 22 target power value setting section, 23 target voltage Value setting unit 24 Power detection unit 30 Current control unit 31 Target current value setting unit 32 Storage unit 33 First FET control unit

Claims (3)

A voltage conversion device that converts an input voltage into a predetermined output voltage,
a semiconductor switch connected between output terminals to which the output voltage is output and to which the output voltage is applied;
a voltage detection unit that detects an output voltage value between the output terminals;
a current detection unit that detects a value of current flowing through the semiconductor switch;
a target current value setting unit that derives a target current value corresponding to the output voltage value detected by the voltage detection unit;
a semiconductor switch control unit that controls the on-resistance of the semiconductor switch so that the current value detected by the current detection unit approaches the target current value ,
further comprising a storage unit storing a target resistance value corresponding to the output voltage value detected by the voltage detection unit;
The target current value setting unit refers to the storage unit to derive a target resistance value corresponding to the output voltage value detected by the voltage detection unit, and the output voltage value detected by the voltage detection unit and the Deriving the target current value using the target resistance value and
A voltage conversion device characterized by: A voltage conversion device that converts an input voltage into a predetermined output voltage,
a semiconductor switch connected between output terminals to which the output voltage is output and to which the output voltage is applied;
a voltage detection unit that detects an output voltage value between the output terminals;
a current detection unit that detects a value of current flowing through the semiconductor switch;
a target current value setting unit that derives a target current value corresponding to the output voltage value detected by the voltage detection unit;
a semiconductor switch control unit that controls the on-resistance of the semiconductor switch so that the current value detected by the current detection unit approaches the target current value;
with
further comprising a storage unit storing a target current value corresponding to the output voltage value detected by the voltage detection unit;
The voltage conversion device, wherein the target current value setting unit derives the target current value corresponding to the output voltage value detected by the voltage detection unit by referring to the storage unit. A voltage conversion device according to claim 1 or claim 2 ;
and an RF output device that converts a DC voltage output from the voltage conversion device into an AC voltage and outputs the RF output device.

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