Power supply device

Abstract

A current fluctuating due to a load fluctuation is limited to protect a semiconductor switch. A protection circuit includes a switch circuit that turns on when a predetermined conduction voltage is applied thereto, and a sub-reactance circuit having a predetermined reactance value is connected in parallel to a main reactance circuit through which a high frequency current generated by a semiconductor switch flows. When the switch circuit is turned on, the main reactance circuit and the sub-reactance circuit are connected in parallel, and a high frequency current flows through this parallel connection circuit. The impedance value of the parallel connection circuit is set to be larger than the impedance value of the main reactance circuit so that the current is limited due to the turning on of the switch circuit, and thus, the semiconductor switch is protected.

Claims

1. A power supply device comprising: a DC power source configured to output a DC voltage; a high frequency amplifying circuit configured to generate a high frequency current by repeatedly turning on and turning off a semiconductor switch connected to the DC power source; a high frequency output circuit configured to supply the high frequency current to a load; a main reactance circuit having a predetermined reactance value, the main reactance circuit having a first end connected to the high frequency amplifying circuit and a second end connected to the high frequency output circuit; a protection circuit connected in parallel to the main reactance circuit between the high frequency amplifying circuit and the high frequency output circuit, the protection circuit including: a DC voltage source configured to supply a predetermined reference voltage; a switch circuit configured to turn on when a turning on voltage larger than the predetermined reference voltage is applied, the switch circuit including: a reference capacitance element to be charged by the reference voltage; and a diode element to be reverse-biased by a charged voltage of the reference capacitance element; and a sub-reactance circuit having a predetermined reactance value, wherein: an absolute value of an impedance of a parallel connection circuit of the protection circuit and the main reactance circuit, when the switch circuit is turned on, is set to be larger than an absolute value of an impedance of the parallel connection circuit of the protection circuit and the main reactance circuit when the switch circuit is turned off, once the switch circuit is turned on, an absolute value of an impedance on a load side of the high frequency amplifying circuit becomes larger than an absolute value of an impedance when the protection circuit is turned off, so that the high frequency current is limited, and the turning on voltage is applied to the switch circuit, the diode element is forward-biased to turn on, and the switch circuit is then turned on.

2. The power supply device according to claim 1, wherein among an inductive reactance and a capacitive reactance, a reactance value of the main reactance circuit is set to a value of either one of the inductive reactance and the capacitive reactance, while the sub-reactance circuit is set to a value of the other one of the inductive reactance and the capacitive reactance.

3. The power supply device according to claim 1, further comprising an auxiliary power source, wherein the reference capacitance element is charged by the auxiliary power source.

4. The power supply device according to claim 1, wherein the reference capacitance element is charged by the DC power source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a first exemplary circuit.

(2) FIG. 2 is a second exemplary circuit.

(3) FIG. 3 is a detailed circuit diagram (1) of the first exemplary circuit of the present embodiment.

(4) FIG. 4 is a detailed circuit diagram (1) of the second exemplary circuit of the present embodiment.

(5) FIG. 5 is a detailed circuit diagram (2) of the first exemplary circuit of the present embodiment.

(6) FIG. 6 is a detailed circuit diagram (2) of the second exemplary circuit of the present embodiment.

(7) FIG. 7 is a detailed circuit diagram (3) of the first exemplary circuit of the present embodiment.

(8) FIG. 8 is a detailed circuit diagram (3) of the second exemplary circuit of the present embodiment.

(9) FIG. 9 is a detailed circuit diagram (4) of the first exemplary circuit of the present embodiment.

(10) FIG. 10 is a detailed circuit diagram (4) of the second exemplary circuit of the present embodiment.

(11) FIG. 11 is a graph for illustrating a relationship between an inductance value of a sub-reactance circuit and an impedance value of a high frequency current limiting circuit.

(12) FIG. 12 is a graph illustrating the dependence of the impedance value of the high frequency current limiting circuit on the reactance values of a diode element of a protection circuit.

(13) FIG. 13(a) is a simplified circuit diagram.

(14) FIG. 13(b) is a simplified circuit diagram.

(15) FIG. 14(a) illustrates a relationship between the output current being current-limited and the output current not being current-limited.

(16) FIG. 14(b) illustrates a relationship between the output current being current-limited and the output current not being current-limited.

(17) FIG. 15 illustrates the direction of the current flowing during each of periods A to D.

(18) FIG. 16 illustrates an example when a main reactance circuit is capacitive and a sub-reactance circuit is inductive.

(19) FIG. 17(a) is a graph illustrating a state being current-limited.

(20) FIG. 17(b) is a graph illustrating a state not being current-limited.

(21) FIG. 18 illustrates the current during each of the periods A to D in current limiting.

(22) FIG. 19 illustrates a half-wave voltage doubler rectifying circuit.

(23) FIG. 20(a) illustrates how currents flow.

(24) FIG. 20(b) illustrates how currents flow.

(25) FIG. 21 illustrates the direction of the current flowing during each of the periods A to D.

(26) FIG. 22 illustrates a transformer-coupled half-wave voltage doubler rectifying circuit.

(27) FIG. 23(a) illustrates how currents flow in the transformer-coupled rectifying circuit.

(28) FIG. 23(b) illustrates how currents flow in the transformer-coupled rectifying circuit.

(29) FIG. 24 illustrates the direction of the current flowing during each of the periods A to D.

(30) FIG. 25 illustrates a first exemplary circuit when a class-E amplifying circuit is applied to a high frequency amplifying circuit.

(31) FIG. 26 illustrates how currents flow.

(32) FIG. 27 illustrates a second exemplary circuit when a class-D amplifying circuit is applied to a high frequency amplifying circuit.

(33) FIG. 28 illustrates a third exemplary circuit when a class-D amplifying circuit is applied to a high frequency amplifying circuit.

(34) FIG. 29 illustrates internal impedances.

DETAILED DESCRIPTION OF EMBODIMENTS

(35) Hereinafter, the description of a parasitic capacitance connected in parallel to a semiconductor element, such as a diode element, will be omitted in the attached drawings.

(36) Reference numeral 10 of FIG. 1 represents a first exemplary power supply device which supplies a high frequency power to a load 25, while reference numeral 60 of FIG. 2 represents a second exemplary power supply device which supplies a high frequency power to a load 75.

(37) The power supply device 10 (60) includes: a DC power source 11 (61) which outputs a DC power source voltage; a high frequency amplifying circuit 12 (62) which switches a power source voltage to generate a high frequency output current; a main reactance circuit 13 (63) having a predetermined reactance value, and a filter circuit 15 (65) for removing high frequency waves. In the description of the embodiments, the filter circuit may be referred to also as a high frequency output circuit.

(38) The high frequency amplifying circuit 12 (62) of the first (second) exemplary power supply device 10 (60) respectively includes an output inductance circuit 21 (71) having a predetermined inductive reactance value, a semiconductor switch 22 (72) to turn on or turn off, an output capacitance element 23 (73) charged by a part of the current flowing through the output inductance circuit 21 (71), and a control circuit 24 (74) so as to control the turning on and turning off of the semiconductor switch 22 (72). A transistor element can be used for the semiconductor switch 22 (72).

(39) One end of the output inductance circuit 21 (71) of the first (second) exemplary power supply device 10 (60) is electrically connected to the DC power source 11 (61), while the other end of the output inductance circuit 21 (71) is electrically connected to a semiconductor output terminal 20 (70) of the semiconductor switch 22 (72).

(40) The DC power source 11 (61) includes a DC voltage outputting device 17 (67) and a power-source capacitance element 27 (77) for outputting a constant voltage. The DC voltage outputting device 17 (67) and the power-source capacitance element 27 (77) are connected in parallel with each other. One end of the DC voltage outputting device 17 (67) and one end of the power-source capacitance elements 27 (77) are electrically connected to one end of the output inductance circuit 21 (71), respectively, while the other end of the DC voltage outputting device 17 (67) and the other end of the power-source capacitance element 27 (77) are electrically connected respectively to the earth potential.

(41) Once the semiconductor switch 22 (72) is turned on under the control of the control circuit 24 (74), a current flows into the output inductance circuit 21 (71) of the first (second) exemplary power supply device 10 (60). The current flowing into the output inductance circuit 21 (71) will flow to the earth potential through the semiconductor switch 22 (72) of the first (second) exemplary power supply device 10 (60).

(42) The output capacitance element 23 (73) is connected in parallel with the semiconductor switch 22 (72). The charged output capacitance element 23 (73) is discharged via the semiconductor switch 22 (72) and the voltage at the semiconductor output terminal 20 (70) of the first (second) exemplary power supply device 10 (60) drops.

(43) Once the semiconductor switch 22 (72) transitions from a turning on state to a turning off state under the control of the control-circuit 24 (74), an induced electromotive force having the polarity for maintaining the current flowing through the output inductance circuit 21 (71) is generated in the output inductance circuit 21 (71) to charge the output capacitance element 23 (73), thereby raising the voltage of the semiconductor output terminal 20 (70) of the first (second) exemplary power supply device 10 (60).

(44) One end of the main reactance circuit 13 (63) of the first (second) exemplary power supply device 10 (60) is electrically connected to the semiconductor output terminal 20 (70), while the other end is electrically connected to the output terminal 16 (66) via the filter circuit 15 (65).

(45) Due to the operation of the high frequency amplifying circuit 12 (62), a high frequency voltage swinging within a positive voltage range is generated at the semiconductor output terminal 20 (70), and a high frequency current output by the high frequency amplifying circuit 12 (62) is supplied to the main reactance circuit 13 (63) from the semiconductor output terminal 20 (70) and flows through the main reactance circuit 13 (63), so that a high frequency output voltage is applied to the output terminal 16 (66).

(46) The load 25 (75) is electrically connected to the output terminal 16 (66). The output voltage is supplied to the load 25 (75) from the output terminal 16 (66). In the first (second) exemplary power supply device 10 (60), the output current flows through the filter circuit 15 (65) and is supplied to the load 25 (75) from the output terminal 16 (66).

(47) The first (second) exemplary power supply device 10 (60) is a high frequency power supply device for a vacuum processing apparatus used for generation and maintenance of plasma. The load 25 (75) represents the impedance of the plasma.

(48) In an unsteady state, such as when plasma is going to be generated, when plasma becomes unstable, or when plasma disappears, the impedance of the plasma varies, and therefore the value of the impedance of the load 25 (75) at the unsteady state will vary.

(49) The first (second) exemplary power supply device 10 (60) includes a protection circuit 14 (64) connected in parallel to the main reactance circuit 13 (63).

(50) Reference numerals Q.sub.1, Q.sub.2 (Q.sub.3, Q.sub.4) in FIG. 1 to FIG. 10 represent the electrodes of the main reactance circuit 13 (63). One electrode Q.sub.1 (Q.sub.3) is connected to the high frequency amplifying circuit 12 (62), while another electrode Q.sub.2 (Q.sub.4) is connected to the filter circuit 15 (65), which is the high frequency output circuit.

(51) FIG. 3 shows an example of the internal circuit of the protection circuit 14 of the first exemplary power supply device 10, while FIG. 4 shows an example of the internal circuit of the protection circuit 64 of the second exemplary power supply device 60.

(52) The protection circuit 14 (64) includes a switch circuit 19 (69) and a sub-reactance circuit 30 (80) having a predetermined reactance value.

(53) The sub-reactance circuit 30 (80) of the first (second) power supply device 10 (60) includes a first sub-reactance element 28.sub.1 (78.sub.1) and a second sub-reactance element 28.sub.2 (78.sub.2). The first sub-reactance element 28.sub.1 (78.sub.1), the switch circuit 19 (69), and the second sub-reactance element 28.sub.2 (78.sub.2) are connected in series. Accordingly, even if the switch circuit 19 (69) is arranged between the first sub-reactance element 28.sub.1 (78.sub.1) and the second sub-reactance element 28.sub.2 (78.sub.2), the switch circuit 19 (69) and the sub-reactance circuit 30 (80) are connected in series. This series-connected circuit constitutes the protection circuit 14 (64), and the protection circuit 14 (64) is connected in parallel to the main reactance circuit 13 (63).

(54) The switch circuit 19 (69) turns on when a turning on voltage higher than a predetermined reference voltage is applied thereto, while when a voltage below the predetermined reference voltage is applied, the switch circuit 19 (69) turns off.

(55) Hereinafter, a state where the switch circuit 19 (69) turns on is referred to as a turning on state, while a state where the switch circuit 19 (69) turns off is referred to as a turning off state. Even when the switch circuit 19 (69) is in a turning off state, a current is caused to flow into the switch circuit 19 (69) due to a parasitic capacitance later discussed. Therefore, the output current generated by the high frequency amplifying circuit 12 (62) will flow into both the main reactance element 13 (63) and the protection circuit 14 (64), both when the switch circuit 19 (69) is in a turning on state and when the switch circuit 19 (69) is in a turning off state.

(56) The absolute value of the impedance of the protection circuit 14 (64) when the switch circuit 19 (69) is in a turning off state is set so as to be larger than the absolute value of the impedance of the main reactance circuit 13 (63), while the absolute value of the impedance of the protection circuit 14 (64) when the switch circuit 19 (69) is in a turning on state is set so as to be smaller than the absolute value of the impedance of the main reactance circuit 13 (63). Accordingly, when the switch circuit 19 (69) is in a turning off state, the current flowing through the protection circuit 14 (64) becomes smaller than the current flowing through the main reactance circuit 13 (63), while when the switch circuit 19 (69) is in a turning on state, the current flowing through the protection circuit 14 (64) becomes larger than the current flowing through the main reactance circuit 13 (63).

(57) The reactance value of the main reactance circuit 13 (63) is set so as to exceed 1, while the resistance value of the main reactance circuit 13 (63) is set a value smaller than the reactance value thereof.

(58) Moreover, a difference between a reactance value of the protection circuit 14 (64) when the switch circuit 19 (69) is in a turning on state and a reactance value of the protection circuit 14 (64) when the switch circuit 19 (69) is in a turning off state is set so as to be larger than the reactance value of the main reactance circuit 13 (63), and the resistance value of the switch circuit 19 (69) is set to a value smaller than the reactance value of the main reactance circuit 13 (63).

(59) The value of the reactance of the sub-reactance circuit 30 (80) is set a value in a manner such that the absolute value of the impedance of a parallel circuit of the protection circuit 14 (64) and the main reactance circuit 13 (63) in a turning on state larger than the absolute value of an impedance of a parallel circuit of the protection circuit 14 (64) and the main reactance circuit 13 (63) in a non-conduction state. Therefore, once the protection circuit 14 (64) transitions from a turning off state to a turning on state, the output current will hardly flow.

(60) Moreover, the value of the resistance of the sub-reactance circuit 30 (80) is set to a small value in comparison to the reactance value of the main reactance circuit.

(61) The content of the switch circuit 19 (69) will be discussed.

(62) The switch circuit 19 (69) of the first (second) power supply device 10 (60) includes a plurality of diode elements and a reference capacitance element 18 (68) to be charged to a predetermined reference voltage.

(63) Here, the switch circuit 19 (69) includes first to fourth diode elements D.sub.00 to D.sub.04 (D.sub.11 to D.sub.14). The cathode terminal of the fourth diode element D.sub.04 (D.sub.14) is electrically connected to the anode terminal of the first diode element D.sub.00 (D.sub.11), and the cathode terminal of the second diode element D.sub.02 (D.sub.12) is electrically connected to the anode terminal of the third diode element D.sub.03 (D.sub.13).

(64) The cathode terminal of the first diode element D.sub.01 (D.sub.11) and the cathode terminal of the third diode element D.sub.03 (D.sub.13) are electrically connected, and the anode terminal of the fourth diode element D.sub.04 (D.sub.14) and the anode terminal of the second diode element D.sub.02 (D.sub.12) are electrically connected.

(65) The first to fourth diode elements D.sub.01, D.sub.02, D.sub.03 and D.sub.04 (D.sub.1, D.sub.12, D.sub.13 and D.sub.14) have parasitic capacitances D.sub.01, D.sub.02, D.sub.03 and D.sub.04 (D.sub.11, D.sub.12, D.sub.13 and D.sub.14) of the diode elements as a parallel element, respectively.

(66) The first to fourth diode elements D.sub.01, D.sub.02, D.sub.03 and D.sub.04 (D.sub.11, D.sub.12, D.sub.13 and D.sub.14) applied with a forward voltage turn on, and a current flows through the protection circuit 14 (64). When a reverse voltage is applied to the diode elements D.sub.01, D.sub.02, D.sub.03 and D.sub.04 (D.sub.11, D.sub.12, D.sub.13 and D.sub.14), respectively, a current will not flow through a junction section of the diode element itself and the diode elements D.sub.01 to D.sub.04 (D.sub.11 to D.sub.14) are shut off but a current will flow through the parasitic capacitances D.sub.01, D.sub.02, D.sub.03 and D.sub.004 (D.sub.1, D.sub.12, D.sub.13 and D.sub.14) of the diode elements.

(67) The main reactance circuit 13 (63) has two terminals. Hereinafter, the connection portion between the anode terminal of the first diode element D.sub.01 (D.sub.11) and the cathode terminal of the fourth diode element D.sub.04 (D.sub.14) will be referred to as a first connection point P.sub.1 (P.sub.11), and the connection portion between the anode terminal of the third diode element D.sub.03 (D.sub.13) and the cathode terminal of the second diode element D.sub.02 (D.sub.12) will be referred to as a second connection point P.sub.2 (P.sub.12). One end of the first sub-reactance element 28.sub.1 (78.sub.1) is electrically connected to the first connection point P.sub.1(P.sub.11), while the other end is electrically connected to one end of the main reactance circuit 13 (63).

(68) One end of the second sub-reactance element 28.sub.2 (78.sub.2) is electrically connected to the second connection point P.sub.2 (P.sub.12), while the other end is electrically connected to the other end of the main reactance circuit 13 (63) and one end of the filter circuit 15 (65). The other end of the filter circuit 15 (65) is electrically connected to the output terminal 16 (66).

(69) Hereinafter, the portion where the cathode terminal of the first diode element D.sub.01 (D.sub.11) and the cathode terminal of the third diode element D.sub.03 (D.sub.13) are electrically connected will be referred to as a cathode point P.sub.K (P.sub.KK), and the portion where the anode terminal of the fourth diode element D.sub.04 (D.sub.14) and the anode terminal of the second diode element D.sub.02 (D.sub.12) are electrically connected will be referred to as an anode point P.sub.A (P.sub.AA). One end of the reference capacitance element 18 (68) is electrically connected to the cathode point P.sub.K (P.sub.KK), while the other end is electrically connected to the anode point P.sub.A (P.sub.AA). The first to fourth diode elements D.sub.01 to D.sub.04 (D.sub.11 to D.sub.14) and the reference capacitance element 18 (68) constitute an H-bridge circuit.

(70) In this embodiment including the power supply devices discussed later, a filter circuit can be used. Here, an identical filter circuit 15 (65) is assumed to be used.

(71) This filter circuit 15 (65) includes: a blocking capacitance element 35 (85), a first filter circuit 36 (86) formed by connecting an inductance element and a capacitance element in parallel, a second filter circuit 37 (87) made of an inductance element, and a third filter circuit 34 (84) made of a capacitance element. The blocking capacitance element 35 (85), the first filter circuit 36 (86), and the second filter circuit 37 (87) are connected in series so as to electrically connect the output terminal 16 (66) to the portion where the main reactance circuit 13 (63) and the protection circuit 14 (64) are connected. The third filter circuit 34 (84) connects the output terminal 16 (66) to the earth potential, so that the output current having frequency easily passes between the high frequency amplifying circuit 12 (62) and the output terminal 16 (66).

(72) Next, as shown in FIG. 3, the items specific to the first exemplary power supply device 10 will be discussed.

(73) The first exemplary power supply device 10 includes an auxiliary power source 26.

(74) The auxiliary power source 26 includes a positive voltage terminal 38 for outputting a DC positive voltage and a negative voltage terminal 39 for outputting a voltage negative to the voltage of the positive voltage terminal 38. The positive voltage terminal 38 is electrically connected to the cathode point P.sub.K, while the negative voltage terminal 39 is electrically connected to the anode point P.sub.A. The positive voltage which the auxiliary power source 26 outputs from the positive voltage terminal 38 is applied to the cathode point P.sub.K, while the negative voltage output from the negative voltage terminal 39 is applied to the anode point P.sub.A. The reference capacitance element 18 is charged by the voltage output by the auxiliary power source 26.

(75) When a voltage of which the reference capacitance element 18 has been charged is called as the reference voltage, a voltage of the auxiliary power source 26, which is the voltage of the positive voltage terminal 38 to the negative voltage terminal 39, is the reference voltage. The reference voltage appearing between the both ends of the reference capacitance element 18 is applied as a reverse bias to a series circuit of the first and fourth diode elements D.sub.01, D.sub.04 and a series circuit of the second and third diode elements D.sub.02, D.sub.03 in the bridge circuit. Thus, electric continuity of the first to fourth diode elements D.sub.01 to D.sub.04 is prevented.

(76) Note that, here a common-mode choke coil 29 is inserted between the auxiliary power source 26 and the reference capacitance element 18. Among two magnetically coupled windings 31, 32 in the common-mode choke coil 29, one end of the winding 31 is electrically connected to the anode point P.sub.A, while the other end is electrically connected to the negative voltage terminal 39. One end of the winding 32 is electrically connected to the cathode point P.sub.K, while the other end is electrically connected to the positive voltage terminal 38.

(77) The two windings 31, 32 are designed so as to have the same polarity. When a current heading toward the auxiliary power source 26 flows through both the two windings 31, 32 or when a current heading toward the protection circuit 14 flows through the both two windings 31, 32, the two windings 31, 32 function as an inductance element to make the current difficult to flow. When a voltage having the same polarity and the same magnitude output by the high frequency amplifying circuit 12 is applied to the anode point P.sub.A and the cathode point P.sub.K, then this voltage is attenuated or shut off by the common-mode choke coil 29 so as to be hardly applied between the positive voltage terminal 38 and negative voltage terminal 39 of the auxiliary power source 26.

(78) Next, as shown in FIG. 4, the second exemplary power supply device 60 will be described.

(79) The second exemplary power supply device 60 also includes a common-mode choke coil 79. Among two windings 81, 82 magnetically coupled within the common-mode choke coil 79, one end of the winding 81 is electrically connected to the anode point P.sub.AA, while the other end is electrically connected to the earth potential.

(80) One end of the winding 82 is electrically connected to the cathode point P.sub.KK, while the other end is electrically connected to a portion where a DC power source 61 and the output inductance circuit 71 are connected.

(81) Because the anode point P.sub.AA of the reference capacitance element 68 is DC-connected to the earth potential and the cathode point P.sub.KK is DC-connected to the DC power source 61, the reference capacitance element 68 is charged by the DC voltage output by the DC power source 61.

(82) Assuming that a voltage having the same polarity and the same magnitude output by the high frequency amplifying circuit 62 is applied to the anode point P.sub.A and cathode point P.sub.KK, this voltage is attenuated or shut off by the common-mode choke coil 79 so as to be hardly applied to the DC power source 61.

(83) As discussed above, if the charged voltage of the reference capacitance element 68 is referred to as the reference voltage, the reference capacitance element 18 (68) of the first (second) exemplary power supply device 10 (60) is charged by the reference voltage. When a voltage larger than the reference voltage and large enough to turn on the first diode element D.sub.01 (D.sub.11) and second diode element D.sub.02 (D.sub.12) is applied between the first connection point P.sub.1 (P.sub.11) and the second connection point P.sub.2 (P.sub.12), or when a voltage large enough to turn on the third diode element D.sub.03 (D.sub.13) and fourth diode element D.sub.04 (D.sub.14) is applied between the first connection point P.sub.1 (P.sub.11) and the second connection point P.sub.2 (P.sub.12), current will flow through the first diode element D.sub.01 (D.sub.11), the reference capacitance element 18 (68), and the second diode element D.sub.02 (D.sub.12), or a current will flow the inside of the switch circuit 19 (69) through the third diode element D.sub.3 (D.sub.13), the reference capacitance element 18 (68), and the fourth diode element D.sub.04 (D.sub.14).

(84) That is, the switch circuit 19 (69) turns on when a voltage having a magnitude obtained by adding the reference voltage to two times the turning on voltage of the diode element is applied between the first connection point P.sub.1 (P.sub.11) and the second connection point P.sub.2 (P.sub.12).

(85) Note that the voltage output by the auxiliary power source 26 is set to an appropriate value in a manner such that the switch circuit will not turn on when plasma is in a steady state.

(86) When the switch circuit 19 (69) is in a turning off state, the absolute value of the impedance of the protection circuit 14 (64) is set to be larger than the absolute value of the impedance of the main reactance circuit 13 (63). Therefore, in a high frequency output current heading toward the load 25 (75) from the high frequency amplifying circuit 12 (62), the amount of a current flowing through the main reactance circuit 13 (63) is larger than the amount of a current flowing through the sub-reactance circuit 30 (80).

(87) Hereinafter, a current which flows through the protection circuit 14 (64) when the switch circuit 19 (69) is in a turning off state may be referred to as a turning off current, while a current which flows through the protection circuit 14 (64) when the switch circuit 19 (69) is in a turning on state may be referred to as a turning on current. The cases where a turning off current flows into the protection circuit 14 (64) include a case where the voltage at the first connection point P.sub.1 (P.sub.11) is positive relative to the voltage at the second connection point P.sub.2 (P.sub.12), and a case where the voltage at the second connection point P.sub.2 (P.sub.12) is positive relative to the voltage at the first connection point P.sub.1 (P.sub.11).

(88) When the voltage at the first connection point P.sub.1 (P.sub.11) is positive relative to the voltage at the second connection point P.sub.2 (P.sub.12), the current which flows into the switch circuit 19 (69) corresponding to the turning off current will flow from the first connection point P.sub.1 (P.sub.11) into the switch circuit 19 (69), flow through the parasitic capacitance CD.sub.01 (CD.sub.11) of the first diode element D.sub.01 (D.sub.1), the parasitic capacitance CD.sub.04 (CD.sub.14) of the fourth diode element D.sub.04 (D.sub.14), the reference capacitance element 18 (68), the parasitic capacitance CD.sub.03 (CD.sub.13) of the third diode element D.sub.03 (D.sub.13), and the parasitic capacitance CD.sub.02 (CD.sub.12) of the second diode element D.sub.02 (D.sub.12), and flow from the second connection point P.sub.2 (P.sub.12) to the outside of the switch circuit 19 (69).

(89) On the contrary, when the voltage at the second connection point P.sub.2 (P.sub.12) is positive relative to the voltage at the first connection point P.sub.1, the current which flows into the switch circuit 19 (69) corresponding to the turning off current will flow from the second connection point P.sub.2 (P.sub.12) into the switch circuit 19 (69), flow through the parasitic capacitance CD.sub.03 (CD.sub.13) of the third diode element D.sub.03 (D.sub.13), the parasitic capacitance CD.sub.02 (CD.sub.12) of the second diode element D.sub.02 (D.sub.12), the reference capacitance element 18 (68), the parasitic capacitance CD.sub.01 (CD.sub.11) of the first diode element D.sub.00 (D.sub.11), and the parasitic capacitance CD.sub.04 (CD.sub.14) of the fourth diode element D.sub.04 (D.sub.14), and flow from the first connection point P.sub.1 (P.sub.11) to the outside.

(90) That is, the impedance of the protection circuit 14 (64), when the switch circuit 19 (69) is in a turning off state, is a combined impedance of a circuit formed of the sub-reactance circuit 30 (80), the parasitic capacitance CD.sub.01 (CD.sub.11) of the first diode element D.sub.01 (D.sub.11), the parasitic capacitance CD.sub.04 (CD.sub.14) of the fourth diode element D.sub.04 (D.sub.14), the reference capacitance element 18 (68), the parasitic capacitance CD.sub.03 (CD.sub.13) of the third diode element D.sub.03 (D.sub.13), and the parasitic capacitance CD.sub.02 (CD.sub.12) of the second diode element D.sub.02 (D.sub.12).

(91) Note that, the absolute value of the impedance of the protection circuit 14 (64) when the switch circuit 19 (69) is in a turning off state is set so as to be larger than the absolute value of an impedance of the main reactance circuit 13 (63). The protection circuit 14 (64) and the main reactance circuit 13 (63) are connected in parallel, and thus, the current flowing through the main reactance circuit 13 (63) becomes larger than the current flowing through the protection circuit 14 (64).

(92) When the switch circuit 19 (69) is in a turning off state, if a voltage which is larger than the reference voltage by two times the forward voltage of the diode element is applied between the first connection point P.sub.1 (P.sub.11) and the second connection point P.sub.2 (P.sub.12), then this voltage serves as a turning on voltage to turn on the switch circuit 19 (69) and a turning on current flows.

(93) Here, when the turning on voltage at the first connection point P.sub.1 (P.sub.11) is positive relative to the voltage at the second connection point P.sub.2 (P.sub.12), the current which flows out from the first connection point P.sub.1 (P.sub.11) will flow into the second connection point P.sub.2 (P.sub.12) through the first diode element D.sub.01 (D.sub.11), the reference capacitance element 18 (68), and the second diode element D.sub.02 (D.sub.12).

(94) On the contrary, when the turning on voltage at the first connection point P.sub.2 (P.sub.12) is positive relative to the voltage at the second connection point P.sub.1 (P.sub.11), the current which flows out from the second connection point P.sub.2 (P.sub.12) will flow into the first connection point P.sub.1 (P.sub.11) through the third diode element D.sub.03 (D.sub.13), the reference capacitance element 18 (68), and the fourth diode element D.sub.04 (D.sub.14).

(95) That is, the impedance of the protection circuit 14 (64) when the switch circuit 19 (69) is in a turning on state is a combined impedance of a circuit formed of the sub-reactance circuit 30 (80), the first diode element D.sub.01 (D.sub.11), the reference capacitance element 18 (68), and the second diode element D.sub.02 (D.sub.12), or a combined impedance of a circuit formed of the sub-reactance circuit 30 (80), the third diode element D.sub.03 (D.sub.13), the reference capacitance element 18 (68), and the fourth diode element D.sub.04 (D.sub.14).

(96) Accordingly, between the high frequency amplifying circuit 12 (62) and the load 25 (75), a current will flow in accordance with the impedance value of a circuit formed by parallel connecting the protection circuit 14 (64) and the main reactance circuit 13 (63). Therefore, when the switch circuit 19 (69) is in a turning on state, the high frequency amplifying circuit 12 (62) and the load 25 (75) will be connected to each other via an impedance value different from the impedance value in a turning off state.

(97) In the first (second) exemplary power supply circuit 10 (60), the reactance value of the sub-reactance circuit 30 (80) is set in a manner such that the absolute value of the impedance of a circuit formed by parallel connecting the protection circuit 14 (64) and the main reactance circuit 13 (63) becomes larger than the absolute value of an impedance of the main reactance circuit 13 (63) in a turning off state. The high frequency amplifying circuit 12 (62) is electrically connected to the load 25 (75) via the absolute value of an impedance which is larger when the switch circuit 19 (69) is in a non-conduction state than when it is in a conduction state. Accordingly, at this time the current output by the high frequency amplifying circuit 12 (62) or the current flowing into the high frequency amplifying circuit 12 (62) is limited, and the semiconductor switch 22 (72) is protected.

(98) Note that, if a reactance value of the main reactance circuit 13 (63), a reactance value of the sub-reactance circuit 30 (80), and a reactance value of the switch circuit 19 (69) in a turning on state are set in a manner such that a total sum thereof becomes close to zero, then when the switch circuit 19 (69) is in a turning on state, the absolute value of an impedance of a parallel circuit of the protection circuit 14 (64) and the main reactance circuit 13 (63) can be set to be larger than that when the total sum is not close to zero.

(99) In the power supply device 10 (60) shown in FIG. 3 (FIG. 4), an inductance element is used for the main reactance circuit 13 (63) so as to be an inductive reactance, while a capacitance element is used for the sub-reactance circuit 30 (80) so as to be a capacitive reactance. However, as in a power supply device 41 (91) of FIG. 5 (FIG. 6), a capacitive element may be used for the main reactance circuit 13 (63) so as to be a capacitive reactance, while an inductive element may be used for the sub-reactance circuit 30 (80) so as to be an inductive reactance.

(100) Next, in a power supply device 42 (92) of FIG. 7 (FIG. 8), a switch circuit 19 (69) includes the reference capacitance element 18 (68), a fifth diode element D.sub.21 (D.sub.31) connected in series to the reference capacitance element 18 (68), and a sixth diode element D.sub.22 (D.sub.32) connected in parallel to a circuit formed by series connecting the reference capacitance element 18 (68) and fifth diode element D.sub.21 (D.sub.31).

(101) In this switch circuit 19 (69), a first sub-reactance element 28.sub.1 (78.sub.1) having an inductive reactance and a second sub-reactance element 28.sub.2 (78.sub.2) having an inductive reactance are connected in series. The reference capacitance element 18 (68) is charged by the auxiliary power source 26 or the DC power source 61 so that the potential difference between the both ends of the capacitance element 18 becomes a predetermined reference voltage.

(102) Here, a terminal on the high frequency amplifying circuit 12 (62) side is charged so as to have a higher voltage than a terminal on the load 25 (75) side. The cathode terminal of the fifth diode element D.sub.21 (D.sub.31) connected in series to the reference capacitance element 18 (68) faces the load 25 (75) side, while the anode terminal thereof faces the high frequency amplifying circuit 12 (62).

(103) When the switch circuit 19 (69) is in a turning on state, a voltage equal to or higher than the reference voltage will not be applied to the both ends of the switch circuit 19 (69), and thus, the switch circuit 16 (69) will not turn on.

(104) When the current flowing through the main reactance circuit 13 (63) and the voltage applied thereto increase due to a rapid change of the impedance of the load 25 (75), the voltage between the first connection point P.sub.1 (P.sub.11) and the second connection point P.sub.2 (P.sub.12) of the switch circuit 19 (69) will increase as well. Here, if this voltage becomes equal to or higher than a voltage obtained by adding the forward turning on voltage of the fifth diode element D.sub.21 (D.sub.31) to the reference voltage, the fifth diode element D.sub.21 (D.sub.31) is forward-biased, the reference capacitance element 18 (68) and the fifth diode element D.sub.21 (D.sub.31) turn on, and the turning on current flows into the protection circuit 14 (64).

(105) At this time, the high frequency amplifying circuit 12 (62) is connected to the load 25 (75) through an impedance of the circuit formed by connecting the main reactance circuit 13 (63) and the protection circuit 14 (64) in parallel.

(106) The absolute value of an impedance of the circuit formed by parallel connecting the main reactance circuit 13 (63) and the protection circuit 14 (64) is set in a manner such that the absolute value of an impedance of the switch circuit 16 (69) in a turning on state becomes larger than the absolute value of an impedance of the switch circuit 16 (69) in a turning off state. As the result, the current output from the high frequency amplifying circuit 12 (62) is limited, and thus, the semiconductor switch 22 (72) is protected.

(107) In the power supply device 42 (92) shown in FIG. 7 (FIG. 8), an inductance element is used for the main reactance circuit 13 (63), the sub-reactance elements 28.sub.1, 28.sub.2 (78.sub.1, 78.sub.2) are used for the sub-reactance circuit 30 (80), and the main reactance circuit 13 (63) is an inductive reactance and the sub-reactance circuit 30 (80) is a capacitive reactance. However, as shown in a power supply device 43 (93) of FIG. 9 (FIG. 10), a capacitance element may be used for the main reactance circuit 13 (63), an inductance element may be used for the sub-reactance element 28 (78) of the sub-reactance circuit 30 (80), the main reactance circuit 13 (63) may have a capacitive reactance, and the sub-reactance circuit 30 (80) may be an inductive reactance.

(108) Moreover, a sub-primary winding may be electrically connected between the high frequency amplifying circuit 12 (62) and the output terminal 16 (66) for supplying a current to the load 25 (75). The protection circuit 14 (64) may be provided in a sub-secondary winding magnetically coupled with the sub-primary winding.

REFERENCE SIGNS LIST

(109) 10, 41 to 45, 60, 91 to 95 power supply device 11, 61 DC power source 12, 62 high frequency amplifying circuit 13, 63 main reactance circuit 14, 64 protection circuit 16, 66 output terminal 18, 68 reference capacitance element 19, 69 switch circuit 21, 71 output inductance circuit 25, 75 load 30, 80 sub-reactance circuit D.sub.01 to D.sub.04, D.sub.11 to D.sub.14, D.sub.21, D.sub.31 diode element CD.sub.01 to CD.sub.04 or CD.sub.11 to CD.sub.14, CD.sub.21, CD.sub.31 parasitic capacitance of diode element L Coil C Capacitor