High-voltage amplifier

Abstract

To provide a high-voltage amplifier capable of stably holding through-current without individual adjustments.SOLUTION: A high-voltage amplifier, including: an input circuit 105 for amplifying an input signal; a positive electrode side level shift circuit 107 connected to the input circuit 105; a negative electrode side level shift circuit 109 connected to the input circuit 105; a high-voltage output circuit 111 including a positive electrode side output circuit 112 for amplifying a signal from the positive electrode side level shift circuit 107 and a negative electrode side output circuit 115 for amplifying a signal from the negative electrode side level shift circuit 109; and a feedback circuit 120 for feeding back an output signal from the high-voltage output circuit 111 to the input signal, is configured to be provided with detection circuits 114 and 117 for detecting currents of the positive electrode side output circuit 112 and the negative electrode side output circuit 115, and offset adjustment circuits 118 and 119 for increasing the offset amount of the negative electrode side level shift circuit 109 to a negative side when the current of the positive electrode side output circuit 112 increases and increasing the offset amount of the positive electrode side level shift circuit 107 to a positive side when the current of the negative electrode side output circuit 115 increases.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a high-voltage amplifier that amplifies a low-voltage signal to a high-voltage signal.

Background Art

[0002] A circuit configuration for amplifying a low-voltage signal to a high-voltage signal is described in Patent Document 1. This Patent Document 1 describes an amplification circuit that can be used as an operational amplifier even when the voltage difference between a high-potential power supply and a low-potential power supply is equal to or higher than the breakdown voltage of a single MOSFET (metal-oxide-semiconductor field-effect transistor).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technique described in Patent Document 1, no consideration is given to controlling the through-current flowing from the high-potential power supply through the high-voltage output circuit to the low-potential power supply.

[0005] Actually, there are non-idealities of the elements used in the amplifier, for example, variations in characteristics based on manufacturing accuracy in the MOSFET used in the output circuit, secular deterioration, and changes in characteristics due to variations such as environmental temperature.

[0006] Such non-idealities of the elements cause variations in the magnitude of the through-current in the positive-side output circuit and the negative-side output circuit of the high-voltage amplifier. When the through-current varies, it affects the heat generation amount, linearity, available current amount, etc. of the high-voltage amplification circuit.

[0007] Therefore, in order to maintain the through-current according to the design specifications, for each high-voltage amplifier, constant adjustment or element selection in the manufacturing stage, or constant adjustment or element replacement during use is required.

[0008] However, such individual adjustment for each high-voltage amplifier is very complicated and time-consuming, leading to an increase in manufacturing costs and maintenance costs. Also, compensation for variations such as environmental temperature is not easy.

[0009] Under such circumstances, there is a desire to provide a high-voltage amplifier capable of stably maintaining the through-current without individual adjustment.

Means for Solving the Problem

[0010] Among the inventions disclosed in the present application, the outline of representative ones will be briefly described as follows.

[0011] A high-voltage amplifier according to a representative embodiment of the present invention includes an input circuit that amplifies an input signal, a positive-side level shift circuit that shifts the input amplified signal from the input circuit to the positive side, a negative-side level shift circuit that shifts the input amplified signal to the negative side, a positive-side output circuit that amplifies the positive-side level shift signal from the positive-side level shift circuit, a negative-side output circuit that amplifies the negative-side level shift signal from the negative-side level shift circuit, a high-voltage output circuit including these, and a feedback circuit that feeds back the high-voltage output signal from the high-voltage output circuit to the input signal. The high-voltage amplifier is provided with a positive-side current detection circuit that detects the current flowing through the positive-side output circuit, a negative-side current detection circuit that detects the current flowing through the negative-side output circuit, a positive-side offset adjustment circuit that adjusts the offset amount of the positive-side level shift circuit to increase to the positive side when the negative-side detection current of the negative-side current detection circuit increases, and a negative-side offset adjustment circuit that adjusts the offset amount of the negative-side level shift circuit to increase to the negative side when the positive-side detection current of the positive-side current detection circuit increases.

Effect of the Invention

[0012] Among the inventions disclosed in this application, the effects obtained by representative ones will be briefly described as follows.

[0013] According to a representative embodiment of the present invention, it is possible to provide a high-voltage amplifier capable of stably holding a through-current without individual adjustment.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described. Note that each of the embodiments described below is an example for realizing the present invention and does not limit the technical scope of the present invention. Problems, configurations, and effects other than those described above will be clarified by the description of the following embodiments.

[0016] In addition, in each of the following embodiments, components having the same function are denoted by the same reference numerals, and repeated descriptions thereof are omitted unless particularly necessary.

[0017] (Embodiment 1) The high-voltage amplifier according to Embodiment 1 will be described.

[0018] <Overview of the High-Voltage Amplifier According to Embodiment 1> The high-voltage amplifier according to Embodiment 1 detects the current flowing through the positive electrode side and the current flowing through the negative electrode side of the high-voltage output circuit, feeds back a signal to the level shift stages of the positive electrode and the negative electrode based on the detected current value, and adjusts the level shift stage output voltage, thereby automatically controlling the output stage through-current to an appropriate value. As a result, even if there are variations in the characteristics of circuit elements, characteristic variations due to temperature fluctuations, time changes, etc., low heat generation and high linearity can be achieved automatically. In this embodiment, the input signal value, that is, the input voltage, is assumed to be several volts to several tens of volts, and the output signal value, that is, the output voltage, is assumed to be about several hundred volts, but it is not limited thereto.

[0019] <Example of the Configuration and Connection Form of the High-Voltage Amplifier> FIG. 1 is a block diagram showing an example of the configuration of the high-voltage amplifier according to Embodiment 1. The high-voltage amplifier 101 according to Embodiment 1 is a voltage feedback type inverting amplifier circuit.

[0020] As shown in FIG. 1, the high-voltage amplifier 101 includes an error amplifier circuit 105 (input circuit), a positive electrode side level shift circuit 107, a negative electrode side level shift circuit 109, a high-voltage output circuit 111, a negative electrode side gain / offset adjustment circuit 118, a positive electrode side gain / offset adjustment circuit 119, a feedback circuit 120, and voltage dividing resistors 127, 128, 131, 132. The high-voltage output circuit 111 includes a positive electrode side output circuit 112, a positive electrode side current detection circuit 114, a negative electrode side output circuit 115, and a negative electrode side current detection circuit 117.

[0021] The output terminal of the error amplification circuit 105 is connected to the positive-side level shift circuit 107 and the negative-side level shift circuit 109. The output terminal of the positive-side level shift circuit 107 is connected to the positive-side output circuit 112. The output terminal of the negative-side level shift circuit 109 is connected to the negative-side output circuit 115. The voltage-dividing resistors 127, 128, 132, and 131 are connected in series between the line supplying the positive voltage VH and the line supplying the negative voltage VL. The connection midpoint of the voltage-dividing resistors 127 and 128 is connected to the positive-side output circuit 112. The connection midpoint of the voltage-dividing resistors 131 and 132 is connected to the negative-side output circuit 115. The positive-side output circuit 112, the positive-side current detection circuit 114, the negative-side current detection circuit 117, and the negative-side output circuit 115 are connected in series. The connection midpoint of the voltage-dividing resistors 128 and 132 is connected to the connection midpoint between the positive-side current detection circuit 114 and the negative-side current detection circuit 117. The connection midpoint between the positive-side current detection circuit 114 and the negative-side current detection circuit 117 serves as the output terminal of the high-voltage amplifier 101. A load 124 is connected to this output terminal.

[0022] Note that the positive-side current detection circuit 114 may be arranged on the upstream side or the downstream side in the current path of the positive-side output circuit 112. Similarly, the negative-side current detection circuit 117 may be arranged on the upstream side or the downstream side in the current path of the negative-side output circuit 115.

[0023] The positive-side current detection circuit 114 is connected to the negative-side gain / offset adjustment circuit 118. The negative-side gain / offset adjustment circuit 118 is connected to the negative-side level shift circuit 109. The negative-side current detection circuit 117 is connected to the positive-side gain / offset adjustment circuit 119. The positive-side gain / offset adjustment circuit 119 is connected to the positive-side level shift circuit 107.

[0024] The error amplification circuit 105 amplifies the error between the target voltage setting signal (input signal) Vin and the feedback signal Sf and outputs an error amplification signal (input amplification signal) Sd.

[0025] The positive-side level shift circuit 107 shifts the input error amplification signal Sd to the positive side and outputs a positive-side level shift signal Shs. The negative-side level shift circuit 109 shifts the input error amplification signal Sd to the negative side and outputs a negative-side level shift signal Sls.

[0026] The high-voltage output circuit 111 includes a positive-side output circuit 112 and a negative-side output circuit 115. The positive-side output circuit 112 amplifies the input positive-side level shift signal Shs. The negative-side output circuit 115 amplifies the input negative-side level shift signal Sls. The high-voltage output circuit 111 outputs a high-voltage output signal Vout by amplifying these level shift signals.

[0027] The positive-side current detection circuit 114 detects a positive-side output circuit current iX flowing through the positive-side output circuit 112 of the high-voltage output circuit 111. The negative-side current detection circuit 117 detects a negative-side output circuit current iY flowing through the negative-side output circuit 115 of the high-voltage output circuit 111.

[0028] In this embodiment, the positive-side current detection circuit 114 is configured to output a positive-side current detection signal when its positive-side detected current iX exceeds a preset positive-side limit value. Also, the negative-side current detection circuit 117 is configured to output a negative-side current detection signal when its negative-side detected current iY exceeds a preset negative-side limit value.

[0029] The negative-side gain / offset adjustment circuit 118 adjusts the gain and offset amount of the negative-side level shift circuit 109 based on the positive-side current detection signal output from the positive-side current detection circuit 114. The positive-side gain / offset adjustment circuit 119 adjusts the gain and offset amount of the positive-side level shift circuit 107 based on the negative-side current detection signal output from the negative-side current detection circuit 117.

[0030] For example, when the positive-side detection current iX by the positive-side current detection circuit 114 increases, the negative-side gain / offset adjustment circuit 118 adjusts so as to increase the offset amount of the negative-side level shift circuit 109 to the negative side. Also, when the negative-side detection current iY by the negative-side current detection circuit 117 increases, the positive-side gain / offset adjustment circuit 119 adjusts so as to increase the offset amount of the positive-side level shift circuit 107 to the positive side.

[0031] In addition, in the present embodiment, the negative-side gain / offset adjustment circuit 118 adjusts so as to increase the offset amount of the negative-side level shift circuit 109 to the negative side according to the positive-side current detection signal output from the positive-side current detection circuit 114. Also, the positive-side gain / offset adjustment circuit 119 adjusts so as to increase the offset amount of the positive-side level shift circuit 107 to the positive side according to the negative-side current detection signal output from the negative-side current detection circuit 117. In this case, there is an advantage that it is easy to set the current limit as designed.

[0032] The feedback circuit 120 generates a feedback signal Sf so that the value of the high-voltage output signal Vout becomes a predetermined amplification factor with respect to the value of the target voltage setting signal Vin.

[0033] Here, the circuit constituting the high-voltage amplifier 101 will be described in more detail. The high-voltage amplifier 101 is roughly composed of an input stage, a level shift stage, and an output stage.

[0034] The input stage has a configuration including an error amplification circuit 105. The error amplification circuit 105 operates so as to amplify the difference between the value of the target voltage setting signal Vin and the value of the feedback signal Sf. By this operation, the convergence error between the value of the high-voltage output signal Vout and the target voltage value is reduced.

[0035] The level shift stage is composed of a positive electrode side level shift circuit 107 and a negative electrode side level shift circuit 109. The positive electrode side level shift circuit 107 and the negative electrode side level shift circuit 109 apply a bias signal suitable for the operation of the output circuit input transistors 121 and 122 to the error amplification signal Sd, and output them as a positive electrode side level shift signal Shs and a negative electrode side level shift signal Sls.

[0036] For example, in the output circuit input transistor 121, the voltage range suitable for operation is a voltage that is lower than the positive electrode voltage VH by the threshold value Vth between the gate and the source. Therefore, the positive electrode side level shift circuit 107 is adjusted so that the value of the positive electrode side level shift signal Shs at 0V input (Vin = 0) becomes (VH - Vth). Similarly, in the output circuit input transistor 122, the voltage range suitable for operation is a voltage that is higher than the negative electrode voltage VL by the threshold value Vth between the gate and the drain. Therefore, the negative electrode side level shift circuit 109 is adjusted so that the value of the negative electrode side level shift signal Sls at 0V input becomes (VL + Vth).

[0037] The output stage is composed of voltage dividing resistors 127, 128, 131, 132 and a high voltage output circuit 111. In this embodiment, the voltage dividing resistors 127, 128, 131, 132 each have the same resistance value. The relationship between the voltage dividing resistors and the high voltage output circuit 111 will be described in detail in the explanation of the "Principle of High Voltage Resistance Improvement by Transistor Multistage Configuration of the Output Stage" described later.

[0038] The positive electrode side output circuit 112 and the negative electrode side output circuit 115 included in the high voltage output circuit 111 achieve a push-pull operation by increasing and decreasing their equivalent resistance values with respect to each other.

[0039] For example, when outputting a positive voltage, the equivalent resistance value of the positive electrode side output circuit 112 decreases, and the equivalent resistance value of the negative electrode side output circuit 115 increases. Also, when outputting a negative voltage, the equivalent resistance value of the positive electrode side output circuit 112 increases, and the equivalent resistance value of the negative electrode side output circuit 115 decreases. Further, when outputting a voltage near 0V, the equivalent resistance values of the positive electrode side output circuit 112 and the negative electrode side output circuit 115 are equal and become medium values.

[0040] 〈Operation of High-Voltage Amplifier〉 How the high-voltage amplifier 101 operates with these configurations will be described.

[0041] In the stable state, the value of the target voltage setting signal Vin and the value of the feedback signal Sf are balanced, and the value of the high-voltage output signal Vout is maintained at a constant state.

[0042] Here, for example, when the value of the target voltage setting signal Vin is increased significantly to the positive side from the stable state, the value of the error amplification signal Sd also increases by the error amplification circuit 105. Therefore, the value of the positive electrode side level shift signal Shs and the value of the negative electrode side level shift signal Sls also increase by the positive electrode side level shift circuit 107 and the negative electrode side level shift circuit 109.

[0043] When the positive electrode side level shift signal Shs increases, the drain-source resistance of the output circuit input transistor 121 increases, so the positive electrode side output circuit current iX of the positive electrode side output circuit 112 decreases. On the other hand, when the value of the negative electrode side level shift signal Sls increases, the drain-source resistance of the output circuit input transistor 122 decreases, so the negative electrode side output circuit current iY of the negative electrode side output circuit 115 increases. The output current iZ, which is the difference between the positive electrode side output circuit current iX and the negative electrode side output circuit current iY, decreases, and the value of the high-voltage output signal Vout determined by the output current iZ, the feedback circuit 120, and the load 124 decreases. Due to the decrease in the value of the high-voltage output signal Vout, the value of the feedback signal Sf decreases. When the value of the feedback signal Sf is balanced with the value of the target voltage setting signal Vin again, these operations converge, and the high-voltage output signal Vout stabilizes at a constant value.

[0044] For example, when the value of the target voltage setting signal Vin is greatly increased in the negative direction from the stable state, the operation opposite to the case where the value of the target voltage setting signal Vin is increased in the positive direction occurs.

[0045] That is, the value of the error amplification signal Sd decreases by the error amplification circuit 105. Therefore, the values of the positive-side level shift signal Shs and the negative-side level shift signal Sls also decrease by the positive-side level shift circuit 107 and the negative-side level shift circuit 109.

[0046] When the value of the negative-side level shift signal Sls decreases, the drain-source resistance of the output circuit input transistor 122 increases, so the negative-side output circuit current iY of the negative-side output circuit 115 decreases. On the other hand, when the value of the positive-side level shift signal Shs decreases, the drain-source resistance of the output circuit input transistor 121 decreases, so the positive-side output circuit current iX of the positive-side output circuit 112 increases. The output current iZ, which is the difference between the positive-side output circuit current iX and the negative-side output circuit current iY, increases, and the value of the high-voltage output signal Vout determined by the output current iZ, the feedback circuit 120, and the load 124 increases. As the value of the high-voltage output signal Vout increases, the value of the feedback signal Sf increases. When the value of the feedback signal Sf is balanced with the value of the target voltage setting signal Vin again, these operations converge, and the value of the high-voltage output signal Vout stabilizes at a constant value.

[0047] <Principle of High Voltage Resistance Improvement by Transistor Multi-Stage Configuration of Output Stage> Next, the principle of high voltage resistance improvement by the transistor multi-stage configuration of the output stage will be described. In the high voltage amplifier 101, in the high voltage output circuit 111, high voltage output is possible by connecting transistors in multiple stages. Specifically, as shown in FIG. 1, in the positive-side output circuit 112, a configuration in which the output circuit input transistor 121 and the voltage dividing transistor 125 are connected in series is adopted. Similarly, in the negative-side output circuit 115, a configuration in which the output circuit input transistor 122 and the voltage dividing transistor 126 are connected in series is adopted.

[0048] For example, when taking the negative electrode voltage VL which is the minimum negative voltage of the value of the high voltage output signal Vout and Vout = VL, a differential voltage of VH - VL, which is the difference between the positive electrode voltage VH and the negative electrode voltage VL, is applied to the positive electrode side output circuit 112. At this time, since the divided voltage V1 generated by the voltage dividing resistors 127 and 128 becomes (VH + VL) / 2, the source voltage of the voltage dividing transistor 125 becomes approximately (VH + VL) / 2. That is, the drain-source voltage between each of the output circuit input transistor 121 and the voltage dividing transistor 125 becomes approximately (VH - VL) / 2.

[0049] Similarly, when taking the positive electrode voltage VH which is the maximum positive voltage of the value of the high voltage output signal Vout and Vout = VH, a differential voltage of VH - VL, which is the difference between the positive electrode voltage VH and the negative electrode voltage VL, is applied to the negative electrode side output circuit 115. At this time, since the divided voltage V2 generated by the voltage dividing resistors 131 and 132 becomes (VH + VL) / 2, the source voltage of the voltage dividing transistor 126 becomes approximately (VH + VL) / 2. That is, the drain-source voltage between each of the output circuit input transistor 122 and the voltage dividing transistor 126 becomes approximately (VH - VL) / 2.

[0050] Therefore, according to this configuration, voltage division of the drain-source voltage can be performed according to the number of stages of the transistors. Therefore, even when the inter-power supply voltage (VH - VL) exceeds the element breakdown voltage of the transistor, high voltage output can be achieved by mounting a plurality of transistors.

[0051] <Relationship between Through-Current and Crossover Distortion> Incidentally, in a conventional high-voltage amplifier using a level shift circuit and a transistor on the positive electrode side and the negative electrode side respectively, there is no gain / offset adjustment circuit connected to the level shift circuit. In such a conventional high-voltage amplifier, the through-current iW flowing through the output circuits on the positive electrode side and the negative electrode side is determined depending on the level shift voltages supplied by the positive electrode side level shift circuit 107 and the negative electrode side level shift circuit 109. When the level shift amount is made closer to the gate-source voltage threshold value of each transistor, the through-current iW increases. However, on the other hand, the crossover distortion occurring in the vicinity of Vout = 0V is reduced. Conversely, when the level shift amount is moved away from the gate-source voltage threshold value of each transistor, the through-current iW decreases. However, on the other hand, the crossover distortion increases.

[0052] That is, the reduction of the through-current iW and the reduction of the crossover distortion are in a trade-off relationship. In order to implement such that these balance states are as designed, for example, it is necessary to adjust the level shift voltage of several 100V in units of several 10mV, and extremely strict adjustment is imposed. Furthermore, it is difficult to cope with the characteristic changes of elements during the operation of the high-voltage amplifier, for example, the threshold voltage fluctuation of the transistor due to self-heating, etc.

[0053] Hereinafter, it will be described in detail with reference to the drawings that these problems are improved according to the present embodiment.

[0054] 〈Time changes of various signals and currents during operation of high-voltage amplifier〉 FIG. 2 is a graph showing an example of the time changes of various signal values and currents during the operation of the high-voltage amplifier according to Embodiment 1. All the various signal values and currents in this graph are relative values. In FIG. 2, (a) shows the value of the positive electrode side level shift signal Shs, (b) shows the positive electrode side output circuit current iX, (c) shows the value of the negative electrode side level shift signal Sls, (d) shows the negative electrode side output circuit current iY, (e) shows the through-current iW, (f) shows the output current iZ, and (g) shows the value of the high-voltage output signal Vout.

[0055] First, assume that the high-voltage amplifier 101 is performing a current supply operation. Then, \(i_X = i_W + i_Z\) and \(i_Y = i_W\).

[0056] For example, assume that the threshold value between the gate and source of the transistor constituting the high-voltage output circuit 111 varies due to the heat generation of the circuit element. As shown in FIGS. 2(b) and 2(d), assume that starting from time \(t_A\), the positive-side output circuit current \(i_X\) and the negative-side output circuit current \(i_Y\) begin to increase. Accordingly, as shown in FIG. 2(e), starting from time \(t_A\), the through current \(i_W\) begins to increase. Then, as shown in FIG. 2(b), starting from time \(t_B\), the positive-side output circuit current \(i_X\) exceeds the preset positive-side limit value \(i_L\). When the positive-side output circuit current \(i_X\) exceeds the positive-side limit value \(i_L\), the positive-side current detection circuit 114 operates, and the negative-side gain / offset adjustment circuit 118 increases the offset amount of the negative-side level shift circuit 109 to the negative side. Note that the offset amount may be substantially increased to the negative side by decreasing the gain of the negative-side level shift circuit 109. In this case, there is an advantage that the positive-side gain / offset adjustment circuit 119 and the negative-side gain / offset adjustment circuit 118 are easy to design when created with analog circuits.

[0057] As the offset amount of the negative-side level shift circuit 109 increases to the negative side, as shown in FIG. 2(c), the value of the negative-side level shift signal \(S_{ls}\) begins to decrease starting from time \(t_C\). As the value of the negative-side level shift signal \(S_{ls}\) decreases, the voltage between the gate and source of the output circuit input transistor 122 decreases, and the equivalent resistance value of the negative-side output circuit 115 increases. When the equivalent resistance value of the negative-side output circuit 115 increases, the negative-side output circuit current \(i_Y\) decreases, and a part of the through current \(i_W\) flowing through the negative-side output circuit 115 is supplied as the output current \(i_Z\) to the feedback circuit 120 and the load 124. Therefore, as shown in FIG. 2(f), the output current \(i_Z\) begins to increase starting from time \(t_D\). Also, as shown in FIG. 2(g), the voltage value of the high-voltage output signal \(V_{out}\) also begins to increase starting from time \(t_D\).

[0058] As the voltage of the high-voltage output signal Vout increases, the voltage of the feedback signal Sf also increases, so that the error between the value of the target voltage setting signal Vin and the value of the feedback signal Sf becomes larger. When the value of the error amplification signal Sd generated by the error amplification circuit 105 is input to the positive-side level shift circuit 107, as shown in Fig. 2(a), the value of the positive-side level shift signal Shs starts to increase from the time point of tE. At this time, the error amplification signal Sd is also input to the negative-side level shift circuit 109. On the other hand, since the offset amount of the negative-side level shift circuit 109 has increased negatively by the negative-side gain / offset adjustment circuit 118, the voltage increase of the negative-side level shift signal Sls becomes negligibly small. As the value of the positive-side level shift signal Shs increases, the gate-source voltage of the output circuit input transistor 121 decreases, and the equivalent resistance value of the positive-side output circuit 112 increases. When the equivalent resistance value of the positive-side output circuit 112 increases, as shown in Fig. 2(b), the positive-side output circuit current iX starts to decrease from the time point of tF. As the positive-side output circuit current iX decreases, as shown in Fig. 2(f), the output current iZ decreases from tF. Then, as shown in Fig. 2(g), the voltage of the high-voltage output signal Vout also starts to decrease from tF and returns to the target value St at the time point of tG.

[0059] Through these series of operations, the through-current iW can always be suppressed below the limit value iM. As a result, in order to improve the linearity near 0V, even if the initial values of the gains and offset amounts of the positive-side level shift circuit 107 and the negative-side level shift circuit 109 are set so that the positive-side output circuit current iX and the negative-side output circuit current iY become large, it is possible to operate while keeping the through-current iW at an appropriate value.

[0060] Note that in this embodiment, each current detection circuit is configured to output a signal when the detected current exceeds a predetermined limit value, and each gain / offset adjustment circuit is configured to increase the offset amount in response to that signal. However, other configurations may also be used. For example, each current detection circuit may be configured to output a signal value corresponding to the detected current, and each gain / offset adjustment circuit may be configured to increase the offset amount when the signal value exceeds a predetermined threshold. In this case, there is an advantage that it is easy to design when the positive-side gain / offset adjustment circuit 119 and the negative-side gain / offset adjustment circuit 118 are created using a programmable semiconductor chip or the like.

[0061] <Example of implementation of high-voltage amplifier> FIG. 3 is a diagram showing an example of the implementation of the high-voltage amplifier according to Embodiment 1. The high-voltage amplifier 101a in the implementation example shown in FIG. 3 is an example in which the configuration shown in FIG. 1 is implemented using photocouplers 302 and 305 and a variable current source controlled by the photocouplers 302 and 305.

[0062] As shown in FIG. 3, the positive-side current detection circuit 114 is configured using the resistor 301 and the photocoupler input terminal 303 of the photocoupler 302. The negative-side current detection circuit 117 is configured using the resistor 304 and the photocoupler input terminal 306 of the photocoupler 305.

[0063] The resistor 301 and the resistor 304 are connected in series between the output side of the positive-side output circuit 112 and the output side of the negative-side output circuit 115. Voltage-dividing resistors 127, 128, 132, and 131 are connected in series between the power supply line of the positive voltage VH and the power supply line of the negative voltage VL. The connection midpoint between the voltage-dividing resistor 128 and the voltage-dividing resistor 132 is connected to the connection point between the resistor 301 and the resistor 304. This connection point becomes the output terminal of the high-voltage amplifier 101a. A load 124 is connected to the output terminal.

[0064] The photocoupler input terminal 303 of the photocoupler 302 is connected in parallel with the resistor 301. The photocoupler input terminal 306 of the photocoupler 305 is connected in parallel with the resistor 304.

[0065] The positive - side gain / offset adjustment circuit 119 is composed of the constant - current supply unit 312 of the positive - side level - shift circuit 107 and the photocoupler output terminal 308 of the photocoupler 305. The negative - side gain / offset adjustment circuit 118 is composed of the constant - current supply unit 311 of the negative - side level - shift circuit 109 and the photocoupler output terminal 307 of the photocoupler 302.

[0066] The positive - side constant - current supply unit 312 is composed of the resistor R1 and the resistor R2, the Zener diode ZD1, and the transistor 310 which is a p - type channel MOSFET. The resistor R1 and the Zener diode ZD1 are connected in series between the positive power supply line V+ and the negative power supply line V-. The connection point between the resistor R1 and the Zener diode ZD1 is connected to the gate of the transistor 310. The source of the transistor 310 is connected to the positive power supply line V+ via the resistor R2. The drain of the transistor 310 is connected to the positive - side level - shift circuit 107.

[0067] The negative - side constant - current supply unit 311 is composed of the resistor R3 and the resistor R4, the Zener diode ZD2, and the transistor 309 which is an n - type channel MOSFET. The second Zener diode ZD2 and the resistor R3 are connected in series between the positive power supply line V+ and the negative power supply line V-. The connection point between the Zener diode ZD2 and the resistor R3 is connected to the gate of the transistor 309. The source of the transistor 309 is connected to the negative power supply line V- via the resistor R4. The drain of the transistor 309 is connected to the negative - side level - shift circuit 109.

[0068] The positive-side level shift circuit 107 is composed of resistors R5 to R7 and transistors TR3 to TR6 which are p-channel MOSFETs. The negative-side level shift circuit 109 is composed of resistors R8 to R10 and transistors TR7 to TR10 which are n-channel MOSFETs.

[0069] Between the power supply line of the positive voltage VH and the drain of the transistor 310, the transistors TR3 and TR4 connected in series, and the resistors R5, transistor TR5, and transistor TR6 connected in series are connected in parallel. Between the power supply line of the positive voltage VH and the ground, the resistors R6 and R7 connected in series are connected. The gates of the transistors TR3 and TR5 are connected to the connection point between the resistors R6 and R7, respectively. The gate of the transistor TR4 is connected to the output terminal of the error amplifier circuit 105. The gate of the transistor TR6 is connected to the ground.

[0070] Between the power supply line of the negative voltage VL and the drain of the transistor 309, the transistors TR7 and TR8 connected in series, and the resistors R8, transistor TR9, and transistor TR10 connected in series are connected in parallel. Between the power supply line of the negative voltage VL and the ground, the resistors R9 and R10 connected in series are connected. The gates of the transistors TR7 and TR9 are connected to the connection point between the resistors R9 and R10, respectively. The gate of the transistor TR8 is connected to the output terminal of the error amplifier circuit 105. The gate of the transistor TR10 is connected to the ground.

[0071] The feedback circuit 120 is composed of resistors R11 and R12. The resistor R11 is connected between the output terminal of the high-voltage amplifier 101a and the positive terminal of the operational amplifier OP1 that constitutes the error amplifier circuit 105. The twelfth resistor R12 is connected between the input terminal of the high-voltage amplifier 101a and the positive terminal of the operational amplifier OP1 that constitutes the error amplifier circuit 105.

[0072] The error amplification circuit 105 is a non-inverting amplifier circuit using a so-called operational amplifier OP1, and is composed of a resistor R13, a resistor R14, and the operational amplifier OP1.

[0073] The photocoupler output terminal 308 of the photocoupler 305 is connected between the gate and the source of the transistor 310. The photocoupler output terminal 307 of the photocoupler 302 is connected between the gate and the source of the transistor 309.

[0074] In the positive electrode side constant current supply unit 312, the gate of the transistor 310 is normally held at a potential obtained by adding the Zener voltage to the potential of the negative power supply line V-. Therefore, this first transistor 310 operates so that a constant current flows from the drain to the source.

[0075] In the negative electrode side constant current supply unit 311, the gate of the transistor 309 is normally held at a potential obtained by subtracting the Zener voltage from the potential of the positive power supply line V+. Therefore, this transistor 309 operates so that a constant current flows from the source to the drain.

[0076] The gate of transistor TR5 is normally held at the divided potential of resistor R6 and resistor R7, and a constant current flows through resistor R5, transistor TR5, and transistor TR6 toward the drain side of transistor 310 in the positive-side constant current supply unit 312. As a result, the positive-side level shift circuit 107 outputs a signal level-shifted to a potential obtained by subtracting the voltage drop of resistor R5 from the potential of the power supply line of the positive voltage VH. When the target voltage setting signal Vin changes, the output signal of the error amplification circuit 105 changes as a signal obtained by amplifying the target voltage setting signal Vin with a predetermined gain. When the output signal of the error amplification circuit 105 changes, the gate signal of transistor TR4 in the positive-side level shift circuit 107 changes. Then, the resistance values of transistor TR3 and transistor TR4 change, and the ratio of the current flowing through transistor TR3 and transistor TR4 to the current flowing through resistor R5, transistor TR5, and transistor TR6 changes. Then, the voltage between terminals due to the voltage drop of resistor R5 changes. As a result, the output signal of the positive-side level shift circuit 107 changes.

[0077] Similarly, the gate of transistor TR9 is normally held at the divided potential of resistor R9 and resistor R10, and a constant current flows from the drain side of transistor 309 in the negative-side constant current supply section 311 to resistor R8, transistor TR9, and transistor TR10 so as to operate. As a result, the negative-side level shift circuit 109 outputs a signal level-shifted to a potential obtained by adding the voltage drop of resistor R8 to the potential of the power supply line of the negative voltage VL. When the target voltage setting signal Vin changes, the output signal of the error amplification circuit 105 changes as a signal obtained by amplifying the target voltage setting signal Vin with a predetermined gain. When the output signal of the error amplification circuit 105 changes, the gate signal of transistor TR8 in the negative-side level shift circuit 109 changes. Then, the resistance values of transistor TR7 and transistor TR8 change, and the ratio of the current flowing through transistor TR7 and transistor TR8 to the current flowing through resistor R8, transistor TR9, and transistor TR10 changes. Then, the inter-terminal voltage due to the voltage drop of resistor R8 changes. As a result, the output signal of the negative-side level shift circuit 109 changes.

[0078] With respect to the change in the target voltage setting signal Vin, the direction of change in the output signal of the positive-side level shift circuit 107 and the direction of change in the output signal of the negative-side level shift circuit 109 are the same as each other. Therefore, the positive-side output circuit 112 and the negative-side output circuit 115 perform a push-pull operation.

[0079] In the positive electrode side current detection circuit 114, the current limit value (positive electrode side limit value) iL is determined by the way of current shunting at the resistor 301 and the photocoupler input terminal 303. When a current equal to or greater than the limit value iL flows through the resistor 301 in the positive electrode side current detection circuit 114, the photocoupler input terminal 303 emits light and operates. Here, if the limit value iL is ilim and the threshold voltage of the photodiode is Vpth, the resistance value of the resistor 301 is theoretically obtained by Vpth / ilim. In the negative electrode side gain / offset adjustment circuit 118, when the positive electrode side current detection circuit 114 operates, the resistance value of the photocoupler output terminal 307 decreases. When the resistance value of the photocoupler output terminal 307 decreases, in order to clamp between the gate and source of the transistor 309 of the constant current supply unit 311 of the negative electrode side level shift circuit 109, the current supplied to the negative electrode side level shift circuit 109 decreases. As a result, the gain of the negative electrode side level shift circuit 109 decreases, and the offset amount increases to the negative side.

[0080] In the negative electrode side current detection circuit 117, the current limit value (negative electrode side limit value) iL is determined by the way of current shunting at the resistor 304 and the photocoupler input terminal 306. When a current equal to or greater than the limit value iL flows through the negative electrode side current detection circuit 117, the photocoupler input terminal 306 emits light and operates. In the positive electrode side gain / offset adjustment circuit 119, when the negative electrode side current detection circuit 117 operates, the resistance value of the photocoupler output terminal 308 decreases. When the resistance value of the photocoupler output terminal 308 decreases, in order to clamp between the gate and source of the transistor 310 of the constant current supply unit 312 of the positive electrode side level shift circuit 107, the current supplied to the positive electrode side level shift circuit 107 decreases. As a result, the gain of the positive electrode side level shift circuit 107 decreases, and the offset amount increases to the positive side.

[0081] As described above, according to the implementation example shown in FIG. 3, since the operation of the high voltage amplifier described above is realized, the through current iW can be suppressed to the limit value iM. Furthermore, the linearity in the vicinity of the high voltage output signal Vout = 0V can be ensured, and the crossover distortion can be reduced.

[0082] Also, according to this implementation example, the positive electrode side current detection circuit 114 and the negative electrode side current detection circuit 117 are electrically insulated from the positive electrode side gain / offset adjustment circuit 119 and the negative electrode side gain / offset adjustment circuit 118. Therefore, the high voltage of the output stage does not directly reach the signal path input to the gain / offset adjustment circuit, and the risk that the high voltage adversely affects the adjustment circuit due to an unexpected situation and damages the elements can be suppressed.

[0083] In this implementation example, an optocoupler is used for this insulation, but other methods may be used to achieve insulation. For example, a method using a Hall element or the like in the current detection circuit, or a method of transmitting the output signal of the current detection circuit using an isolation transformer may be adopted.

[0084] (Embodiment 2) FIG. 4 is a block diagram showing an example of the configuration of the high voltage amplifier according to Embodiment 2. The high voltage amplifier according to this embodiment is obtained by adding a predetermined function to the high voltage amplifier according to Embodiment 1.

[0085] As shown in FIG. 4, the configuration of the high voltage amplifier 102 according to Embodiment 2 is a configuration in which a signal path 401 from the positive electrode side current detection circuit 114 to the positive electrode side gain / offset adjustment circuit 119 and a signal path 402 from the negative electrode side current detection circuit 117 to the negative electrode side gain / offset adjustment circuit 118 are added to the configuration of Embodiment 1.

[0086] In Embodiment 1, when the positive - side output - circuit current iX flowing through the positive - side output circuit 112 increases, the value of the negative - side level - shift signal Sls decreases through the positive - side current - detection circuit 114, the negative - side gain / offset adjustment circuit 118, and the negative - side level - shift circuit 109. This operation increases the equivalent resistance of the output - circuit input transistor 122 and serves to decrease the negative - side output - circuit current iY. In this case, the control of the positive - side output - circuit current iX depends on the value of the high - voltage output signal Vout generated by the output current iZ. Therefore, for example, if the load 124 has a low resistance, the output current iZ will continue to increase until the value of the high - voltage output signal Vout reaches the target value.

[0087] Therefore, as shown in FIG. 4, a signal path 401 is added. According to such a configuration, when the positive - side output - circuit current iX equal to or greater than the limit value iL is detected by the positive - side current - detection circuit 114, the positive - side gain / offset adjustment circuit 119 decreases the gain of the positive - side level - shift circuit 107 and increases the offset amount to the positive side. Then, the value of the positive - side level - shift signal Shs increases, and the positive - side output - circuit current iX operates so as not to exceed the limit value iL. That is, even when the output current iZ surges suddenly, such as when the load 124 is in a short - circuit state, the output current iZ can be limited, and destruction of circuit elements due to overcurrent can be prevented.

[0088] The signal path 402 functions in the same manner as the signal path 401 on the negative side and exhibits the same effects. Therefore, the description thereof is omitted here.

[0089] <Modification Example> Note that the limit value iL for limiting the positive - side output - circuit current iX and the negative - side output - circuit current iY and the limit value iM for limiting the through - current iW may be set to different values, respectively.

[0090] For example, when the output circuit current iX on the positive electrode side exceeds the limit value ilimb (limit value B), the positive electrode side current detection circuit 114 outputs a detection signal to the negative electrode side gain / offset adjustment circuit 118, and when the output circuit current iX on the positive electrode side exceeds the limit value ilima (limit value A), it is configured to output a detection signal to the positive electrode side gain / offset adjustment circuit 119.

[0091] Also, when the output circuit current iY on the negative electrode side exceeds the limit value ilima, the negative electrode side current detection circuit 117 outputs a detection signal to the negative electrode side gain / offset adjustment circuit 118, and when the output circuit current iY on the negative electrode side exceeds the limit value ilimb, it is configured to output a detection signal to the positive electrode side gain / offset adjustment circuit 119.

[0092] Furthermore, the positive electrode side gain / offset adjustment circuit 119 is configured to adjust the offset amount of the positive electrode side level shift circuit 107 to increase it positively according to the detection signal from at least one of the positive electrode side current detection circuit 114 and the negative electrode side current detection circuit 117.

[0093] Also, the negative electrode side gain / offset adjustment circuit 118 is configured to adjust the offset amount of the negative electrode side level shift circuit 109 to increase it negatively according to the detection signal from at least one of the positive electrode side current detection circuit 114 and the negative electrode side current detection circuit 117.

[0094] According to the configuration of the second embodiment as described above, even when the load 124 is in a low resistance or short - circuit state, the output current iZ can be limited, and destruction of circuit elements due to overcurrent can be prevented.

[0095] Note that in Embodiment 2, each current detection circuit is configured to output a signal when the detected current exceeds a limit value, and each gain / offset adjustment circuit is configured to increase the offset in response to the signal. However, other configurations may also be used. For example, each current detection circuit may be configured to output a signal value corresponding to the detected current, and each gain / offset adjustment circuit may be configured to increase the offset amount when the signal value of each current detection circuit exceeds a predetermined threshold value. Also, for example, each current detection circuit may be configured to output a signal value corresponding to the detected current, and each gain / offset adjustment circuit may be configured to gradually increase the offset amount as the signal value of each current detection circuit increases. Such a configuration is also applicable to a modification of Embodiment 2.

[0096] (Embodiment 3) FIG. 5 is a block diagram showing an example of the configuration of the high-voltage amplifier according to Embodiment 3. As shown in FIG. 5, in the high-voltage amplifier 103 according to Embodiment 3, the positive electrode side current detection circuit 114 shown in FIG. 4 is replaced with a current detection circuit 501 (first current detection circuit) and a current detection circuit 502 (second current detection circuit) connected in series, and the negative electrode side current detection circuit 117 shown in FIG. 4 is replaced with a current detection circuit 503 (third current detection circuit) and a current detection circuit 504 (fourth current detection circuit) connected in series. Also, the current detection circuit 501 is connected to the positive electrode side gain / offset adjustment circuit 119, and the current detection circuit 502 is connected to the negative electrode side gain / offset adjustment circuit 118. Also, the current detection circuit 503 is connected to the negative electrode side gain / offset adjustment circuit 118, and the current detection circuit 504 is connected to the positive electrode side gain / offset adjustment circuit 119.

[0097] The positive - side gain / offset adjustment circuit 119 adjusts the offset amount of the 107 of the positive - side level - shift circuit based on the first output signal from the current detection circuit 501 and the third output signal from the current detection circuit 503. Also, the negative - side gain / offset adjustment circuit 118 adjusts the offset amount of the negative - side level - shift circuit 109 based on the second output signal from the current detection circuit 502 and the fourth output signal from the current detection circuit 504.

[0098] In this embodiment, the current detection circuit 501 (the first current detection circuit) is designed to output a first detection signal when the detected positive - side output circuit current iX (the first detection current) exceeds the limit value ilimc (the first limit value). The current detection circuit 502 (the second current detection circuit) is designed to output a second detection signal when the detected positive - side output circuit current iX (the second detection current) exceeds the limit value ilimd (the second limit value). Also, the current detection circuit 503 (the third current detection circuit) is designed to output a third detection signal when the detected negative - side output circuit current iY (the third detection current) exceeds the limit value ilime (the third limit value). The current detection circuit 504 (the fourth current detection circuit) is designed to output a fourth detection signal when the detected negative - side output circuit current iY (the fourth detection current) exceeds the limit value ilimf (the fourth limit value). Thus, on each of the positive - side and negative - side, the current detection circuit that sends a signal to the positive - side gain / offset adjustment circuit 119 and the current detection circuit that sends a signal to the negative - side gain / offset adjustment circuit 118 may be arranged separately.

[0099] In addition, as another embodiment, the following embodiment can also be considered. The current detection circuit 501 is designed to output a first detection current signal representing the detected positive - side output circuit current iX. The current detection circuit 502 is designed to output a second detection current signal representing the detected positive - side output circuit current iX. Also, the current detection circuit 503 is designed to output a third detection current signal representing the detected negative - side output circuit current iY. The current detection circuit 504 is designed to output a fourth detection current signal representing the detected negative - side output circuit current iY.

[0100] The positive electrode side gain / offset adjustment circuit 119 adjusts the offset amount of the positive electrode side level shift circuit 107 based on the magnitudes of the values of the first detection current signal from the current detection circuit 501 and the third detection current signal from the current detection circuit 503. Also, the negative electrode side gain / offset adjustment circuit 118 adjusts the offset amount of the negative electrode side level shift circuit 109 based on the magnitudes of the values of the second detection current signal from the current detection circuit 502 and the fourth detection current signal from the current detection circuit 504.

[0101] For example, as the first detection current signal and the third detection current signal increase, the positive electrode side gain / offset adjustment circuit 119 increases the offset amount of the positive electrode side level shift circuit 107 in the positive direction. Also, as the second detection current signal and the fourth detection current signal increase, the negative electrode side gain / offset adjustment circuit 118 increases the offset amount of the negative electrode side level shift circuit 109 in the negative direction.

[0102] Also for example, when the value of the first detection current signal exceeds a predetermined threshold, or when the value of the third detection current signal exceeds a predetermined threshold, the positive electrode side gain / offset adjustment circuit 119 increases the offset amount of the positive electrode side level shift circuit 107 in the positive direction. Also, when the value of the second detection current signal exceeds a predetermined threshold, or when the value of the fourth detection current signal exceeds a predetermined threshold, the negative electrode side gain / offset adjustment circuit 118 increases the offset amount of the negative electrode side level shift circuit 109 in the negative direction.

[0103] According to the configuration of the third embodiment as described above, the limit value of the current, which is the threshold for the condition for outputting the current detection signal, can be set independently for each current detection circuit, and the degree of freedom in design can be expanded.

[0104] As described above, various embodiments of the present invention have been explained. However, the present invention is not limited to the above-described embodiments and includes various modifications. Also, the above-described embodiments have been explained in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. All of these belong to the scope of the present invention. Furthermore, numerical values, names, etc. included in the text and drawings are merely examples, and the effects of the present invention are not impaired even if different ones are used.

[0105] For example, in the above embodiment, an MOSFET is used in the output circuit, but other elements such as bipolar transistors and vacuum tubes may be used.

[0106] Also, it is possible to add, delete, or replace a part of the configuration of each embodiment with other configurations. Further, each of the above configurations, functions, circuits, etc. may be realized by designing a part or all of them, for example, with an integrated circuit or a programmable semiconductor chip.

Description of Reference Numerals

[0107] 101... high-voltage amplifier, 105... error amplification circuit, 107... positive-side level shift circuit, 109... negative-side level shift circuit, 118... negative-side gain / offset adjustment circuit, 119... positive-side gain / offset adjustment circuit, 111... high-voltage output circuit, 112... positive-side output circuit, 114... positive-side current detection circuit, 115... negative-side output circuit, 117... negative-side current detection circuit, 120... feedback circuit, 127, 128, 131, 132... voltage-dividing resistors, Vin... signal for setting target voltage, Vout... high-voltage output signal, iW... through-current, iX... positive-side output circuit current, iY... negative-side output circuit current, iZ... output current.

Claims

1. An input circuit for amplifying an input signal, a positive-side level shift circuit for shifting the input amplified signal from the input circuit to the positive side, a negative-side level shift circuit for shifting the input amplified signal to the negative side, a positive-side output circuit for amplifying the positive-side level shift signal from the positive-side level shift circuit, and a negative-side output circuit for amplifying the negative-side level shift signal from the negative-side level shift circuit, a high-voltage output circuit including the same, a feedback circuit for feeding back the high-voltage output signal from the high-voltage output circuit to the input signal, A high-voltage amplifier comprising: a positive-side current detection circuit for detecting the current flowing through the positive-side output circuit, a negative-side current detection circuit for detecting the current flowing through the negative-side output circuit, a positive-side offset adjustment circuit for adjusting the offset amount of the positive-side level shift circuit to increase in the positive side when the negative-side detection current of the negative-side current detection circuit increases, a negative-side offset adjustment circuit for adjusting the offset amount of the negative-side level shift circuit to increase in the negative side when the positive-side detection current of the positive-side current detection circuit increases, An output terminal to which a load is connected is provided between the positive-side output circuit and the negative-side output circuit, The positive-side current detection circuit is disposed on the upstream side or the downstream side of the positive-side output circuit, The negative-side current detection circuit is disposed on the upstream side or the downstream side of the negative-side output circuit, The positive-side current detection circuit and the negative-side current detection circuit are electrically insulated from the positive-side offset adjustment circuit and the negative-side offset adjustment circuit, High-voltage amplifier.

2. In the high-voltage amplifier according to Claim 1, The positive-side current detection circuit outputs a positive-side current detection signal when the positive-side detection current exceeds a positive-side limit value, The negative-side current detection circuit outputs a negative-side current detection signal when the negative-side detection current exceeds a negative-side limit value, The positive-side offset adjustment circuit adjusts the offset amount of the positive-side level shift circuit to increase in the positive side according to the negative-side current detection signal, The negative-side offset adjustment circuit adjusts the offset amount of the negative-side level shift circuit to increase in the negative side according to the positive-side current detection signal, High-voltage amplifier.

3. In the high-voltage amplifier according to Claim 1, When at least one of the positive-side detected current and the negative-side detected current increases, the positive-side offset adjustment circuit adjusts so as to increase the offset amount of the positive-side level shift circuit in the positive direction. When at least one of the positive-side detected current and the negative-side detected current increases, the negative-side offset adjustment circuit adjusts so as to increase the offset amount of the negative-side level shift circuit in the negative direction. High-voltage amplifier.

4. In the high-voltage amplifier according to claim 3, When the positive-side detected current exceeds the positive-side limit value, the positive-side current detection circuit outputs a positive-side current detection signal. When the negative-side detected current exceeds the negative-side limit value, the negative-side current detection circuit outputs a negative-side current detection signal. The positive-side offset adjustment circuit adjusts so as to increase the offset amount of the positive-side level shift circuit in the positive direction according to at least one of the positive-side current detection signal and the negative-side current detection signal. The negative-side offset adjustment circuit adjusts so as to increase the offset amount of the negative-side level shift circuit in the negative direction according to at least one of the positive-side current detection signal and the negative-side current detection signal. High-voltage amplifier.

5. In the high-voltage amplifier according to claim 3, The positive-side current detection circuit outputs a positive-side current detection signal to the negative-side offset adjustment circuit when the positive-side detected current exceeds limit value A, and outputs the positive-side current detection signal to the positive-side offset adjustment circuit when the positive-side detected current exceeds limit value B. The negative-side current detection circuit outputs a negative-side current detection signal to the positive-side offset adjustment circuit when the negative-side detected current exceeds the limit value A, and outputs the negative-side current detection signal to the negative-side offset adjustment circuit when the negative-side detected current exceeds the limit value B. The positive-side offset adjustment circuit adjusts so as to increase the offset amount of the positive-side level shift circuit in the positive direction according to at least one of the positive-side current detection signal and the negative-side current detection signal. The negative-side offset adjustment circuit adjusts so as to increase the offset amount of the negative-side level shift circuit in the negative direction according to at least one of the positive-side current detection signal and the negative-side current detection signal. High-voltage amplifier.

6. In the high-voltage amplifier according to claim 1, the positive-side current detection circuit has a first current detection circuit and a second current detection circuit connected in series, the negative-side current detection circuit has a third current detection circuit and a fourth current detection circuit connected in series, the positive-side offset adjustment circuit adjusts the offset amount of the positive-side level shift circuit based on a first output signal from the first current detection circuit and a third output signal from the third current detection circuit, the negative-side offset adjustment circuit adjusts the offset amount of the negative-side level shift circuit based on a second output signal from the second current detection circuit and a fourth output signal from the fourth current detection circuit, High-voltage amplifier.

7. In the high-voltage amplifier according to claim 6, the first current detection circuit outputs a first detection signal when a first detection current by the first current detection circuit exceeds a first limit value, the second current detection circuit outputs a second detection signal when a second detection current by the second current detection circuit exceeds a second limit value, the third current detection circuit outputs a third detection signal when a third detection current by the third current detection circuit exceeds a third limit value, the fourth current detection circuit outputs a fourth detection signal when a fourth detection current by the fourth current detection circuit exceeds a fourth limit value, the positive-side offset adjustment circuit increases the offset amount of the positive-side level shift circuit to the positive side according to the first detection signal or the third detection signal, the negative-side offset adjustment circuit increases the offset amount of the negative-side level shift circuit to the negative side according to the second detection signal or the fourth detection signal, High-voltage amplifier.

8. In the high-voltage amplifier according to claim 1, the positive-side offset adjustment circuit adjusts the offset amount of the positive-side level shift circuit by changing the gain of the positive-side level shift circuit, the negative-side offset adjustment circuit adjusts the offset amount of the negative-side level shift circuit by changing the gain of the negative-side level shift circuit, High-voltage amplifier.

9. In the high-voltage amplifier according to claim 1, the maximum output voltage from the output terminal is a voltage of 200 V or more and less than 1000 V, High-voltage amplifier.

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