Power amplifier and target detection device

Abstract

To provide a power amplifier which is suitable to a capacitive load, has high efficiency and can achieve the low EMI, and a target detection device using the power amplifier.SOLUTION: A power amplifier 1 comprises: a first switching element SW1 and a second switching element SW2 that are turned on / off alternately; and an output smoothing circuit 2 that is connected to a switching output end N. A capacitive load TD is connected to the output smoothing circuit 2. A compensation inductor Lp is connected in parallel to the switching output end N. At the timing when electric currents Isw1, Isw2 flowing in the first switching element SW1 or the second switching element SW2 in the on-state are positive or zero-cross, the first switching element SW1 or the second switching element SW2 in the on-state is turned off.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a class D power amplifier suitable for capacitive loads and a target detection device using this power amplifier.

Background Art

[0002] As a power amplifier, a class D power amplifier using pulse width modulation (hereinafter also referred to as PWM modulation) is known (for example, Patent Documents 1 and 2). FIG. 10 shows a general half-bridge type class D power amplifier 100. This power amplifier 100 is connected in series between a power supply E and a ground portion, and includes a first switching element SW1 and a second switching element SW2 that are alternately turned on and off by a modulated input signal wave, and an output smoothing circuit 101 connected to a switching output terminal N connected between the first switching element SW1 and the second switching element SW2. A capacitive load TD such as a piezoelectric element (hereinafter also referred to as a transducer) is connected to the output smoothing circuit 101.

[0003] For example, MOSFETs are used for the first switching element SW1 and the second switching element SW2. In FIG. 10, the MOSFETs are represented by a switch, a diode, and a capacitor which are its functional configurations. The output smoothing circuit 101 includes a smoothing inductor Ls connected in series to the switching output terminal N and a smoothing capacitor Cp connected in parallel to the switching output terminal N, and constitutes a so-called LPF (Low pass filter). In the figure, the arrow indicated by Isw1 indicates the forward current flowing through the first switching element SW1, and the arrow indicated by Isw2 indicates the forward current flowing through the second switching element SW2. Also, the arrow indicated by Isw indicates the current output from the switching output terminal N, and Vo indicates the output voltage.

[0004] Such a power amplifier 100 pulse-modulates an input wave signal of a sine wave by a pulse modulator (not shown) and inputs it to a first switching element SW1 and a second switching element SW2, and amplifies the power by alternately turning on and off the first switching element SW1 and the second switching element SW2.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, the first switching element SW1 and the second switching element SW2 each composed of a MOSFET include a diode as their functional configuration. This diode turns off when the current of the switching element is in the forward direction when the first switching element SW1 and the second switching element SW2 transition from the on state to the off state. However, when the current of the switching element is in the reverse direction, even if the switches of the first switching element SW1 and the second switching element SW2 turn off, due to the presence of the functionally included diode, it is not immediately turned off, and the conducting state is maintained, and the currents Isw1 and Isw2 continue to flow in the reverse direction (hereinafter also referred to as reverse current). In such a state, when the other switching element through which Isw is not flowing is turned on, a reverse bias is applied to the conducting diode, and the diodes of the first switching element SW1 and the second switching element SW2 turn off. The time from when this diode turns on to when it turns off is called the reverse recovery time. During this reverse recovery time When excessive spike-like currents Isw1 and Isw2 flow in the reverse direction of the diodes, there are problems that the power loss increases and EMI (Electromagnetic Interference) occurs. Such problems occur more significantly when the load connected to the output smoothing circuit 101 is a capacitive load.

[0007] In the technology disclosed in Patent Document 1, in order to reduce power loss, the ripple current of the smoothing inductor is made larger than the load current so that a negative inductor current is generated during load. However, in Patent Document 1, when the ripple current of the smoothing inductor is made larger than the load current, the conduction loss increases and an unnecessary ripple voltage is generated in the output voltage. Also, in the technology disclosed in Patent Document 2, by connecting a compensation coil in parallel to the switching output terminal, the reverse current flowing through the switching element is canceled to improve power efficiency. However, Patent Document 2 assumes that the signal wave frequency and the switching frequency are the same, and does not consider various problems that occur when modulation such as PWM with different signal wave frequencies and switching frequencies is performed to control the amplitude and phase of the output signal waveform. Therefore, depending on the modulation state of the input wave signal, the reverse current cannot be canceled.

[0008] Therefore, an object of the present invention is to provide a power amplifier suitable for a capacitive load, capable of achieving high efficiency and low EMI, and a target detection device using this power amplifier.

Means for Solving the Problems

[0009] To solve the above problems, the invention according to claim 1 is a power amplifier including a first switching element and a second switching element that are connected in series between a power supply and a ground portion and are alternately turned on and off by a control signal in which an input signal wave is modulated, and an output smoothing circuit connected to a switching output terminal connected between the first switching element and the second switching element, wherein a capacitive load is connected to the output smoothing circuit. A compensation inductor is connected in parallel to the switching output terminal, and the first switching element or the second switching element in the on state is turned off at a timing when the current flowing through the first switching element or the second switching element in the on state becomes positive or zero-crosses. As described above, set the minimum on-time ratio and the maximum on-time ratio of the first switching element and the second switching element. The minimum on-time ratio is 5 to 30 percent, and the maximum on-time ratio is the value obtained by subtracting the minimum on-time ratio from 1. The power amplifier is characterized by the above.

[0012] Claim 2 The invention according to claim to 1 In the power amplifier according to claim, the capacitive reactance generated by the capacitive load and the smoothing capacitor constituting the output smoothing circuit is made smaller than or zero by the inductive reactance generated by the compensation inductor and the smoothing inductor constituting the output smoothing circuit.

[0013] Claim 3 The invention according to claim is the power amplifier according to claim 1 or 2 In the power amplifier according to claim, the phase of the input signal wave input at the start of the switching operation by the first switching element and the second switching element or at the start of modulation from the non-modulation state is set to 90° or 270°.

[0014] Claim 4 The invention according to claim is the power amplifier according to any one of claims 1 to 3 In the power amplifier according to claim, the excitation inductance of a transformer is used as the compensation inductor.

[0015] Claim 5The invention described in [reference] is a target detection device that emits ultrasonic waves, receives the ultrasonic waves reflected by a target, and detects the target, comprising driving means for driving a transducer for emitting the ultrasonic waves. As the driving means, the power amplifier according to any one of claims 1 to 4 is used, and the output smoothing circuit outputs a signal frequency modulated in amplitude and phase below the cut-off frequency. The target detection device is characterized by this.

Effects of the Invention

[0016] According to the invention described in claim 1, when the first switching element or the second switching element transitions from the on state to the off state and the other switching element transitions from the off state to the on state, no excessive spike-like current flows in the reverse direction during the reverse recovery time until the diode functionally included in the switching element turns off. Therefore, power loss can be reduced and the generation of EMI can be suppressed.

[0017] Also, according to the invention described in claim 1 , the minimum on-time ratio and the maximum on-time ratio of the first switching element and the second switching element are set such that the first switching element or the second switching element in the on state turns off at the timing when the current flowing through the first switching element or the second switching element in the on state becomes positive or zero-crosses. Therefore, no excessive spike-like current flows in the reverse direction during the reverse recovery time, so power loss can be reduced and the generation of EMI can be suppressed.

[0018] According to the invention described in claim 1 , since the minimum on-time ratio is 5 to 30 percent of one cycle of the control signal and the maximum on-time ratio is the value obtained by subtracting the minimum on-time ratio from one cycle of the control signal, it is possible to set optimal minimum and maximum on-time ratios according to the period of the control signal.

[0019] Furthermore, according to the invention described in claim 2According to the invention described in , the capacitive reactance generated by the capacitive load and the smoothing capacitor constituting the output smoothing circuit is reduced or made zero by the inductive reactance generated by the compensating inductor and the smoothing inductor constituting the output smoothing circuit. Therefore, the effective current value of the current flowing through the first switching element and the second switching element can be reduced, and the power loss can be reduced.

[0020] Also, according to the invention described in claim 3 Since the phase of the input signal wave input at the start of the switching operation by the first switching element and the second switching element or at the start of modulation from the non-modulation state is set to 90° or 270°, a transient large current does not flow through the compensating inductor. As a result, when selecting the compensating inductor, it is possible to suppress the increase in size of the compensating inductor and the transient voltage fluctuations included in the output signal waveform.

[0021] Furthermore, according to the invention described in claim 4 Since the exciting inductance of the transformer is used as the compensating inductor, it is possible to provide the voltage conversion function by the transformer and the insulation function between the input and output without increasing the number of components.

[0022] Also, according to the invention described in claim 5 Since the output smoothing circuit outputs a signal frequency modulated in amplitude and phase below the cut-off frequency, in the signal wave band of the target detection device, a region with a small gain and phase change below the cut-off frequency of the output smoothing circuit can be used, and the influence on the amplitude-frequency modulation wave used in the target detection device is reduced.

Brief Description of the Drawings

[0023]

Figure 1

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Embodiments for Carrying Out the Invention

[0024] Hereinafter, this invention will be described based on the illustrated embodiments.

[0025] [First Embodiment] Figs. 1 to 3 show a first embodiment of the present invention. Fig. 1 shows a half-bridge type class-D power amplifier 1 according to this first embodiment. This power amplifier 1 is connected in series between a power supply E and a ground portion, and includes a first switching element SW1 and a second switching element SW2 that are alternately turned on and off by a control signal in which an input signal wave is modulated, and an output smoothing circuit 2 connected to a switching output terminal N connected between the first switching element SW1 and the second switching element SW2. The output smoothing circuit 2 is connected to a capacitive load TD such as a piezoelectric element (hereinafter also referred to as a transducer).

[0026] For example, MOSFETs are used for the first switching element SW1 and the second switching element SW2. In Fig. 1, the MOSFET is represented by its functional components, a switch, a diode, and a capacitor. The output smoothing circuit 2 includes a smoothing inductor Ls connected in series to the switching output terminal N and a smoothing capacitor Cp connected in parallel to the switching output terminal N, and constitutes a so-called LPF (Low pass filter). In the figure, the arrow indicated by Isw1 represents the forward current flowing through the first switching element SW1, and the arrow indicated by Isw2 represents the forward current flowing through the second switching element SW2. Also, the arrow indicated by Isw represents the current output from the switching output terminal N, and Vo represents the output voltage. Further, the arrow indicated by Vsw represents the voltage output from the switching output terminal N.

[0027] Such a power amplifier 1 inputs a digital control signal obtained by pulse-modulating a sine wave input wave signal by a pulse modulator (for example, a PWM modulation circuit etc.) not shown in the figure to the first switching element SW1 and the second switching element SW2, and alternately turns on and off the first switching element SW1 and the second switching element SW2 to amplify the power.

[0028] FIG. 2 is a diagram showing waveforms of respective parts of the power amplifier 1 shown in FIG. 1. ILp and ILs indicate currents flowing through the compensation inductor LP and the smoothing inductor Ls. The power amplifier 1 according to the present embodiment controls the first switching element SW1 or the second switching element SW2 in the on state to turn off at the timing when the current Isw1 flowing through the first switching element SW1 in the on state or the current Isw2 flowing through the second switching element SW2 is positive or crosses zero. That is, the first switching element SW1 and the second switching element SW2 are controlled to perform zero-voltage switching.

[0029] Specifically, as shown in the currents Isw1 and Isw2 in FIG. 2, the power amplifier 1 turns off the first switching element SW1 and the second switching element SW2 in the on state at the timings T1a and T2a when the currents Isw1 and Isw2 are positive and the timings T1b and T2b when the currents Isw1 and Isw2 cross zero.

[0030] According to this, when the first switching element SW1 and the second switching element SW2 transition from the on state to the off state, no current flows through the diodes of the first switching element SW1 and the second switching element SW2, so the reverse recovery phenomenon does not occur. When the other switching element transitions from the off state to the on state, excessive spike-like currents Isw1 and Isw2 do not flow in the reverse direction of the diode. Therefore, power loss can be reduced and the generation of EMI can be suppressed.

[0031] Also, the power amplifier 1 according to the present embodiment sets (limits) the minimum on-time ratio and the maximum on-time ratio of the first switching element SW1 and the second switching element SW2 in order to appropriately turn off the first switching element SW1 or the second switching element SW2 in the on state at the timing when the current Isw1 or Isw2 flowing through the first switching element SW1 or the second switching element SW2 in the on state is positive or crosses zero.

[0032] Specifically, as shown by the voltage Vsw output from the switching output terminal N in Fig. 2, by setting (limiting) the minimum on-time ratio Ds and the maximum on-time ratio Dm, the first switching element SW1 and the second switching element SW2 in the on state are appropriately turned off at the timings T1a, T2a when the currents Isw1, Isw2 become positive and the timings T1b, T2b when the currents Isw1, Isw2 cross zero. This is because, in order for the polarity of the current flowing through the switching element to change from negative to zero-cross or positive, a certain period of positive voltage or negative voltage is required at Vsw output to the switching output terminal N. Ds and Dm are set because it is necessary to manage that time.

[0033] As shown in Fig. 3, the control signals Vg1 and Vg2 input to the first switching element SW1 and the second switching element are signals with inverted positive and negative. The minimum on-time ratio Ds is the value obtained by dividing the minimum turn-on time Ton(min) of the control signals Vg1, Vg2 by one period T of the control signals Vg1, Vg2. Also, the maximum on-time ratio Dm is the value obtained by dividing the maximum turn-on time Ton(max) of the control signals Vg1, Vg2 by one period T of the control signals Vg1, Vg2. The minimum on-time ratio Ds is, for example, 5 to 30 percent, preferably 10 to 20 percent, of one period T of the control signals Vg1, Vg2. Also, the maximum on-time ratio Dm is the value obtained by subtracting the minimum on-time ratio Ds from one period of the control signals Vg1, Vg2. Note that the minimum on-time ratio Ds and the maximum on-time ratio Dm are set to optimal values by simulation results using a circuit simulator or by actually fabricating and adjusting the power amplifier 1.

[0034] Also, the power amplifier 1 according to this embodiment appropriately sets the inductive reactance by the smoothing inductor Ls and the compensating inductor Lp, cancels the capacitive reactance by the capacitive load TD and the smoothing capacitor Cp at the signal wave frequency, and reduces or makes zero the capacitive reactance. reactance.

[0035] FIG. 4 shows waveforms of respective parts when no adjustment is made to cancel capacitive reactance caused by a capacitive load TD and a smoothing capacitor Cp by inductive reactance of a smoothing inductor Ls and a compensating inductor Lp in the power amplifier 1 shown in FIG. 1. As is clear from comparing the currents Isw1 and Isw2 in FIG. 3 with the currents Isw1 and Isw2 in FIG. 2, when the capacitive reactance caused by the capacitive load TD and the smoothing capacitor Cp is not canceled by the inductive reactance of the smoothing inductor Ls and the compensating inductor Lp, the effective current values of the currents Isw1 and Isw2 increase. In this example, Isw1 and Isw2 in FIG. 4 are increased by about 1.7 times compared with Isw1 and Isw2 in FIG. 2. As described above, according to the power amplifier 1 of the present embodiment, by reducing the effective current values of the currents Isw1 and Isw2 flowing through the first switching element SW1 and the second switching element SW2, power loss can be reduced.

[0036] [Second Embodiment] FIG. 5 is a diagram showing waveforms of respective parts of a power amplifier according to a second embodiment of the present invention. The configuration of the power amplifier of the present embodiment is the same as that of the power amplifier 1 of the first embodiment, but is different from the first embodiment in that the phase of an input signal wave input at the start of the switching operation by the first switching element SW1 and the second switching element SW2 or at the start of modulation is set to 90° or 270°.

[0037] The power amplifier 1 inputs an input wave signal consisting of an analog sine wave and a clock signal into a pulse modulator (e.g., a PWM modulation circuit, etc.) not shown in the figure, and inputs the digital control signal output from the pulse modulator into the first switching element SW1 and the second switching element SW2 to alternately turn them on and off. Here, in the power amplifier 1 shown in FIG. 1, it is assumed that the phase of the input signal wave Vi input at the start of the switching operation by the first switching element SW1 and the second switching element SW2, or at the start of modulation from the non-modulation state, starts from 0° as shown in FIG. 5(B). In this case, a large current ILp corresponding to the integral value of the voltage of the input signal wave Vi transiently flows through the compensation inductor Lp. Therefore, when selecting the compensation inductor Lp, it is necessary to consider the allowable current based on this transient large current, resulting in an increase in the size of the compensation inductor Lp.

[0038] On the other hand, as shown in FIG. 5(A), the power amplifier of this embodiment sets the phase of the input signal wave Vi input at the start of the switching operation by the first switching element SW1 and the second switching element SW2, or at the start of modulation from the non-modulation state, to 90° or 270°. As is clear from comparing the current ILp in FIG. 5(A) with the current ILp in FIG. 5(B), by setting the phase of the input signal wave Vi to 90° or 270°, the transient large current does not flow. Therefore, when selecting the compensation inductor Lp, it is possible to suppress unnecessary increase in size. Also, it is possible to simultaneously suppress the transient voltage fluctuations included in the output signal waveform. And it is also effective when starting modulation from the non-modulation state.

[0039] [Third Embodiment] FIG. 6 shows a power amplifier 1A according to a third embodiment of the present invention. In the power amplifier 1A of the present embodiment, the same components as those of the power amplifier 1 in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The power amplifier 1A according to the present embodiment constitutes a compensation inductor by a transformer T having an exciting inductance. Thereby, the power amplifier 1A according to the present embodiment can have the same number of components as the power amplifier 1 according to the first embodiment, and can further include a voltage conversion function by the transformer T and an insulation function between input and output.

[0040] [Fourth Embodiment] FIG. 7 is a block diagram showing a schematic configuration of a target detection device 10 according to a fourth embodiment of the present invention. The target detection device 10 is, for example, a fish school detection device, and includes a transmission / reception wave unit 11, a main body unit 12, an operation unit 13, and a monitor 14. The transmission / reception wave unit 11 includes a plurality of transmission / reception wave devices 111. The transmission / reception wave device 111 is a transducer for emitting ultrasonic waves, and corresponds to the piezoelectric element (capacitive load) TD described in the first to third embodiments above. The transmission / reception wave device 111 emits ultrasonic waves toward the water, receives the reflected waves reflected by targets such as a fish school, and converts them into received voltages.

[0041] The main body 12 includes a plurality of transmitting and receiving circuits 121 respectively connected to the transceivers 111, and a control circuit 122 connected to the transmitting and receiving circuits 121. The transmitting and receiving circuit 121 includes a transmitting section 121a and a receiving section 121b. The transmitting section 121a is a circuit for driving the transceiver 111 to emit ultrasonic waves. The power amplifier 1 or the power amplifier 1A described above is used for the transmitting section 121a. The receiving section 121b is a circuit that amplifies the received voltage output from the transceiver 111, performs A / D conversion, and outputs the detected signal to the control circuit 122. The control circuit 122 has a transmitting and receiving control function for controlling the transmitting and receiving circuit 121 according to an operation by the user on the operation unit 13, and a signal processing function for generating a detection image based on the detection signal output from the receiving section 121b and displaying it on the monitor 14. In the present embodiment, the output smoothing circuit 2 of the power amplifier 1 or the power amplifier 1A used as the transmitting section 121a is configured to output a signal frequency modulated in amplitude and phase below the cut-off frequency.

[0042] FIG. 8 is a graph showing the input / output characteristics of the conventional power amplifier 100 shown in FIG. 10 when used as the driving means of the transceiver 111, and characteristic curves of the amplitude and phase of the input current and the amplitude and phase of the output voltage are drawn. In the target detection device 10, the frequency indicated by the rectangular frame in the figure is the signal waveband for emitting ultrasonic waves from the transducer. This signal waveband overlaps with the cut-off frequency of the output smoothing circuit 101. Since the power amplifier 100 reduces the capacitive reactance only with the smoothing inductor Ls, the change in amplitude and phase with respect to the frequency of the output voltage becomes very large, and when used in the target detection device 10, the influence on the amplitude-frequency modulation wave becomes large. In particular, when using a plurality of transceivers and synthesizing the respective sound wave outputs to give directivity to the sound waves in a specific direction, there has been a problem that adjustment is difficult.

[0043] On the other hand, FIG. 9 is a graph showing the input / output characteristics of the power amplifier 1 or the power amplifier 1A when the power amplifier 1 or the power amplifier 1A described in the first to third embodiments is used as the driving means of the transceiver 111, and the characteristic curves of the amplitude and phase of the input current and the amplitude and phase of the output voltage are drawn. In the present embodiment, since the output smoothing circuit 2 outputs a signal frequency modulated in amplitude and phase below the cut-off frequency, the peaks of the input current and the output voltage are outside the signal waveband. Therefore, in the signal waveband of the target detection device 10, a region with a gain below the cut-off frequency of the output smoothing circuit 2 and a small phase change can be used, and the influence on the amplitude / frequency modulated wave used in the target detection device 10 is reduced.

[0044] As described above, the embodiments of the present invention have been described. However, the specific configuration is not limited to the above embodiments, and even if there are design changes and the like within the scope not departing from the gist of the present invention, they are included in the present invention. For example, in the above embodiments, PWM modulation has been described as an example of the modulation method, but it is also applicable to power amplifiers using other modulation methods. Further, as an example of a device using a power amplifier, a target detection device has been illustrated, but it is also applicable to other devices.

Explanation of Reference Numerals

[0045] 1, 1A Power amplifier 2 Output smoothing circuit 10 Target detection device 11 Transceiving unit 111 Transceiver 12 Main body unit 13 Operation unit 14 Monitor SW1 First switching element SW2 Second switching element N Switching output terminal Ls Smoothing inductor Cp Smoothing capacitor TD Capacitive load Lp Compensation inductor

Claims

1. A first switching element and a second switching element that are connected in series between a power supply and a ground portion and are alternately turned on and off by a control signal in which an input signal wave is modulated, and an output smoothing circuit connected to a switching output terminal connected between the first switching element and the second switching element, wherein a capacitive load is connected to the output smoothing circuit, and a power amplifier, A compensation inductor is connected in parallel to the switching output terminal, and the first switching element and the second switching element are turned off at a timing when the current flowing through the first switching element or the second switching element in the on state is positive or crosses zero, and the minimum on-time ratio and the maximum on-time ratio of the first switching element and the second switching element are set, The minimum on-time ratio is 5 to 30 percent, and the maximum on-time ratio is a value obtained by subtracting the minimum on-time ratio from 1, A power amplifier characterized by the above.

2. The capacitive reactance generated by the capacitive load and the smoothing capacitor constituting the output smoothing circuit is made smaller than or zero by the inductive reactance generated by the compensation inductor and the smoothing inductor constituting the output smoothing circuit. The power amplifier according to claim 1.

3. The power amplifier according to claim 1 or 2, wherein the phase of the input signal wave input at the start of the switching operation by the first switching element and the second switching element or at the start of modulation is set to 90° or 270°.

4. The power amplifier according to any one of claims 1 to 3, wherein the excitation inductance of a transformer is used as the compensation inductor.

5. A target detection device that emits ultrasonic waves, receives the ultrasonic waves reflected by a target, and detects the target, As driving means for driving a transducer for emitting the ultrasonic waves, the power amplifier according to any one of claims 1 to 4 is used, and the output smoothing circuit outputs a signal frequency modulated in amplitude and phase below a cut-off frequency. A target detection device characterized by the above.

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