Power supply circuit, apparatus, and ultrasonic flowmeter

Abstract

This power supply circuit includes: a switching circuit that, on the basis of a feedback signal that changes according to an output voltage generated by switching of a switching element, controls the switching so that the output voltage is a first voltage, and when the feedback signal changes to a first state where the output voltage is higher than the first voltage, stops the switching; and a control circuit that changes the feedback signal to the first state in a first period in which a prescribed circuit processes a prescribed signal.

Description

Power Supply Circuit, Device, and Ultrasonic Flowmeter

[0001] The present disclosure relates to a power supply circuit, a device, and an ultrasonic flowmeter.

[0002] As a type of power supply circuit, a switching regulator is known. For example, Patent Document 1 discloses an ultrasonic flowmeter that uses a plurality of switching regulators as a power supply unit.

[0003] Japanese Patent Application Laid-Open No. 2016-206127

[0004] A switching power supply such as a switching regulator may be arranged near a circuit that processes a minute signal such as an output signal from a sensor. In this case, the switching noise generated by the switching of the switching power supply may affect the processing of the minute signal. For example, the switching noise generated from the switching power supply may be superimposed on the minute signal output from the sensor, which may cause an error in the processing result of the minute signal.

[0005] An object of the present disclosure is to suppress the generation of switching noise during a period when a predetermined circuit processes a predetermined signal.

[0006] As one aspect of the present disclosure, a switching circuit is provided that controls the switching so that the output voltage becomes a first voltage based on a feedback signal that changes according to an output voltage generated by the switching of a switching element, and stops the switching when the feedback signal changes to a first state when the output voltage is higher than the first voltage. A power supply circuit is provided that includes a control circuit that changes the feedback signal to the first state during a first period when a predetermined circuit processes a predetermined signal.

[0007] According to the present disclosure, the generation of switching noise can be suppressed during a period when a predetermined circuit processes a predetermined signal.

[0008] This is a diagram illustrating an example of a power supply circuit according to the first embodiment. This is a timing chart showing an example of operation of the switching control circuit shown in Figure 1. This is a diagram illustrating an example of equipment including the power supply circuit shown in Figure 1. This is a diagram illustrating an example of the timing for stopping the switching operation of the power supply circuit shown in Figure 1. This is a diagram illustrating the advantages of the power supply circuit shown in Figure 1. This is a diagram illustrating an example of a power supply circuit according to the second embodiment. This is a diagram illustrating an example of a power supply circuit according to the third embodiment. This is a diagram illustrating a first modified example of the power supply circuit according to the first embodiment. This is a diagram illustrating a second modified example of the power supply circuit according to the first embodiment.

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0010] <First Embodiment> Figure 1 is a diagram illustrating an example of a power supply circuit according to the first embodiment. The power supply circuit 100 shown in Figure 1 generates a power supply voltage (output voltage Vout) supplied to a circuit that processes minute signals, such as the output signal of a sensor 300 described later. The power supply circuit 100 is a step-down switching power supply that generates an output voltage Vout lower than the input voltage Vin, or a step-up switching power supply that generates an output voltage Vout higher than the input voltage Vin. The power supply circuit 100 according to the first embodiment is an isolated switching power supply (isolated DC / DC converter) in which the input and output are electrically isolated by a transformer TR. The input voltage Vin may be produced by rectifying an AC voltage with a diode bridge or the like (not shown).

[0011] The power supply circuit 100 includes a switching circuit 140 and a control circuit 130.

[0012] The switching circuit 140 includes a switching element Q1. By switching the switching element Q1, the switching circuit 140 generates an output voltage Vout, which is generated between the output terminals OUT1 and OUT2, based on the input voltage Vin between the input terminal IN and ground GND. The output voltage Vout is output to a load (not shown) electrically connected to the output terminals OUT1 and OUT2. The output terminal OUT2 is grounded to a secondary ground GNDA, which is different from the primary ground GND.

[0013] The switching element Q1 is, for example, a transistor formed by an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The switching element Q1 may also be other semiconductor elements formed by a bipolar transistor or the like.

[0014] The switching circuit 140 includes a capacitor C1 that smooths the DC input voltage Vin, and a transformer TR to which the smoothed input voltage Vin is input. The voltage conversion transformer TR has a primary winding Np and a secondary winding Ns. Capacitor C1 is electrically connected to one end of the primary winding Np, and the switching element Q1 is electrically connected to the other end of the primary winding Np.

[0015] The switching circuit 140 has a rectifier diode D3 connected in series with one end of the secondary winding Ns on the secondary side of the transformer TR, and a smoothing capacitor C4 connected between the cathode terminal of diode D3 and the other end of the secondary winding Ns. The switching circuit 140 induces an AC voltage in the secondary winding Ns by intermittently supplying current to the primary winding Np through the switching of the switching element Q1. The switching circuit 140 rectifies the induced AC voltage with diode D3 and smooths the rectified voltage with capacitor C4 to generate a DC output voltage Vout.

[0016] The switching circuit 140 may include a coil L3 and a capacitor C5 on the secondary side of the transformer TR as a filter to reduce switching ripple noise and the like generated by the switching operation of the primary side switching element Q1.

[0017] The switching circuit 140 includes a feedback circuit 150 that feeds back a feedback signal (in this example, a feedback current Ib) representing the magnitude of the output voltage Vout detected on the secondary side to the primary side.

[0018] The feedback circuit 150 includes a photocoupler PC through which a feedback current Ib flows to the light-emitting side. The photocoupler PC has a secondary-side light-emitting element Pcs through which the feedback current Ib flows, and a primary-side photodetector Pcr that receives light emitted from the light-emitting element Pcs. The photocoupler PC converts the light emitted from the light-emitting element Pcs into an electrical signal using the photodetector Pcr, based on the feedback current Ib. The feedback circuit 150 may also have a series circuit of a capacitor C2 and a resistor R1 connected in parallel with the photodetector Pcr. The series circuit of capacitor C2 and resistor R1 stabilizes the electrical signal from the photodetector Pcr. The error amplifier 11 has the characteristic that its output voltage (feedback voltage Vb) changes with the electrical signal from the photodetector Pcr. For example, the more the current output from the photodetector Pcr increases (i.e., the more the feedback current Ib increases), the lower the output voltage (feedback voltage Vb) of the error amplifier 11 becomes. The feedback circuit 150 converts the feedback current Ib, which represents the magnitude of the output voltage Vout, into a feedback voltage Vb, which also represents the magnitude of the output voltage Vout.

[0019] The feedback circuit 150 includes a shunt regulator 20, resistors R6, R7, R8, R9, and a capacitor C6. The shunt regulator 20 flows a shunt current Ish that changes the feedback current Ib. The shunt regulator 20 changes the magnitude of the shunt current Ish according to the magnitude of the output voltage Vout. The magnitude of the feedback current Ib changes according to the magnitude of the shunt current Ish.

[0020] In this example, the shunt regulator 20 increases the shunt current Ish as the voltage Vd, which is the voltage obtained by dividing the output voltage Vout by the resistors R6 and R7, increases. The feedback current Ib increases in accordance with the increase in the shunt current Ish, and the feedback voltage Vb decreases in accordance with the increase in the feedback current Ib. The feedback current Ib flows through the resistor R8, the light-emitting element Pcs, and the shunt regulator 20. The characteristics of the change in the feedback current Ib are adjusted by the capacitor C6 and the resistor R9.

[0021] The switching circuit 140 has a switching control circuit 110 on the primary side of the transformer TR. The switching control circuit 110 controls the switching of the switching element Q1 so that the output voltage Vout becomes a first voltage V1, based on a feedback current Ib (feedback voltage Vb) that changes according to the output voltage Vout generated by the switching of the switching element Q1. The first voltage V1 is the target value of the output voltage Vout.

[0022] The switching control circuit 110 reduces the on-duty cycle of the switching element Q1 as the feedback current Ib increases (the feedback voltage Vb decreases) due to an increase in the output voltage Vout. When the on-duty cycle of the switching element Q1 decreases, the output voltage Vout decreases. Conversely, the switching control circuit 110 increases the on-duty cycle of the switching element Q1 as the feedback current Ib decreases (the feedback voltage Vb increases) due to a decrease in the output voltage Vout. When the on-duty cycle of the switching element Q1 increases, the output voltage Vout increases.

[0023] In this way, the switching control circuit 110 performs negative feedback control, decreasing the on-duty cycle of the switching element Q1 as the output voltage Vout increases, and increasing the on-duty cycle of the switching element Q1 as the output voltage Vout decreases. Through this negative feedback control, the switching control circuit 110 stabilizes the output voltage Vout to the first voltage V1.

[0024] The switching control circuit 110 stops switching the switching element Q1 when the feedback current Ib changes to a first state S1, which is when the output voltage Vout is higher than the first voltage V1. The first state S1 is a state in which the output voltage Vout is higher than the second voltage V2 or higher than the first voltage V1. The first state S1 is the state in which the feedback current Ib is a second current value that is higher than the first current value when the output voltage Vout is the first voltage V1. In other words, the first state S1 is the state in which the feedback voltage Vb is a second voltage value (for example, zero or a voltage value slightly higher than zero) that is lower than the first voltage value when the output voltage Vout is the first voltage V1.

[0025] When the feedback current Ib changes to the first state S1, the output voltage Vout is considered excessive with respect to the first voltage V1, so the switching control circuit 110 sets the on-duty cycle of the switching element Q1 to zero. This stops the switching of the switching element Q1. During the period when the switching element Q1 is stopped, the power required for the operation of the unillustrated loads connected to the output terminals OUT1 and OUT2 is supplied from capacitor C4 or capacitor C5.

[0026] The power supply circuit 100 includes a control circuit 130 that forcibly changes the feedback current Ib to a first state S1 during a first period A1 in which a predetermined circuit processes a predetermined signal. As described above, the switching control circuit 110 of the switching circuit 140 stops the switching of the switching element Q1 when the feedback current Ib changes to the first state S1. Therefore, by the control circuit 130 forcibly changing the feedback current Ib to the first state S1 during the first period A1, the switching of the switching element Q1 is stopped by the switching control circuit 110 of the switching circuit 140.

[0027] Therefore, according to the first embodiment, the switching of the switching element Q1 is stopped during the first period A1 in which the predetermined circuit processes the predetermined signal, so that the switching noise generated by the switching of the switching element Q1 is suppressed during the first period A1. As a result, the error that the switching noise causes in the processing result of the predetermined signal is reduced.

[0028] The control circuit 130 stops the switching of the switching element Q1 by directly manipulating the feedback current Ib. This eliminates the need to prepare a dedicated stop command signal to stop the switching of the switching element Q1, or to add a dedicated photocoupler to transmit such a stop command signal. As a result, the power supply circuit 100 can be miniaturized.

[0029] In the first embodiment, the control circuit 130 forces the feedback current Ib to change to a first state S1 during the first period A1 by directly changing the feedback current Ib. In this example, the control circuit 130 includes a switch Q2 connected in parallel with the shunt regulator 20. The control circuit 130 forces the feedback current Ib to change to a first state S1 during the first period A1 by directly changing the feedback current Ib by turning on the switch Q2.

[0030] When switch Q2 is turned on, a current path is created that bypasses the shunt regulator 20. When the control circuit 130 switches switch Q2 from off to on, at least a portion of the feedback current Ib flows to switch Q2 through the resistor R10. Since the impedance of the current path through switch Q2 is smaller than the impedance of the shunt regulator 20, the feedback current Ib increases when switch Q2 is turned on. As a result, the feedback current Ib changes to the first state S1.

[0031] In the configuration shown in Figure 1, where a current path bypassing the shunt regulator 20 is generated, the feedback current Ib should increase as the current bypassing the shunt regulator 20 increases. For this reason, the impedance of the current path through switch Q2 is preferably smaller than the impedance of the shunt regulator 20, but it may be the same as or greater than the impedance of the shunt regulator 20.

[0032] Examples of switch Q2 include digital transistors, analog switches, FETs, and bipolar transistors. Switch Q2 may also be any other switching element.

[0033] For example, the control circuit 130 stops the switching of the switching element Q1 by forcibly changing the feedback current Ib to a first state S1 during a first period A1 in which a predetermined circuit located near the power supply circuit 100 is processing a predetermined signal. The predetermined circuit may be a circuit to which the power supply voltage is supplied from the power supply circuit 100. In this case, the control circuit 130 stops the switching of the switching element Q1 by forcibly changing the feedback current Ib to a first state S1 during a first period A1 in which a predetermined circuit operating with the output voltage Vout as the power supply voltage is processing a predetermined signal. This reduces the error that switching noise superimposed on the output voltage Vout (power supply voltage) has on the processing result of the predetermined signal.

[0034] Furthermore, the power supply voltage for the predetermined circuit does not necessarily have to be supplied from the power supply circuit 100. That is, the predetermined circuit may be supplied with power from a power supply circuit other than the power supply circuit 100. In this case, for example, the control circuit 130 stops the switching of the switching element Q1 by forcibly changing the feedback current Ib to a first state S1 during the first period A1 in which the predetermined circuit, which operates with a power supply voltage supplied from a power supply circuit other than the power supply circuit 100, is processing a predetermined signal.

[0035] The control circuit 130 may forcibly change the feedback current Ib to a first state S1 during a first period A1 in which a predetermined circuit processes a predetermined signal, according to the control signal Wsig supplied to the control terminal PW. The control signal Wsig may be supplied from the predetermined circuit or from a circuit other than the predetermined circuit.

[0036] As shown in Figures 8 and 9, the control circuit 130 may forcibly change the feedback current Ib to the first state S1 during the first period A1 by changing the shunt current Ish.

[0037] Figure 8 is a diagram illustrating a first modified example of the power supply circuit according to the first embodiment. In Figure 8, the control circuit 130 includes a switch Q3 connected in parallel with the resistor R6. The control circuit 130 changes the shunt current Ish by turning on the switch Q3, thereby forcing the feedback current Ib to change to the first state S1 during the first period A1.

[0038] When switch Q3 is turned on, a current path is created that bypasses the resistor R6. When the control circuit 130 switches switch Q3 from off to on, the voltage Vd rises to the output voltage Vout, and the shunt current Ish increases. The feedback current Ib increases in accordance with the increase in the shunt current Ish. As a result, the feedback current Ib changes to the first state S1.

[0039] Examples of switch Q3 include digital transistors, analog switches, FETs, and bipolar transistors. Switch Q3 may be any other switching element.

[0040] Figure 9 is a diagram illustrating a second modified example of the power supply circuit according to the first embodiment. In Figure 9, the control circuit 130 includes a switch Q4 connected in series with the resistor R7. The positions of the switch Q4 and the resistor R7 may be swapped. The control circuit 130 changes the shunt current Ish by turning off the switch Q4, thereby forcing the feedback current Ib to change to the first state S1 during the first period A1.

[0041] When the control circuit 130 switches switch Q4 from on to off, the voltage Vd rises to the output voltage Vout, and the shunt current Ish increases. In accordance with the increase in the shunt current Ish, the feedback current Ib increases. As a result, the feedback current Ib changes to the first state S1.

[0042] Examples of switch Q4 include digital transistors, analog switches, FETs, and bipolar transistors. Switch Q4 may be any other switching element.

[0043] <Details of the switching control circuit 110>Next, a configuration example of the switching control circuit 110 will be described in more detail with reference to FIGS. 1 and 2. FIG. 2 is a timing chart showing an operation example of the switching control circuit 110 shown in FIG. 1. Note that the switching control circuit 110 is not limited to the configuration shown in FIG. 1. The function of the switching control circuit 110 may be realized by other circuit configurations.

[0044] In FIG. 1, the switching control circuit 110 generates a drive pulse p for switching the switching element Q1 by pulse width modulation so that the output voltage Vout becomes the first voltage V1 based on the feedback current Ib (feedback voltage Vd). Instead of pulse width modulation, the switching control circuit 110 may generate the drive pulse p by another known modulation method such as pulse frequency modulation.

[0045] As the feedback current Ib increases (as the feedback voltage Vb decreases) due to an increase in the output voltage Vout, the switching control circuit 110 decreases the duty ratio of the drive pulse p for turning on the switching element Q1. When the duty ratio of the drive pulse p decreases, the pulse width of the drive pulse p becomes narrow, so the on-duty ratio of the switching element Q1 decreases, and the output voltage Vout decreases. Conversely, as the feedback current Ib decreases (as the feedback voltage Vb increases) due to a decrease in the output voltage Vout, the switching control circuit 110 increases the duty ratio of the drive pulse p for turning on the switching element Q1. When the duty ratio of the drive pulse p increases, the pulse width of the drive pulse p becomes wide, so the on-duty ratio of the switching element Q1 increases, and the output voltage Vout increases.

[0046] In this way, the switching control circuit 110 performs negative feedback control in which the duty ratio of the drive pulse p is decreased as the output voltage Vout increases, and the duty ratio of the drive pulse p is increased as the output voltage Vout decreases. The switching control circuit 110 stabilizes the output voltage Vout at the first voltage V1 by such negative feedback control.

[0047] The switching control circuit 110 is, for example, an integrated circuit (IC) having at least terminals T1, T2, T3, and T4. In the example shown in FIG. 1, the switching control circuit 110 includes an error amplifier 11, a diode D1, resistors R2 and R3, a Zener diode D2, a comparator 12, a flip-flop 13, an oscillator 14, a NOR circuit 15, and a drive circuit 16.

[0048] The oscillator 14 outputs an oscillation signal OSC having a set oscillation frequency. The oscillation signal OSC is input as a set signal S to the set terminal of the flip-flop 13 and is also input to the NOR circuit 15. The output signal of the comparator 12 is input as a reset signal R to the reset terminal of the flip-flop 13. The flip-flop 13 performs a flip-flop operation of outputting a signal Q from an output terminal and outputting a signal QB from an inverted output terminal based on the set signal S and the reset signal R. The signal QB is a signal obtained by inverting the logic of the signal Q.

[0049] The NOR circuit 15 outputs a logic signal q that is a NOR of the oscillation signal OSC (set signal S), the signal QB, and a low-level fixed signal (input signal of the ground GND). The drive circuit 16 converts the logic signal q from the NOR circuit 15 into a drive pulse p having a voltage level capable of driving the switching element Q1 and supplies the drive pulse p having the same logic as the logic signal q to the switching element Q1.

[0050] Therefore, during the period in which the high-level oscillation signal OSC (set signal S) is input to the NOR circuit 15, the drive pulse p is fixed to a low level for turning off the switching element Q1 (see FIG. 2). Thereby, a length equal to or longer than a certain dead time is ensured as the period during which the switching element Q1 is off.

[0051] In Figure 1, the error amplifier 11 has an output terminal electrically connected to a compensation terminal T1, an inverting input terminal electrically connected to a feedback terminal T2, and a non-inverting input terminal to which a constant reference voltage REF is applied. The output voltage of the error amplifier 11 is offset by the forward voltage of diode D1 and then divided by resistors R2 and R3. The threshold voltage Va after voltage division is input to the inverting input terminal of comparator 12. In this way, the threshold voltage Va is set by the output voltage (feedback voltage Vb) of the error amplifier 11.

[0052] In Figure 1, the switching circuit 140 has resistors R4 and R5 and a capacitor C3 on the primary side of the transformer TR. Resistor R4 is electrically connected between the switching element Q1 and ground GND. Capacitor C3 is electrically connected between the current sensing terminal T3 and ground GND. Resistor R5 is electrically connected between the node between the switching element Q1 and resistor R4 and the node between terminal T3 and capacitor C3.

[0053] Terminal T3 is electrically connected to the non-inverting input terminal of the comparator 12 for current sensing. As shown in Figure 2, as the set signal S changes from a high level to a low level, the drive pulse p changes from a low level to a high level, and the switching element Q1 starts to turn on. When the switching element Q1 starts to turn on, the inductor current (sense current) flowing through the resistive element R4 starts to increase, so the sense voltage Vs input to the non-inverting input terminal of the comparator 12 starts to rise. When the sense voltage Vs reaches the threshold voltage Va, the comparator 12 outputs a reset signal R. The output of the reset signal R changes the drive pulse p from a high level to a low level, and the switching element Q1 turns off.

[0054] The switching control circuit 110 adjusts the output voltage Vout by adjusting the on-duty cycle of the switching element Q1 according to the duty cycle of the drive pulse p. The switching control circuit 110 decreases the on-duty cycle of the switching element Q1 in order to lower the output voltage Vout as the feedback current Ib increases (the feedback voltage Vb decreases) due to the increase in the output voltage Vout. Conversely, the switching control circuit 110 increases the on-duty cycle of the switching element Q1 in order to raise the output voltage Vout as the feedback current Ib decreases (the feedback voltage Vb increases) due to the decrease in the output voltage Vout. The switching control circuit 110 stabilizes the output voltage Vout to the first voltage V1 through this negative feedback control.

[0055] In Figure 1, the control circuit 130 forces the feedback current Ib to change to the first state S1. In the first state S1, the feedback current Ib becomes a second current value that is higher than the first current value when the output voltage Vout is the first voltage V1, so the feedback voltage Vb becomes a second voltage value that is lower than the first voltage value when the output voltage Vout is the first voltage V1. As a result, the feedback voltage Vb becomes zero or slightly higher than zero, and the threshold voltage Va becomes zero and is always lower than the sense voltage Vs, so the reset signal R and signal QB are fixed at a high level. As a result, the logic of the drive pulse p is fixed at a low level regardless of whether the logic of the oscillation signal OSC is low level or not. Therefore, when the feedback current Ib changes to the first state S1, the switching element Q1 remains off, and the switching of the switching element Q1 stops.

[0056] Therefore, when the control circuit 130 forcibly changes the feedback current Ib to the first state S1 during the first period A1 in which the predetermined circuit processes the predetermined signal, the switching circuit 140 stops switching the switching element Q1. As a result, the switching noise generated by the switching of the switching element Q1 is suppressed during the first period A1, and the error that such switching noise causes in the processing result of the predetermined signal is reduced.

[0057] <Equipment including power supply circuit 100> Next, equipment including power supply circuit 100 will be described with reference to Figure 3.

[0058] Figure 3 is a diagram illustrating an example of equipment 10 including the power supply circuit 100 shown in Figure 1.

[0059] The device 10 is, for example, a measuring device (a so-called ultrasonic flow meter) that measures the flow rate of fluid FL in a pipe PL. The device 10 includes a power supply circuit 100, a signal processing circuit 200 that operates using the output voltage Vout supplied from the power supply circuit 100 as the power supply voltage, and a sensor 300 that is placed on the outer surface OF of the pipe PL.

[0060] The sensor 300 is, for example, an ultrasonic sensor having two paired ultrasonic probes 320 (320a, 320b). The two ultrasonic probes 320 are positioned on the outer surface OF of the piping PL and transmit and receive ultrasonic waves. Each of the two ultrasonic probes 320 has an ultrasonic transducer 322 and a wedge 324. Ultrasonic probe 320a has an ultrasonic transducer 322a and a wedge 324a. Ultrasonic probe 320b has an ultrasonic transducer 322b and a wedge 324b.

[0061] The wedge 324a has a surface SPa that is inclined with respect to the outer surface OF of the pipe PL, for example. The wedge 324b has a surface SPb that is inclined with respect to the outer surface OF of the pipe PL, for example. An ultrasonic transducer 322a is attached to the surface SPa of the wedge 324a, and an ultrasonic transducer 322b is attached to the surface SPb of the wedge 324b. The material of the wedge 324 is, for example, resin.

[0062] The ultrasonic waves generated by ultrasonic transducer 322a propagate through the wedge 324a, the pipe PL, and the fluid FL at an angle corresponding to the inclination angle of surface SPa with respect to the outer surface OF of the pipe PL. The ultrasonic waves generated by ultrasonic transducer 322b propagate through the wedge 324b, the pipe PL, and the fluid FL at an angle corresponding to the inclination angle of surface SPb with respect to the outer surface OF of the pipe PL. Ultrasonic transducer 322a is connected to switch 240a included in the signal processing circuit 200. Ultrasonic transducer 322b is connected to switch 240b included in the signal processing circuit 200. Switch 240 (240a, 240b) sets one of the ultrasonic transducers 322a and 322b to be a transducer that transmits ultrasonic waves, and the other of the ultrasonic transducers 322a and 322b to be a transducer that receives ultrasonic waves.

[0063] The signal processing circuit 200 is connected, for example, to the output terminals OUT1 and OUT2 of the power supply circuit 100, and the output voltage Vout is supplied as the power supply voltage from the output terminals OUT1 and OUT2. The signal processing circuit 200 processes the signal Rsig output from the sensor 300. The signal processing circuit 200 is an example of a "predetermined circuit". The signal Rsig is an example of a "sensor output signal" and an example of a "predetermined signal".

[0064] For example, the signal processing circuit 200 includes a control unit 220, switches 240 (240a, 240b), a transmitting unit 260, a receiving unit 262, a time measurement unit 280, and a flow rate calculation unit 282.

[0065] The control unit 220 controls each element of the signal processing circuit 200. The control unit 220 may be implemented by a GPU (Graphics Processing Unit), a DSP (Digital Signal Processor), or an FPGA (Field Programmable Gate Array), etc. Alternatively, the control unit 220 may be a processor that controls each element of the signal processing circuit 200. Specifically, the control unit 220 may be configured to include, for example, one or more CPUs (Central Processing Units). In this case, the control unit 220 controls each element of the signal processing circuit 200 by, for example, executing a control program read from a storage device (not shown).

[0066] If the control unit 220 is configured to include multiple CPUs, some or all of the functions of the control unit 220 may be realized by these multiple CPUs cooperating and operating according to a program such as a control program. The control unit 220 may also be configured to include one or more CPUs and hardware such as a GPU, DSP, or FPGA. In this case, some or all of the functions of the control unit 220 may be realized by hardware such as a DSP.

[0067] Switch 240a connects the ultrasonic probe 320a (more specifically, the ultrasonic transducer 322a) to one of the transmitting unit 260 and the receiving unit 262, in response to instructions from the control unit 220. Similarly, switch 240b connects the ultrasonic probe 320b (more specifically, the ultrasonic transducer 322b) to one of the transmitting unit 260 and the receiving unit 262, in response to instructions from the control unit 220. Switches 240 (240a, 240b) are controlled so that the ultrasonic transducer 322a is connected to one of the transmitting unit 260 and the receiving unit 262, and the ultrasonic transducer 322b is connected to the other of the transmitting unit 260 and the receiving unit 262.

[0068] In the first embodiment, the switches 240 (240a, 240b) switch the respective connection destinations (ultrasonic transducer 322a or ultrasonic transducer 322b) of the transmitting unit 260 and the receiving unit 262 according to instructions from the control unit 220. This switches the relationship between the transmission and reception of ultrasound by the ultrasonic transducers 322a and 322b.

[0069] The transmitting unit 260 transmits ultrasonic waves to the fluid FL in the piping PL by driving the ultrasonic transducer 322a or ultrasonic transducer 322b of the sensor 300 in response to instructions from the control unit 220. Specifically, the transmitting unit 260 transmits a signal Tsig to the ultrasonic transducer 322a or ultrasonic transducer 322b via switch 240a or switch 240b to drive the ultrasonic transducer 322.

[0070] The receiving unit 262 receives a signal Rsig corresponding to the ultrasonic waves received by the ultrasonic transducer 322a or ultrasonic transducer 322b from the ultrasonic transducer 322a or ultrasonic transducer 322b via switch 240a or switch 240b. The signal Rsig corresponding to the ultrasonic waves received by the ultrasonic transducer 322 is the signal obtained when the ultrasonic waves that reached the ultrasonic transducer 322 are converted into an electrical signal by the ultrasonic transducer 322. Based on the signal Rsig received from the sensor 300 (more specifically, the ultrasonic transducer 322a or ultrasonic transducer 322b), the receiving unit 262 generates a pulse signal STsig for measuring the time from transmission to reception of the ultrasonic waves. The receiving unit 262 outputs the pulse signal STsig to the time measurement unit 280. The method for generating the pulse signal STsig will be explained later in Figure 4.

[0071] In the example shown in Figure 3, the transmitter 260 is connected to the ultrasonic transducer 322a via switch 240a, and the receiver 262 is connected to the ultrasonic transducer 322b via switch 240b. In this case, the ultrasonic waves generated by the ultrasonic transducer 322a in response to the signal Tsig from the transmitter 260 pass through the wedge 324a and the pipe PL, and enter the fluid FL inside the pipe PL. The ultrasonic waves that enter the fluid FL inside the pipe PL are reflected by the inner surface IF of the pipe PL, pass through the pipe PL and the wedge 324b, and propagate to the ultrasonic transducer 322b. The ultrasonic waves propagated to the ultrasonic transducer 322b are converted into an electrical signal, signal Rsig, by the ultrasonic transducer 322b. Signal Rsig is received by the receiver 262 via switch 240b. The receiver 262 outputs a pulse signal STsig based on signal Rsig to the time measurement unit 280.

[0072] The time measurement unit 280 measures the time from transmission to reception of ultrasound (hereinafter also referred to as ultrasound propagation time) based on a pulse signal STsig or the like. In the first embodiment, the control unit 220 switches between switches 240a and 240b so that the propagation times in two directions, where the relationship between the transmission and reception of ultrasound by the ultrasonic transducers 322a and 322b is reversed, are measured by the time measurement unit 280. That is, the time measurement unit 280 measures the ultrasound propagation time Tab from ultrasonic transducer 322a to ultrasonic transducer 322b and the ultrasound propagation time Tba from ultrasonic transducer 322b to ultrasonic transducer 322a.

[0073] The flow rate calculation unit 282 calculates the flow rate Q of the fluid FL in the piping PL based on the ultrasonic propagation time (propagation time Tab and propagation time Tba) measured by the time measurement unit 280.

[0074] For example, the propagation time Tab of ultrasound from ultrasonic transducer 322a to ultrasonic transducer 322b is expressed by equation (1). The propagation time Tba of ultrasound from ultrasonic transducer 322b to ultrasonic transducer 322a is expressed by equation (2).

[0075] Tab = Lf / (Cf + Vsin(θf)) ... (1) Tba = Lf / (Cf - Vsin(θf)) ... (2) Here, Cf is the speed of sound in the fluid FL, V is the velocity of the fluid FL flowing in the Z direction, θf is the angle of incidence in the fluid FL (angle of refraction from the pipe PL to the fluid FL or angle of incidence from the fluid FL to the pipe PL), and Lf is the length of the ultrasonic sound ray SL (propagation path) propagating through the fluid FL.

[0076] Solving for the flow velocity V using equations (1) and (2), the flow velocity V can be expressed as: V = (Lf / 2sin(θf) × ((1 / Tab) - (1 / Tba)) ... (3)

[0077] The flow rate Q of the fluid FL is expressed as Q = V × A ... (4), where A is the cross-sectional area of ​​the piping PL.

[0078] The cross-sectional area A is given by A = π × r, where PL is the inner diameter of the pipe. ２... (5) is the expression.

[0079] The angle of incidence θf in the fluid FL is calculated, for example, based on Snell's Law. According to Snell's Law, the following relationship holds: Cw / sin(θw) = Cp / sin(θp) = Cf / sin(θf) ... (6) Here, Cw is the speed of sound in the wedge 324, and θw is the angle of incidence in the wedge (angle of incidence from wedge 324a to pipe PL or angle of refraction from pipe PL to wedge 324a). Cp is the speed of sound in pipe PL, and θp is the angle of incidence in the pipe (angle of refraction from wedge 324a to pipe PL, angle of incidence from pipe PL to fluid FL, or angle of incidence from pipe PL to wedge 324a). Cf is the speed of sound in the fluid FL, and θf is the angle of incidence in the fluid (angle of refraction from pipe PL to fluid FL or angle of incidence from fluid FL to pipe PL).

[0080] Since Cw, sin(θw), and Cf are known values, the in-fluid incidence angle θf can be determined from equation (6). Therefore, the flow rate measuring unit 50 can calculate the flow rate Q based on equations (1) to (5).

[0081] <Timing for stopping switching> Next, with reference to Figure 4, the timing for stopping the switching operation of the power supply circuit 100 will be explained.

[0082] Figure 4 is a diagram illustrating an example of the timing for stopping the switching operation of the power supply circuit 100 shown in Figure 1. In Figure 4, the signal Tsig transmitted from the transmitting unit 260, the control signal Wsig used by the control circuit 130 to switch whether or not to change the feedback current Ib to the first state S1, the signal Rsig received by the receiving unit 262, and the pulse signal STsig received by the time measuring unit 280 are shown. The horizontal axis in Figure 4 represents time. First, an example of the method for generating the pulse signal STsig will be explained.

[0083] The pulse signal STsig is generated by the receiving unit 262 based on the signal Rsig, as explained in Figure 3. The voltage Vc shown in Figure 4 is, for example, the voltage of the signal Rsig output from the sensor 300 when the ultrasonic transducer 322 is not transmitting ultrasound. The voltage Vthld shown in Figure 4 is a predetermined voltage that is compared with the voltage of the signal Rsig by, for example, a comparator (not shown) included in the receiving unit 262.

[0084] For example, the receiving unit 262 identifies a specific timing (e.g., time T41) when the voltage of signal Rsig becomes greater than or equal to the voltage Vthld relative to voltage Vc, based on the comparison result of a comparator (not shown) that compares the voltage of signal Rsig with the voltage Vthld. Then, after the specific timing, the receiving unit 262 raises the pulse signal STsig at the first timing (e.g., time T42) when the voltage of signal Rsig becomes greater than or equal to voltage Vc. After raising the pulse signal STsig, the receiving unit 262 lowers the pulse signal STsig at the first timing when the voltage of signal Rsig becomes less than or equal to voltage Vc. Note that the timing for lowering the pulse signal STsig may also be a predetermined time after the pulse signal STsig has been raised.

[0085] The time measurement unit 280 determines the propagation time Tab and propagation time Tba by measuring the time Tst from the time T10 when the signal Tsig for transmitting ultrasonic waves from the ultrasonic transducer 322 is transmitted to the time T42 when the pulse signal STsig first rises.

[0086] Next, the timing of signals Tsig and Rsig will be explained using the example of a case where the transmitting unit 260 is connected to the ultrasonic transducer 322a via switch 240a and the receiving unit 262 is connected to the ultrasonic transducer 322b via switch 240b.

[0087] For example, the transmitting unit 260 transmits the signal Tsig to the ultrasonic transducer 322a from time T10 to time T20. As a result, the ultrasonic transducer 322a transmits ultrasonic waves. Then, for example, the ultrasonic waves transmitted from the ultrasonic transducer 322a are propagated to the ultrasonic transducer 322b, and the receiving unit 262 receives the signal Rsig corresponding to the ultrasonic waves received by the ultrasonic transducer 322b.

[0088] In the example shown in Figure 4, the signal Rsig, which is obtained by converting the ultrasonic waves transmitted from the ultrasonic transducer 322a by the signal Tsig into an electrical signal by the ultrasonic transducer 322b, is received by the receiving unit 262 from time T40 to time T50. In this case, for example, the period from time T40 to time T50 corresponds to the signal processing period TPs during which the signal Rsig is processed by the signal processing circuit 200 (more specifically, the receiving unit 262). For example, at time T41, the voltage of the signal Rsig with respect to voltage Vc becomes equal to or greater than the voltage Vthld with respect to voltage Vc. Then, at time T42, when the voltage of the signal Rsig becomes equal to or greater than the voltage Vc, the receiving unit 262 raises the pulse signal STsig. Note that the signal processing period TPs is an example of the "first period".

[0089] The control circuit 130 stops the switching operation of the switching element Q1 at least during the signal processing period TPs. In other words, the switching operation of the power supply circuit 100 is stopped during the signal processing period TPs.

[0090] For example, the control signal Wsig for switching whether or not the feedback current Ib changes to the first state S1 transitions from a low level to a high level at time T30, which is before time T40, the start time of the signal processing period TPs. Then, the control signal Wsig is maintained at a high level during the period TPw from time T30 to time T60, which is after time T50, the end time of the signal processing period TPs, and transitions from a high level to a low level at time T60. As a result, the feedback current Ib is set to the first state S1 at time T30 and maintained in the first state S1 during the period TPw. In other words, in the first embodiment, the feedback current Ib is forcibly changed to the first state S1 during the period TPw, which includes the signal processing period TPs, and the forced change of the feedback current Ib to the first state S1 is released during periods other than period TPw. As a result, the switching operation of the switching element Q1 stops during the period TPw.

[0091] The switching circuit 140 controls the switching of the switching element Q1 so that the output voltage Vout becomes the first voltage V1, based on the feedback current Ib, during the period when the change of the feedback current Ib to the first state S1 is released by the control circuit 130 (in Figure 4, the period other than period TPw). The period other than period TPw is an example of a "second period," and is an example of a predetermined period during which a predetermined signal is not processed.

[0092] Thus, in the first embodiment, the switching operation of the switching element Q1 is stopped during the period TPw which includes the signal processing period TPs. As a result, it is possible to suppress the generation of switching noise caused by the switching operation during the signal processing period TPs. In this way, in the first embodiment, it is possible to suppress the propagation of switching noise to the signal processing circuit 200 and the sensor 300 during the signal processing period TPs.

[0093] Here, for example, if switching noise occurs during the signal processing period TPs, the SNR (Signal-to-Noise Ratio) of the signal Rsig processed by the receiving unit 262 will decrease compared to when switching noise does not occur during the signal processing period TPs. In particular, when the signal Rsig is a small signal such as the output signal of the sensor 300, it is more susceptible to switching noise than when the signal is large, and the SNR decreases. When the SNR is low, errors are more likely to occur in the signal processing results compared to when the SNR is high. For example, if switching noise occurs during the signal processing period TPs, the switching noise may cause jitter in the pulse signal STsig. If jitter occurs in the pulse signal STsig, for example, the variation in the measurement results of the ultrasonic propagation time Tab and propagation time Tba may increase, and the accuracy of calculating the fluid flow rate Q of FL may decrease.

[0094] In contrast, in the first embodiment, as described above, it is possible to suppress the occurrence of switching noise during the signal processing period TPs, and thus it is possible to suppress errors caused by switching noise in the processing result of the signal Rsig. As a result, in the first embodiment, for example, the device 10 can suppress variations in the measurement results of the ultrasonic propagation time Tab and propagation time Tba, and can accurately calculate the flow rate Q of the fluid FL.

[0095] Here, as a method for stopping the switching operation of the power supply circuit 100 during the signal processing period TPs, a control method can be considered in which the enable signal supplied to the enable terminal of the switching control circuit is set to an inactive level during the signal processing period TPs. However, when the operation of the switching control circuit is stopped using the enable signal supplied to the enable terminal, it may take longer to switch between stopping and restarting the switching operation compared to when using the control circuit 130 in the first embodiment. For example, in an ultrasonic flow meter, it is sufficient to have a period of several tens to several hundreds of microseconds as the period TPw. In contrast, when the operation of the switching control circuit is stopped using the enable signal supplied to the enable terminal, the switching operation may be stopped for a period of several milliseconds. In this case, the period during which the switching operation is stopped becomes unnecessarily long.

[0096] For example, during periods when the switching operation is stopped, current is supplied to the output terminal OUT1 from capacitor C4 or capacitor C5 (Figure 1). Therefore, if the period during which the switching operation is stopped is long, the capacitance of capacitor C4 or capacitor C5 needs to be larger than when the period during which the switching operation is stopped is short. If the capacitance of capacitor C4 or capacitor C5 is large, the capacitor C4 or capacitor C5 will be larger than when the capacitance of capacitor C4 or capacitor C5 is small, making it difficult to miniaturize the power supply circuit 100.

[0097] In contrast, in the first embodiment, the switching operation of the power supply circuit 100 can be stopped during the signal processing period TPs by directly manipulating the feedback signal (feedback current Ib) used in feedback control, without using an enable signal. In this case, since the operation of the switching control circuit 120 is not stopped by the enable signal, the switching operation is quickly resumed when the control signal Wsig transitions to a low level. Therefore, in the first embodiment, it is possible to suppress the period during which the switching operation is stopped from becoming unnecessarily long, and thus it is possible to suppress the enlargement of capacitor C4 or capacitor C5. For this reason, in the first embodiment, it is possible to easily miniaturize the power supply circuit 100 while suppressing the generation of switching noise during the signal processing period TPs. Furthermore, in the first embodiment, since it is possible to suppress the period during which the switching operation is stopped from becoming unnecessarily long, the usability of the power supply circuit 100 can be improved.

[0098] The interval between the transmission time of signal Tsig (times T10 and T20) and the start and end times of the signal processing period TPs (times T40 and T50) is estimated to some extent based on parameters such as the wedge 324, piping PL, and fluid FL. A period with a certain range of variation between the estimated start and end times of the signal processing period TPs is then defined as period TPw. The measured values ​​of the start and end times of the signal processing period TPs may also be fed back into the setting of period TPw.

[0099] <Other advantages when using the power supply circuit according to the first embodiment> Next, with reference to Figure 5, other advantages when using the power supply circuit 100 according to the first embodiment will be described.

[0100] Figure 5 is a diagram illustrating the advantages of the power supply circuit 100 shown in Figure 1. Figure 5, "with control circuit 130," shows an overview of a device 10 having the power supply circuit 100 according to the first embodiment. Figure 5, "without control circuit 130," shows an overview of a device 10Z having a power supply circuit 100Z, which is compared to the power supply circuit 100. The power supply circuit 100Z is the same as the power supply circuit 100 shown in Figure 1, except that the control circuit 130 is omitted from the power supply circuit 100.

[0101] Figure 5 assumes that the signal processing circuit 200 is included in the printed circuit board PB. Therefore, for example, device 10 has a power supply circuit 100, a printed circuit board PB including the signal processing circuit 200, and a sensor 300. First, we will describe device 10Z, which is compared to device 10.

[0102] Device 10Z is the same as device 10, except that it has a power supply circuit 100Z instead of power supply circuit 100, and has a shielding member SLD. For example, device 10Z has a power supply circuit 100Z, a printed circuit board PB including a signal processing circuit 200, a shielding member SLD, and a sensor 300. Since the power supply circuit 100Z does not have a control circuit 130, switching noise is generated in the power supply circuit 100Z during the signal processing period TPs in which the signal Rsig is processed.

[0103] Therefore, in device 10Z, as shown in Figure 5, "without control circuit 130", a shielding member SLD is placed between the power supply circuit 100Z and the sensor 300 to prevent switching noise from propagating from the power supply circuit 100Z to the sensor 300. The shielding member SLD may be a shielding sheet or a shielding plate. In device 10Z, the shielding member SLD placed between the power supply circuit 100Z and the sensor 300 suppresses the inclusion of switching noise in the signal Rsig (output signal of sensor 300) output from the sensor 300. However, in device 10Z, there is a risk that switching noise may propagate from the power supply circuit 100Z to the sensor 300 via the connection wiring between the sensor 300 and the signal processing circuit 200. The connection wiring between the sensor 300 and the signal processing circuit 200 is, for example, wiring for transmitting the signal Rsig from the sensor 300 to the signal processing circuit 200.

[0104] Furthermore, in device 10Z, the shielding member SLD is positioned between the power supply circuit 100Z and the sensor 300, resulting in a more complex structure compared to device 10. Consequently, device 10Z is larger than device 10. Moreover, device 10Z is more expensive than device 10.

[0105] In contrast, in the first embodiment, it is possible to suppress the generation of switching noise during the signal processing period TPs in which the signal Rsig is processed, so the shielding member SLD can be omitted, as shown in Figure 4 with the control circuit 130. As a result, in the first embodiment, the device 10 can have a simple structure. For this reason, in the first embodiment, the device 10 can be made smaller and its cost can be reduced.

[0106] As described above, the power supply circuit 100 according to the first embodiment includes a switching circuit 140 and a control circuit 130. The switching circuit 140 controls the switching of the switching element Q1 so that the output voltage Vout becomes a first voltage V1, based on a feedback current Ib that changes according to the output voltage Vout generated by the switching of the switching element Q1. When the feedback current Ib changes to a first state S1, where the output voltage Vout is higher than the first voltage V1, the switching circuit 140 stops switching the switching element Q1. The control circuit 130 changes the feedback current Ib to the first state S1 during a first period A1 in which the signal processing circuit 200 processes a signal Rsig, which is an example of a predetermined signal. The device 10 according to the first embodiment includes a power supply circuit 100, a sensor 300, and a signal processing circuit 200, and the signal processing circuit 200 processes the signal Rsig, which is the output signal of the sensor 300.

[0107] Therefore, in the first embodiment, the switching operation of the switching element Q1 is stopped during the signal processing period TPs in which the signal Rsig is processed by the signal processing circuit 200. As a result, in the first embodiment, it is possible to suppress the generation of switching noise caused by the switching operation during the signal processing period TPs. As a result, in the first embodiment, it is possible to suppress the generation of switching noise caused by the switching operation during the signal processing period TPs without providing a shielding member SLD to prevent noise propagation from the power supply circuit 100 to the sensor 300. As a result, in the first embodiment, it is possible to suppress errors caused by switching noise in the processing result of the signal Rsig while suppressing an increase in the cost or size of the device 10.

[0108] <Second Embodiment> Figure 6 is a diagram illustrating an example of a power supply circuit according to the second embodiment. In the second embodiment, the description of the same configuration, operation, and effects as in the first embodiment will be omitted by referring to the above description. The power supply circuit 100A shown in Figure 6 generates a power supply voltage (output voltage Vout) supplied to a circuit that processes minute signals such as the output signal of the sensor 300 described above. The power supply circuit 100A is a step-down switching power supply that generates an output voltage Vout that is lower than the input voltage Vin. The power supply circuit 100A according to the second embodiment is a non-isolated switching power supply (non-isolated DC / DC converter) in which the input and output are not electrically isolated.

[0109] For example, the power supply circuit 100A generates the output voltage Vout by switching between a storage period in which energy is stored in the inductor L100 and a release period in which the energy stored in the inductor L100 is released. As a result, the output voltage Vout, based on the storage period, the release period, and the input voltage Vin, is output from the output terminal PVo. The power supply circuit 100A is an asynchronous rectification type power supply circuit.

[0110] The power supply circuit 100A includes a switching circuit 140A and a control circuit 130A.

[0111] The switching circuit 140A includes a switching element SW120. By switching the switching element SW120, the switching circuit 140A generates an output voltage Vout between the output terminal PVo and ground GND, based on the input voltage Vin between the input terminal PVi and ground GND. The output voltage Vout is output to a load (not shown) that is electrically connected to the output terminal PVo and ground GND.

[0112] The switching element SW120 is, for example, a transistor formed by an N-channel MOSFET. The switching element SW120 may also be other semiconductor elements formed by a bipolar transistor or the like.

[0113] The switching circuit 140A includes a capacitor C100 that smooths the DC input voltage Vin, and a switching control circuit 120 to which the smoothed input voltage Vin is input. The switching control circuit 120 includes a switching element SW120 and terminals Pv, Pe, Ps, Pf, and Pg. The capacitor C100 is electrically connected to terminals Pv and Pe. The switching element SW120 is connected between terminal Pv and terminal Ps.

[0114] The switching circuit 140A includes an inductor L100, a diode D122, and a capacitor C102. The inductor L100 has a terminal P1 electrically connected to terminal Ps and a terminal P2 electrically connected to the output terminal PVo. The diode D122 has a cathode electrically connected to terminal P1 and an anode electrically connected to ground GND. The capacitor C102 is connected between the output terminal PVo and ground GND. The switching circuit 140A generates a DC output voltage Vout by switching the switching element SW120 in an asynchronous rectification manner.

[0115] The switching circuit 140A has a feedback circuit (voltage divider circuit 160) that feeds back a feedback signal (in this example, a feedback voltage Vd) representing the magnitude of the detected output voltage Vout to terminal Pf of the switching control circuit 120. The voltage divider circuit 160 includes a circuit in which resistors R100 and R102 are connected in series. The voltage divider circuit 160 outputs a feedback voltage Vd, which is the voltage obtained by dividing the output voltage Vout by resistors R100 and R102. The feedback voltage Vd represents the magnitude of the output voltage Vout. In this example, the higher the output voltage Vout, the higher the feedback voltage Vd, and the lower the output voltage Vout, the lower the feedback voltage Vd.

[0116] The switching control circuit 120 controls the switching of the switching element SW120 so that the output voltage Vout becomes a first voltage V1, based on a feedback voltage Vd that changes according to the output voltage Vout generated by the switching of the switching element SW120. The first voltage V1 is the target value of the output voltage Vout.

[0117] The switching control circuit 120 decreases the on-duty cycle of the switching element SW120 as the feedback voltage Vd increases due to an increase in the output voltage Vout. When the on-duty cycle of the switching element SW120 decreases, the output voltage Vout decreases. Conversely, the switching control circuit 120 increases the on-duty cycle of the switching element SW120 as the feedback voltage Vd decreases due to a decrease in the output voltage Vout. When the on-duty cycle of the switching element SW120 increases, the output voltage Vout increases.

[0118] In this way, the switching control circuit 120 performs negative feedback control, decreasing the on-duty cycle of the switching element SW120 as the output voltage Vout increases, and increasing the on-duty cycle of the switching element SW120 as the output voltage Vout decreases. Through this negative feedback control, the switching control circuit 120 stabilizes the output voltage Vout to the first voltage V1.

[0119] The switching control circuit 120 stops switching the switching element SW120 when the feedback voltage Vd changes to a first state S1, where the output voltage Vout is higher than the first voltage V1. The first state S1 is a state where the output voltage Vout is higher than the second voltage V2, which is higher than the first voltage V1. The first state S1 is a state where the feedback voltage Vd is a second voltage value that is higher than the first voltage value when the output voltage Vout is the first voltage V1.

[0120] When the feedback voltage Vd changes to the first state S1, the output voltage Vout is considered excessively high relative to the first voltage V1, so the switching control circuit 120 sets the on-duty cycle of the switching element SW120 to zero. As a result, the switching element SW120 is kept in the off state, and the switching of the switching element SW120 stops. During the period when the switching element SW120 is stopped, the power required for the operation of the load (not shown) connected to the output terminal PVo is supplied from the capacitor 102.

[0121] The power supply circuit 100A includes a control circuit 130A that forcibly changes the feedback voltage Vd to a first state S1 during a first period A1 in which a predetermined circuit processes a predetermined signal. As described above, the switching control circuit 120 of the switching circuit 140A stops the switching of the switching element SW120 when the feedback voltage Vd changes to the first state S1. Therefore, by the control circuit 130A forcibly changing the feedback voltage Vd to the first state S1 during the first period A1, the switching of the switching element SW120 is stopped by the switching control circuit 120 of the switching circuit 140A.

[0122] Therefore, according to the second embodiment, the switching of the switching element SW120 is stopped during the first period A1 in which the predetermined circuit processes the predetermined signal, so that the switching noise generated by the switching of the switching element SW120 is suppressed during the first period A1. As a result, the error that the switching noise causes in the processing result of the predetermined signal is reduced.

[0123] The control circuit 130A directly manipulates the feedback voltage Vd to stop the switching of the switching element SW120. This eliminates the need to prepare a dedicated stop command signal to stop the switching of the switching element SW120. As a result, the power supply circuit 100A can be made smaller.

[0124] Terminal Pe is, for example, an enable terminal. In this case, when terminal Pe is connected to the input terminal PVi as shown in Figure 6, the input voltage Vin, which is the power supply voltage, is input as a high-level signal. This causes the switching control circuit 120 to start and continue the switching operation of the switching element SW120. By inputting a low-level signal to this terminal Pe, the switching of the switching element SW120 by the switching control circuit 120 can be stopped. However, generally speaking, stopping switching by inputting a signal to the enable terminal has poor responsiveness, and it takes several milliseconds from the input of a low-level signal until the switching stops. In the case of an ultrasonic flow meter, it is required to stop the switching in tens to hundreds of microseconds, so even if terminal Pe, which is the enable terminal, is used, the switching cannot be stopped in time. In contrast, the method of stopping the switching of the switching element SW120 by directly manipulating the feedback voltage Vd has good responsiveness and can be suitably applied when it is necessary to stop the switching in a short time, such as in an ultrasonic flow meter.

[0125] In the second embodiment, the control circuit 130A includes a switch FT2 connected in series with the voltage divider circuit 160. The control circuit 130A forces the feedback voltage Vd to change to a first state S1 during the first period A1 by turning off the switch FT2. In this example, the control circuit 130A forces the feedback voltage Vd to change to a first state S1 during the first period A1 by turning off the switch FT2, thereby raising the feedback voltage Vd to the output voltage Vout.

[0126] During the period when the change of the feedback voltage Vd to the first state S1 is canceled by the control circuit 130A, the switching circuit 140A controls the switching of the switching element SW120 based on the feedback voltage Vd so that the output voltage Vout becomes the first voltage V1. The control circuit 130A cancels the change of the feedback voltage Vd to the first state S1 by turning on the switch FT2.

[0127] Examples of switch FT2 include digital transistors, analog switches, FETs, and bipolar transistors. Switch FT2 may be any other switching element.

[0128] The control circuit 130A may forcibly change the feedback voltage Vd to a first state S1 during a first period A1 in which a predetermined circuit processes a predetermined signal, according to the control signal Wsig supplied to the control terminal PW. The control signal Wsig may be supplied from the predetermined circuit or from a circuit other than the predetermined circuit. In this example, when the control signal Wsig is at a low level, the switch FT2 is turned off, so the feedback voltage Vd changes to the first state S1, and when the control signal Wsig is at a high level, the switch FT2 is turned on, so the change of the feedback voltage Vd to the first state S1 is canceled.

[0129] <Third Embodiment> Figure 7 is a diagram illustrating an example of a power supply circuit according to the third embodiment. In the third embodiment, the description of the configuration, operation, and effects similar to those of the first and second embodiments will be omitted by referring to the above description. The power supply circuit 100B shown in Figure 7 generates a power supply voltage (output voltage Vout) supplied to a circuit that processes minute signals such as the output signal of the sensor 300 described above. The power supply circuit 100B is a step-down switching power supply that generates an output voltage Vout that is lower than the input voltage Vin. The power supply circuit 100B according to the third embodiment is a non-isolated switching power supply (non-isolated DC / DC converter) in which the input and output are not electrically isolated.

[0130] The power supply circuit 100B includes a switching circuit 140B and a control circuit 130B. The switching circuit 140B according to the third embodiment may be the same as the switching circuit 140A according to the second embodiment. The control circuit 130B according to the third embodiment differs from the control circuit 130A according to the second embodiment.

[0131] The power supply circuit 100B includes a control circuit 130B that forcibly changes the feedback voltage Vd to a first state S1 during a first period A1 in which a predetermined circuit processes a predetermined signal. As described above, the switching control circuit 120 of the switching circuit 140B stops the switching of the switching element SW120 when the feedback voltage Vd changes to the first state S1. Therefore, by the control circuit 130B forcibly changing the feedback voltage Vd to the first state S1 during the first period A1, the switching of the switching element SW120 is stopped by the switching control circuit 120 of the switching circuit 140B.

[0132] Therefore, according to the third embodiment, the switching of the switching element SW120 is stopped during the first period A1 in which the predetermined circuit processes the predetermined signal, so that the switching noise generated by the switching of the switching element SW120 is suppressed during the first period A1. As a result, the error that the switching noise causes in the processing result of the predetermined signal is reduced.

[0133] The control circuit 130B directly manipulates the feedback voltage Vd to stop the switching of the switching element SW120. This eliminates the need to prepare a dedicated stop command signal to stop the switching of the switching element SW120. As a result, the power supply circuit 100B can be miniaturized.

[0134] In the third embodiment, the control circuit 130B includes a switch FT1 connected in parallel with the resistor R100 of the voltage divider circuit 160. The control circuit 130B forces the feedback voltage Vd to change to a first state S1 during the first period A1 by turning on the switch FT1. In this example, the control circuit 130B forces the feedback voltage Vd to change to a first state S1 during the first period A1 by turning on the switch FT1 and raising the feedback voltage Vd to the output voltage Vout.

[0135] During the period when the change of the feedback voltage Vd to the first state S1 is canceled by the control circuit 130B, the switching circuit 140B controls the switching of the switching element SW120 based on the feedback voltage Vd so that the output voltage Vout becomes the first voltage V1. The control circuit 130B cancels the change of the feedback voltage Vd to the first state S1 by turning off the switch FT1.

[0136] Examples of switch FT1 include digital transistors, analog switches, FETs, and bipolar transistors. Switch FT1 may be any other switching element.

[0137] The control circuit 130B includes resistors R103 and R104 and a switch FT2. In this example, switch FT1 is a P-channel MOSFET, and switch FT2 is an N-channel MOSFET. Resistor R103 is connected between the gate and source of switch FT1. Resistor R104 is connected between the gate of switch FT1 and the drain of switch FT2.

[0138] The control circuit 130A may forcibly change the feedback voltage Vd to a first state S1 during a first period A1 in which a predetermined circuit processes a predetermined signal, according to the control signal Wsig supplied to the control terminal PW. The control signal Wsig may be supplied from the predetermined circuit or from a circuit other than the predetermined circuit. In this example, when the control signal Wsig is at a high level, switches FT1 and FT2 are turned on, so the feedback voltage Vd changes to the first state S1, and when the control signal Wsig is at a low level, switches FT1 and FT2 are turned off, so the change of the feedback voltage Vd to the first state S1 is canceled.

[0139] <Modifications> In the above-described embodiment, the case in which the device 10 is an ultrasonic flow meter was illustrated, but the present invention is not limited to this embodiment. For example, the device 10 may be an analyzer such as a gas analyzer. Also, the sensor 300 is not limited to one that uses ultrasound. For example, the sensor 300 may use infrared light or the like. Also, for example, the sensor 300 may detect the concentration of a gas such as oxygen. Furthermore, in the above-described embodiment, the case in which the signal processing circuit 200 is a "predetermined circuit" was illustrated, but the "predetermined circuit" is not limited to the signal processing circuit 200. For example, it may be a circuit to which the power voltage is supplied from a power supply circuit separate from the power supply circuit 100.

[0140] The present invention is not limited by the embodiments described above. The embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, and modifications are possible without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0141] This international application claims priority based on Japanese Patent Application No. 2024-207751, filed on 28 November 2024, and the entire contents of Japanese Patent Application No. 2024-207751 are incorporated herein by reference.

[0142] 10, 10Z Equipment 100, 100A, 100B Power supply circuit 110, 120 Switching control circuit 130, 130A, 130B Control circuit 140, 140A, 140B Switching circuit 150 Feedback circuit 160 Voltage divider circuit 200 Signal processing circuit 300 Sensor Q1, SW120 Switching element Q2, Q3, Q4, FT1, FT2 Switch

Claims

1. A power supply circuit comprising: a switching circuit that controls the switching so that the output voltage becomes a first voltage based on a feedback signal that changes according to the output voltage generated by the switching of a switching element, and stops the switching when the feedback signal changes to a first state where the output voltage is higher than the first voltage; and a control circuit that changes the feedback signal to the first state during a first period in which a predetermined circuit processes a predetermined signal.

2. The power supply circuit according to claim 1, wherein the switching circuit controls the switching based on the feedback signal so that the output voltage becomes a first voltage during a second period in which the change of the feedback signal to the first state is canceled by the control circuit.

3. The power supply circuit according to claim 2, wherein the second period is a period during which the predetermined circuit does not process the predetermined signal.

4. The power supply circuit according to any one of claims 1 to 3, wherein the switching circuit has a feedback circuit including a photocoupler through which the feedback current, which is the feedback signal, flows to the light-emitting side, and the control circuit changes the feedback current to a first state during the first period.

5. The power supply circuit according to claim 4, wherein the feedback circuit includes a shunt regulator that carries a shunt current that changes the feedback current, and the control circuit changes the feedback current to the first state during the first period by changing the shunt current.

6. The power supply circuit according to claim 4, wherein the feedback circuit includes a shunt regulator that carries a shunt current that changes the feedback current, and the control circuit includes a switch connected in parallel with the shunt regulator, and by turning on the switch, the feedback current is changed to the first state during the first period.

7. The power supply circuit according to any one of claims 1 to 3, wherein the switching circuit has a voltage divider circuit that outputs a feedback voltage which is the feedback signal, and the control circuit changes the feedback voltage to a first state during the first period.

8. The power supply circuit according to claim 7, wherein the control circuit includes a switch connected to the voltage divider circuit, and the feedback voltage is changed to the first state during the first period by turning the switch on or off.

9. The power supply circuit according to any one of claims 1 to 3, wherein the control circuit includes a switch for changing the feedback signal to a first state during the first period.

10. A device comprising a power supply circuit according to any one of claims 1 to 3, a sensor, and the predetermined circuit, wherein the predetermined signal is the output signal of the sensor.

11. An ultrasonic flow meter comprising: a power supply circuit according to any one of claims 1 to 3; an ultrasonic sensor; and the predetermined circuit, wherein the predetermined signal is the output signal of the ultrasonic sensor.

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