Power supply unit and method for detecting the state of a heating resistor

Abstract

The present invention provides a power supply device capable of accurately estimating the wear status of a heating resistor, and a method for detecting the state of a heating resistor. [Solution] The power supply unit 1 includes a power supply unit 2 that outputs first DC power, a power conversion circuit 3 including an inverter 4 that converts the first DC power to AC power and a rectifier and smoothing circuit 5 that converts the AC power to second DC power, a heating resistor 61 to which second DC power is supplied, an inverter control circuit 7 that outputs inverter drive signals Sg1 to Sg4, and a load current detection unit 8 that detects the magnitude of the load current If supplied to the heating resistor 61 by the power conversion circuit 3 due to the second DC power. The inverter control circuit 7 includes a frequency control unit that controls the drive frequency, which is the frequency of the inverter drive signals Sg1 to Sg4, so that the magnitude of the load current If approaches a target value of the load current If, and a heating resistor detection unit that detects the state of the heating resistor 61 based on the drive frequency.

Description

[Technical Field]

[0001] The present invention relates to a power supply device and a method for detecting the state of a heating resistor. [Background technology]

[0002] Power supply devices that provide power to heating resistors such as filaments are known. Because heating resistors are used at high temperatures, they wear out with use, and if the wear becomes severe, they may break. Therefore, it is desirable to predict in advance when the heating resistor will need to be replaced by estimating its wear state before it breaks.

[0003] The apparatus described in Patent Document 1 includes a buck-boost circuit that raises or lowers the voltage supplied to the filament, and predicts the remaining life of the filament using a measurement of the current flowing on the low-voltage side of the buck-boost circuit. For example, in the apparatus described in Patent Document 1, the time derivative of the current flowing on the low-voltage side is obtained, and the remaining time until the end of the life is calculated by dividing the difference between the current value on the low-voltage side and the current value at the end of the life by the obtained time derivative. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2020 / 161795 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, it may not be possible to accurately estimate the state of wear of the heating resistor based solely on the measured value of the current. For example, in a power supply device that performs constant current control to keep the load current supplied to the heating resistor constant, it is difficult to say that it is appropriate to accurately estimate the state of wear of the heating resistor based on the magnitude of the load current controlled to a constant value. Therefore, in a power supply device that controls a specific electrical parameter to a constant value, it is desirable to estimate the state of wear of the heating resistor in an electrical parameter other than the specific electrical parameter.

[0006] An object of the present invention is to provide a power supply device capable of accurately estimating the state of wear of a heating resistor and a method for detecting the state of the heating resistor.

Means for Solving the Problems

[0007] A power supply device according to one aspect of the present disclosure includes: [1] a power supply unit that outputs first DC power, an inverter that converts the first DC power into AC power, and a rectifying and smoothing circuit that converts the AC power into second DC power. A power conversion circuit, a heating resistor to which the second DC power is supplied, an inverter control circuit connected to the inverter and outputting an inverter drive signal for controlling the inverter, and a load current that the power conversion circuit supplies to the heating resistor. A load current detection unit that detects the magnitude of the load current due to the second DC power, wherein the inverter control circuit includes a frequency control unit that controls the drive frequency, which is the frequency of the inverter drive signal, so that the magnitude of the load current approaches the target value of the load current, and a heating resistor detection unit that detects the state of the heating resistor based on the drive frequency.

[0008] In the power supply device described in [1] above, the frequency control unit controls the drive frequency, which is the frequency of the inverter drive signal, so that the magnitude of the load current approaches the target value of the load current. At this time, the magnitude of the drive frequency reflects the state of the heating resistor, such as wear. Therefore, the state of the heating resistor can be detected based on the drive frequency. By detecting the state of the heating resistor based on the drive frequency, the state of the heating resistor can be accurately estimated without depending on the value of the load current.

[0009] A power supply device relating to one aspect of the present disclosure may be [2] "the power supply device according to [1], further comprising: a switching circuit connected to the power supply unit and converting the first DC power supplied from the power supply unit into AC power; a resonant circuit connected between the switching circuit and the rectifier-smoothing circuit and boosting or stepping down the AC voltage due to the AC power; and the heating resistor detection unit detecting the impedance of the heating resistor from the drive frequency controlled by the frequency control unit based on the frequency characteristics of the heating resistor and the power conversion circuit." The impedance of the resonant circuit included in the power conversion circuit decreases, for example, as the drive frequency approaches the resonant frequency of the resonant circuit. That is, the impedance of the resonant circuit changes with the drive frequency, and consequently the input power to the heating resistor changes with the drive frequency. Based on the frequency characteristics of the input power to the heating resistor, the heating resistor detection unit can detect the impedance of the heating resistor from the drive frequency and can detect the impedance of the heating resistor in real time. Furthermore, since the impedance of the heating resistor is closely related to its state of wear, the state of the heating resistor can be accurately estimated based on the detected impedance.

[0010] A power supply device relating to one aspect of this disclosure may be [3] "the power supply device according to [2], wherein the heating resistor detection unit acquires the initial frequency of the drive frequency, the fluctuating frequency after the drive frequency has changed from the initial frequency, and the initial impedance of the heating resistor corresponding to the initial frequency, and calculates the fluctuating impedance of the heating resistor corresponding to the fluctuating frequency based on the initial frequency, the fluctuating frequency, and the initial impedance." In this case, the fluctuating impedance of the heating resistor can be easily detected based on the initial frequency and initial impedance, and the wear state of the heating resistor can be estimated.

[0011] A power supply device relating to one aspect of the present disclosure may be [4] "the power supply device according to [2], wherein the heating resistor detection unit includes a storage unit that stores the correspondence between the drive frequency and the impedance of the heating resistor, and detects the impedance of the heating resistor based on the drive frequency controlled by the frequency control unit." In this case, the impedance of the heating resistor can be easily detected based on the pre-stored correspondence between the drive frequency and the impedance of the heating resistor, and the wear state of the heating resistor can be estimated.

[0012] A method for detecting the state of a heating resistor using a power supply device relating to one aspect of the present disclosure is [5] "A method for detecting the state of a heating resistor using a power supply device, wherein the power supply device comprises a power supply unit that outputs a first DC power, a power conversion circuit including an inverter that converts the first DC power to AC power and a rectifier and smoothing circuit that converts the AC power to a second DC power, a heating resistor to which the second DC power is supplied, an inverter control circuit connected to the inverter and outputting an inverter drive signal that controls the inverter, and a load current detection unit that detects the magnitude of the load current supplied to the heating resistor by the power conversion circuit due to the second DC power, wherein the method comprises the steps of controlling a drive frequency which is the frequency of the inverter drive signal so that the magnitude of the load current approaches a target value of the load current, and detecting the state of the heating resistor based on the drive frequency."

[0013] In the method described in [5] above, the frequency control unit controls the drive frequency, which is the frequency of the inverter drive signal, so that the magnitude of the load current approaches the target value of the load current. At this time, the magnitude of the drive frequency reflects the state of the heating resistor, such as wear. Therefore, the state of the heating resistor can be detected based on the drive frequency. By detecting the state of the heating resistor based on the drive frequency, the state of the heating resistor can be accurately estimated without depending on the value of the load current. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a power supply device capable of accurately estimating the wear state of a heating resistor, and a method for detecting the state of a heating resistor. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic diagram of the circuit diagram of a power supply device according to one embodiment of the present disclosure. [Figure 2] A block diagram showing an example of the internal circuitry of an inverter control circuit, as shown in Figure 1. [Figure 3] This graph shows an example of the frequency characteristics of the gain in a power conversion circuit that includes a heating resistor. [Figure 4] Figure 1 is a circuit diagram showing an example of an equivalent circuit in which the resonant circuit, transformer, rectifier / smoothing circuit, and heating resistor are integrated on the secondary side of the transformer in the power conversion circuit shown. [Figure 5] This graph shows an example of the frequency characteristics of the load power of a power conversion circuit including a heating resistor, when the impedance of the heating resistor changes stepwise from an initial impedance to multiple fluctuating impedances. [Figure 6] This flowchart shows an example of a method for deriving the correspondence between the drive frequency and the impedance of the heating resistor. [Figure 7] This flowchart shows an example of a detection method for detecting the state of a heating resistor. [Figure 8] This block diagram shows an example of the internal circuitry of an inverter control unit of a modified power supply. [Modes for carrying out the invention]

[0016] Hereinafter, with reference to the drawings, preferred embodiments of a power supply device and a method for detecting the state of a heating resistor according to one embodiment of the present disclosure will be described in detail.

[0017] [Power supply unit configuration and operation] Figure 1 is a schematic diagram of the circuit of a power supply unit 1 according to one embodiment of the present disclosure. The power supply unit 1 is a power supply unit for supplying power to a heating resistor 61 which is a load, and for heating the heating resistor 61. The heating resistor 61 may be used as, for example, a heater or as the cathode of an energy ray tube. In this disclosure, an example is described in which the energy ray tube is an X-ray tube 6 and the heating resistor 61 is applied to the X-ray tube 6.

[0018] The power supply unit 1 comprises a power supply unit 2, a power conversion circuit 3, a heating resistor 61, an inverter control circuit 7, a load current detection unit 8, and a tube current detection unit 9.

[0019] The power supply unit 2 outputs a first DC power (DC voltage). The power supply unit 2 functions as an AC / DC converter that converts AC power generated in the AC power supply AP into the first DC power. The power supply unit 2 is a power supply circuit that supplies the first DC power to the inverter 4 included in the power conversion circuit 3. The power supply unit 2 is, for example, a switching type AC / DC converter. In that case, the power supply unit 2 may have a switching element (not shown).

[0020] The power supply unit 2 receives a tube current instruction signal S, which indicates a target value for the magnitude of the tube current Iout flowing through the X-ray tube 6. ISET The following is input: Tube current indicator signal S ISET This can be set arbitrarily by the user, for example. Power supply unit 2 operates in feedforward control. Power supply unit 2 receives, for example, a tube current instruction signal S.ISET The magnitude of the first DC power may be varied according to the magnitude of the tube current instruction signal S. As an example, the power supply unit 2 receives the tube current instruction signal S. ISET Depending on the magnitude, the frequency or duty cycle of the signal driving the switching element may be varied.

[0021] The power supply unit 2 has a function to limit the first DC power to a predetermined range. Internally, for example, an upper limit value for the first DC power is set in the power supply unit 2, and the power supply unit 2 limits the magnitude of the first DC power so as not to exceed the upper limit value. The upper limit value may be a value less than or equal to the rated power of the semiconductor switch included in the switching circuit 41 connected downstream of the power supply unit 2.

[0022] The power conversion circuit 3 supplies a second DC power (DC voltage) to the heating resistor 61 that is greater than the magnitude of the first DC power. As a result, the power conversion circuit 3 supplies a load current If, due to the second DC power, to the heating resistor 61. The power conversion circuit 3 includes an inverter 4 and a rectifier / smoothing circuit 5. The inverter 4 converts the first DC power into AC power (AC voltage) and supplies the AC power to the rectifier / smoothing circuit 5. The inverter 4 includes a switching circuit 41 and a resonant circuit 42.

[0023] The switching circuit 41 converts the first DC power into AC power. The switching circuit 41 includes semiconductor switches S1 to S4. In the example in Figure 1, the semiconductor switches S1 to S4 are composed of MOSFETs. The semiconductor switches S1 to S4 may also be composed of, for example, insulated gate bipolar transistors (IGBTs). Each of the semiconductor switches S1 to S4 includes a control terminal, a first current terminal, and a second current terminal. The control terminal corresponds to the gate terminal of the MOSFET, the first current terminal corresponds to the drain terminal of the MOSFET, and the second current terminal corresponds to the source terminal of the MOSFET. In the example in Figure 1, the switching circuit 41 includes a configuration in which two leg circuits 411 and 412 are connected in parallel. Leg circuit 411 is a circuit in which the second current terminal of semiconductor switch S1 and the first current terminal of semiconductor switch S2 are connected. The REG circuit 412 is a circuit in which the second current terminal of semiconductor switch S3 and the first current terminal of semiconductor switch S4 are connected.

[0024] The switching circuit 41 further includes power terminals 41a and 41b connected to the power supply unit 2, control terminals 41c to 41f connected to the inverter control circuit 7, and output terminals 41g and 41h connected to the subsequent resonant circuit 42. Power terminal 41a is connected to the first current terminals of semiconductor switches S1 and S3, i.e., the high side of the switching circuit. Power terminal 41b is connected to the second current terminals of semiconductor switches S2 and S4, i.e., the low side of the switching circuit 41. First power is supplied to the switching circuit 41 from the power supply unit 2 via power terminals 41a and 41b, respectively.

[0025] Each of the control terminals 41c to 41f is a control terminal for the respective semiconductor switches S1 to S4. The inverter control circuit 7 outputs inverter drive signals Sg1 to Sg4, which will be described later, to the control terminals 41c to 41f. Output terminal 41g is located at the point between semiconductor switch S1 and semiconductor switch S2, and output terminal 41h is located at the point between semiconductor switch S3 and semiconductor switch S4. The resonant circuit 42 is connected to output terminals 41g and 41h.

[0026] In the example shown in Figure 1, the switching circuit 41 can operate as a full-bridge circuit. The inverter control circuit 7 changes the polarity of the voltage supplied to the resonant circuit 42 by, for example, alternately switching semiconductor switches S1 to S4. As a result, the switching circuit 41 converts the first DC power into AC power.

[0027] The resonant circuit 42 steps up or down the AC voltage supplied by the AC power from the switching circuit 41 at the resonant frequency. The resonant circuit 42 is connected between the switching circuit 41 and the rectifier / smoothing circuit 5. The resonant circuit 42 includes a transformer TR with a primary winding N1 and a secondary winding N2 isolated from the primary winding N1, and a resistor R1 and a resonant capacitor Cr connected between one end N1a of the primary winding N1 of the transformer TR and the output terminal 41g of the inverter 4. The resonant capacitor Cr is connected in series with the resistor R1. The resonant capacitor Cr is connected in series with the primary winding N1. The resistor R1 functions, for example, as a DC resistor on the primary winding N1 side of the resonant circuit 42. The secondary winding N2 of the transformer TR is connected to a heating resistor 61, which is a load, via the rectifier / smoothing circuit 5.

[0028] The transformer TR contains several parasitic components. The transformer TR includes a resonant inductance Lr (parasitic inductance) and an excitation inductance Lp. The resonant inductance Lr is the leakage inductance of the transformer TR. The resonant inductance Lr exists in the primary winding N1 so as to be connected in series with the resonant capacitor Cr. The excitation inductance Lp exists so as to be connected in parallel with the primary winding N1. The resonant circuit 42 is a series resonant circuit (LLC resonant circuit) composed of the resonant capacitor Cr, the resonant inductance Lr, and the excitation inductance Lp.

[0029] The resonant circuit 42 steps up or down the AC voltage supplied by the AC power from the switching circuit 41 at the resonant frequency. The resonant circuit 42 then supplies the stepped-up or stepped-down AC power to the rectifier and smoothing circuit 5.

[0030] The rectifier-smoothing circuit 5 converts the AC power supplied from the resonant circuit 42 into a second DC power. The magnitude of the second DC power is greater than the magnitude of the first DC power. The rectifier-smoothing circuit 5 includes a rectifier circuit 51 and a smoothing circuit 52. The rectifier circuit 51 is connected to the resonant circuit 42 via a resistor R2. The resistor R2 is connected between one end N2a of the secondary winding N2 and the rectifier circuit 51. The rectifier circuit 51 is, for example, a circuit composed of four diodes connected in a bridge configuration. The smoothing circuit 52 includes, for example, at least one smoothing capacitor. The smoothing circuit 52 may also consist of a group of capacitors connected in series with each other. The AC voltage generated by the AC power stepped up or down in the resonant circuit 42 is converted into a DC voltage by being rectified in the rectifier circuit 51 and smoothed in the smoothing circuit 52. The rectifier-smoothing circuit 5 then supplies the DC power corresponding to the converted DC voltage as the second DC power to the heating resistor 61. As a result, the heating resistor 61 is supplied with a load current If, which is the second DC power.

[0031] The X-ray tube 6 includes a heating resistor 61 as the cathode and an anode 62 positioned opposite the heating resistor 61. In the X-ray tube 6, a load current If is supplied to the heating resistor 61, causing it to heat up. This causes thermionic electrons to be emitted from the heating resistor 61. Meanwhile, a high voltage generated by an external high-voltage power supply Vc from the power supply unit 1 is applied between the heating resistor 61 and the anode 62. Thermionic electrons emitted from the heating resistor 61 move from the heating resistor 61 to the anode 62 due to the potential difference between the anode 62 and the heating resistor 61, and are focused on the anode. As a result, a tube current Iout flows through the X-ray tube 6. Qualitatively, the tube current Iout corresponds to the amount of thermionic electrons emitted from the heating resistor 61.

[0032] The inverter control circuit 7 outputs inverter drive signals Sg1 to Sg4 to the inverter 4 to control the inverter 4. The inverter control circuit 7 is connected to the inverter 4. In the example in Figure 1, the inverter control circuit 7 includes four output terminals, each of which is connected to the control terminals 41c to 41f of the switching circuit. Inverter drive signal Sg1 is output to semiconductor switch S1. Inverter drive signal Sg2 is output to semiconductor switch S2. Inverter drive signal Sg3 is output to semiconductor switch S3. Inverter drive signal Sg4 is output to semiconductor switch S4.

[0033] The load current detection unit 8 detects the magnitude of the load current If. The input terminal of the load current detection unit 8 is connected, for example, between the switching circuit 41 and the resonance circuit 42. In the example of FIG. 1, the input terminal of the load current detection unit 8 is connected to a node between the output terminal 41h and the other end N1b of the primary winding N1 of the transformer TR. The output terminal of the load current detection unit 8 is connected to the inverter control circuit 7. In the example of FIG. 1, the load current detection unit 8 detects a current having a magnitude corresponding to the load current If from the primary winding N1 side (primary side of the inverter 4) of the transformer TR. Note that the load current detection unit 8 may detect the load current If from the secondary winding N2 side (secondary side of the inverter 4) of the transformer TR. In this case, the input terminal of the load current detection unit 8 may be connected, for example, between the other end N2b of the secondary winding N2 of the transformer TR and the rectifying and smoothing circuit 5.

[0034] The load current detection unit 8 generates a load current detection signal S indicating the magnitude of the load current If. If If The load current detection signal S is, for example, a voltage signal. The load current detection unit 8 may include a current transformer and a shunt resistor. In this case, the load current detection unit 8 reduces the magnitude of the load current If by the current transformer and then converts the load current If into a voltage by the shunt resistor, thereby generating the load current detection signal S. If If The load current detection unit 8 only needs to be able to generate the load current detection signal S, and is not limited to the above configuration.

[0035] The tube current detection unit 9 detects the magnitude of the tube current Iout. The input terminal of the tube current detection unit 9 is connected to the anode 62 of the X-ray tube 6. The output terminal of the tube current detection unit 9 is connected to the inverter control circuit 7. The tube current detection unit 9 generates a tube current detection signal S indicating the magnitude of the tube current Iout. IOUT IOUT The tube current detection signal S is, for example, a voltage signal. Similar to the load current detection unit 8, the tube current detection unit 9 may include a current transformer and a shunt resistor, or may include a configuration other than a current transformer and a shunt resistor.

[0036] Figure 2 is a block diagram showing an example of the inside of an inverter control circuit 7. The inverter control circuit includes a control element 71 (second control element), a control element 72 (first control element), a frequency control unit 73, and a heating resistor detection unit 74. Control elements 71 and 72 are, for example, operational amplifiers. Control element 71 includes an input terminal 71a (third input terminal), an input terminal 71b (fourth input terminal), and an output terminal 71c. Control element 72 includes an input terminal 72a (first input terminal), an input terminal 72b (second input terminal), and an output terminal 72c. The output terminal 71c of control element 71 is connected to the input terminal 72b of control element 72. The output terminal 72c of control element 72 is connected to the input terminal of the frequency control unit 73. One of the multiple output terminals of the frequency control unit 73 is connected to the input terminal of the heating resistor detection unit 74.

[0037] Input terminal 71a receives the tube current detection signal S. IOUT The following is input. Input terminal 71b receives a tube current instruction signal S, which indicates the target value of the magnitude of the tube current Iout. ISET The following is input. The control element 71 receives the tube current detection signal S from the output terminal 71c. IOUT and tube current indicator signal S ISET The load current instruction signal S is a signal corresponding to the difference between the two. Ifdr The control element 71 outputs the tube current detection signal S to the control element 72. IOUT The tube current indicator signal S ISET If it is greater than, the load current instruction signal S Ifdr The size is reduced, and the tube current detection signal S IOUT The tube current indicator signal S ISET If it is smaller than, the load current instruction signal S Ifdr The size may be increased. Through this operation, the control element 71 receives the tube current instruction signal S ISET and tube current detection signal S IOUT Based on this, the tube current indicator signal S is such that the tube current Iout is the target value of the magnitude of the tube current Iout. ISET The load current instruction signal S approaches this value. Ifdr Control.

[0038] Input terminal 72a receives the load current detection signal S. If The following is input. Input terminal 72b receives a load current instruction signal S, which indicates the target value of the magnitude of the load current If. Ifdr The input is received. The control element 72 receives the load current detection signal S from the output terminal 72c. If and load current instruction signal S Ifdr The signal corresponding to the difference is the frequency indication signal S freq The signal is output to the frequency control unit 73. The control element 72 receives the load current detection signal S. If The load current instruction signal S Ifdr If it is greater than, the frequency indication signal S freq The size of the load current detection signal S is reduced. If The load current instruction signal S Ifdr If it is smaller than, the frequency indication signal S freq The magnitude may be increased. Through this operation, the control element 72 receives the load current instruction signal S Ifdr and load current detection signal S If Based on this, the load current If is the target value of the load current If, and the load current instruction signal S is the target value of the magnitude of the load current If. Ifdr The frequency indicator signal S approaches freq Control.

[0039] The frequency control unit 73 controls the drive frequency, which is the frequency of the inverter drive signals Sg1 to Sg4, so that the magnitude of the load current If approaches the target value of the load current If. The input terminal of the frequency control unit 73 receives the frequency instruction signal S freq The following is input. The frequency control unit 73 receives the frequency instruction signal S freq The drive frequency is variably controlled according to the magnitude of the signal. The frequency control unit 73 may include, for example, a VCO (voltage-controlled oscillator). In this case, the frequency control unit 73 controls the frequency instruction signal S freq As the magnitude increases, the drive frequency is increased, and the frequency instruction signal S freq If the size decreases, the driving frequency can be reduced.

[0040] The frequency control unit 73 includes four output terminals as output terminals of the inverter control circuit 7, and each output terminal is connected to the respective control terminals 41c to 41f of the switching circuit. The frequency control unit 73 may also have a function to adjust the timing of the output of inverter drive signals Sg1 to Sg4. This may cause the semiconductor switches S1 to S4 to switch alternately.

[0041] The frequency control unit 73 varies the drive frequency, which changes the magnitude of the AC power output from the switching circuit 41. For example, as the drive frequency approaches the resonant frequency of the resonant circuit 42, the magnitude of the load current If increases. As a result, the magnitude of the AC power output from the switching circuit 41 increases. With this configuration, the control element 72 receives a load current instruction signal S, where the load current If is the target value of the magnitude of the load current If. Ifdr The frequency indicator signal S approaches freq You may control this.

[0042] The heating resistor detection unit 74 detects the state of the heating resistor 61 based on the drive frequency controlled by the frequency control unit 73. Because the heating resistor 61 is used at high temperatures, it wears down with use. The wire diameter of the heating resistor 61 becomes thinner as it wears down. As a result, the impedance of the heating resistor 61 changes. For example, as the heating resistor 61 wears down, its impedance increases. Therefore, by detecting the impedance of the heating resistor 61, the heating resistor detection unit 74 can estimate the wear state of the heating resistor 61. The impedance of the heating resistor 61 includes, for example, the resistance value of the heating resistor 61 itself, as well as the resistance value of the wiring connected to the heating resistor 61.

[0043] The heating resistor detection unit 74 detects the impedance of the heating resistor 61 from the drive frequency controlled by the frequency control unit 73, based on the frequency characteristics of the heating resistor 61 and the power conversion circuit 3. Figure 3 is a graph showing an example of the frequency characteristics of the gain of the power conversion circuit 3 including the heating resistor 61. In Figure 3, the horizontal axis represents the drive frequency, and the vertical axis represents the gain. The gain is, for example, the ratio of the second DC power to the first DC power. As shown in Figure 3, the gain of the power conversion circuit 3 changes with the change in drive frequency. Similarly, the impedance of the resonant circuit 42 changes with the change in drive frequency. The frequency control unit 73 can calculate the impedance of the heating resistor 61 based on the change in impedance of the power conversion circuit 3 including the resonant circuit 42. For example, the impedance of the heating resistor 61 at the time the power supply unit 1 is started to drive is the initial impedance Ra, and the drive frequency at that time is the frequency (initial frequency) fa. When a certain amount of time has elapsed since the start of operation of the power supply unit 1, the impedance of the heating resistor 61 changes from the initial impedance Ra to the impedance (variable impedance) Rb, and the driving frequency at that time is defined as the frequency (variable frequency) fb. As described above, the control element 71 controls the tube current Iout to the tube current instruction signal S ISET The load current instruction signal S approaches this value. Ifdr Because the impedance of the heating resistor 61 is controlled, the tube current Iout can remain constant even if the impedance of the heating resistor 61 changes. As a result, the output power Pa generated at the initial impedance Ra and the output power Pb generated at the impedance Rb are calculated by the following formulas. Note that the output voltage Ea is the output voltage generated at the initial impedance Ra, and the output voltage Eb is the output voltage generated at the impedance Rb.

number

number

[0044] Figure 4 is a circuit diagram showing an example of an equivalent circuit 3A in which the resonant circuit 42, transformer TR, rectifier / smoothing circuit 5, and heating resistor 61 are integrated on the secondary side of the transformer TR in the power conversion circuit 3. The variables in the equivalent circuit 3A are as shown in equations (2) to (5) below.

number

[0045] The equivalent circuit 3A includes two resonant frequencies f0 and f1 calculated by the following equations (6) and (7).

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[0046] As shown in Figure 3, the gain of the power conversion circuit 3 is greatest at, for example, the resonant frequency f1. On the other hand, the impedance of the resonant circuit 42 is greatest at, for example, the resonant frequency f1. Note that frequency fa is greater than frequency fb, and resonant frequency f1 is less than frequency fb. The impedance Rb of the heating resistor 61 at frequency fb is calculated from equations (1) to (7) above by the following equation (8). The frequency control unit 73 may monitor the impedance of the heating resistor 61 from the change in drive frequency based on, for example, equation (8).

number

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[0047] The heating resistor detection unit 74 acquires frequency fa, frequency fb, and initial impedance Ra. The heating resistor detection unit 74 includes a storage unit 741, and the initial impedance Ra may be pre-stored in the storage unit 741. The heating resistor detection unit 74 may pre-store frequency fa, or it may use the drive frequency input from the frequency control unit 73 immediately after the start of operation of the power supply unit 1 as frequency fa. The heating resistor detection unit 74 receives frequency fb from the frequency control unit 73 after a certain period of time has elapsed since the start of operation of the power supply unit 1. Frequency fb is input to the frequency instruction signal S freq It changes depending on the size.

[0048] If the impedance Rb changes after a certain period of time has elapsed since the start of operation of the power supply unit 1, the frequency fb changes, and the tube current Iout, i.e., the input power to the heating resistor 61, is kept constant. For this reason, the heating resistor detection unit 74 may repeatedly calculate the impedance Rb at predetermined timings. The predetermined timing may be, for example, an interval of 5 μs to 20 μs. The heating resistor detection unit 74 may display the calculated impedance Rb on a display unit (not shown) included in or provided outside the power supply unit 1. For example, a user may determine the wear status of the heating resistor 61 from the magnitude of the impedance Rb displayed on the display unit.

[0049] The heating resistor detection unit 74 may detect the impedance of the heating resistor 61 using a different means instead of calculating it by equation (8). For example, the heating resistor detection unit 74 stores the correspondence between the drive frequency and the impedance of the heating resistor 61 in the memory unit 741. The heating resistor 61 then detects its impedance based on the drive frequency controlled by the frequency control unit 73. Figure 5 is a graph showing an example of the frequency characteristics of the load power of the power conversion circuit 3 including the heating resistor 61 when the impedance (load resistance) of the heating resistor 61 changes stepwise from an initial impedance RF1 to a plurality of fluctuating impedances RF2 to RF10. The initial impedance RF1 may be the same impedance as the initial impedance Ra mentioned above. Any of the fluctuating impedances RF2 to RF10 may be the same impedance as the impedance Rb mentioned above. The horizontal axis of Figure 5 represents the drive frequency, and the vertical axis represents the load power. The load power referred to here is a value calculated by the product of the load current If and the load voltage generated at the heating resistor 61. The memory unit 741 may store the correspondence between the drive frequency based on the frequency characteristics in Figure 5 and the impedance (load resistance) of the heating resistor 61. Note that the characteristics in Figure 5 are based on equation (8).

[0050] The frequency characteristics of each impedance in Figure 5 show that the magnitude of the load power is greatest in the driving frequency range of approximately 45,000 Hz to 65,000 Hz. Furthermore, the frequency characteristics of each impedance show a tendency for the load power to decrease as the driving frequency increases from the driving frequency corresponding to the peak. Specifically, the frequency characteristics of each impedance show a sharp decrease in load power in the driving frequency range of approximately 50,000 Hz to 80,000 Hz, and thereafter the load power tends to decrease more gradually. In addition, the frequency characteristics of each impedance have ranges above and below a certain reference power Wsd.

[0051] As shown in Figure 5, the frequency characteristics change depending on the impedance of the heating resistor 61. The impedance of the heating resistor 61 changes from an initial impedance RF1 to several fluctuating impedances RF2 to RF10 over time. The fluctuating impedances RF2 to RF10 increase in the order of RF2, RF3, RF4, RF5, RF6, RF7, RF8, RF9, and RF10. For example, if the initial impedance RF1 is 5Ω, the multiple fluctuating impedances RF2 to RF10 increase by 0.5Ω each. The magnitude of the load power peak and the decrease trend of the load power change depending on the impedance of the heating resistor 61. The load power peak increases as the impedance of the heating resistor 61 increases, and the drive frequency shifts to the lower side. The smaller the impedance of the heating resistor 61, the smaller the load power peak, the higher the drive frequency, and the more gradually the load power decreases in the high drive frequency range. On the other hand, the larger the impedance of the heating resistor 61, the larger the peak load power, and the lower the drive frequency, resulting in a rapid decrease in load power in the low drive frequency range. For example, with an initial impedance of RF1, the peak load power is smallest, the drive frequency corresponding to the peak is highest, and the load power decreases gradually as the drive frequency increases. On the other hand, with a variable impedance of RF10, for example, the peak load power is largest, the drive frequency corresponding to the peak is lowest, and the load power decreases rapidly as the drive frequency increases.

[0052] The driving frequencies shown by the frequency characteristics of each impedance at the reference power Wsd shift to the lower side as the impedance of the heating resistor 61 increases. If the initial frequency F1 is the driving frequency shown by the frequency characteristics of the initial impedance RF1 at the reference power Wsd, and the fluctuating frequency F2 is the driving frequency shown by the frequency characteristics of the fluctuating impedance RF2 at the reference power Wsd, then the fluctuating frequency F2 is lower than the initial frequency F1. The fluctuating frequencies F2 to F10 corresponding to fluctuating impedances RF2 to RF10 decrease in the order of F2, F3, F4, F5, F6, F7, F8, F9, and F10. The fluctuating frequency F10 is the lowest. Note that the initial frequency F1 may be the same frequency as the frequency fa mentioned above. Any of the fluctuating frequencies F2 to F10 may be the same frequency as the frequency fb mentioned above.

[0053] Figure 6 is a flowchart illustrating an example of a method for deriving the correspondence between the drive frequency and the impedance of the heating resistor 61, using the frequency characteristics shown in Figure 5 as an example. The derivation method includes steps ST11 to ST13. First, in step ST11, the reference power Wsd is set. The reference power Wsd may be a statistical value of the magnitude of the load power measured in the past. Next, in step ST12, the drive frequency corresponding to the impedance of the heating resistor 61 is determined based on the reference power Wsd. In step ST12, first, the initial frequency F1 is set to the drive frequency shown by the frequency characteristics of the initial impedance RF1 at the reference power Wsd. Next, the fluctuating frequency F2 is set to the drive frequency shown by the frequency characteristics of the fluctuating impedance RF2 at the reference power Wsd. Subsequently, the same process is repeated for fluctuating impedances RF3 to RF10 to determine fluctuating frequencies F3 to F10. Subsequently, in step ST13, the correspondence between the initial frequency F1 and the fluctuating frequencies F2 to F10, corresponding to the initial impedance RF1 and the fluctuating impedances RF2 to RF10, is stored in the storage unit 741. The storage unit 741 may store the correspondence as a lookup table or as a mathematical model.

[0054] Figure 7 is a flowchart showing an example of a state detection method for detecting the state of the heating resistor 61 using the power supply device 1 described above. The state detection method includes steps ST21 and ST22. First, in step ST21, the frequency control unit 73 controls the drive frequency, which is the frequency of the inverter drive signals Sg1 to Sg4, so that the magnitude of the load current If approaches the target value of the load current If. The frequency control unit 73 controls the frequency instruction signal S freq The drive frequency is variably controlled according to the magnitude of the power. Subsequently, in step ST22, the heating resistor detection unit 74 detects the state of the heating resistor 61 based on the drive frequency. Based on the frequency characteristics of the heating resistor 61 and the power conversion circuit 3, the heating resistor detection unit 74 detects the impedance of the heating resistor 61 from the drive frequency controlled by the frequency control unit 73. The heating resistor detection unit 74 may calculate the fluctuating impedance RF2 corresponding to the fluctuating frequency F2 of the heating resistor 61 based on the initial frequency F1, fluctuating frequency F2, and initial impedance RF1 using equation (2). Alternatively, the heating resistor detection unit 74 may detect the impedance of the heating resistor 61 based on the correspondence between the drive frequency and the impedance of the heating resistor 61 stored in the storage unit 741.

[0055] [Mechanism of Action and Effects] In power supply unit 1, the magnitude of the load current If is the target value of the load current indicated by the load current instruction signal S. Ifdr The frequency control unit 73 controls the drive frequency, which is the frequency of the inverter drive signals Sg1 to Sg4, to approach the specified value. At this time, the magnitude of the drive frequency reflects the state of the heating resistor 61, such as wear. Therefore, the state of the heating resistor 61 can be detected based on the drive frequency. By detecting the state of the heating resistor 61 based on the drive frequency, the heating resistor detection unit 74 can accurately estimate the state of the heating resistor 61 without depending on the value of the load current If.

[0056] The inverter 4 is connected to the power supply unit 2 and further includes a switching circuit 41 that converts the first DC power supplied from the power supply unit 2 into AC power, and a resonant circuit 42 that is connected between the switching circuit 41 and the rectifier / smoothing circuit 5 and steps up or down the AC voltage from the AC power. The heating resistor detection unit 74 detects the impedance of the heating resistor 61 from the drive frequency controlled by the frequency control unit 73, based on the frequency characteristics of the heating resistor 61 and the power conversion circuit 3. The impedance of the resonant circuit 42 included in the power conversion circuit 3 decreases, for example, as the drive frequency approaches the resonant frequency of the resonant circuit 42. That is, the impedance of the resonant circuit 42 changes with the drive frequency, and consequently the input power to the heating resistor 61 changes with the drive frequency. Based on the frequency characteristics of the input power to the heating resistor 61, the heating resistor detection unit 74 can detect the impedance of the heating resistor 61 from the drive frequency and can detect the impedance of the heating resistor 61 in real time. Furthermore, since the impedance of the heating resistor 61 is closely related to the state of wear of the heating resistor 61, the state of the heating resistor 61 can be accurately estimated based on the detected impedance.

[0057] The heating resistor detection unit 74 acquires the initial drive frequency F1, the fluctuating frequency F2 after the drive frequency changes from the initial frequency F1, and the initial impedance RF1 of the heating resistor 61 corresponding to the initial frequency F1. Based on the initial frequency F1, the fluctuating frequency F2, and the initial impedance RF1, it calculates the fluctuating impedance RF2 of the heating resistor 61 corresponding to the fluctuating frequency F2. In this case, the fluctuating impedance RF2 of the heating resistor 61 can be easily detected using the initial frequency F1 and initial impedance RF1 as a reference, and the wear state of the heating resistor 61 can be estimated.

[0058] The heating resistor detection unit 74 includes a storage unit 741 that stores the correspondence between the drive frequency and the impedance of the heating resistor, and detects the impedance of the heating resistor (initial impedance RF1 and fluctuating impedances RF2 to RF10) based on the drive frequency (initial frequency F1 and fluctuating frequencies F2 to F10) controlled by the frequency control unit 73. In this case, the impedance of the heating resistor 61 can be easily detected based on the pre-stored correspondence between the drive frequency and the impedance of the heating resistor 61, and the wear state of the heating resistor 61 can be estimated.

[0059] [Differentiation] While embodiments of this disclosure have been described above, this disclosure is not necessarily limited to the embodiments described above, and various modifications are possible without departing from its essence.

[0060] In the embodiment described above, the inverter control circuit 7 includes a heating resistor detection unit 74, but the power supply unit 1 may have the heating resistor detection unit 74 located outside the inverter control circuit 7. Furthermore, the power supply unit 1 may also include a heating resistor state determination unit. For example, the heating resistor state determination unit receives the impedance of the heating resistor 61 after its fluctuation from the heating resistor detection unit 74. The heating resistor state determination unit determines whether the heating resistor needs to be replaced based on the impedance after its fluctuation, and may notify the user if replacement is necessary. The heating resistor state determination unit may, for example, display a message indicating that replacement is necessary on a display unit.

[0061] The power supply unit 1 and the method for detecting the state of the heating resistor 61 (see Figure 7) may be used for purposes other than estimating the wear state of the heating resistor 61. For example, the power supply unit 1 and the method for detecting the state of the heating resistor 61 may be used for individual difference testing among multiple heating resistors 61. For example, the impedance of multiple heating resistors 61 may be compared by detecting the impedance of multiple heating resistors 61 from the driving frequency, or the quality of each heating resistor 61 may be judged. Alternatively, the power supply unit 1 and the method for detecting the state of the heating resistor may be used for purposes other than the X-ray tube 6. For example, the power supply unit 1 and the method for detecting the state of the heating resistor may be used in an atomic clock that measures time based on the transition frequency of atoms, or in a photo-excited magnetic sensor that detects the strength of a magnetic field using the spin state of atoms. The atomic clock or photo-excited magnetic sensor includes, for example, a vapor cell containing an alkali metal and a heating resistor that heats the vapor cell so that the alkali metal vaporizes. In the power supply unit 1 and the method for detecting the heating resistor, the impedance of the heating resistor may be detected from the drive frequency of the electrical signal used to energize the heating resistor.

[0062] The frequency control unit may employ an analog system instead of a digital system. Figure 8 is a block diagram showing an example of the internal structure of the inverter control circuit 7A of a modified power supply unit 1A. The inverter control circuit 7A differs from the inverter control circuit 7 in that it includes a frequency control unit 73A instead of a frequency control unit 73. The frequency control unit 73A includes an output unit 732, a current control unit 734, and a triangular wave generation unit 735. The current control unit 734 includes a conversion element 736 and a diode D1. The conversion element 736 includes an input terminal 736a, a first output terminal 736b, and a second output terminal 736c. The input terminal 736a is connected to the output terminal 72c of the control element 72. The first output terminal 736b is connected to the cathode of the diode D1, and the second output terminal 736c is connected to the reference potential GND. For example, the input terminal 736a receives a frequency instruction signal S from the control element 72. freq The following is input. The conversion element 736 receives, for example, the frequency indication signal S. freq It converts the signal S into an electric current. The conversion element 736, as an example, converts the frequency indicator signal Sfreq A current of a magnitude corresponding to the size of the device is passed from the first output terminal 736b to the second output terminal 736c.

[0063] The triangular wave generator 735 includes a diode D2, a constant current source CS, a threshold voltage source VS, a comparator 737, a discharge switch 738, and a capacitor Ch. One end of the constant current source CS is connected to a reference potential GND, and the other end of the constant current source CS is connected to the anode of diode D1 and the anode of diode D2. The comparator 737 includes a first input terminal 737a, a second input terminal 737b, and an output terminal 737c. The discharge switch 738 includes an input terminal 738a, a first output terminal 738b, and a second output terminal 738c. The first input terminal 737a of the comparator 737 is connected to the cathode of diode D2, and the second input terminal 737b of the comparator 737 is connected to the threshold voltage source VS. The output terminal 737c of the comparator 737 is connected to the input terminal 738a of the discharge switch 738. The first output terminal 738b of the discharge switch 738 is connected to one electrode of capacitor Ch, and the second output terminal 738c of the discharge switch 738 is connected to the reference potential GND. One electrode of capacitor Ch is connected to the input terminal of output unit 732. The other electrode of capacitor Ch is connected to the reference potential GND.

[0064] The frequency control unit 73A operates, for example, as follows: The constant current source CS supplies a constant current to capacitor Ch via diode D2. This causes the voltage of capacitor Ch to gradually increase. The comparator 737 monitors the voltage of capacitor Ch input to the first input terminal 737a. Specifically, the comparator 737 compares the voltage of capacitor Ch with the threshold voltage generated by the threshold voltage source VS. The threshold voltage is, for example, a preset value. When the voltage of capacitor Ch reaches the threshold voltage, the comparator 737 changes its output. For example, the comparator 737 outputs a Hi-level output signal when the voltage of capacitor Ch exceeds the threshold voltage, and outputs a Low-level output signal when the voltage of capacitor Ch falls below the threshold voltage. The magnitude of the Hi-level output signal may be, for example, the same as the magnitude of the power supply voltage supplied to the comparator 737, and the magnitude of the Low-level output signal may be, for example, the same as the magnitude of the reference potential GND.

[0065] When the output signal of comparator 737 changes (for example, from a low level to a high level), the discharge switch 738 is activated, and the discharge switch 738 discharges the charge from capacitor Ch. This causes the voltage of capacitor Ch to drop rapidly, and charging may start again. Repeated charging and discharging cycles generate a triangular wave Sg6. The frequency of the triangular wave Sg6 can vary depending on the magnitude of the charging current that charges capacitor Ch. The conversion element 736, as an example, receives a frequency indicator signal S freq A current of a magnitude corresponding to the magnitude of the signal is passed from the first output terminal 736b to the second output terminal 736c. This divides the charging current that charges the capacitor Ch. That is, the frequency indicator signal S freq When the magnitude of changes, the magnitude of the current flowing through the conversion element 736 changes, and as a result, the magnitude of the charging current that charges capacitor Ch changes. This causes the frequency of the triangular wave Sg6 to change.

[0066] The triangular wave generation unit 735 receives the frequency indication signal S freqA triangular wave Sg6 with a frequency corresponding to its magnitude is output to the output unit 732. The output unit 732 generates a drive signal synchronized with the frequency of the triangular wave Sg6 and outputs it to the switching circuit 41 as inverter drive signals Sg1 to Sg4.

[0067] The heating resistor 61 may be used as the cathode of an electron source, as an example of an energy ray tube. When the energy ray tube is an electron source, the electron beam window corresponds to the anode. Even when the energy ray tube is an electron source, the tube current Iout can be accurately controlled by a control system combining two control systems (first control loop LP1, second control loop LP2) to obtain a tube current indicator signal S, which is the target value of the magnitude of the tube current Iout. ISET The inverter 4 can be controlled to converge to a certain value.

[0068] In the power supply unit 1 described above, an example was explained in which the power supply unit 2 outputs a DC voltage as the first DC power, and the power conversion circuit 3 supplies a DC voltage as the second DC power to the heating resistor 61. Alternatively, the power supply unit 2 may output a DC current as the first DC power, and the power conversion circuit 3 may supply a DC current as the second DC power to the heating resistor 61. [Explanation of Symbols]

[0069] 1,1A...Power supply unit, 2...Power supply unit, 3...Power conversion circuit, 4...Inverter, 5...Rectifier and smoothing circuit, 7...Inverter control circuit, 8...Load current detection unit, 41...Switching circuit, 42...Resonant circuit, 61...Heating resistor, 73...Frequency control unit, 74...Heating resistor detection unit, 741...Memory unit, F1...Initial frequency, F2~F10...Fluctuating frequency, If...Load current, RF1...Initial impedance, RF2~RF10...Fluctuating impedance, Sg1~Sg4...Inverter drive signal.

Claims

1. A power supply unit that outputs first DC power, A power conversion circuit including an inverter that converts the first DC power to AC power, and a rectifier and smoothing circuit that converts the AC power to a second DC power, The heating resistor to which the second DC power is supplied, An inverter control circuit connected to the inverter and outputting an inverter drive signal to control the inverter, The power conversion circuit includes a load current detection unit that detects the magnitude of the load current supplied to the heating resistor by the second DC power, wherein the load current is supplied by the power conversion circuit to the heating resistor. The inverter control circuit is A frequency control unit controls the drive frequency, which is the frequency of the inverter drive signal, so that the magnitude of the load current approaches the target value of the load current. A power supply device having a heating resistor detection unit that detects the state of the heating resistor based on the aforementioned driving frequency.

2. The aforementioned inverter is A switching circuit connected to the power supply unit, which converts the first DC power supplied from the power supply unit into AC power, The system further comprises a resonant circuit connected between the switching circuit and the rectifier / smoothing circuit, which steps up or down the AC voltage generated by the AC power, The aforementioned heating resistance detection unit is The power supply device according to claim 1, wherein the impedance of the heating resistor is detected from the drive frequency controlled by the frequency control unit based on the frequency characteristics of the heating resistor and the power conversion circuit.

3. The aforementioned heating resistance detection unit is The initial frequency of the drive frequency, the fluctuating frequency after the drive frequency has changed from the initial frequency, and the initial impedance of the heating resistor corresponding to the initial frequency are obtained. The power supply device according to claim 2, wherein the fluctuating impedance of the heating resistor corresponding to the fluctuating frequency is calculated based on the initial frequency, the fluctuating frequency, and the initial impedance.

4. The aforementioned heating resistance detection unit is It includes a storage unit that stores the relationship between the drive frequency and the impedance of the heating resistor, The power supply device according to claim 2, wherein the impedance of the heating resistor is detected based on the drive frequency controlled by the frequency control unit.

5. A method for detecting the state of a heating resistor using a power supply device, The aforementioned power supply device is A power supply unit that outputs first DC power, A power conversion circuit including an inverter that converts the first DC power to AC power, and a rectifier and smoothing circuit that converts the AC power to a second DC power, The heating resistor to which the second DC power is supplied, An inverter control circuit connected to the inverter and outputting an inverter drive signal to control the inverter, The power conversion circuit includes a load current detection unit that detects the magnitude of the load current supplied to the heating resistor by the second DC power, wherein the load current is supplied by the power conversion circuit to the heating resistor. The aforementioned method, A step of controlling the drive frequency, which is the frequency of the inverter drive signal, so that the magnitude of the load current approaches the target value of the load current, A method for detecting the state of a heating resistor, comprising the step of detecting the state of the heating resistor based on the driving frequency.

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