DC-DC converter, control circuit, and semiconductor device

Abstract

The invention relates to a DC-DC converter, a control circuit, and a semiconductor device. Provided is a DC-DC converter capable of determining deterioration of a welded portion of a capacitor. A DC-DC converter (1) is provided with: switching elements (2, 3); an inductor (4) connected to the switching elements (2, 3); a capacitor (5) connected to the inductor (4); and a control circuit (10) that performs ON / OFF control on the switching elements (2, 3) on the basis of the PWM signal. The control circuit (10) has: a digital filter that calculates a Duty command value for controlling the Duty of the PWM signal on the basis of an error value between the target voltage and the output voltage (Vout); an initial data storage unit that stores the transition of the Duty command value in the initial state as initial data; and a comparison unit that compares the initial data with the comparison data, thereby determining the deterioration of any one of the switching elements (2, 3), the inductor (4), and the capacitor (5).

Description

Technical Field

[0001] Embodiments of the present disclosure relate to a DC-DC converter, a control circuit, and a semiconductor device. Background Art

[0002] A DC-DC converter that supplies a stable output voltage to a load circuit includes components such as a switching element, an inductor, and a capacitor. Therefore, when the DC-DC converter repeatedly undergoes temperature cycling, cracks are generated at the solder joints of the components, the on-resistance increases, and ultimately a failure occurs. When a failure occurs in the DC-DC converter, it is possible to damage the load circuit and other components, causing the damage to spread. Therefore, the DC-DC converter preferably has a failure prediction function that notifies the user of the precursor of the failure before the failure occurs, and performs preventive maintenance.

[0003] As a failure prediction method for a DC-DC converter, the following technique has been proposed: comparing the theoretical value of the Duty (duty ratio) of the PWM signal that drives the switching element with the actual Duty, and determining that it is abnormal and outputting a FAULT signal when the error between the theoretical value and the actual value is large (for example, refer to Patent Document 1). In Patent Document 1, when the solder joints of the switching element and the inductor deteriorate, a change in the increasing direction of the Duty is detected, and the precursor of the failure is predicted.

[0004] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-158713

[0005] However, the prior art has the following problem: when the solder in the capacitor section deteriorates, the precursor of the failure cannot be predicted. Summary of the Invention

[0006] The present disclosure aims to provide a DC-DC converter, a control circuit, and a semiconductor device that can predict the precursor of a failure even when the solder joint of the capacitor deteriorates.

[0007] The DC-DC converter of the present disclosure includes: a switching element; an inductor connected to the switching element; a capacitor connected to the inductor; and a control circuit that controls the conduction and disconnection of the switching element according to a PWM signal. The DC-DC converter is characterized in that it has: a duty ratio calculation unit that calculates a duty ratio command value for controlling the duty ratio of the PWM signal based on the error value between the target voltage and the output voltage; an initial data storage unit that stores the transition of the duty ratio command value in the initial state as initial data; a comparison data collection unit that collects the transition of the duty ratio command value calculated by the duty ratio calculation unit as comparison data; and a comparison unit that compares the initial data and the comparison data with each other for the jitter of the duty ratio command value with respect to the theoretical value, thereby determining the deterioration of the solder joint of the capacitor.

[0008] Even when the solder in the capacitor section of the DC-DC converter of the present disclosure deteriorates, it is possible to detect the change in the jitter of the Duty command value with respect to the theoretical value due to unstable feedback control, predict the precursor of a failure, and perform preventive maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 FIG. is a diagram showing the structure of the first embodiment of the DC-DC converter.

[0010] Figure 2 FIG. shows Figure 1 the operation waveform of the DC-DC converter shown.

[0011] Figure 3 FIG. is shown by Figure 1 the Duty command value calculated by the D digital filter.

[0012] Figure 4 FIG. shows Figure 1 the structure of the initial data collection storage unit and the determination unit shown.

[0013] Figure 5 FIG. shows Figure 1 the flowchart of the collection operation of the initial data collection storage unit and the determination unit shown.

[0014] Figure 6 FIG. shows Figure 1 the flowchart of the deterioration determination operation of the determination unit shown.

[0015] Figure 7 FIG. is shown by Figure 4 the comparison error cumulative value and the initial error cumulative value calculated by the comparison unit.

[0016] Figure 8 is a diagram showing Figure 1 the trend analysis in the comparison unit shown.

[0017] Figure 9 is a diagram showing the structure of the second embodiment of the DC-DC converter.

[0018] Figure 10 is a diagram showing an example of initial data and comparison data including temperature.

[0019] Figure 11 is a diagram showing the structure of the third embodiment of the DC-DC converter.

[0020] Figure 12 is a diagram showing an example of initial data and comparison data including ammeter measurement values.

[0021] Figure 13 is a diagram showing the structure of the fourth embodiment of the DC-DC converter.

[0022] Reference numeral description

[0023] 1, 1a, 1b, 1c: DC-DC converter; 2, 3: switching element; 4: inductor; 5: capacitor; 6: load circuit; 10, 10a, 10b: control circuit; 11: ADC; 12: subtractor; 13: digital filter; 14: PWM generation unit; 15: initial data collection and storage unit; 16: determination unit; 17: temperature detection unit; 18: current detection unit; 151: initial data collection unit; 152: initial data temporary storage unit; 153: initial data storage unit; 161: comparison data collection unit; 162: comparison data temporary storage unit; 163: comparison unit. Detailed description of the preferred embodiments

[0024] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0025] (First Embodiment)

[0026] The DC-DC converter 1 of the first embodiment is a step-down converter that controls power by PWM (Pulse Width Modulation). The DC-DC converter 1 steps down the input voltage Vin and supplies the output voltage Vout that has been feedback-controlled to be equal to the target voltage value to the load circuit (Load, load) 6.

[0027] Referring to Figure 1 , the DC-DC converter 1 includes a high-side switching element 2, a low-side switching element 3, an inductor 4, a capacitor 5, and a control circuit 10. Hereinafter, the switching element 2 and the switching element 3 are described as MOS-FETs, but are not limited thereto.

[0028] The drain terminal of the switching element 2 is connected to the positive electrode of the input voltage Vin, and the source terminal of the switching element 2 is connected to one end of the inductor 4 and the drain terminal of the switching element 3. The other end of the inductor 4 is connected to the positive electrode side terminal of the capacitor 5. The source terminal of the switching element 3 and the negative electrode side input terminal of the capacitor 5 are connected to a common line, and the common line is at the same potential as the negative electrode of the input voltage Vin.

[0029] The control circuit 10 is an information processing circuit such as a microcomputer having a CPU (Central Processing Unit), a ROM (ReadOnly Memory), a RAM (Random Access Memory), etc. A control program for controlling the operation of the DC-DC converter 1 is stored in the ROM. The control circuit 10 reads out the control program stored in the ROM and expands the control program into the RAM, thereby controlling the entire device.

[0030] The control circuit 10 outputs drive signals SW, SW based on the generated PWM signals ― to the gate terminals of the switching element 2 and the switching element 3 respectively, and exclusively controls the conduction and disconnection of the switching element 2 and the switching element 3. By controlling the conduction and disconnection of the switching element 2 and the switching element 3, the current passing through the inductor 4 is supplied to the capacitor 5 and the load circuit 6, and a stable output voltage Vout is generated.

[0031] The control circuit 10 includes an ADC (Analog-Digital Converter) 11, a subtractor 12, a digital filter 13, a PWM generation unit 14, an initial data collection and storage unit 15, and a determination unit 16. Part or all of the control circuit 10 can be configured as a semiconductor device integrated on a substrate, i.e., a control IC.

[0032] The ADC 11 converts the output voltage Vout into a digital value of a specified number of bits and outputs the digital conversion value of the output voltage Vout to the subtractor 12.

[0033] The subtractor 12 generates an error value between the digital conversion value of the target voltage, i.e., the target voltage value, and the digital conversion value input from the ADC 11, and outputs the generated error value to the digital filter 13.

[0034] The digital filter 13 performs PI, PID operations based on the error value input from the subtractor 12 and a preset response characteristic (proportional gain, differential gain, integral gain, etc.), calculates a Duty command value for making the output voltage Vout approach the target voltage, and outputs it to the PWM generation unit 14.

[0035] The PWM generation unit 14 generates a PWM signal based on the time ratio (duty ratio) of the Duty command value input from the digital filter 13.

[0036] The initial data collection and storage unit 15 stores the transition of the Duty command value calculated by the digital filter 13 as initial data during a preset learning period after the first power-on.

[0037] After the end of the learning period, the determination unit 16 uses the Duty command value calculated by the digital filter 13 as comparison data, performs deterioration determination based on the initial data of the initial data collection and storage unit 15, and outputs a deterioration signal FAULT when it is determined that deterioration has progressed.

[0038] Figure 1 The resistors R2 to R5 shown represent the conduction losses of the switching element 2, the switching element 3, the inductor 4, and the capacitor 5, respectively. When the temperature cycle is repeated, cracks are generated at the solder joints of the components, so the conduction loss increases.

[0039] Figure 2 Fig. (a) shows the operation waveforms (load current Iout, PWM signal) when the conduction losses of the resistors R2 to R5 are normal (initial state before power-on). Since the control circuit 10 uses digital control, quantization errors occur in the conversion values of the ADC 11. Due to this quantization error, as Figure 3 shown in Fig. (a), even in a state where the load is constant, the Duty (Duty command value) of the PWM signal fluctuates slightly (varies) with respect to the theoretical value determined by the ratio of the input voltage Vin to the output voltage Vout (Vout / Vin). The Duty of the PWM signal increases under heavy load where the load current Iout increases sharply and decreases under light load where the load current Iout decreases sharply.

[0040] Figure 2 Fig. (b) shows the operation waveforms (load current Iout, PWM signal) when deterioration occurs at the solder joint of the capacitor 5 and the conduction loss of the resistor R5 increases. When the conduction loss of the resistor R5 increases, the zero point Fz = 1 / (2×π×R1×C) determined by R5 and C (capacitance of the capacitor 5) shifts to the low-frequency side. Therefore, the frequency band becomes wider and the phase margin decreases, making the feedback control in the control circuit 10 unstable. As a result, as Figure 3 shown in Fig. (b), the fluctuation of the Duty (Duty command value) of the PWM signal with respect to the theoretical value is larger than the Figure 3 fluctuation in the normal state shown in Fig. (a).

[0041] Figure 2Figure (c) shows the operation waveforms (load current Iout, PWM signal) when the solder joints of switch element 2, switch element 3, and inductor 4 deteriorate and the conduction losses of resistors R2 to R4 increase. When at least one of the conduction losses of conduction resistors R2 to R4 increases, the Duty (Duty command value) of the PWM signal is controlled to be a Duty larger than the theoretical value. As a result, as shown in Figure 3 Figure (c), the error amount of the Duty (Duty command value) of the PWM signal with respect to the theoretical value is larger than Figure 3 the error amount in the normal state shown in Figure (a).

[0042] Referring to Figure 4 Figure (a), the initial data collection and storage unit 15 includes an initial data collection unit 151, an initial data temporary storage unit 152, and an initial data storage unit 153. The initial data collection unit 151 collects the Duty command value calculated by the digital filter 13 at each moment during a preset learning period after the first power-on, and stores the collected Duty command value as initial data in the initial data temporary storage unit 152 and the initial data storage unit 153. The initial data becomes array data including a time concept representing the change of the Duty command value as shown in Figure 2 Figure. The initial data temporary storage unit 152 is composed of a register that deletes data when the power is turned off, and the initial data storage unit 153 is composed of a non-volatile memory that does not delete data when the power is turned off. When the power is temporarily turned off and then turned on, the initial data is loaded from the initial data storage unit 153 to the initial data temporary storage unit 152.

[0043] Referring to Figure 4 Figure (b), the determination unit 16 includes a comparison data collection unit 161, a comparison data temporary storage unit 162, and a comparison unit 163. The comparison data collection unit 161 collects the Duty command value calculated by the digital filter 13 at each moment during a specified period, and stores the collected Duty command value as comparison data in the comparison data temporary storage unit 162. The comparison data becomes array data including a time concept representing the change of the Duty command value as shown in Figure 2 Figure. The comparison data temporary storage unit 162 is composed of a register that deletes data when the power is turned off. The timing for the comparison data collection unit 161 to collect comparison data can be appropriately set according to when the power is turned on, the power-on time, etc.

[0044] The comparison unit 163 compares the comparison data stored in the comparison data temporary storage unit 162 with the initial data stored in the initial data temporary storage unit 152, thereby determining whether there is deterioration. The comparison unit 163 compares the comparison data with the initial data for the jitter and error amount of the Duty (Duty command value) of the PWM signal with respect to the theoretical value, and determines whether there is deterioration. In addition, the theoretical value of the Duty (Duty command value) is determined by the ratio of the input voltage Vin to the output voltage Vout (Vout / Vin). However, when the changes in the input voltage Vin and the output voltage Vout are negligible, it can be set as a fixed value.

[0045] Next, refer to Figure 5 to describe in detail the collection operations of the initial data and the comparison data.

[0046] When the power supply is started, the control circuit 10 determines whether it is the initial state, that is, the first power supply start (step S101). In the case of the power supply start in the initial state in step S101, the initial data collection unit 151 of the initial data collection and storage unit 15 performs the collection operation of the initial data.

[0047] The initial data collection unit 151 sets the variable n to 1 (step S102), collects the Duty command value calculated by the digital filter 13, and stores the collected Duty command value as the nth initial data in the initial data temporary storage unit 152 and the initial data storage unit 153 (step S103).

[0048] The initial data collection unit 151 increments the variable n (step S104), and determines whether the variable n has reached the preset initial data collection number N (step S105). In the case where the variable n is less than the initial data collection number N in step S105, the initial data collection unit 151 returns to step S103 and then collects the Duty command value calculated by the digital filter 13.

[0049] The collection of the Duty command value is repeated until the variable n reaches the initial data collection number N. In the case where the variable n reaches the initial data collection number N in step S105, regarding the initial data, the transition of the N Duty command values collected during the preset learning period after the first power supply start is stored as array data in the initial data temporary storage unit 152 and the initial data storage unit 153.

[0050] In the case where the power supply is started in a non-initial state in step S101 and in the case where the variable n reaches the initial data collection number N in step S105, the comparison data collection unit 161 of the determination unit 16 waits for a preset comparison data collection timing (step S106). When the comparison data collection timing is reached in step S106, the comparison data collection unit 161 performs an operation to collect comparison data.

[0051] The comparison data collection unit 161 sets the variable m to 1 (step S107), collects the Duty command value calculated by the digital filter 13, and stores the collected Duty command value as the m-th comparison data in the comparison data temporary storage unit 162 (step S108).

[0052] The comparison data collection unit 161 increments the variable m (step S109), and determines whether the variable m has reached a preset comparison data collection number M (step S110). In the case where the variable m is less than the comparison data collection number M in step S110, the comparison data collection unit 161 returns to step S108 and then collects the Duty command value calculated by the digital filter 13.

[0053] The collection of the Duty command value is repeated until the variable m reaches the comparison data collection number M. In the case where the variable m reaches the comparison data collection number M in step S105, regarding the comparison data, the trend of the M collected Duty command values is stored as array data in the comparison data temporary storage unit 162.

[0054] When the comparison data composed of M Duty command values is stored in the comparison data temporary storage unit 162, the comparison unit 163 of the determination unit 16 performs deterioration determination by comparing with the initial data stored in the initial data temporary storage unit 152 (step S111).

[0055] The comparison unit 163 determines whether there is deterioration in the determination result of step S111 (step S112). In the case where the determination result in step S112 shows deterioration, the comparison unit 163 outputs a deterioration signal FAULT that notifies the user of the precursor of a failure (step S113). Through the deterioration signal FAULT, the user can identify the deterioration of the solder joints of the components (switching element 2, switching element 3, inductor 4, capacitor 5) constituting the DC-DC converter 1 and can perform preventive maintenance. In the case where the determination result in step S112 shows no deterioration, the comparison data collection unit 161 deletes the comparison data (step S114), returns to step S106, and waits for the next comparison data collection timing.

[0056] Next, with reference to Figure 6 , the deterioration determination operation of step S111 will be described in detail.

[0057] The comparison unit 163 sets the variable n to 1 (step S201), and calculates the absolute value of the difference between the n-th Duty command value of the initial data and the theoretical value as the error Dref. n (Step S202). The comparison unit 163 increments the variable n (step S203), and determines whether the variable n has reached a preset initial data collection number N (step S204).

[0058] If, in step S204, the variable n is less than the initial data collection number N, the process returns to step S202, and the error Dref between the n-th Duty command value of the initial data and the theoretical value is calculated. n .

[0059] If, in step S204, the variable n has reached the initial data collection number N, the comparison unit 163 calculates the initial error cumulative value Dref obtained by accumulating the errors Dref1 to Dref calculated in step S202. N (Step S205). 1-N

[0060] Next, the comparison unit 163 sets the variable m to 1 (step S206), and calculates the absolute value of the difference between the m-th Duty command value of the comparison data and the theoretical value as the error Dcmp. m (Step S202). The comparison unit 163 increments the variable n (step S203), and determines whether the variable n has reached a preset initial data collection number N (step S204).

[0061] If, in step S204, the variable n is less than the initial data collection number N, the process returns to step S202, and the error Dref between the n-th Duty command value of the learning data and the theoretical value is calculated. n .

[0062] If, in step S204, the variable n is less than the initial data collection number N, the comparison unit 163 calculates the initial error cumulative value Dref obtained by accumulating the errors Dref1 to Dcmp calculated in step S202. m (Step S205). 1-N

[0063] The comparison unit 163 sets the variable m to 1 (step S206), and calculates the absolute value of the difference between the m-th Duty command value of the comparison data and the theoretical value as the error Dcmp. m (Step S207). The comparison unit 163 increments the variable m (step S208), and determines whether the variable m has reached a preset comparison data collection number M (step S209).

[0064] If the variable m is less than the number of comparison data collected M in step S209, the process returns to step S207 to calculate the error Dcmp between the mth Duty command value and the theoretical value of the comparison data. m .

[0065] When the variable n reaches the comparison data collection number M in step S209, the comparison unit 163 calculates the difference between the error Dcmp1 to the error Dcmp calculated in step S207. M The comparison error cumulative value Dcmp obtained by accumulating 1-M (Step S210).

[0066] Next, the comparison unit 163 determines whether the comparison error cumulative value Dcmp calculated in step S210 is 1-M The initial error accumulation value Dref calculated in step S205 1-N The difference between the initial data collection number N and the comparison data collection number M is greater than the preset degradation threshold (step S211). In addition, the initial data collection number N and the comparison data collection number M are set to the same number, so that the initial data and the comparison data can be compared under the same conditions. When the initial data collection number N is different from the comparison data collection number M, the comparison error cumulative value Dcmp is calculated. 1-M / M and initial error accumulation value Dref 1-N / N can be used for comparison.

[0067] In step S211, the error cumulative value Dcmp is compared 1-M and the initial error accumulation value Dref 1-N When the difference between is greater than the degradation threshold, the comparison unit 163 determines that there is degradation (step S212). In step S211, the error cumulative value Dcmp is compared with 1-M and the initial error accumulation value Dref 1-N When the difference is smaller than the degradation threshold, it is determined that there is no degradation (step S213).

[0068] Reference Figure 7 As the degradation of the soldering parts of the components (switching element 2, switching element 3, inductor 4, capacitor 5) constituting the DC-DC converter 1 progresses, the comparison error cumulative value Dcmp 1-M That is, the more the degradation of the weld progresses, the greater the comparison error cumulative value Dcmp 1-M The initial error accumulation value Dref with the initial state 1-N Therefore, by setting an appropriate degradation threshold, degradation of the welded portion of the components (switching element 2, switching element 3, inductor 4, capacitor 5) constituting the DC-DC converter 1 can be detected.

[0069] Reference Figure 2(a), (b) and Figure 3 (a), (b) thereof, the initial error cumulative value Dref 1-N and the comparison error cumulative value Dcmp 1-M become values corresponding to the jitter of the Duty (Duty command value) of the PWM signal with respect to the theoretical value. Therefore, the initial error cumulative value Dref 1-N and the comparison error cumulative value Dcmp 1-M are the initial data conversion value and the comparison data conversion value representing the magnitude of the jitter of the Duty (Duty command value) with respect to the theoretical value.

[0070] Refer to Figure 2 (a), (c) of Figure 3 (a), (c) thereof, the initial error cumulative value Dref 1-N and the comparison error cumulative value Dcmp 1-M become values corresponding to the error amount of the Duty (Duty command value) of the PWM signal with respect to the theoretical value. Therefore, the initial error cumulative value Dref 1-N and the comparison error cumulative value Dcmp 1-M are also the initial data conversion value and the comparison data conversion value representing the error amount of the Duty (Duty command value) with respect to the theoretical value.

[0071] The calculation of the initial error cumulative value Dref 1-N can also be executed when the initial data collection unit 151 collects the initial data, and the initial error cumulative value Dref 1-N is stored as the initial data in the initial data temporary storage unit 152 and the initial data storage unit 153. In this case, the storage capacities of the initial data temporary storage unit 152 and the initial data storage unit 153 can be reduced.

[0072] The comparison unit 163 performs a trend analysis on the change of the Duty command value at each moment. Thus, the deterioration determination of the welding unit can also be performed. For example, as Figure 8 shown, when the cycle of the change of the Duty command value changes in the initial data and the comparison data, the comparison unit 163 can detect that a difference in the trend has occurred. By setting the initial data and the comparison data as array data considering the time concept, finer changes can be detected, and high-precision deterioration prediction can be performed. The comparison unit 163 can also use artificial intelligence such as machine learning as a means of trend analysis. In addition, as a method for quantitatively grasping the change of the Duty command value, fast Fourier transform can also be used.

[0073] The initial data stored in the initial data storage unit 153 can be prepared in advance, or data accumulated in the cloud or the like can be provided from the outside. In this case, a program for the initial data collection operation is not required, so the control of the control circuit 10 can be simplified.

[0074] (Second Embodiment)

[0075] Refer to Figure 9 , in addition to the structure of the DC-DC converter 1 of the first embodiment, the DC-DC converter 1a of the second embodiment further includes a temperature detection unit 17 in the control circuit 10a. The temperature detection unit 17 detects the ambient temperature. The on-resistances of the switching element 2 and the switching element 3 have temperature characteristics, and the higher the temperature, the higher the on-resistance. Therefore, even if the deterioration of the soldering portion does not progress, in a high-temperature state, the Duty command value increases, and it is impossible to accurately determine the presence or absence of deterioration.

[0076] Therefore, as Figure 10 shown, the initial data and the comparison data are set as array data including the ambient temperature measured by the temperature detection unit 17. The comparison unit 163 compares the initial data and the comparison data in consideration of the change in the on-resistance caused by the temperature change, and performs deterioration determination. Thereby, higher-precision deterioration detection can be performed.

[0077] (Third Embodiment)

[0078] Refer to Figure 11 , in addition to the structure of the DC-DC converter 1a of the second embodiment, the DC-DC converter 1b of the third embodiment further includes a current detection unit 18 in the control circuit 10b. The current detection unit 18 detects the current flowing through the inductor 4.

[0079] As Figure 12 shown, the initial data and the comparison data are set as array data including the current measurement value measured by the current detection unit 18. The comparison unit 163 analyzes the change in the current measurement value and the Duty command value at each moment, thereby performing deterioration determination of the soldering portion. Thereby, the comparison unit 163 can detect finer changes and can perform higher-precision deterioration detection.

[0080] (Fourth Embodiment)

[0081] The DC-DC converter 1c of the fourth embodiment is a boost converter that controls power by PWM (Pulse Width Modulation), which is different from the DC-DC converter 1 of the first embodiment. The DC-DC converter 1c magnetizes the inductor 4 with energy during the period when the switching element 3 is turned on and the switching element 2 is turned off, and releases the energy stored in the inductor 4 to the capacitor 5 and the load circuit 6 during the period when the switching element 3 is turned off and the switching element 2 is turned on.

[0082] The DC-DC converter 1c indicates that the present disclosure can also be applied to a boost converter as other power topologies. Thus, the present disclosure can also be applied to various power topologies such as buck-boost converters.

[0083] Hereinafter, the characteristic points in the above embodiments are summarized.

[0084] This embodiment is a DC-DC converter 1, which includes: switching elements 2 and 3; an inductor 4 connected to the switching elements 2 and 3; a capacitor 5 connected to the inductor 4; and a control circuit 10 that performs on-off control of the switching elements 2 and 3 according to a PWM signal. The control circuit 10 includes: a digital filter 13 (duty calculation unit) that calculates a duty command value (duty ratio command value) for controlling the PWM signal according to the error value between the target voltage and the output voltage Vout; an initial data storage unit 153 that stores the transition of the duty command value in the initial state as initial data; a comparison data collection unit 161 that collects the transition of the duty command value calculated by the digital filter 13 as comparison data; and a comparison unit 163 that compares between the initial data and the comparison data for the jitter of the duty command value with respect to the theoretical value, thereby performing deterioration determination of the welding part of the capacitor 5.

[0085] According to this feature, in the case where the welding of the capacitor part deteriorates, the DC-DC converter 1 can also detect the change in the jitter of the duty command value with respect to the theoretical value due to unstable feedback control, predict the precursor of the failure, and can perform preventive maintenance.

[0086] In addition, according to this embodiment, there is an initial data collection unit 151 that stores the transition of the duty command value calculated by the digital filter 13 as initial data in the initial data storage unit 153 during the learning period of the initial state.

[0087] According to this feature, the initial data can reflect the characteristics of each device.

[0088] In addition, according to the present embodiment, the initial data is the initial error cumulative value Dref obtained by accumulating the error between the Duty command value and the theoretical value. 1-N The initial data storage unit 153 stores the data. The comparison unit 163 converts the Duty command value in the comparison data into a comparison error cumulative value Dcmp obtained by accumulating the error between the Duty command value and the theoretical value. 1-M Then, a deterioration determination of the welding portion of the capacitor 5 is performed by comparing the initial error cumulative value Dref 1-N with the comparison error cumulative value Dcmp. 1-M

[0089] According to this feature, the control circuit 10 does not require a program for the initial data collection operation. Therefore, the control can be simplified. The deterioration determination can be performed by a simple comparison between the initial error cumulative value Dref 1-N and the comparison error cumulative value Dcmp. 1-M

[0090] In addition, according to the present embodiment, the initial data and the comparison data are array data of the Duty command value at each moment. The comparison unit 163 performs a deterioration determination by trend analysis of the initial data and the comparison data.

[0091] According to this feature, the comparison unit 163 can perform a deterioration determination with higher accuracy including the concept of time.

[0092] In addition, according to the present embodiment, there is a temperature detection unit 17 that detects the ambient temperature. The initial data and the comparison data include the temperature at each moment detected by the temperature detection unit 17.

[0093] According to this feature, the advantage is that the comparison unit 163 can perform a deterioration detection considering the temperature dependence of the on-resistance of the switching elements 2 and 3.

[0094] In addition, according to the present embodiment, there is a current detection unit 18 that detects the current flowing through the inductor 4. The initial data and the comparison data include the current at each moment detected by the current detection unit 18.

[0095] According to this feature, the comparison unit 163 performs a deterioration analysis considering the inductor current. Thus, a deterioration determination with higher accuracy can be performed.

[0096] In addition, the present invention is not limited to the above-described embodiments. It is understood that the embodiments can be appropriately changed within the scope of the technical concept of the present invention. In addition, the number, position, shape, etc. of the above-described structural components are not limited to the above-described embodiments and can be the number, position, shape, etc. suitable for implementing the present invention. In addition, in each figure, the same reference numerals are assigned to the same structural elements.

Claims

1. A DC-DC converter having: a switching element; an inductor connected to the switching element; a capacitor connected to the inductor; and a control circuit for controlling conduction and disconnection of the switching element according to a PWM signal, wherein the DC-DC converter is characterized in that the DC-DC converter has: a duty ratio calculation unit that calculates a duty ratio command value for controlling the duty ratio of the PWM signal based on an error value between a target voltage and an output voltage; an initial data storage unit that stores the transition of the duty ratio command value in an initial state as initial data; a comparison data collection unit that collects the transition of the duty ratio command value calculated by the duty ratio calculation unit as comparison data; and a comparison unit that compares between the initial data and the comparison data with respect to jitter of the duty ratio command value with respect to a theoretical value, thereby performing deterioration determination of a welding portion of the capacitor.

2. The DC-DC converter according to claim 1, wherein the DC-DC converter has an initial data collection unit that stores, during a learning period in an initial state, the transition of the duty ratio command value calculated by the duty ratio calculation unit as the initial data in the initial data storage unit.

3. The DC-DC converter according to claim 1 or 2, wherein the initial data is stored in the initial data storage unit as an initial error cumulative value obtained by accumulating an error between the duty ratio command value and the theoretical value, the comparison unit converts the duty ratio command value in the comparison data into a comparison error cumulative value obtained by accumulating an error with respect to the theoretical value, and compares between the initial error cumulative value and the comparison error cumulative value, thereby performing deterioration determination of a welding portion of the capacitor.

4. The DC-DC converter according to claim 1 or 2, wherein the initial data and the comparison data are array data of the duty ratio command value at each moment, the comparison unit performs deterioration determination through trend analysis of the initial data and the comparison data.

5. The DC-DC converter according to claim 4, wherein the DC-DC converter has a temperature detection unit that detects the ambient temperature, the initial data and the comparison data include the temperature at each moment detected by the temperature detection unit.

6. The DC-DC converter according to claim 4, wherein the DC-DC converter has a current detection unit that detects a current flowing through the inductor, the initial data and the comparison data include the current at each moment detected by the current detection unit.

7. A control circuit for controlling a DC-DC converter having: a switching element; an inductor connected to the switching element; and a capacitor connected to the inductor, wherein the control circuit is characterized in that the control circuit has: A PWM generation unit that generates a PWM signal for controlling conduction and disconnection of the switching element; A duty ratio calculation unit that calculates a duty ratio command value for controlling the duty ratio of the PWM signal based on an error value between a target voltage and an output voltage; An initial data storage unit that stores the transition of the duty ratio command value in an initial state as initial data; A comparison data collection unit that collects the transition of the duty ratio command value calculated by the duty ratio calculation unit as comparison data; And A comparison unit that compares between the initial data and the comparison data with respect to jitter of the duty ratio command value with respect to a theoretical value, thereby performing deterioration determination of a welding portion of the capacitor.

8. A semiconductor device, characterized in that, The control circuit according to claim 7 is integrated on a substrate.

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