JP7559590B2 - Booster - Google Patents

Description

The present invention relates to a booster device.

Conventionally, boost devices are known that boost and output an input power supply voltage.

In addition, in an overcurrent protection circuit that detects an overcurrent and determines that an abnormality has occurred and stops operation, there is known technology that prevents erroneous determinations due to temporary overcurrents, such as when the power is turned on. For example, the switching regulator disclosed in Patent Document 1 limits the current by discharging the capacitor of the soft start circuit when an overcurrent is detected.

JP 2014-3850 A

The switching regulator in Patent Document 1 uses a soft start circuit, which makes the circuit configuration complex and increases the start-up time when the power is turned on.

The present invention was created in consideration of the above points, and its purpose is to provide a boost device that prevents erroneous detection of an overcurrent abnormality, simplifies the circuit configuration, and shortens the start-up time.

The present invention is a boost device that boosts and outputs an input power supply voltage. This boost device includes a boost switching element (25), a drive circuit (41, 42), an overcurrent monitoring circuit (44), and a control unit (50, 42).

The boost switching element is provided between one end of the coil (21), the other end of which is connected to the power source (15), and ground, and boosts the voltage at the other end of the coil by switching operation. The drive circuit operates the boost switching element in PWM mode. The overcurrent monitoring circuit monitors the current flowing through the boost switching element. The control unit judges an abnormality based on a notification from the overcurrent monitoring circuit and takes action.

The overcurrent monitoring circuit counts the number of overcurrent detections for the state of the current flowing through the boost switching element at each communication interval with the control unit, and when the number of overcurrent detections exceeds a predetermined number, or when the current or the integrated value of the current squared value exceeds a threshold at each communication interval with the control unit, it determines that a first condition is met and transmits a notification signal to the control unit. When the notification signal received from the overcurrent monitoring circuit continues for a predetermined determination time or longer, the control unit determines that a second condition is met, determines that an abnormality exists, and takes action. The control unit also sets the determination time to a different value depending on a plurality of situations including when the boost device is in operation, or masks the notification signal.

In this invention, the overcurrent monitoring circuit does not determine an abnormality just by detecting an overcurrent, but sends a notification signal to the control unit when a first condition is met. The control unit only determines an abnormality and takes action when a second condition is also met. This prevents the overcurrent detected when the power is turned on or during an initial check from being erroneously determined to be an abnormality.

In addition, the present invention does not use a soft start circuit as in the conventional technology of Patent Document 1, and instead detects an overcurrent at an overcurrent threshold set below the rated value of the boost switching element when powering on or during an initial check, and passes current. In other words, while assuming that the first condition is likely to be met when powering on or during an initial check, erroneous judgment is prevented by preventing the second condition from being met. This simplifies the circuit configuration and shortens the start-up time.

1 is a configuration diagram of a booster device and its peripherals according to a first embodiment; 1 is a schematic configuration diagram of an electric power steering device to which a boost device according to a first embodiment is applied; FIG. 13 is a circuit diagram showing an overcurrent that occurs when a diode or coil has a short circuit. 4 is a time chart showing the operation of the boost device according to the first embodiment. 6 is a time chart illustrating an example in which a first condition is satisfied. FIG. 4 is a diagram showing the configuration of an overcurrent detection threshold setting unit. 5 is a flowchart showing a process when an overcurrent is detected. 4 is a flowchart of an abnormality determination. 11 is a flowchart showing a process for preventing erroneous determination. 5 is a flowchart showing a procedure to be taken when an abnormality is determined. FIG. 11 is a configuration diagram of a booster device and its peripherals according to a second embodiment.

Below, several embodiments of the boost device of the present invention will be described with reference to the drawings. The first and second embodiments are collectively referred to as "the present embodiment". The boost device of this embodiment boosts the power supply voltage in an electric power steering device of a vehicle. The boost devices of the first and second embodiments are denoted by the reference numerals "301" and "302", respectively, and common points will be described in the explanation of boost device 301. The first and second embodiments differ in the elements that function as a "control unit".

First Embodiment
1 shows a boost device 301 and its peripheral configuration according to the first embodiment. The boost circuit 20 boosts and outputs the power supply voltage input from the battery 15 so that operation can continue even when the battery 15 has a low voltage. The voltage before boosting by the boost circuit 20 is denoted as VL, and the voltage after boosting is denoted as VH. The inverter 60 converts the DC power of the battery 15 into AC power and supplies it to the motor 80. The motor 80 is, for example, a three-phase brushless motor.

The boost circuit 20 is a chopper-type boost circuit including a coil 21, a diode 23, a capacitor 24, and a boost MOS 25 as a "boost switching element." The boost MOS 25 is composed of an n-channel MOSFET. Note that in this specification, MOSFET will be omitted and simply referred to as "MOS."

One end of the coil 21 is connected to the battery 15 as a "power source." A power supply relay 16 or an element such as a diode (not shown) may be connected between the battery 15 and the coil 21. The power supply relay 16 may be a mechanical relay or a semiconductor switching element. The anode of the diode 23 is connected to the other end of the coil 21, and the cathode is connected to the output end. The capacitor 24 is provided between the cathode of the diode 23 and ground.

The boost MOS 25 is provided between the connection point N at the other end of the coil 21 and ground. That is, the drain terminal is connected to the connection point N, and the source terminal is grounded. The gate terminal of the boost MOS 25 is connected to the drive circuit 41. The boost MOS 25 performs switching operation based on the PWM command signal output from the drive circuit 41. Accordingly, the coil 21 repeatedly stores and releases inductive energy, thereby boosting the voltage at the other end of the coil 21, i.e., the output side. In short, the boost MOS 25 boosts the voltage on the output side of the coil 21 through switching operation.

The boost device 301 of the first embodiment includes at least the boost MOS 25, which is one of the components of the boost circuit 20. The boost device 301 also includes a drive circuit 41, an overcurrent monitoring circuit 44, and a microcomputer 50 as a "controller". The drive circuit 41 operates the boost MOS 25 in PWM mode. The overcurrent monitoring circuit 44 monitors the current flowing through the boost MOS 25 and detects an overcurrent. The technical significance of the overcurrent monitoring circuit 44 will be described later.

The boost MOS 25, drive circuit 41, and overcurrent monitoring circuit 44 are built into the same IC. In this specification, this IC is referred to as ASIC 40, which means an application-specific IC. When the overcurrent monitoring circuit 44 detects an overcurrent, as a protective function, the overcurrent monitoring circuit 44 commands the drive circuit 41 to forcibly turn off the boost MOS 25. The ASIC 40 and microcomputer 50 that make up the boost device 301 communicate with each other. The microcomputer 50 determines whether an abnormality has occurred based on a notification from the overcurrent monitoring circuit and takes action. In more detail, a notification signal indicating the detection of an overcurrent is output from the overcurrent monitoring circuit 44 to the microcomputer 50.

Furthermore, as a measure to be taken when an abnormality is detected, the microcomputer 50 instructs the drive circuit 41 to stop the operation of the boost MOS 25, for example. Furthermore, the microcomputer 50 monitors a monitoring voltage, which is "a voltage monitored in the circuit before or after boost." For example, as the voltage of the circuit before boost, the power supply voltage of the battery 15, i.e., the pre-relay voltage VLa on the battery 15 side of the power supply relay 16 in FIG. 1, is monitored. Alternatively, the post-relay voltage VLb between the power supply relay 16 and the coil 21 may be monitored. Alternatively, the post-boost voltage VH, which is the voltage of the circuit after boost, may be monitored.

Figure 2 shows a schematic configuration of a steering system 99 including an electric power steering (EPS) device 90. Note that the electric power steering device 90 in Figure 2 is a column assist type, but the boost device 301 of this embodiment can also be applied to a rack assist type electric power steering device. The steering system 99 includes a handle 91, a steering shaft 92, a steering torque sensor 94, a pinion gear 96, a rack shaft 97, wheels 98, and the electric power steering device 90.

A pinion gear 96 provided at the tip of the steering shaft 92 meshes with a rack shaft 97. A pair of wheels 98 are provided at both ends of the rack shaft 97 via tie rods or the like. When the driver turns the steering wheel 91, the steering shaft 92 connected to the steering wheel 91 rotates. A steering torque sensor 94 provided midway along the steering shaft 92 detects the steering torque trq. The rotational motion of the steering shaft 92 is converted by the pinion gear 96 into linear motion of the rack shaft 97, and the pair of wheels 98 are steered to an angle according to the amount of displacement of the rack shaft 97.

The electric power steering device 90 includes a boost device 301, an inverter 60, a motor 80, a reduction gear 89, etc. In this embodiment, the microcomputer 50, which is one element of the boost device 301, also functions as a motor control device in the electric power steering device 90. The microcomputer 50 as a motor control device acquires information such as steering torque trq, steering speed, and vehicle speed from the outside, and controls the driving of the motor 80 so that the motor 80 outputs the desired assist torque calculated from this information. The assist torque output by the motor 80 is transmitted to the steering shaft 92 via the reduction gear 89.

Next, referring to FIG. 3, an example of an overcurrent abnormality caused by an element failure in the boost circuit 20 will be described. When the coil 21 shorts out, the power of the battery 15 is applied directly to the boost MOS 25 without being converted into inductive energy, and when the boost MOS 25 is on, an overcurrent flows as shown by the dashed-dotted arrow. When the diode 23 shorts out, the current discharged from the capacitor 24 flows back through the diode 23, and when the boost MOS 25 is on, an overcurrent flows through the boost MOS 25 as shown by the dashed-dotted arrow. This may destroy the boost MOS 25.

In such a case, in order to protect the boost MOS 25, it is necessary to detect the overcurrent and take measures such as stopping the flow of power if an abnormality occurs. However, when the power is turned on, etc., an overcurrent may be detected temporarily even if the circuit is normal, and it is necessary to prevent this from being mistakenly determined to be an abnormality.

However, using a soft start circuit as in the conventional technology of Patent Document 1 (JP Patent Publication No. 2014-3850) results in a complex circuit configuration, which results in a long start-up time when the power is turned on. Therefore, the present embodiment aims to simplify the circuit configuration and shorten the start-up time in a boost device that prevents erroneous determination of an overcurrent abnormality.

Next, a series of processes from overcurrent detection to the action taken when an abnormality is determined according to this embodiment will be described with reference to Figures 4 to 10. In the explanation of the flowcharts in Figures 7 to 10, the symbol "S" indicates a step.

The time chart in Figure 4 shows the notification operation of overcurrent detection by the overcurrent monitoring circuit 44. The communication interval from the overcurrent monitoring circuit 44 to the microcontroller 50 is set to, for example, 1 ms. When the boost operation permission signal is on, the drive circuit 41 switches the boost MOS 25, for example, with a PWM period of 5 ms, that is, at a frequency of 200 kHz. Therefore, the boost MOS 25 switches on and off 200 times during the communication interval of 1 ms.

As shown in FIG. 5, if the on-time of the boost MOS 25 in one PWM cycle T is Ton and the off-time is Toff, the duty ratio is expressed as "Ton/T." During normal operation of the boost device 301, the duty ratio is calculated according to the boost output target value, and a PWM command signal is generated. FIG. 5 illustrates the command signal when the duty ratio is approximately 50%.

The overcurrent threshold used for overcurrent detection by the overcurrent monitoring circuit 44 is set for the current when the boost MOS 25 is on. The overcurrent threshold is set below the breakdown tolerance mainly based on the rating of the boost MOS 25 and the solder reliability of the board mounting. The overcurrent threshold may also be set variably according to the heat generation of the boost MOS 25.

6, for example, an overcurrent threshold calculation unit 43 provided in an ASIC 40 calculates an overcurrent threshold according to the current heat generation of the boost MOS 25, and outputs the overcurrent threshold to an overcurrent monitoring circuit 44. The heat generation of the boost MOS 25 may be detected by a temperature sensor, or may be estimated by adding Joule heat calculated from a current squared value or the like to an initial temperature. For example, the greater the heat generation of the boost MOS 25, the lower the overcurrent threshold is set so that an overcurrent is more easily detected, thereby adjusting the boost MOS 25 to be better protected from overheating.

The overcurrent monitoring circuit 44 counts the number of times an overcurrent is detected at each communication interval. As shown in FIG. 5, each time the overcurrent monitoring circuit 44 detects an overcurrent, the drive circuit 41 forcibly turns off the boost MOS 25, and keeps it off until the next duty-on timing. Therefore, in the switch operation upon overcurrent detection, the on time is shortened by the time indicated by the two-dot chain line in response to the PWM command signal. Because the boost MOS 25 is forcibly turned off, the current becomes zero. Then, as long as the cause of the overcurrent continues, the current again exceeds the overcurrent threshold during the next duty-on period, and an overcurrent is detected.

For example, when the boost device 301 is powered on or in overboost mode during an initial check, the boost operation permission signal is turned on and then a temporary overcurrent state occurs. During this period, the overcurrent monitoring circuit 44 counts the number of overcurrent detections at each communication interval. When the number of overcurrent detections at each communication interval exceeds a predetermined number, N, the overcurrent monitoring circuit 44 determines that the "first condition is met" for the state of the current flowing through the boost MOS 25 and outputs an overcurrent flag as a notification signal. On the other hand, when the boost operation permission signal is off before the start of the boost operation or after the temporary overcurrent state has ended, the number of overcurrent detections at each communication interval falls below N, and the overcurrent flag is not output.

Here, counting the number of overcurrent detections is not limited to cases where an overcurrent is detected continuously every cycle, as shown in [Example 1] in Figure 5, but also includes cases where an overcurrent is not detected along the way, as shown in [Example 2], as long as the total number is counted. In addition to cases where the current actually falls below the threshold as shown in [Example 2], it also includes cases where the current reaches the threshold but is not counted due to a detection error. In short, regardless of whether the detections are continuous or discontinuous, when the total number of overcurrent detections per communication interval exceeds N, an overcurrent flag is output.

After that, it is assumed that at time tx, an element such as a coil or diode shorts out, resulting in a permanent overcurrent abnormality (i.e., a true abnormality). After that, overcurrent is constantly detected, and when the total number of overcurrent detections per communication interval exceeds N, an overcurrent flag is output. When the overcurrent flag received from the overcurrent monitoring circuit 44 continues for a predetermined determination time or longer, the microcontroller 50 determines that the "second condition is met" and determines that an abnormality has occurred. Then, as a measure to be taken when an abnormality has been determined, the microcontroller 50 changes the boost operation permission signal from on to off, and stops the operation of the boost MOS 25.

The basic flow of the above process is shown in the flowcharts of Figures 7 and 8. In the flowcharts and the following explanations of the flowcharts, the microcomputer 50 of the first embodiment is generalized and referred to as the "controller". Therefore, the same flowcharts and explanations are also used in the second embodiment. In S11 of Figure 7, it is determined whether the overcurrent monitoring circuit 44 has detected an overcurrent. If the answer is YES in S11, the drive circuit 41 turns off the boost MOS 25 in S12 and keeps it in the off state until the next duty-on timing.

In S13 of FIG. 8, the overcurrent monitoring circuit 44 counts the number of overcurrent detections at each communication interval with the control unit. In S14, it is determined whether the number of overcurrent detections exceeds a predetermined number N. If the result in S14 is YES, the overcurrent monitoring circuit 44 determines that the first condition is met and transmits an overcurrent flag as a notification signal to the control unit.

In S26, the control unit determines whether the notification signal from the overcurrent monitoring circuit 44 continues for the determination time or longer. If the result is YES in S26, the control unit determines in S30 that the second condition is met and determines that an abnormality has occurred. The control unit then takes action in S40. If the result is NO in S26, the control unit determines that the second condition is not met.

In determining whether the second condition is met, the determination time may be set to a time longer than the maximum time for which the overcurrent state exists when the power is turned on or in overboost mode during an initial check. This prevents erroneous determination of an abnormality, since the first condition is met when the power is turned on or in overboost mode during an initial check but the second condition is not met. Alternatively, erroneous determinations may be prevented by the control unit changing the abnormality determination process depending on the situation, such as when the power is turned on. Next, an example of a process for preventing erroneous determinations will be described with reference to FIG. 9.

Figure 9 shows the process in which the control unit sets the judgment time to a different value depending on the situation, or masks the notification signal. Here, the power supply voltage equivalent to the pre-relay voltage VLa in Figure 1 is described as being monitored as the "monitored voltage". Specifically, the control unit sets the judgment time to a different value depending on the operating mode or power supply voltage of the boost device 301, or masks the notification signal in a specific operating mode or in a specific range of power supply voltage. In this way, the control unit judges an abnormality based on both external and internal information, including the notification from the overcurrent monitoring circuit 44, the power supply voltage monitoring value, and internal values such as the status code.

In S21 to S24 in FIG. 9, the success or failure of four judgment items related to "a specific operating mode or a specific monitoring voltage" is judged in order. The order of these judgments is arbitrary. In S21, it is judged whether the boost device 301 is being powered on. In general, when the power is turned on, erroneous judgments are likely to occur due to inrush current.

In S22, in the initial check that diagnoses circuit abnormalities at startup, it is determined whether it is time to temporarily increase the boost output target value. In the initial check, the boost output target value is set higher than the normal value to diagnose that the boost function is normal, which makes it easy for erroneous judgments to occur.

In S23, it is determined whether the power supply voltage is equal to or lower than a predetermined voltage threshold. The lower the power supply voltage, the larger the step-up ratio becomes, and a large current flows, making it more likely that an erroneous judgment will occur. In S24, it is determined whether the absolute value of the time rate of change of the power supply voltage is equal to or higher than a predetermined voltage fluctuation threshold, that is, whether the power supply voltage has suddenly fluctuated. For example, when the power supply voltage is interrupted for some reason and then restored, a large current may flow instantaneously, making it more likely that an erroneous judgment will occur.

If the answer is YES in any of S21 to S24, in S25 the control unit sets the judgment time longer than the reference value or masks the notification signal. By setting the judgment time longer than the reference value in a specific operating mode or a specific power supply voltage, the second condition is less likely to be satisfied, and erroneous judgment can be prevented. Furthermore, by masking the notification signal in a specific operating mode or a specific power supply voltage, the possibility of the second condition being satisfied is eliminated, and erroneous judgment can be reliably prevented. Note that in S23 and S24, instead of the power supply voltage VLa before the relay, the post-relay voltage VLb or the post-boost voltage VH may be compared with the threshold value as the "monitoring voltage".

Figure 10 shows an example of a procedure to be taken when an abnormality is determined. If the control unit determines an abnormality and the answer is YES in S41, the control unit stops the operation of the boost MOS 25 in S42, or changes the duty ratio to operate the boost MOS 25. Figure 4 shows an example of stopping the operation of the boost MOS 25, but depending on the state of the element failure, it is also possible to change the duty ratio and operate the boost MOS 25 in a limited manner.

The microcomputer 50 as a control unit further controls the driving of the motor 80 of the electric power steering device 99 using the power of the battery 15. As a measure when an abnormality is determined, the microcomputer 50 may further stop the driving of the motor 80 or limit the output of the motor 80 in S43. When the driving is stopped, only the communication of the input/output signals used for control may be continued, or the system may be shut down including the communication system.

(Functions and Effects of the First Embodiment)
As described above, in the first embodiment, the overcurrent monitoring circuit 44 does not determine an abnormality simply by detecting an overcurrent, but transmits a notification signal to the microcomputer 50 when the first condition is met. The microcomputer 50 determines an abnormality and takes action only when the second condition is met. This prevents the microcomputer 50 from erroneously determining an abnormality in the case of an overcurrent at power-on or during an initial check. Furthermore, if an abnormality is determined to be due to an element failure or the like, the microcomputer 50 stops the operation of the boost MOS 25, thereby preventing the PWM operation from continuing in a broken state.

In addition, in the first embodiment, unlike the conventional technology of Patent Document 1, a soft start circuit is not used, and when power is turned on or an initial check is performed, current is passed while detecting an overcurrent with respect to an overcurrent threshold set below the rated value of the boost MOS 25. In other words, while assuming that there is a high probability that the first condition will be satisfied when power is turned on or an initial check is performed, erroneous judgment is prevented by preventing the second condition from being satisfied. This simplifies the circuit configuration and shortens the start-up time.

Furthermore, when the microcontroller 50 receives a notification signal from the overcurrent monitoring circuit 44, in addition to determining whether the notification signal should continue based on the judgment time, it can also perform a comprehensive abnormality judgment by combining processing such as changing the judgment time based on the operating mode and power supply voltage, and masking the notification signal. This makes it possible to judge abnormalities and take measures according to the situation. Furthermore, when the design of the judgment conditions is changed due to power supply fluctuation testing or changes to the constants of external elements, it is easy to respond by changing the condition settings in software.

In addition, in the first embodiment, the boost MOS 25, the drive circuit 41, and the overcurrent monitoring circuit 44 are built into the same ASIC 40, which results in a compact layout on the board. Note that the ASIC 40 may also integrate functions other than the boost device. Also, since the microcomputer 50 is responsible for the function of the "control unit," this is advantageous in terms of computing power and communication with the outside.

Second Embodiment
Next, a second embodiment will be described with reference to FIG. 11. In the boost device 302 of the second embodiment, the drive circuit 42 in the ASIC 40 also functions as a "controller". In other words, the notification signal generated when the first condition is satisfied is not sent from the overcurrent monitoring circuit 44 of the ASIC 40 to the microcomputer 50, but is sent from the overcurrent monitoring circuit 44 inside the ASIC 40 to the drive circuit 42. The drive circuit 42 that receives the notification signal determines whether the second condition is satisfied, and when the second condition is satisfied, determines that an abnormality has occurred and takes action. Also, the drive circuit 42 may obtain information on the power supply voltage instead of the microcomputer 50.

The effects of the second embodiment can be interpreted in the same way as in the first embodiment by replacing "microcomputer 50" with "drive circuit 42" in the description of the control unit. When focusing only on the functions of overcurrent detection and abnormality determination, as shown by the dashed line in FIG. 11, the second embodiment does not require the microcomputer 50, so the boost device 302 can be configured more simply. In addition, when an abnormality is determined, the operation of the boost MOS 25 can be immediately stopped without communication delay, improving reliability.

However, in reality, the ASIC 40 cannot process the same amount of calculations as the microcomputer 50, so the microcomputer 50 is necessary for drive control calculations for the motor 80. Therefore, the drive circuit 42 may also serve as part of the function of the "control unit," so that the drive circuit 42 and the microcomputer 50 work together to share the function of the "control unit."

Other Embodiments
(a) The “first condition” in the overcurrent monitoring circuit may be satisfied when the number of overcurrent detections continuously or intermittently exceeds a predetermined number of times at each communication interval with the control unit, or, for example, when the integrated value of the current or the current squared value exceeds a threshold value at each communication interval with the control unit.

(b) Regarding the "second condition" in the control unit, the notification signal (e.g., an overcurrent flag) may be interpreted as "continuing" for a judgment time or longer as being interrupted for a short period of time, for example, within a predetermined time. In other words, only when the interruption time exceeds a predetermined time may the continuation not be satisfied and the timer reset. Also, instead of the judgment time, the success or failure of the second condition may be judged based on the number or frequency of receiving notification signals within a predetermined period of time.

(c) The boost switching element is not limited to a MOSFET, and may be configured with a FET other than a MOSFET or a bipolar transistor. The boost switching element, drive circuit, and overcurrent monitoring circuit are not limited to being built into the same ASIC 40, and may be directly mounted on a board or built into separate ICs. Also, a capacitor or the like may be used as a "power source" other than the battery 15.

(d) The present invention is not limited to use in driving an assist motor in an electric power steering device, but may also be used in driving any electric actuator or for outputting other electrical equipment.

The present invention is not limited to these embodiments, and can be implemented in various forms without departing from the spirit of the invention.

The control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described in the present disclosure may be realized by one or more dedicated computers configured by combining a processor and a memory programmed to execute one or more functions with a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transient tangible recording medium as instructions executed by the computer.

15 ... Battery (power source),
21... Coil,
25...Boost MOS (boost switching element),
301, 302...Boost device,
41 Drive circuit,
42 ... Drive circuit (control unit [second embodiment]),
44... Overcurrent monitoring circuit,
50...Microcomputer (control unit [first embodiment]).

Claims (13)

A boosting device that boosts and outputs an input power supply voltage,
a boost switching element (25) provided between one end of a coil (21) connected to a power source (15) and the other end of the coil and configured to boost the voltage of the other end of the coil by switching operation;
A drive circuit (41, 42) for PWM-operating the boost switching element;
an overcurrent monitoring circuit (44) for monitoring a current flowing through the boost switching element;
a control unit (50, 42) that judges an abnormality based on a notification from the overcurrent monitoring circuit and takes appropriate action;
Equipped with
the overcurrent monitoring circuit counts the number of overcurrent detections for each communication interval with the control unit regarding the state of the current flowing through the boost switching element, and when the number of overcurrent detections exceeds a predetermined number, or when an integrated value of the current or the squared value of the current for each communication interval with the control unit exceeds a threshold value, determines that a first condition is satisfied and transmits a notification signal to the control unit;
the control unit determines that a second condition is satisfied when the notification signal received from the overcurrent monitoring circuit continues for a predetermined determination time or longer, determines that an abnormality has occurred, and takes action;
The control unit sets the determination time to a different value depending on a plurality of situations including when the boost device is in operation, or masks the notification signal . The boost device of claim 1, wherein the control unit sets the judgment time to a different value depending on an operating mode or a monitored voltage, which is a voltage monitored in a circuit before or after boosting, during a period including when the boost device is in operation, or masks the notification signal in a specific operating mode or in a specific range of the monitored voltage. The boost device according to claim 2 , wherein the control unit sets the determination time to be longer than a reference value or masks the notification signal when the boost device is powered on. 4. The boost device according to claim 2 , wherein the control unit sets the determination time to be longer than a reference value or masks the notification signal when temporarily increasing the boost output target value during an initial check of the boost device. 5. The boost device according to claim 2 , wherein the control unit sets the determination time to be longer than a reference value or masks the notification signal when the monitored voltage is equal to or lower than a predetermined voltage threshold value. The boost device according to any one of claims 2 to 5, wherein the control unit sets the judgment time to be longer than a reference value or masks the notification signal when an absolute value of the time rate of change of the monitored voltage is equal to or greater than a predetermined voltage fluctuation threshold. A boosting device that boosts and outputs an input power supply voltage,
a boost switching element (25) provided between one end of a coil (21) connected to a power source (15) and the other end of the coil and configured to boost the voltage of the other end of the coil by switching operation;
A drive circuit (41, 42) for PWM-operating the boost switching element;
an overcurrent monitoring circuit (44) for monitoring a current flowing through the boost switching element;
a control unit (50, 42) that judges an abnormality based on a notification from the overcurrent monitoring circuit and takes appropriate action;
Equipped with
the overcurrent monitoring circuit counts the number of overcurrent detections for each communication interval with the control unit regarding the state of the current flowing through the boost switching element, and when the number of overcurrent detections exceeds a predetermined number, or when an integrated value of the current or the squared value of the current for each communication interval with the control unit exceeds a threshold value, determines that a first condition is satisfied and transmits a notification signal to the control unit;
the control unit determines whether a second condition is satisfied based on the number or frequency of reception of the notification signal within a predetermined period of time for the notification signal received from the overcurrent monitoring circuit, and when the second condition is satisfied, determines that an abnormality has occurred and takes action;
The control unit sets a determination threshold for the number or frequency of reception of the notification signal within a predetermined period to different values depending on a plurality of situations including when the boost device is in operation. 8. The boost device according to claim 1 , wherein each time the overcurrent monitoring circuit detects an overcurrent, the drive circuit forcibly turns off the boost switching element and keeps the element in the off state until the next duty-on timing. 9. The boost device according to claim 1 , wherein an overcurrent threshold used for overcurrent detection by said overcurrent monitoring circuit is variably set according to heat generation of said boost switching element. The boost device according to any one of claims 1 to 9 , wherein the control unit, as a measure taken when an abnormality is determined, stops operation of the boost switching element or changes a duty ratio to operate the boost switching element. The control unit further controls driving of a motor (80) using the power of the power source,
The boosting device according to claim 10 , wherein the control unit further stops driving the motor or limits an output of the motor as a measure to be taken when an abnormality is determined. The boost device according to any one of claims 1 to 11 , wherein the boost switching element, the drive circuit and the overcurrent monitoring circuit are built into a single IC (40). The booster device according to any one of claims 1 to 12 , wherein the drive circuit (42) also performs at least a part of the function of the control unit.

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