Voltage detection circuit and method for detecting gain failure of voltage detection circuit

Abstract

The present invention enables diagnosis of a gain failure during execution of normal control for controlling a rotary electric machine. To achieve this, a voltage detection circuit 1 for detecting an input voltage applied between two terminals has a voltage conversion circuit 115, a switching part 102, and a diagnostic circuit 100. The voltage conversion circuit 115 converts the input voltage with a predetermined gain and outputs the converted input voltage. The switching part 102 switches a voltage applied to the voltage conversion circuit 115 between the input voltage and a diagnostic input voltage. The diagnostic circuit 100 diagnoses a gain failure of the voltage conversion circuit 115 on the basis of a diagnostic output voltage output from the voltage conversion circuit 115 in a diagnosis period to which the diagnostic input voltage is applied. In the diagnosis period, the voltage conversion circuit 115 outputs the diagnostic output voltage, and a normal output voltage output from the voltage conversion circuit in response to the input voltage being applied immediately before the diagnosis period.

Description

Voltage detection circuit and method for detecting gain failure of voltage detection circuit

[0001] The present invention relates to a voltage detection circuit and a voltage detection method.

[0002] The voltage value of the high-voltage power supply (hereinafter referred to as HV voltage value) supplied to the rotating electric machine is used for torque control of the inverter that controls the rotating electric machine. The microcomputer (hereinafter referred to as MCU) of the inverter monitors the HV voltage value using a voltage detection circuit and controls the torque of the rotating electric machine based on the monitored HV voltage value.

[0003] Here, the measured value of the HV voltage may deviate from the expected value due to a change in gain caused by a fault in the voltage detection circuit. For example, as disclosed in Patent Document 1, a technique has been devised for diagnosing a gain fault so that the gain fault can be recognized on the microcomputer side.

[0004] JP 2012-186874 A

[0005] However, the above-mentioned conventional technology has a problem in that it is not possible to diagnose a gain failure while normal control for controlling a rotating electrical machine is being performed.

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to make it possible to diagnose a gain failure while normal control for controlling a rotating electrical machine is being carried out.

[0007] As one aspect for solving the above problem, a voltage detection circuit that detects an input voltage applied between two terminals includes a voltage conversion circuit that converts the input voltage with a predetermined gain and outputs it, a switching unit that switches the voltage applied to the voltage conversion circuit between the input voltage and a diagnostic input voltage, and a diagnostic circuit that diagnoses a gain failure of the voltage conversion circuit based on the diagnostic output voltage output from the voltage conversion circuit during a diagnostic period in which the diagnostic input voltage is applied, and is characterized in that during the diagnostic period, the voltage conversion circuit outputs, in addition to the diagnostic output voltage, the normal output voltage that was output from the voltage conversion circuit when the input voltage was applied immediately before the diagnostic period.

[0008] According to the present invention, it is possible to diagnose a gain failure while normal control for controlling a rotating electrical machine is being performed.

[0009] FIG. 1 is a diagram showing the configuration of a voltage detection circuit according to embodiment 1. FIG. 2 is a diagram showing the configuration of a diagnostic circuit according to embodiment 1. FIG. 3 is a sequence diagram showing diagnostic processing executed in the voltage detection circuit according to embodiment 1. FIG. 4 is a diagram showing the configuration of a diagnostic circuit according to embodiment 2. FIG. 5 is a sequence diagram showing diagnostic processing executed in the voltage detection circuit according to embodiment 2. FIG. 6 is a diagram showing the configuration of a voltage detection circuit according to embodiment 3. FIG. 7 is a diagram showing the configuration of a diagnostic circuit according to embodiment 3. FIG. 8 is a sequence diagram showing diagnostic processing executed in the voltage detection circuit according to embodiment 3.

[0010] Hereinafter, embodiments of the present application will be described with reference to the drawings. Note that the following embodiments do not limit the present invention, and not all of the components and combinations thereof described in the embodiments are necessarily essential to the solution of the invention. The number of each component in the following embodiments may be singular or plural, unless otherwise specified.

[0011] In the following embodiments, the same reference numerals are used to designate the same features as those in the previous embodiments, and the description of the latter embodiments will be omitted, with the focus being on the differences. Furthermore, in the following embodiments, a combination of part or all of one embodiment with part or all of another embodiment is also included in the present application as long as there is no contradiction and there is consistency.

[0012] In the following description, identical or similar components will be denoted by the same reference numeral. When there are multiple identical or similar components, they may be denoted by the same reference numeral with different subscripts. When there is no need to distinguish between multiple components, the subscripts may be omitted.

[0013] [Embodiment 1] (Configuration of voltage detection circuit 1 according to embodiment 1) Fig. 1 is a diagram showing the configuration of a voltage detection circuit 1 according to embodiment 1. The voltage detection circuit 1 is assumed to be mounted on a vehicle such as a hybrid vehicle, but is not limited to this.

[0014] The voltage detection circuit 1 has an HV voltage sensor function 109 and a diagnostic function 110. The HV voltage sensor function 109 and the diagnostic function 110 also include some functions of a microcomputer (hereinafter referred to as MCU) 103.

[0015] The HV voltage sensor function 109 includes a voltage conversion circuit 115. The voltage conversion circuit 115 includes a positive HV voltage 104, a negative HV voltage 105, and a differential amplifier circuit 115c.

[0016] Voltage conversion circuit 115 receives HV voltage 101 or the voltage of constant voltage source 114 and outputs first output circuit voltage 106, second output circuit voltage 107, and third output circuit voltage 108. HV voltage 101 is referred to as the normal input voltage. Constant voltage source 114 is referred to as the diagnostic input voltage. Voltage conversion circuit 115 converts HV voltage 101 to a voltage referenced to the GND of microcomputer 103 and divides it into a positive HV voltage 104 with a gain P and a negative HV voltage 105 with a gain N.

[0017] The positive HV voltage 104 is divided by gains P and N to a voltage level that can be input to the microcomputer 103, amplified by amplifier 115a, and output as first output circuit voltage 106. The negative HV voltage 105 is divided by gains P and N to a voltage level that can be input to the microcomputer 103, amplified by amplifier 115b, and output as second output circuit voltage 107.

[0018] The differential amplifier circuit 115c with a gain PN generates a third output circuit voltage 108 by amplifying the difference between the first output circuit voltage 106 and the second output circuit voltage 107, and branches the third output circuit voltage 108 to be outputted to the first input terminal 1081 and the second input terminal 1082. The third output circuit voltage 108 corresponds to a voltage obtained by combining the positive side HV voltage 104 and the negative side HV voltage 105, and is at a voltage level that can be inputted to the microcomputer 103.

[0019] The diagnostic function 110 includes a constant voltage source 114, a switching unit 102, and a diagnostic circuit 100. The switching unit 102 is a switch that switches the connection so that either the HV voltage 101 or the constant voltage source 114 is input to the voltage conversion circuit 115 in response to a control signal 111S output by a microcomputer 103.

[0020] The HV voltage 101 is a power source of high-voltage voltage supplied to, for example, a rotating electric machine (not shown) mounted on a vehicle. In this specification, the term "HV voltage 101" may refer to the voltage value of the "HV voltage 101" or the high-voltage power source of the "HV voltage 101."

[0021] The constant voltage source 114 is a fixed voltage source having the same level as the HV voltage 101, and may be, for example, an existing power source (15 V or 18 V) on the same board as the driver of the rotating electrical machine mounted on the vehicle. Note that the constant voltage source 114 may not be an existing power source, but may be a dedicated power source.

[0022] The third output circuit voltage 108 is branched and input to the diagnostic circuit 100 of the microcomputer 103 from a first input terminal 1081 and a second input terminal 1082 .

[0023] 2 is a diagram showing the configuration of the diagnostic circuit 100 according to embodiment 1. The diagnostic circuit 100 has a diagnostic input unit 112, a normal input unit 113, and a diagnostic unit 117.

[0024] The diagnostic input unit 112 receives the third output circuit voltage 108 output from the first input terminal 1081 via the second input terminal 1082 .

[0025] The third output circuit voltage 108 during the diagnostic period ΔT1 determined by the control signal 111S output from the microcomputer 103 is a diagnostic output voltage that is the output voltage of the voltage conversion circuit 115 to which the constant voltage source 114 is input, because the switching unit 102 is connected to the constant voltage source 114. The third output circuit voltage 108 during the normal period other than the diagnostic period ΔT1 is a normal output voltage that is the output voltage of the voltage conversion circuit 115 to which the HV voltage 101 is input, because the switching unit 102 is connected to the HV voltage 101.

[0026] The diagnostic input unit 112 performs AD (Analog to Digital) conversion on the input diagnostic output voltage. The diagnostic output voltage may be a physical value of the third output circuit voltage 108 converted by software of the microcomputer 103.

[0027] 2 is provided between the first input terminal 1081 and a branch point 1083 between the first input terminal 1081 and the second input terminal 1082. The voltage holding circuit 115d includes a diode 115d1, a resistor 115d2, and a capacitor 115d3. The anode of the diode 115d1 is connected to the output of the voltage conversion circuit 115. The resistor 115d2 is connected in parallel with the diode 115d1. The capacitor 115d3 is connected to the cathode of the diode 115d1 and holds the output voltage of the voltage conversion circuit 115.

[0028] The voltage holding circuit 115d holds the third output circuit voltage 108 immediately before each diagnostic period ΔT1 using a resistor 115d2 and a capacitor 115d3. Because the switching unit 102 is connected to the HV voltage 101 side, the third output circuit voltage 108 immediately before each diagnostic period ΔT1 is the normal output voltage, which is the output voltage of the voltage conversion circuit 115 to which the HV voltage 101 is input.

[0029] During each diagnostic period ΔT1, the normal input unit 113 receives a masked output voltage, in which the diagnostic output voltage is masked by the normal output voltage held in the voltage holding circuit 115d, via the first input terminal 1081.

[0030] Furthermore, during normal periods other than the diagnostic period ΔT1, the normal input unit 113 receives the third output circuit voltage 108 via the diode 115d1 and the first input terminal 1081. Because the switching unit 102 is connected to the HV voltage 101 side, the third output circuit voltage 108 during each normal period is the normal output voltage, which is the output voltage of the voltage conversion circuit 115 to which the HV voltage 101 is input.

[0031] (Diagnostic Processing According to the First Embodiment) FIG. 3 is a sequence diagram showing the diagnostic processing executed by the diagnostic circuit 100 according to the first embodiment.

[0032] The normal output voltage during periods other than the diagnostic period ΔT1 and the diagnostic output voltage during the diagnostic period ΔT1 are alternately switched and input to the diagnostic input unit 112. The timing of switching between the normal output voltage and the diagnostic output voltage is controlled by the microcomputer 103. The diagnostic output voltage is set to a voltage sufficiently lower than the HV voltage 101 (a voltage lower than the minimum voltage in the voltage range of the HV voltage 101).

[0033] When a gain failure occurs in the voltage conversion circuit 115, the diagnostic output voltage input from the diagnostic input unit 112 falls outside the predetermined range of the diagnostic threshold Vth1, and it is determined that a gain failure has occurred. The diagnostic threshold Vth1 is a value calculated by multiplying the constant voltage of the constant voltage source 114 by the circuit gain of the voltage conversion circuit 115.

[0034] In the example shown in Figure 3(a), during the diagnostic period ΔT1 from time t15 to t16 and the diagnostic period ΔT1 from time t17 to t18, the diagnostic output voltage deviates from the diagnostic threshold value Vth1 and falls outside the specified range, so it is determined that a gain failure has occurred in the voltage conversion circuit 115.

[0035] 3 can be arbitrarily set by the microcomputer 103. The timing of each diagnostic period ΔT1 corresponds to times t1 to t2, t3 to t4, t5 to t6, t7 to t8, t9 to t10, t11 to t12, t13 to t14, t15 to t16, t17 to t18, and t19 to t20.

[0036] Furthermore, the diagnostic period ΔT1 for each of times t1 to t2, t3 to t4, t5 to t6, t7 to t8, t9 to t10, t11 to t12, t13 to t14, t15 to t16, t17 to t18, and t19 to t20 is determined as follows: That is, the diagnostic period ΔT1 is determined so as to be longer than the time during which the microcomputer 103 can perform sampling (the task time of the microcomputer 103), and so as to minimize the drop in the HV voltage 101 based on the voltage holding performance of the voltage holding circuit 115d. The voltage holding performance of the voltage holding circuit 115d refers to the degree to which the mask output voltage described above drops from the normal output voltage after a certain period of time has elapsed.

[0037] 3B, the normal input unit 113 always receives a voltage equivalent to the normal output voltage because the diagnostic output voltage during the diagnostic period ΔT1 is masked by the voltage holding circuit 115d to produce a masked output voltage. If the diagnostic period ΔT1 is long, the voltage holding effect decreases, reducing the masking efficiency of the diagnostic output voltage, causing the diagnostic output voltage to appear as a voltage drop. For this reason, the diagnostic period ΔT1 is set as short as possible, as described above.

[0038] In the first embodiment, in order to detect a gain failure or abnormality of the voltage conversion circuit 115, the output voltage of the voltage conversion circuit 115 when the voltage of the constant voltage source 114 is applied to the input of the voltage conversion circuit 115 is compared with a threshold value to determine whether the output voltage is normal or abnormal. This makes it possible to check the overall gain of the voltage conversion circuit 115.

[0039] Furthermore, by switching between the HV voltage 101 and the constant voltage source 114 using the microcomputer 103, a normal output voltage and a diagnostic output voltage are alternately output from the voltage conversion circuit 115. As the normal output voltage used for normal control, a normal output voltage based on the HV voltage 101 is output during normal times, while during the diagnostic period, the normal output voltage immediately before the diagnostic period is output. This makes it possible to diagnose gain failures in the voltage conversion circuit 115 even during normal control, improving the failure detection rate and the reliability of the voltage detection circuit 1 including the voltage conversion circuit 115.

[0040] Furthermore, in embodiment 1, a redundant voltage detection circuit is provided in the voltage conversion circuit 115, and gain failure diagnosis is performed based on a comparison of the diagnostic results from these two circuits, thereby enabling cost and circuit area to be reduced compared to conventional specifications.

[0041] [Embodiment 2] (Configuration of diagnostic circuit 100B according to embodiment 2) Figure 4 is a diagram showing the configuration of a diagnostic circuit 100B according to embodiment 2. The diagnostic circuit 100B included in the voltage detection circuit 1B according to embodiment 2 differs from the diagnostic circuit 100 according to embodiment 1 in that it has a first AD conversion unit 112B as a hardware processing unit instead of the diagnostic input unit 112. It also differs from the diagnostic circuit 100 according to embodiment 1 in that it has a second AD conversion unit 113B as a hardware processing unit instead of the normal input unit 113. The diagnostic circuit 100B also differs from the diagnostic circuit 100 in that it has a signal switching unit 111 as a hardware processing unit, and a physical value converted diagnosis output voltage output unit 12B, a physical value converted normal output voltage output unit 13B, and a diagnostic unit 117 as software processing units.

[0042] The first AD converter 112B performs AD conversion of the input third output circuit voltage 108. During a diagnostic period ΔT2 determined by a control signal 111S output from the signal switch 111, the third output circuit voltage 108 input to the first AD converter 112B becomes a diagnostic output voltage, which is the output voltage of the voltage conversion circuit 115 to which the constant voltage source 114 is input. Furthermore, during a normal period other than the diagnostic period ΔT2, the third output circuit voltage 108 becomes a normal output voltage, which is the output voltage of the voltage conversion circuit 115 to which the HV voltage 101 is input.

[0043] The physical value converted diagnostic output voltage output section 12B converts the diagnostic output voltage that has been AD converted by the first AD converter 112B into a physical value. The diagnostic section 117 performs diagnosis based on the diagnostic output voltage converted by the physical value converted diagnostic output voltage output section 12B.

[0044] The second AD conversion unit 113B performs AD conversion on the input third output circuit voltage 108. The third output circuit voltage 108 input to the second AD conversion unit 113B is the diagnostic output voltage during the diagnostic period ΔT2 and is the normal output voltage during the normal period, similar to the first AD conversion unit 112B.

[0045] The physical value converted normal output voltage output unit 13B converts the normal output voltage that has been AD converted by the second AD converter 113B into a physical value. The physical value converted normal output voltage output unit 13B also holds the physical value of the normal output voltage immediately before each diagnostic period ΔT2, and outputs the held physical value of the normal output voltage in each diagnostic period ΔT2 immediately thereafter.

[0046] The normal output voltage output by the physical value converted normal output voltage output unit 13B is used for normal control of a rotating electrical machine (not shown) by the microcomputer 103.

[0047] (Diagnostic Processing According to the Second Embodiment) FIG. 5 is a sequence diagram showing the diagnostic processing executed by the diagnostic circuit 100B according to the second embodiment.

[0048] 5(a) and 5(b), the third output circuit voltage 108 is the diagnostic output voltage V4 during the diagnostic period ΔT2 in which the control signal 111S output by the signal switching unit 111 is turned ON. On the other hand, during periods other than the diagnostic period ΔT2 in which the control signal 111S is turned OFF, the third output circuit voltage 108 is the normal output voltage V3.

[0049] The microcomputer 103 performs digital conversion on the input third output circuit voltage 108 by separating it into a first AD conversion by the first AD conversion unit 112B and a second AD conversion by the second AD conversion unit 113B. As shown in Fig. 5(c), the microcomputer 103 controls the timing of the first AD conversion and the second AD conversion using an interrupt of the control signal 111S.

[0050] The physical value converted diagnostic output voltage output unit 12B converts the diagnostic output voltage that has undergone the first AD conversion into a physical value by software. The diagnostic output voltage is set to a voltage that is sufficiently lower than the HV voltage 101 (a voltage that is lower than the minimum voltage in the voltage range of the HV voltage 101).

[0051] When a gain failure occurs in the voltage conversion circuit 115, the physical value of the diagnostic output voltage converted by the physical value conversion diagnostic output voltage output unit 12B falls outside the predetermined range of the diagnostic threshold value Vth2, and it is determined that a gain failure has occurred. The diagnostic threshold value Vth2 is the physical value of the constant voltage value of the constant voltage source 114.

[0052] The second AD conversion unit 113B converts the third output circuit voltage 108 that has undergone the second AD conversion into a physical value using software.

[0053] In the example shown in Figure 5(c), during the diagnostic period ΔT2 from time t29 to t30 and the diagnostic period ΔT2 from time t31 to t32, the diagnostic output voltage deviates from the diagnostic threshold value Vth2 and falls outside the specified range, and it is determined that a gain failure has occurred in the voltage conversion circuit 115.

[0054] The timing of each diagnostic period ΔT2 from time t21 to t22, time t23 to t24, time t25 to t26, time t27 to t28, time t29 to t30, time t31 to t32, and time t33 onward shown in FIG.

[0055] Furthermore, each of the diagnostic periods ΔT2 from time t21 to t22, time t23 to t24, time t25 to t26, time t27 to t28, time t29 to t30, time t31 to t32, and time t33 onward is determined as follows: That is, the diagnostic period ΔT2 is determined to be longer than the time available for sampling by the microcomputer 103 (the task time of the microcomputer 103), and to be as short as possible so that fluctuations in the HV voltage 101 are recognized as quickly as possible. In other words, the length of the diagnostic period ΔT2 is determined based on the sampling performance of the microcomputer 103 that performs AD conversion.

[0056] If the diagnostic period ΔT2 is long, it will take longer to recognize fluctuations in the HV voltage 101, increasing the deviation from the real-time HV voltage 101. For this reason, the diagnostic period ΔT2 is set as short as possible, as described above.

[0057] (Effects of Second Embodiment) In the second embodiment, by using the hardware of the microcomputer 103, it is possible to diagnose a gain failure of the voltage conversion circuit 115 without increasing the processing load of the microcomputer 103.

[0058] (Variation of Second Embodiment) The voltage detection circuit 1B monitors whether or not there is a failure in the first input terminal 1081 and the second input terminal 1082. If a failure occurs in the first input terminal 1081, the physical value converted normal output voltage output unit 13B converts the normal output voltage that has been AD converted by the first AD converter 112B during the normal period into a physical value, outputs the converted physical value, and holds the physical value of the normal output voltage. The physical value converted normal output voltage output unit 13B then outputs the held physical value during the diagnostic period immediately following this normal period. Furthermore, if a failure occurs in the second input terminal 1082, the physical value converted diagnostic output voltage output unit 12B may convert the diagnostic output voltage that has been AD converted by the second AD converter 113B into a physical value and output the physical value.

[0059] In this way, in the event of a terminal failure, the function of the failed terminal is shifted to the normal terminal side and processing continues, allowing the microcontroller 103 to continue control of the rotating electric machine and diagnose gain failures, thereby increasing the failure tolerance of the rotating electric machine control system.

[0060] 6 is a diagram showing the configuration of a voltage detection circuit 1C according to embodiment 3. The voltage detection circuit 1C is different from the voltage detection circuit 1 according to embodiment 2 in that it does not include the first input terminal 1081 and includes a diagnostic circuit 100C instead of the diagnostic circuit 100, but is otherwise similar.

[0061] 7 is a diagram showing the configuration of a diagnostic circuit 100C according to the third embodiment. The diagnostic circuit 100C differs from the diagnostic circuit 100B according to the second embodiment in that it does not include a first AD conversion unit 112B and has an AD conversion unit 113C instead of the second AD conversion unit 113B as a hardware processing unit. Furthermore, compared to the diagnostic circuit 100B, the diagnostic circuit 100C has a physical value conversion unit 15C, a normal-state output voltage output unit 13C, a diagnostic-state output voltage output unit 12C, and a diagnostic unit 117 instead of the physical value converted diagnostic-state output voltage output unit 12B and the physical value converted normal-state output voltage output unit 13B.

[0062] The AD conversion unit 113C performs AD conversion on the input third output circuit voltage 108. During a diagnostic period ΔT3 determined by a control signal 111S output from the signal switching unit 111, the third output circuit voltage 108 input to the AD conversion unit 113C becomes a diagnostic output voltage, which is the output voltage of the voltage conversion circuit 115 to which the constant voltage source 114 is input. Furthermore, during a normal period other than the diagnostic period ΔT3, the third output circuit voltage 108 becomes a normal output voltage, which is the output voltage of the voltage conversion circuit 115 to which the HV voltage 101 is input. In other words, the third output circuit voltage 108 includes the normal output voltage and the diagnostic output voltage.

[0063] The physical value converter 15C converts the third output circuit voltage 108 that has been AD converted by the AD converter 113C into a physical value.

[0064] The normal-time output voltage output unit 13C outputs a normal-time output voltage during a normal period, which is part of the third output circuit voltage 108 converted into a physical value by the physical value conversion unit 15C. The normal-time output voltage is used for normal control of a rotating electric machine (not shown) by the microcomputer 103.

[0065] The diagnostic output voltage output unit 12C outputs the diagnostic output voltage during the diagnostic period ΔT3 from the third output circuit voltage 108 converted into a physical value by the physical value conversion unit 15C. The diagnosis unit 117 performs diagnosis based on the diagnostic output voltage extracted by the diagnostic output voltage output unit 12C.

[0066] In FIG. 7, the positions of the normal output voltage output section 13C and the diagnostic output voltage output section 12C may be interchanged.

[0067] (Diagnostic Processing According to the Third Embodiment) FIG. 8 is a sequence diagram showing the diagnostic processing executed by the diagnostic circuit 100C according to the third embodiment.

[0068] 8(a) and 8(b), the third output circuit voltage 108 is the diagnostic output voltage V6 during the diagnostic period ΔT3 when the control signal 111S output by the signal switching unit 111 is turned ON. On the other hand, during the normal period when the control signal 111S is turned OFF, the third output circuit voltage 108 is the normal output voltage V5.

[0069] The microcomputer 103 performs AD conversion on the input third output circuit voltage 108 using an AD conversion unit 113C and conversion into a physical value using a physical value conversion unit 15C. Then, the microcomputer 103 outputs voltages separately for the third output circuit voltage 108 after conversion into a physical value: a normal output voltage output by a normal output voltage output unit 13C and a diagnostic output voltage output by a diagnostic output voltage output unit 12C. The microcomputer 103 uses an interrupt of the control signal 111S to control the timing of outputting the normal output voltage by the normal output voltage output unit 13C and the timing of outputting the diagnostic output voltage by the diagnostic output voltage output unit 12C.

[0070] The normal output voltage output unit 13C uses software to output the physical value of the normal output voltage from the third output circuit voltage 108. The diagnostic output voltage output unit 12C uses software to output the physical value of the diagnostic output voltage from the third output circuit voltage 108. The diagnostic output voltage is set to a voltage sufficiently lower than the HV voltage (a voltage lower than the minimum voltage of the HV voltage range).

[0071] When a gain failure occurs in the voltage conversion circuit 115, the physical value of the diagnostic output voltage output by the diagnostic output voltage output unit 12C falls outside the predetermined range of the diagnostic threshold Vth3, and it is determined that a gain failure has occurred. The diagnostic threshold Vth3 is the constant voltage value of the constant voltage source 114.

[0072] In the example shown in Figure 8 (c), during the diagnostic period ΔT3 from time t49 to t50 and the diagnostic period ΔT3 from time t51 to t52, the diagnostic output voltage deviates from the diagnostic threshold Vth3 and falls outside the specified range, and it is determined that a gain failure has occurred in the voltage conversion circuit 115.

[0073] The timing of each diagnostic period ΔT3 from time t41 to t42, time t43 to t44, time t45 to t46, time t47 to t48, time t49 to t50, time t51 to t52, and time t53 onward shown in FIG.

[0074] Furthermore, each of the diagnostic periods ΔT3 from time t41 to t42, time t43 to t44, time t45 to t46, time t47 to t48, time t49 to t50, time t51 to t52, and time t53 onward is determined as follows: That is, the diagnostic period ΔT3 is determined to be longer than the time available for sampling by the microcomputer 103 (the task time of the microcomputer 103), and to be as short as possible so that fluctuations in the HV voltage 101 are recognized as quickly as possible. In other words, the length of the diagnostic period ΔT3 is determined based on the sampling performance and task processing performance of the microcomputer 103 that performs the AD conversion.

[0075] If the diagnostic period ΔT3 is long, it will take longer to recognize fluctuations in the HV voltage 101, increasing the deviation from the real-time HV voltage 101. For this reason, the diagnostic period ΔT3 is set as short as possible, as described above.

[0076] (Effects of Third Embodiment) In the third embodiment, the input to the microcomputer 103 is one input to the AD conversion unit 113C, which makes it possible to save input pins of the microcomputer 103 and reduce the size of the voltage detection circuit 1C.

[0077] Although the embodiments of the present application have been described in detail above, the present disclosure is not limited to the above-described embodiments and can be modified in various ways without departing from the spirit of the present invention. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those including all of the described configurations. Furthermore, some of the configurations of the above-described embodiments can be added to, deleted from, or replaced with other configurations.

[0078] 1, 1B, 1C: voltage detection circuit, 12B: physical value converted diagnostic output voltage output unit, 12C: diagnostic output voltage output unit, 13B: physical value converted normal output voltage output unit, 13C: normal output voltage output unit, 15C: physical value conversion unit, 100, 100B, 100C: diagnostic circuit, 101: HV voltage, 102: switching unit, 103: microcomputer, 108: third output circuit voltage, 111: signal switching unit, 1 11S: control signal, 112: diagnostic input section, 112B: first AD conversion section, 113: normal input section, 113B: second AD conversion section, 113C: AD conversion section, 114: constant voltage source, 115: voltage conversion circuit, 115d: voltage holding circuit, 115d1: diode, 115d2: resistor, 115d3: capacitor, 117: diagnostic section, 1081: first input terminal, 1082: second input terminal.

Claims

1. A voltage detection circuit that detects an input voltage applied between two terminals, comprising: a voltage conversion circuit that converts the input voltage with a predetermined gain and outputs it; a switching unit that switches the voltage applied to the voltage conversion circuit between the input voltage and a diagnosis input voltage; and a diagnostic circuit that diagnoses a gain failure of the voltage conversion circuit based on a diagnosis output voltage output from the voltage conversion circuit during a diagnostic period in which the diagnostic input voltage is applied, wherein the voltage conversion circuit outputs, during the diagnostic period, in addition to the diagnostic output voltage, a normal output voltage that was output from the voltage conversion circuit when the input voltage was applied immediately before the diagnostic period.

2. A voltage detection circuit as claimed in claim 1, comprising: a first input terminal and a second input terminal for inputting the output voltage output from said voltage conversion circuit; and a voltage holding circuit comprising a diode having an anode connected to the output of said voltage conversion circuit, a resistor connected in parallel with said diode, and a capacitor connected to the cathode of said diode, said voltage holding circuit being provided between the branch point of said first input terminal and said second input terminal and said first input terminal.

3. A voltage detection circuit as claimed in claim 2, characterized in that the length of said diagnostic period is determined based on the holding performance of said voltage holding circuit to hold the output voltage of said voltage conversion circuit.

4. A voltage detection circuit as claimed in claim 1, comprising: a first input terminal and a second input terminal for inputting an output voltage output from said voltage conversion circuit; a signal switching section for outputting to said switching section a control signal for switching a voltage to be applied to said voltage conversion circuit between said input voltage and said diagnostic input voltage; a first AD conversion section for inputting an output voltage including said normal output voltage and said diagnostic output voltage output from said voltage conversion circuit via said second input terminal and performing AD (Analog to Digital) conversion of said output voltage; a physical value converted diagnostic output voltage output section for converting the diagnostic output voltage AD converted by said first AD conversion section into a physical value and outputting the physical value to said diagnostic circuit; and a second AD conversion section for inputting an output voltage including said normal output voltage and said diagnostic output voltage output from said voltage conversion circuit via said first input terminal and performing AD conversion of said output voltage. a physical value converted normal-state output voltage output unit that converts the normal-state output voltage output from the voltage conversion circuit during a normal period in which the input voltage is applied to the voltage conversion circuit, outputs the converted normal-state output voltage, holds the physical value of the normal-state output voltage, and outputs the held physical value during the diagnostic period immediately following the normal period.

5. A voltage detection circuit as claimed in claim 4, characterized in that the time length of said diagnostic period is determined based on the sampling performance of a microcomputer which performs said AD conversion.

6. A voltage detection circuit as claimed in claim 4, comprising: a voltage detection circuit which monitors the presence or absence of a fault in the first input terminal and the second input terminal; if a fault occurs in the first input terminal, the physical value converted normal output voltage output unit converts the normal output voltage, which has been AD converted by the first AD conversion unit during the normal period, into a physical value, outputs the physical value, holds the physical value of the normal output voltage, and outputs the held physical value during the diagnostic period immediately following the normal period; and if a fault occurs in the second input terminal, the physical value converted diagnostic output voltage output unit converts the diagnostic output voltage, which has been AD converted by the second AD conversion unit, into a physical value, and outputs the physical value.

7. A voltage detection circuit as claimed in claim 1, comprising: a signal switching section which outputs to the switching section a control signal for switching the voltage applied to the voltage conversion circuit between the input voltage and the diagnostic input voltage; an AD conversion section which performs AD (Analog to Digital) conversion of the output voltage including the normal output voltage and the diagnostic output voltage output from the voltage conversion circuit; a physical value conversion section which converts the output voltage after the AD conversion by the AD conversion section into a physical value; a normal output voltage output section which converts the normal output voltage output from the voltage conversion circuit during a normal period in which the input voltage is applied to the voltage conversion circuit into a physical value and outputs it, holds the physical value of the normal output voltage, and outputs the held physical value during the diagnostic period immediately following the normal period; and a diagnostic output voltage output section which converts the diagnostic output voltage output from the voltage conversion circuit during the diagnostic period into a physical value and outputs it.

8. A voltage detection circuit as claimed in claim 6, characterized in that the length of said diagnostic period is determined based on the sampling performance and task processing performance of a microcomputer which performs said AD conversion.

9. A gain failure detection method for a voltage detection circuit, executed by a voltage detection circuit that detects an input voltage applied between two terminals, wherein the voltage detection circuit has: a voltage conversion circuit that converts the input voltage with a predetermined gain and outputs the converted voltage; a switching unit that switches the voltage to be applied to the voltage conversion circuit between the input voltage and a diagnosis input voltage; and a diagnostic circuit that diagnoses a gain failure of the voltage conversion circuit based on a diagnosis output voltage output from the voltage conversion circuit during a diagnostic period in which the diagnostic input voltage is applied, wherein the voltage conversion circuit outputs, during the diagnostic period, in addition to the diagnostic output voltage, a normal output voltage output from the voltage conversion circuit when the input voltage is applied immediately before the diagnostic period.

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