JP2007028812A - Power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply unit capable of preventing a failure from spreading to a second stage step-down circuit when a first stage step-down circuit fails and restarts in the power supply having two stages of step-down circuits. <P>SOLUTION: The first step-down circuit 1 outputs an input voltage Vin reduced to a voltage V1, and the second step-down circuit 2 steps down the voltage V1 to a voltage V2. If the power supply is started, a CPU 3 turns off a switch 8 to stop the power supply to a peripheral circuit 7, and diagnoses whether the first step-down circuit 1 fails or not on the basis of a voltage V1 detected in a voltage detection circuit 4. If it is determined that the first step-down circuit 1 does not fail, the CPU 3 turns on the switch 8 to supply the power to the peripheral circuit 7. When a diagnosis is performed, the CPU 3 supplies a clock and the power to minimum peripheral module necessary for the diagnosis, so that an element temperature may not exceed an allowable temperature by suppressing loss of the second step-down circuit 2 during the diagnosis. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power supply apparatus that steps down a voltage of a battery or the like and supplies power to a load.

  In a power supply apparatus that steps down and stabilizes the input voltage, a loss that is calculated by multiplying the difference between the input power and the output power and the consumption current on the output side occurs. For this reason, there is known a power supply device that consumes a large amount of current by providing two stages of step-down circuits in series to step down the output voltage in two stages (see, for example, Patent Document 1). By making the step-down circuit two stages, the loss is dispersed and the temperature rise of the step-down circuit is suppressed.

JP 2001-241842 A

  However, in such a configuration that steps down in two stages, when an abnormality occurs in the first step-down circuit and the step-down operation cannot be performed, the input / output voltage difference in the second step-down circuit becomes large. As a result, there has been a problem that the loss at the second stage is increased, the element temperature is increased, and the failure of the first step-down voltage circuit cascades to the second step-down voltage circuit.

  The present invention includes a first step-down circuit for stepping down an input voltage to a first voltage and outputting the voltage, and a second step-down circuit for stepping down and outputting the first voltage to a second voltage. This is applied to a power supply device that supplies output power from a load circuit. Then, the output voltage of the first step-down circuit is detected by the detector, and the determination unit determines whether or not the first step-down circuit is out of order based on the detected output voltage. When the power supply device is activated, the control means activates the load circuit in a low current consumption operation state that operates at a current lower than that in the normal activation operation state, and when the determination means determines that the first step-down circuit has not failed. The load circuit state is switched from the low current consumption operation state to the normal startup operation state.

  According to the present invention, when the power supply device is activated, the load circuit is activated in a low current consumption operation state that operates at a current lower than that in the normal activation operation state. Since the state of the load circuit is switched to the normal startup operation state, it is possible to prevent the failure of the first step-down circuit from spreading to the second step-down circuit.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a power supply device according to the present invention. This power supply device is mounted on a vehicle, and a voltage Vin of a battery (not shown) is stepped down to a predetermined voltage V2 by a first step-down voltage circuit 1 and a second voltage step-down circuit 2 connected in series, and the stepped-down voltage V2 is loaded. To an ECU (Electronic Control Unite) 5. The voltage V1 output from the first step-down circuit 1 is detected by the voltage detection circuit 4. A power transistor or the like is used for the step-down circuits 1 and 2.

  The unstabilized input voltage Vin is stepped down to the voltage V1 (<Vin) by the first step-down circuit 1, and the output voltage V1 is further stepped down to the voltage V2 (<V1) by the second step-down circuit 2. In this way, by providing two stages of step-down circuits 1 and 2 and stepping down the input voltage Vin to voltage V2 in two stages, the loss due to the step-down is distributed to the two step-down circuits 1 and 2. 1 and 2 can prevent an excessive increase in temperature, simplify the heat dissipation mechanism, and reduce the size of the entire apparatus.

  A blocking circuit 6 is provided between the input terminal of the input voltage Vin and the first step-down circuit 1. The cutoff circuit 6 includes a switch 61 that turns on / off the input voltage of the first step-down circuit 1 and a holding circuit 62 that performs on / off control of the switch 61 and a holding operation of the on / off state. The holding circuit 62 is controlled by an instruction from the CPU 3 provided in the ECU 5. The holding circuit 62 uses the input voltage Vin directly input from the battery as a power source, and power is supplied even when the switch 61 is in the OFF state.

  The ECU 5 that is a load of the power supply device includes a CPU 3 and a peripheral circuit 7 that are provided to control individual functions of the ECU 5. The peripheral circuit 7 has a hard configuration such as a sensor input / output circuit and a booster circuit. The input voltage V2 of the peripheral circuit 7 is turned on / off by the switch 8. The control of the holding circuit 62 and the on / off control of the switch 8 described above are performed by the CPU 3. When the power supply device is activated, the switch 8 of the peripheral circuit 7 is turned off, and the peripheral circuit 7 is activated with the power supply cut off.

  Inside the CPU 3, a core 31 and other peripheral modules are provided. The peripheral modules include a RAM / ROM 32, an A / D converter 33, general-purpose ports 34 and 35, an FRC (FreeRunCounter) 36, a timer 37, an oscillation circuit 38, and the like. The RAM / ROM 32 stores various data and programs for operating the core. The A / D converter 33 converts the voltage value (analog value) input from the voltage detection circuit 4 into a digital value, and stores the digitally converted voltage value therein.

  The general-purpose ports 34 and 35 output a signal to the outside of the CPU 3 based on a command sent from the core 31. Based on the clock output from the oscillation circuit 38 and the program stored in the RAM / ROM 32, the core 31 acquires and determines information such as the A / D converter 33 and the timer 37, and the general-purpose port. 34 and 35 are operated.

  FIG. 2 is a flowchart showing the control operation of the CPU 3, and shows a series of processing procedures relating to the diagnostic processing of the first step-down circuit 1 performed when the power supply device is activated. When the reset release of the CPU 3 by hardware is performed, step S1 in FIG. 2 is executed. The CPU 3 is set to stop power supply and clock supply to the peripheral modules 32 to 38 in the CPU immediately after releasing the hard reset. Here, the multiplication rate of the oscillation circuit 38 is lowered to set the clock frequency to the minimum, and the power supply and clock supply to peripheral modules other than the core 31 and the oscillation circuit 38 are stopped.

  In step S1, power supply and clock supply to the A / D converter 33 required for diagnosis of the voltage V1 input from the voltage detection circuit 4 are started. In step S2, the A / D converter 33 is initialized. In step S3, similarly to the A / D conversion unit 33, power supply and clock supply to the timer 37 necessary for diagnosis of the voltage V1 are started. Thus, in this embodiment, the low current consumption state is set when the CPU is activated. Then, after initializing the timer 37 in step S4, the timer 37 is started in step S5.

  In step S6, it is determined whether or not the voltage V1 read from the voltage detection circuit 4, that is, the output voltage V1 of the first step-down circuit 1 is equal to or lower than a preset threshold value Vth. This threshold value Vth is a voltage value for determining whether or not the first step-down voltage circuit 1 is operating normally, and is set slightly higher than the output voltage V1 when the first voltage step-down circuit 1 is operating normally. . If it is determined in step S6 that the output voltage V1 is equal to or lower than the threshold value Vth, the process proceeds to step S7, and if it is determined that the output voltage V1 exceeds the threshold value Vth, the process proceeds to step S10.

  In step S7, it is determined whether or not the state of V1 ≦ Vth has continued for a predetermined time Tth. Here, the reason for determining the state continuation time is to prevent erroneous determination due to the fact that noise is mixed in the signal input from the voltage detection circuit 4 to the A / D converter 33 and V1 temporarily fluctuates. It is. In this case, the predetermined time Tth for determining normality / abnormality is set to about several milliseconds to several tens of milliseconds.

  If it is determined in step S7 that the state of V1 ≦ Vth has continued for a predetermined time Tth, the process proceeds to step S8, and if it is determined not to continue, the process returns to step S6. When the process proceeds from step S7 to step S8, power supply and clock supply to the other peripheral modules of the CPU 3 are started, and the normal power supply operation state is changed from the low current consumption state described above. In step S9, the switch 8 is turned on to supply power to the peripheral circuit 7, and thereafter a normal startup routine is executed.

  On the other hand, if it is determined in step S6 that V1> Vth and the process proceeds to step S10, it is determined in step S10 whether the state of V1> Vth has continued for the time Tth. Until the duration of the state of V1 ≦ Vth reaches Tth, NO is determined in step S10, and the process returns to step S6. When the duration of the state of V1> Vth becomes Tth, it is determined as YES in step S10, that is, it is determined that the first step-down voltage circuit 1 is not operating normally, and the process proceeds to step S11. In step S11, a signal instructing to shut off the power is transmitted to the holding circuit 62, and the series of startup / diagnosis operations is terminated. When a cutoff signal is input from the CPU 3 to the holding circuit 62, the holding circuit 62 turns off the switch 61 and holds the off state.

  3 and 4 are diagrams showing changes in voltages Vin, V1, V2, current consumption of the ECU 5 and loss of the second step-down circuit 2 after the power is turned on again. FIG. 3 shows a case where the first step-down circuit 1 is normal, and FIG. 4 shows a case where the first step-down circuit 1 is not operating normally. The terminal voltage of the battery is 14V, and the input voltage Vin changes from 0V to 14V when the power is turned on again. Here, the first step-down circuit 1 is configured to step down the input voltage to 6V and output, and the second step-down circuit 2 is configured to step down the input voltage to 5V and output it. Therefore, when the power is turned on again, the voltage V1 increases from 0V to 6V, and the voltage V2 increases from 0V to 5V.

  The current consumption of the ECU 5 at the time of startup is almost the current consumption of the CPU 3, and the current consumption in the normal startup routine is set to 1A. In the present embodiment, as described above, at the time of voltage diagnosis, the CPU 3 operates in a low current consumption state. When the first voltage step-down circuit 1 is determined to be normal as a result of the voltage diagnosis, the CPU 3 operates in a normal startup routine. Is set.

  In the present embodiment, the current consumed by the normal activation routine is 1 A, but at the time of activation, the CPU 3 is set in the low power consumption state and the peripheral circuit 7 is also in the power cut-off state. The current consumption is controlled to be 0.1A. At this time, the loss of the second step-down circuit 2 at the time of voltage diagnosis is suppressed to (6V−5V) × 0.1A = 0.1W. As a result of the voltage diagnosis, when it is determined as normal and the operation is switched to the normal startup routine, the current consumption increases to 1A, and the loss of the second step-down circuit 2 also increases to (6V-5V) × 1A = 1W.

  On the other hand, when the first step-down circuit 1 fails and the step-down operation cannot be performed, the output voltage V1 of the first step-down circuit 1 becomes 14 V, which is the same as the input voltage Vin, as shown in FIG. At this time, the input voltage of the second step-down circuit 2 becomes 14V, but the output voltage V2 is maintained at 5V, and the input / output voltage difference increases to 9V. However, since the current consumption at the time of voltage diagnosis is reduced to 0.1 A, the loss of the second step-down circuit 2 is kept low at (14V-5V) × 0.1A = 0.9W.

  By the way, in the case of a conventional power supply device, the CPU 3 operates in a normal startup routine, and the peripheral circuit 7 is not turned off, so that the current consumption of the ECU 5 is 1 A from the startup. Therefore, the loss of the second step-down circuit 2 when the first step-down circuit 1 breaks down is (14V-5V) × 1A = 9 W, which is larger than normal (1 W), and the temperature of the second step-down circuit 2 increases rapidly. There was a case of failure. However, in the case of the present embodiment, as shown in FIG. 4, the loss is reduced to 0.9 W, which is the same level as normal, and the failure of the first step-down circuit 1 is propagated to the second step-down circuit 2. Can be prevented.

[Modification 1]
In the above-described embodiment, the switch 8 is turned off and the peripheral circuit 7 is turned off to reduce the power consumption of the ECU 5 until it is determined normal by the voltage diagnosis from the start. However, until the initial setting of the CPU 3 is completed from the start-up, the current consumption of the CPU 3 occupies most of the current consumption of the ECU 5, and since the CPU 3 operates in the low current consumption state, However, the current consumption of the ECU 5 does not increase so much.

  Therefore, the switch 8 may be turned on at the time of startup, and the power supply to the peripheral circuit 7 may be cut off by turning off the switch 8 when it is determined to be abnormal. For example, when there is a peripheral circuit that starts up regardless of the start of the CPU 3, it is preferable to cut off the power supply to the peripheral circuit when the CPU detects an abnormality.

[Modification 2]
In the above-described embodiment, as shown in FIG. 2, when the first step-down voltage circuit 1 is determined to be abnormal, control is performed so as to shut off the power supply of the ECU 5 itself. You may make it maintain a state. In this case, since the loss (0.9 W) of the second step-down circuit 2 is lower than 1 W in the normal startup routine as shown in FIG. 4, it is possible to prevent a failure from spreading to the second step-down circuit 2. In the meantime, the occurrence of abnormality may be notified to the host ECU through a communication circuit or the like. Of course, when such a notification operation is completed, the power may be shut off.

[Modification 3]
5 and 6 are diagrams illustrating a third modification. FIG. 5 shows an assembled state of the step-down element 9 used in the second step-down circuit 2 to the circuit board 11. The step-down element 9 is fixed to a heat capacity member 10 provided on the circuit board 11. In general, the step-down element 9 itself has a heat dissipation structure. However, in Modification 3, a heat capacity member 10 made of a metal block or the like is further provided as a heat countermeasure. Thereby, the heat capacity of the member whose temperature is increased by heat generation is increased, and the degree of temperature increase of the step-down element 9 can be reduced. The heat given to the heat capacity member 10 is radiated to the housing 12 to which the circuit board 11 is fixed via a heat radiation path as indicated by a broken line.

  FIG. 6 is a diagram illustrating changes in voltages Vin, V1, V2, current consumption of ECU 5, loss of second step-down circuit 2, and temperature of step-down element 9 when heat capacity member 10 is provided. FIG. 6 shows a case where the first step-down circuit 1 fails and cannot perform step-down operation. By the way, when the CPU 3 is operated with low current consumption, which of the peripheral modules inside the CPU can be stopped, and the current consumption at that time differs depending on the CPU. Further, when the power supply is supplied to the peripheral circuit 7 from the start of startup, the current consumption becomes larger than that shown in FIGS. In FIG. 6, it is assumed that the CPU 3 is operated with low current consumption and the power is supplied to the peripheral circuit 7 from the start of startup, and the current consumption at that time is 0.5 A.

  When the power is turned on again, the input voltage V1 of the second step-down circuit 2 becomes 14V because the first step-down circuit 1 has failed. As a result, the loss of the second step-down circuit 2 is (14V−5V) × 0.5A = 4.5 W, which increases to 4.5 times the normal loss (1 W). If the loss increases in this way, the temperature rise of the step-down element 9 becomes more severe, and the voltage of the step-down element 9 is exceeded during the voltage diagnosis, leading to an element failure.

  However, as described above, by providing the heat capacity member 10, the heat generated in the step-down element 9 can be released to the heat capacity member 10, and the temperature rise per time of the step-down element 9 can be further reduced. As a result, the temperature of the step-down element 9 after the time Tdeg required for voltage diagnosis elapses can be kept lower than the element allowable temperature Ta. As described above, the provision of the heat capacity member 10 can prevent the temperature of the step-down element 9 from exceeding the allowable temperature Ta during voltage diagnosis even if the power consumption of the CPU 3 is insufficiently reduced at the time of startup. it can.

  In Modification 3, the power supply to the peripheral circuit 7 is supplied at the time of start-up. Therefore, even when the heat capacity member 10 is added, the element temperature still exceeds the allowable temperature Ta during the voltage diagnosis. There is also. In that case, as described above, the power supply to the peripheral circuit 7 is cut off, and the consumption current is made smaller than 0.5 A, so that an increase in the element temperature can be suppressed.

<About failure notification>
As described above, when it is determined by the voltage diagnosis that the first step-down voltage circuit 1 has failed, not only the switch 61 of the cutoff circuit 6 is turned off to stop the power supply but also the low current consumption state is maintained. It is preferable to transmit abnormality occurrence information to the host ECU and notify the user that an abnormality has occurred. Further, in consideration of maintainability when an abnormality occurs, it is desirable that the content of notification of an abnormal state be as detailed as possible. By doing so, it is possible to grasp the fault location correctly and only to replace the minimum necessary parts.

  By the way, when the switch 61 is turned off and the power source of the ECU 5 is shut off when it is determined that there is a failure, it is difficult to transmit detailed information to the host ECU. Therefore, by providing a notification device 20 as shown in FIG. 7, it is possible to light a warning lamp on the meter panel or the like of the vehicle. In FIG. 7, Q1, Q2, and Q3 are transistors that function as switching elements, and 21 is a warning light.

  The transistor Q1 is set to be turned on when the first step-down circuit 1 provided in the ECU 5 is normal. For this reason, the transistor Q2 is also turned on, the transistor Q3 is short-circuited between the base and the emitter and turned off, and the warning lamp 21 is turned off. On the other hand, when the first step-down voltage circuit 1 is diagnosed as being faulty and the switch 61 of FIG. 1 is turned off, the power supply of the CPU 3 is turned off, the base current is not supplied, and the transistor Q1 is turned off. As a result, the transistor Q2 is also turned off, the ground of the transistor Q3 is grounded, the transistor Q3 is turned on, and the warning lamp 21 is lit.

  In the correspondence between the embodiment described above and the elements of the claims, the voltage detection circuit 4 is a detection unit, the CPU 3 is a determination unit and a control unit, the ECU 5 is a load circuit, and the peripheral modules of the CPU 3 are first modules. The load circuit and the peripheral circuit 7 constitute a second load circuit, respectively. The above description is merely an example, and when interpreting the invention, there is no limitation or restriction on the correspondence between the items described in the above embodiment and the items described in the claims. For example, in the above-described embodiment, the power supply device mounted on the vehicle has been described as an example, but the present invention is not limited to the vehicle and can be applied.

It is a block diagram which shows one Embodiment of the power supply device by this invention. It is a flowchart which shows the control operation of CPU3. FIG. 6 is a diagram illustrating changes in voltages Vin, V1, V2, current consumption of a load 5 and loss of a second step-down circuit 2 after the power is turned on again when the first step-down circuit 1 is normal. It is a figure which shows the change of the voltage Vin, V1, V2, the consumption current of ECU5, and the loss of the 2nd step-down circuit 2 after power-on when the 1st step-down circuit 1 is out of order. It is a figure explaining the modification 3, and the assembly | attachment state to the circuit board 11 of the step-down element 9 used for the 2nd step-down circuit 2 is shown. FIG. 4 is a diagram showing changes in voltages Vin, V1, V2, current consumption of ECU 5, loss of second step-down circuit 2, and temperature of step-down element 9 when a heat capacity member 10 is provided. It is a figure explaining the alerting | reporting apparatus.

Explanation of symbols

1: First step-down circuit 2: Second step-down circuit 4: Voltage detection circuit 5: ECU
6: Cut-off circuit 7: Peripheral circuit 9: Step-down element 20: Notification device 62: Holding circuit

Claims (6)

A first step-down voltage circuit that steps down an input voltage to a first voltage and outputs the second voltage step-down circuit that steps down the first voltage to a second voltage and outputs the second voltage; In a power supply device that supplies output power to a load circuit,
A detector for detecting an output voltage of the first step-down circuit;
Determination means for determining whether or not the first step-down voltage circuit is faulty based on the output voltage detected by the detection unit;
When the power supply device is activated, the load circuit is activated in a low current consumption operation state that operates at a current lower than a normal activation operation state, and when the determination unit determines that the first step-down voltage circuit has not failed, A power supply apparatus comprising: control means for switching the state of the load circuit from the low current consumption operation state to the normal startup operation state. The power supply device according to claim 1,
A shut-off circuit that shuts off the input voltage to the first step-down circuit and maintains the shut-off state;
The power supply apparatus according to claim 1, wherein when the determination unit determines that the failure of the first step-down circuit is failed, the control unit causes the blocking circuit to perform blocking and holding. The power supply device according to claim 1,
The load circuit includes a first load circuit in which the start control and the switching control are performed by the control means, and a second load circuit that starts when an output voltage of the second step-down voltage circuit is applied,
The power supply apparatus according to claim 1, wherein the control unit stops power supply to the second load circuit when the determination unit determines that the first step-down circuit has failed. The power supply device according to claim 1,
The load circuit includes a first load circuit in which the start control and the switching control are performed by the control means, and a second load circuit that starts when an output voltage of the second step-down voltage circuit is applied,
The control means stops power from the second step-down circuit to the second load circuit upon activation of the power supply apparatus, and the determination means determines that the first step-down circuit has not failed after the power supply apparatus is activated. Then, power supply to the second load circuit is started. In the power supply device according to any one of claims 1 to 4,
The second step-down circuit is absorbed until heat of the second step-down circuit is absorbed by heat transfer until the control unit completes the control operation based on the determination of the failure of the first step-down circuit by the determination unit from the start of the power supply device. A power supply device is provided, characterized in that a heat capacity member that keeps the temperature of the battery at or below the allowable temperature is provided. In the power supply device according to any one of claims 1 to 5,
A power supply apparatus further comprising a notification unit that notifies determination information when the determination unit determines that the first step-down circuit has failed.

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