JP2014121112A - Voltage control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid the control of suppressing an output of a motor when a voltage of a power supply changes suddenly.SOLUTION: A voltage control circuit includes: a circuit including inverter FETs 41A-41F for adjusting power supplied to an object of power supply, and a reverse connection prevention FET 44 for preventing damage to the circuit from a wrong connection; a single thermistor 46 arranged in a position spaced from the inverter FETs 41A-41F and the reverse connection prevention FET 44 to measure a temperature related to the inverter FETs 41A-41F and the reverse connection prevention FET 44 in the position of arrangement; and a microcomputer 31 for calculating a nominal threshold determined according to an applied supply voltage at predetermined time intervals, smoothing the calculated nominal threshold, and if the temperature measured by the thermistor 46 exceeds the smoothed nominal threshold, controllingly limiting the power output by the inverter FETs 41A-41F.

Description

  The present invention relates to a voltage control circuit.

  A semiconductor element such as an FET (Field Effect Transistor) is mounted as a switching element in an inverter circuit that controls driving of the motor. However, semiconductor elements such as FETs may be damaged when the temperature exceeds a predetermined temperature. The inverter circuit for driving control of the motor senses the temperature of the element, and when the element temperature exceeds a predetermined threshold, the duty ratio of the current pulse supplied to the motor to be controlled is reduced to reduce the motor Control to reduce the rotational speed. By reducing the duty ratio of the pulse of the current supplied to the motor, the voltage applied to the element of the inverter circuit is suppressed, so that the element can be prevented from overheating.

  In Patent Document 1, when the internal temperature of the motor driver exceeds a low temperature side threshold value, the motor driver is controlled to stop the motor for a predetermined time, and when the internal temperature of the motor driver exceeds the high temperature side threshold value Discloses a printing apparatus for turning off the power of a motor driver.

JP 2003-220743 A

  The voltage of the power source of the vehicle may fluctuate greatly in a short time depending on the change in the outside air temperature or the usage status of the on-vehicle equipment. For example, when a lot of equipment such as lighting is used, the voltage of the power source of the vehicle is likely to drop rapidly. If the voltage decreases, the load on the motor driver decreases. However, a temperature sensor such as a thermistor may not respond immediately to a sudden change in voltage and may detect a high temperature even after the voltage has dropped. In such a case, the load on the motor driver has dropped. It is determined that the internal temperature of the motor driver has exceeded the threshold value. As a result, there has been a problem that control for suppressing the rotation of the motor, such as stopping the motor for a predetermined time or turning off the power of the motor driver, is performed more than necessary.

  The present invention has been made in view of the above, and an object of the present invention is to provide a voltage control circuit capable of avoiding the control for suppressing the output of the motor when the voltage of the power supply changes suddenly.

  In order to solve the above problem, the voltage control circuit according to claim 1 is provided at a position apart from the circuit including a plurality of elements for adjusting power supplied to a power supply target and the plurality of elements. A single temperature measuring means for measuring the temperature of the plurality of elements at the provided position, and a temperature determination threshold value determined according to the applied power supply voltage at predetermined time intervals, and the calculated temperature Control for smoothing the determination threshold and controlling so as to limit the power output by the plurality of elements when the temperature measured by the temperature measuring unit exceeds the smoothed temperature determination threshold Means.

  In this voltage control circuit, the control means calculates a temperature determination threshold value according to the voltage applied to the circuit, and smoothes the calculated temperature determination threshold value. When the temperature measured by the temperature measuring means exceeds the smoothed temperature determination threshold, the voltage output from the circuit is limited (suppressed).

  When the voltage changes abruptly, the temperature determination threshold value determined according to the voltage also changes abruptly, but the smoothed temperature determination threshold value changes slowly. This voltage control circuit uses a threshold that slowly changes even after the voltage suddenly changes to determine the overheating state of multiple elements, so that the control of the motor output is suppressed when the power supply voltage changes suddenly. Can be avoided.

  The voltage control circuit according to claim 2 is the voltage control circuit according to claim 1, wherein the control means calculates a moving average value of a predetermined number of temperature determination thresholds up to the most recently calculated temperature determination threshold. As a result, the temperature determination threshold value is smoothed.

  According to this voltage control circuit, the temperature determination threshold value is smoothed so that the degree of change becomes slow by obtaining the moving average value of the temperature determination threshold value calculated in time series, so that the voltage of the power supply changes rapidly. In this case, it is possible to avoid control for suppressing the output of the motor.

  A voltage control circuit according to a third aspect is the voltage control circuit according to the first aspect, wherein the control unit increases the weight of the weighted average value calculated last time and is closest to the weighted average value calculated last time. The current weighted average value calculated with the calculated temperature determination threshold is used as the smoothed temperature determination threshold.

  According to this voltage control circuit, the temperature determination threshold value is smoothed by the weighted average value calculated from the previously calculated weighted average value and the most recently calculated temperature determination threshold value by increasing the weight of the previously calculated weighted average value. Therefore, it is possible to avoid the control for suppressing the output of the motor when the voltage of the power supply changes suddenly.

  The voltage control circuit according to claim 4 is the voltage control circuit according to any one of claims 1 to 3, wherein the plurality of elements are a field effect transistor that constitutes an inverter circuit, a power source that applies the voltage, and It includes a reverse connection prevention field effect transistor and a noise removal coil which are provided between the field effect transistor and prevent circuit damage due to incorrect connection.

  According to this voltage control circuit, overheating of different types of elements constituting the inverter circuit can be prevented by means relating to a single temperature measurement.

  A voltage control circuit according to a fifth aspect is the voltage control circuit according to any one of the first to fourth aspects, wherein the control means reduces the duty ratio of a voltage output from the circuit to reduce the duty ratio. Reduce the output voltage.

  According to this voltage control circuit, by reducing the duty ratio of the voltage output from the circuit, it is possible to reduce the load of the elements constituting the circuit and prevent overheating of each element.

  A voltage control circuit according to a sixth aspect of the present invention is the voltage control circuit according to any one of the first to fifth aspects, wherein the circuit is a motor drive control circuit that controls driving of the motor.

  According to this voltage control circuit, it is possible to prevent overheating of the elements mounted on the board as described above and to avoid the control of suppressing the output of the motor when the voltage of the power supply changes suddenly. Can be controlled to continue.

It is the schematic which shows the structure of the motor unit using the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows an example of the board | substrate of the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows the outline of the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows an example of the change of the pulse output from the inverter circuit of the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows an example of the temperature change by the voltage of each element of the voltage control circuit which concerns on embodiment of this invention. It is a table | surface which shows an example of the aspect of the temperature change of each element by the change of the voltage of the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows an example of the correspondence of the power supply voltage and temperature determination threshold value in the voltage control circuit which concerns on embodiment of this invention. It is a flowchart which shows an example of control of the motor drive control apparatus using the voltage control circuit which concerns on embodiment of this invention. It is a figure which shows an example of calculation of the 10-point average threshold value in the voltage control circuit which concerns on embodiment of this invention. It is an example of the graph which each showed the voltage value, nominal threshold value, thermistor temperature, and 10-point average threshold value in the voltage control circuit which concerns on embodiment of this invention.

  FIG. 1 is a schematic diagram showing a configuration of a motor unit 10 using a voltage control circuit according to the present embodiment. The motor unit 10 according to the present embodiment in FIG. 1 is a so-called blower motor unit used for blowing air from an in-vehicle air conditioner as an example.

  The motor unit 10 according to the present embodiment relates to a three-phase motor having an outer rotor structure in which a rotor 12 is provided outside a stator 14. The stator 14 is an electromagnet in which a lead wire is wound around a core member, and constitutes three phases of a U phase, a V phase, and a W phase.

  Each of the U-phase, V-phase, and W-phase of the stator 14 generates a so-called rotating magnetic field by switching the polarity of the magnetic field generated by the electromagnet under the control of a motor drive control device 20 described later.

  A rotor magnet is provided inside the rotor 12 (not shown), and the rotor magnet rotates the rotor 12 by responding to the rotating magnetic field generated by the stator 14.

  The rotor 12 is provided with a shaft 11 and rotates integrally with the rotor 12. Although not shown in FIG. 1, in this embodiment, the shaft 11 is provided with a multi-blade fan such as a so-called sirocco fan, and the multi-blade fan rotates together with the shaft 11 so It becomes possible.

  The stator 14 is attached to the motor drive control device 20 via the upper case 13. The motor drive control device 20 includes a substrate 22 of a voltage control circuit and a heat sink 21 that dissipates heat generated from elements on the substrate 22.

  A lower case 50 is attached to the motor unit 10 including the rotor 12, the stator 14, and the motor drive control device 20.

  Subsequently, the substrate of the voltage control circuit according to the present embodiment will be described with reference to FIG. FIG. 2 is a diagram illustrating an example of the substrate 22 of the voltage control circuit according to the embodiment of the present invention. In FIG. 2, the board 22 is provided with an external connection connector 23 to which electric power is supplied from an in-vehicle battery and a control signal related to the in-vehicle air conditioner is input via a control device such as an ECU (Electronic Control Unit). It has been.

  An inverter circuit 41 for controlling power supplied to the U phase, V phase, and W phase of the stator 14 is mounted on the substrate 22. The inverter circuit 41 of the motor drive control device 20 according to the present embodiment is a voltage source inverter that operates as a voltage source by connecting large-capacitance capacitors 42A, 42B, 42C, and 42D in parallel to a DC side circuit.

  The inverter circuit 41 includes inverter FETs 41A, 41B, 41C, 41D, 41E, and 41F as switching elements. The inverters FET 41A and 41D switch the power supplied to the U phase, the inverters FET 41B and 41E switch to the V phase, and the inverters FET 41C and 41F switch to the W phase. The electric power controlled by the switching of the inverters FET41A to 41F is supplied to the stator 14 via the power supply terminals 24A, 24B, and 24C.

  On the DC side of the inverter circuit 41 on the substrate 22, a noise removing coil 43 is provided, and a reverse connection prevention FET 44 and a large-capacitance capacitor 42E are provided. A microcomputer 31 for controlling the inverter circuit 41 is mounted on the substrate 22. The reverse connection prevention FET is an FET for protecting the inverter circuit 41 when the vehicle battery is connected with the opposite polarity.

  In the substrate 22 shown in FIG. 2, the inverter FETs 41A to 41F, the coil 43, and the reverse connection prevention FET 44 generate significant heat during operation. In the present embodiment, the heat sink 21 is attached by the fixing bolt 29 on the back side of the portion where the element that generates significant heat during operation is mounted.

  A thermistor 46, which is a temperature sensor that senses the temperature of the substrate, is mounted on the substrate 22 near the inverter FET 41B. In this embodiment, when there is a possibility that the temperature of the element becomes equal to or higher than a predetermined threshold, the duty ratio of the pulse of the current output from the inverter circuit 41 is reduced to prevent damage to the element due to heat.

  FIG. 3 is a diagram schematically illustrating the voltage control circuit according to the present embodiment. Inverters FET41A-41F switch the electric power supplied to the coil of the stator 14 of the motor 16. FIG. For example, the inverter FETs 41A and 41D switch the power supplied to the U-phase coil 14U, the inverter FETs 41B and 41E switch to the V-phase coil 14V, and the inverter FETs 41C and 41F switch the power supplied to the W-phase coil 14W.

  The drains of the inverters FET 41A, 41B, and 41C are connected to the positive electrode of the on-vehicle battery 80 via the noise removing coil 43. The sources of the inverters FET 41D, 41E, and 41F are connected to the negative electrode of the battery 80 via the reverse connection prevention FET 44.

  In the present embodiment, a reverse connection prevention FET 44 and a coil 43 are provided between a battery 80 as a power source and the inverter circuit 41.

  In the present embodiment, the Hall element 12B detects the magnetic field of the sensor magnet 12A provided coaxially with the shaft 11. The microcomputer 31 detects the position (rotational position) of the rotor 12 based on the detected magnetic field, and controls switching of the inverter circuit 41 according to the rotational position of the rotor 12.

  Further, a control signal from an air conditioner ECU that controls the air conditioner and a resistance value signal from the thermistor 46 are input to the microcomputer 31, and the switching of the inverter circuit 41 is controlled based on these input signals. In the present embodiment, a voltage sensor 48 that measures the voltage of the battery 80 is provided on the circuit.

  FIG. 4 is a diagram illustrating an example of changes in pulses output from the inverter circuit 41. When the element is not overheated, a pulse having a duty ratio shown in FIG. A sine wave 60 shown in FIG. 4A shows the average voltage and frequency of the pulse shown in FIG.

  When the element may be overheated, a pulse having a duty ratio smaller than that in the case of FIG. 4A is output as shown in FIG. A sine wave 62 shown in FIG. 4B is the average voltage and frequency of the pulse shown in FIG. 4B, and the average voltage and frequency are lower than in the case of FIG.

  When the duty ratio of the pulse output from the inverter circuit 41 is reduced and the average voltage and frequency of the pulse are reduced, the current flowing through the inverter FETs 41A to 41F, which are switching elements, decreases, so that the inverter FETs 41A to 41F are overheated. Can be prevented.

  Further, in a vehicle equipped with a battery, the voltage that should originally be 12 V may vary depending on the state of charge of the battery. Each element of the motor drive control device according to the present embodiment varies in calorific value as shown in FIG. 5 depending on the voltage of power supplied from the battery via the external connection connector 23. FIG. 5 is a diagram illustrating an example of a temperature change due to the voltage of each element of the voltage control circuit according to the present embodiment.

  In FIG. 5, the inverter FET average temperature 70 that is the average temperature of the inverter FETs 41 </ b> A to 41 </ b> F increases as the battery voltage increases, and is the highest when the battery voltage is a high voltage of approximately 16V. The reverse connection prevention FET temperature 72 which is the temperature of the reverse connection prevention FET 44 and the coil temperature 74 which is the temperature of the noise removing coil 43 are 8 to 11 V of the same voltage than the case where the battery voltage is a high voltage of 11 to 16 V. It tends to become hot when the voltage is low.

  When the battery voltage is high, a larger load is applied to the inverter FETs 41A to 41F than when the battery voltage is low, and the inverter FETs 41A to 41F are likely to be hot. In particular, when the battery voltage is 16 V, the inverter FETs 41A to 41F have the highest temperature due to the influence of the heat generated by the switching losses by the inverter FETs 41A to 41F in addition to the high voltage.

  When the voltage of the battery exceeds 16V, the time for which the inverter FETs 41A to 41F stop energizing in order to limit the current supplied to the motor becomes long, so that the current flowing through the inverter FETs 41A to 41F decreases and the inverter The temperatures of the FETs 41A to 41F are lower than when the battery voltage is 16V.

  When the voltage of the battery is low, the inverter FETs 41A to 41F are in a full-on state in order to increase the current supplied to the motor. As a result, the switching losses of the inverters FET41A to 41F are eliminated, and the low voltage of the power supplied from the battery is also affected, so that the inverters FET41A to 41F have a lower temperature than when the battery voltage is high.

  The reverse connection prevention FET 44 is in an on state when the battery polarity is correctly connected. However, when the voltage supplied from the battery is high, the inverter FETs 41A to 41F stop energization in order to limit the current supplied to the motor. While the inverter FETs 41 </ b> A to 41 </ b> F are not energized, no current flows through the reverse connection prevention FET 44, so that the heat generation of the reverse connection prevention FET 44 is suppressed.

  Further, while the inverter FETs 41A to 41F are not energized, no current flows through the coil 43. Therefore, when the voltage supplied from the battery is high, heat generation of the coil 43 is suppressed.

  When the voltage of the battery is low, the inverters FET 41A to 41F are in a full-on state, and a current continues to flow through the reverse connection prevention FET 44, so that heat generation of the reverse connection prevention FET 44 is promoted.

  When the inverter FETs 41 </ b> A to 41 </ b> F are in a full-on state, current continues to flow through the coil 43, so that heat generation of the coil 43 is promoted when the voltage supplied from the battery is low. FIG. 6 is a table showing an example of an aspect of temperature change of each element due to voltage change of the voltage control circuit according to the present embodiment. When the battery voltage is a low voltage of 8 to 11V, the inverter FETs 41A to 41F tend to rise in temperature while tending to be low temperature, the reverse connection prevention FET 44 and the coil 43 tend to be high temperature, and most when the battery voltage is around 11V. It becomes high temperature. When the battery voltage is 11 to 16 V, the inverter FETs 41A to 41F tend to be high temperature and tend to increase in temperature, and the reverse connection prevention FET 44 and the coil 43 tend to decrease in temperature. When the battery voltage is 16 V or higher, all elements show a tendency to decrease in temperature.

  In FIG. 5, the thermistor temperature 76, which is the temperature of the thermistor 46, shows a monotonically increasing tendency as the voltage increases. As described above, the inverter FETs 41 </ b> A to 41 </ b> F differ from the reverse connection prevention FET 44 and the coil 43 in the form of heat generation with respect to voltage change, but depending on the mounting position of the thermistor 46, the thermistor temperature 76 may be as shown in FIG. 5. It can show a monotonically increasing tendency with respect to the voltage change. In the present embodiment, as an example, the thermistor 46 is mounted near the inverter FET 41B. However, if the thermistor temperature 76 can show a monotonically increasing tendency with respect to a change in voltage, it may be mounted at another position. Good.

  Assuming that the inverter FET average temperature 70, the reverse connection prevention FET temperature 72, and the coil temperature 74 shown in FIG. 5 are the upper limit values of the temperature allowed for each element, the thermistor temperature 76 shown in FIG. It can be an indicator of whether the temperature is within an allowable range.

  Based on the temperature change of the thermistor 46 due to the voltage change shown in FIG. 5, the correspondence between the power supply voltage and the threshold temperature of the element overheating as shown in FIG. 7 can be set. In particular, if the thermistor temperature 76 is linearly monotonically increasing, the threshold can be approximated to a monotonically increasing straight line as shown in FIG. FIG. 7 is a diagram illustrating an example of a correspondence relationship between the power supply voltage and the temperature determination threshold in the voltage control circuit according to the present embodiment.

  In the present embodiment, the correspondence relationship between the power supply voltage and the temperature determination threshold as shown in FIG. 7 is stored in advance in a memory mounted on the substrate 22, and the measured power supply voltage is applied to the correspondence relationship so as to change the temperature. A determination threshold value is calculated. Note that the correspondence between the power supply voltage and the temperature determination threshold may be affected by the relative positional relationship between each element and the thermistor 46 on the substrate 22 as described above. For this reason, it is preferable to determine the correspondence between the power supply voltage and the temperature determination threshold through a simulation using a computer or a test using a prototype.

  FIG. 7 is a flowchart showing an example of control of the motor drive control device using the voltage control circuit according to the present embodiment.

  In the present embodiment, the voltage value of battery 80 measured by voltage sensor 48 in step 800 of FIG. 7 is stored in the memory. In step 802, the microcomputer 31 calculates a nominal threshold value based on the voltage value stored in the memory and stores it in the memory. The nominal threshold value is a temperature determination threshold value corresponding to the voltage value measured in step 800. In this embodiment, a threshold based on the voltage is calculated from the correspondence between the voltage and the threshold shown in FIG. 7, and the calculated threshold is set as a nominal threshold that is a nominal threshold corresponding to the voltage. As will be described later, in the present embodiment, the calculated nominal threshold value is smoothed, and the smoothed nominal threshold value is used as a threshold value for determining the thermistor temperature.

  The voltage value of the battery 80 may be a voltage value measured by the voltage sensor 48, but may be acquired via the external connection connector 23 as measured by an in-vehicle voltage measuring unit.

  In step 804, the nominal threshold value is smoothed. Specifically, a moving average value of a plurality of nominal threshold values up to the most recently calculated nominal threshold value is calculated, and the calculated moving average value is stored in the memory as an average threshold value. FIG. 9 is a diagram illustrating an example of calculation of the 10-point average threshold value obtained by calculating the moving average value of the ten nominal threshold values in the voltage control circuit according to the present embodiment.

  In FIG. 9, the nominal threshold is calculated from the voltage at a predetermined interval from the elapsed time 16:26:08 to 16:30:36, and at the elapsed time 16:30:51, the elapsed time 16:26:08 to 16:30. : The moving average value of the nominal threshold value at 36 is calculated.

  Subsequently, at the elapsed time 16:31:11, a total of ten nominal thresholds are moved from the nominal threshold of the elapsed time 16:30:56 and the nominal threshold of the elapsed time 16:26:28 to 16:30:36. The average value is calculated. Thereafter, as in the elapsed times 16:31:21, 16:31:41, and 16:32:01, the moving average values of the ten nominal thresholds set at the most recent intervals are calculated. The predetermined interval for calculating the nominal threshold value and the predetermined interval for calculating the moving average value of the nominal threshold value are 20 seconds in FIG. 9, but may be appropriately changed according to the temperature characteristics of the voltage control circuit. In the present embodiment, the predetermined number of nominal threshold values used for calculating the average value is 10. However, the number of nominal threshold values is appropriately changed according to the length of the predetermined interval and the manner in which the nominal threshold changes when the voltage rapidly decreases. May be.

The weighted average value S _i-1 previously calculated by increasing the weight of the previously calculated weighted average value S _i-1 and the most recently calculated nominal threshold value S ₀ are calculated based on the following equation (1). The current weighted average value S _i may be used as a smoothed determination threshold. In Expression (1), w represents a weight.
S _i = (wS _i−1 + S ₀ ) / (w + 1) (1)

  In step 806, it is determined whether the temperature detected by the thermistor 46 is equal to or higher than the 10-point average threshold.

  If the determination in step 806 is affirmative, the inverter FETs 41A to 41F, the reverse connection prevention FET 44, or the coil 43 mounted on the substrate 22 may be overheated. In step 808, the duty ratio of the current output from the inverter circuit 41 is decreased as shown in FIG. 4B to protect the element from overheating, and the process ends.

  If the determination in step 806 is negative, the inverter FETs 41A to 41F, the reverse connection prevention FET 44, and the coil 43 have no fear of overheating. Therefore, in step 810, normal control of the inverter circuit 41 is performed without reducing the duty ratio, and processing is performed. finish.

  FIG. 10 is an example of a graph showing the voltage value 90, the nominal threshold value 92, the thermistor temperature 94, and the 10-point average threshold value 96 in the voltage control circuit according to the present embodiment. When the voltage value 90 decreases rapidly, the nominal threshold 92 also decreases rapidly. However, the thermistor temperature 94, which is the temperature detected by the thermistor 46, does not decrease abruptly like the nominal threshold 92, but decreases with a gentle curve.

  If the voltage value 90 decreases, the load of the inverter FET of the voltage control circuit decreases. However, if the thermistor temperature 94 is still high after the voltage drop, it is determined that the temperature of the element of the voltage control circuit has exceeded the nominal threshold value 92 even though the load of the inverter FET of the voltage control circuit is low. As a result, control for suppressing the rotation of the motor, such as reducing the duty ratio of the current output from the inverter circuit 41 or stopping the output from the inverter circuit 41, is performed more than necessary.

  In FIG. 9, the 10-point average threshold value 96, which is the average value of the 10 nominal threshold values set most recently, gradually decreases while maintaining a value higher than the thermistor temperature 94 after the voltage value decreases. Yes. In the present embodiment, when the thermistor temperature 94 becomes equal to or higher than the 10-point average threshold value 96, the control for suppressing the rotation of the motor is performed. Can be avoided.

DESCRIPTION OF SYMBOLS 10 ... Motor unit, 11 ... Shaft, 12 ... Rotor, 12A ... Sensor magnet, 12B ... Hall element, 13 ... Upper case, 14 ... Stator, 14U, 14V, 14W ... coil, 16 ... motor, 20 ... motor drive control device, 21 ... heat sink, 21A ... projection, 22 ... substrate, 23 ... external connection connector, 24A, 24B 24C ... Power supply terminal, 25 ... Ground potential region, 26 ... Insulating member, 27, 28 ... Protrusion, 29 ... Fixing bolt, 31 ... Microcomputer, 41 ... Inverter circuit, 41A, 41B, 41C, 41D, 41E, 41F ... Inverter FET, 42A, 42B, 42C, 42D, 42E ... Capacitor, 43 ... Coil, 44 ... Contact prevention FET, 46 ... Thermistor, 48 ... Voltage sensor, 50 ... Lower case, 60, 62 ... Sine wave, 70 ... Inverter FET average temperature, 72 ... Reverse connection prevention FET temperature 74 ... Thermistor temperature, 76 ... Thermistor temperature, 80 ... Battery, 82 ... Air conditioner ECU, 90 ... Voltage value, 92 ... Nominal threshold, 94 ... Thermistor temperature, 96 ... 10-point average threshold

Claims (6)

A circuit having a plurality of elements for adjusting power supplied to a power supply target;
A single temperature measuring means provided at a position away from the plurality of elements, and measuring the temperature of the plurality of elements at the provided position;
A temperature determination threshold value determined according to the applied power supply voltage is calculated at a predetermined time interval, and the calculated temperature determination threshold value is smoothed, and the temperature measured by the temperature measuring means is smoothed. Control means for controlling the power output by the plurality of elements when the temperature determination threshold is exceeded,
Voltage control circuit with   The voltage control circuit according to claim 1, wherein the control means smoothes the temperature determination threshold by calculating a moving average value of a predetermined number of temperature determination thresholds up to the most recently calculated temperature determination threshold.   The control means increases the weight of the weighted average value calculated last time, and calculates the current weighted average value calculated by the weighted average value calculated last time and the temperature determination threshold value calculated most recently as the smoothed temperature. The voltage control circuit according to claim 1, which is a determination threshold value.   The plurality of elements include a field effect transistor that constitutes an inverter circuit, a reverse connection prevention field effect transistor that is provided between the power supply for applying the power supply voltage and the field effect transistor, and prevents damage to the circuit due to incorrect connection, and noise. The voltage control circuit according to claim 1, comprising a removal coil.   5. The voltage control circuit according to claim 1, wherein the control unit reduces a voltage output from the circuit by reducing a duty ratio of a voltage output from the circuit. The voltage control circuit according to claim 1, wherein the circuit is a motor drive control circuit that controls driving of a motor.