JP2011125101A - Current detector, power supply device and current detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current detector, wherein data tables for temperature correction are generated only at two or more predetermined temperature point and a current detection value is accurately corrected to within a wide range of ambient temperatures which use them, and to provide a power supply device equipped therewith, and a current detection method. <P>SOLUTION: A temperature correction unit 130 includes a computing means 131, a memory 132, a first AD conversion means 133 and a second AD conversion means 134. Voltage-current conversion tables corresponding to typical temperature points are generated and are stored in the memory 132, beforehand. Based on the ambient temperature T, the computing means 131 selects typical temperature points T1, T2 sandwiching it and determines a load current with respect to measured voltage Vt from the voltage-current conversion table corresponding to each typical temperature point. By using these two load currents, the computing means computes a load current at the ambient temperature T through linear interpolation. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a current detection device that detects a current passing through a switch that opens and closes a power supply line to a load, a power supply device including the current detection device, and a current detection method. In particular, the switch uses a semiconductor switch such as a power MOSFET. The present invention relates to a current detection device, a power supply device including the current detection device, and a current detection method.

  In a power supply device used in an automobile or the like, each electrical component is connected to a battery via a harness that is a power supply line in order to supply power to the electrical component such as a headlight. In addition, a switch for opening and closing the power supply line to each electrical component is provided in the middle. Further, overcurrent protection means for protecting the switch and harness from overcurrent is also provided. Conventionally, fuses have been used as overcurrent protection means.

  In recent years, electronic switches and overcurrent protection means have been promoted, and semiconductor switches have been used as switches for opening and closing power supply lines. In addition, various overcurrent protection means configured to turn off the semiconductor switch and interrupt the power supply line in the event of an overcurrent have been proposed instead of the fuse. In the overcurrent protection means using the semiconductor switch, it is required to protect the semiconductor switch from the overcurrent in addition to the harness.

  Semiconductor switches are known to be strongly affected by the ambient temperature and their own heat generation. When a power MOSFET capable of handling high power is used, the on-resistance of the switch is approximately doubled by changes in the ambient temperature. Can also change. Therefore, when such a semiconductor switch is used, the on-resistance of the semiconductor switch is compared with the detected current value in order to accurately determine the current passing through the semiconductor switch and appropriately determine overcurrent or the like. It is necessary to compensate for the effects of temperature changes. Even when a switch other than a semiconductor switch is used, it is necessary to protect the harness by compensating for the influence of the switch resistance value due to temperature change.

  Patent Document 1 describes a field current correction control device 900 that controls a field current supplied to a field coil 902 of a motor 901 as shown in FIG. Here, the measured value of the field current is corrected by the current correction unit 904 based on the change amount of the resistance value due to the temperature change of the current detection resistor 903. As the amount of change in the resistance value of the current detection resistor 903, both the amount of change due to self-heating of the current detection resistor 903 and the amount of change due to a change in ambient temperature are estimated. In order to estimate the amount of change in resistance value due to self-heating, a temperature correction map as shown in FIG. 12 or a correction table as shown in FIG. 13 is prepared and used.

  Patent Document 2 describes a power conversion device including means for detecting a main current of an IGBT (Insulated Gate Bipolar Transistor) as shown in FIG. Since the voltage and current characteristics of the IGBT are nonlinear and the characteristics vary nonlinearly with temperature, the ratio of the main current of the IGBT 911 and the sense current of the sense IGBT 912 shown in FIG. Is used for estimation.

  Further, Patent Document 3 discloses a switching device as shown in FIG. In the switching device shown in the figure, the smoke generation characteristic that changes depending on the ambient temperature as shown in FIG. 16 is defined for the harness 921. In Patent Document 3, the value detected by the temperature sensor when the semiconductor switch 922 is off is used as the ambient temperature of the harness 921. Based on this ambient temperature, the detected current value is corrected in accordance with the temperature change of the smoke generation characteristic shown in FIG.

JP 2005-237049 A JP 2006-271098 A JP 2003-209922 A

  However, in the temperature correction method described in Patent Documents 1 to 3, it is necessary to prepare a data table for temperature correction for each ambient temperature, and it is necessary to cover a wide range of temperatures as the ambient temperature. Has a problem that the amount of data in the data table becomes enormous. Also, there is a problem that a large capacity memory is required to store such a huge data table, resulting in high cost.

  The present invention has been made to solve such a problem. A data table for temperature correction is created only at two or more predetermined temperature points, and a current detection value is obtained at a wide range of ambient temperatures using the data table. An object of the present invention is to provide a current detection device that corrects with high accuracy, a power supply device including the current detection device, and a current detection method.

  A first aspect of a current detection device of the present invention is a current detection device that detects a load current connected in parallel to a switch that turns on / off a load current supplied to a load from a power source via a harness. A current measurement resistor, a voltage detection circuit that detects a voltage drop due to the current measurement resistor and outputs the voltage as a measurement voltage, a temperature sensor that detects an ambient temperature of the switch, the voltage detection circuit, and the temperature sensor A temperature correction unit that calculates the load current by inputting the measurement voltage and the ambient temperature, respectively, and the temperature correction unit performs first AD conversion on the measurement voltage input from the voltage detection circuit. A second AD converting means for AD converting the ambient temperature input from the temperature sensor, and two or more ambient temperatures set in advance as representative temperature points. A memory for storing a voltage-current conversion table composed of voltage-to-current data for converting the measurement voltage created in advance to the load current, and the surroundings of the digital value input from the second AD conversion means Two representative temperature points sandwiching the temperature are obtained, and the 2 values are obtained from the voltage-current conversion table for each of the measured voltage of the digital value input from the first AD converter and the two representative temperature points input from the memory. And calculating means for calculating the load current at the detected ambient temperature by obtaining two current values at each of the representative temperature points and linearly interpolating the two current values.

  In another aspect of the current detection device of the present invention, the load current is input from the calculation means, and it is determined whether a predetermined overcurrent limit condition is satisfied based on the load current, and the overcurrent limit condition is determined. When it is determined that is not satisfied, an abnormality determination unit that controls the switch to be turned off is further provided.

  According to another aspect of the current detection device of the present invention, the determination of the overcurrent limiting condition is performed by integrating a current integrated value obtained by integrating or integrating the load current or the square value of the load current in a latest fixed period. When the current integration value exceeds the current integration threshold, it is determined that the current is not satisfied when the current integration value exceeds the current integration threshold.

  In another aspect of the current detection device of the present invention, the current integration threshold is a threshold calculated based on a predetermined limit overcurrent characteristic set for protecting the switch, and for protecting the harness. The threshold value is a lower value of another threshold value calculated based on the set electric wire limit overcurrent characteristic.

  Another aspect of the current detection device of the present invention is characterized in that the voltage-current conversion table reduces the number of data of the voltage versus current data when the change in the load current with respect to the measurement voltage is small. To do.

  Another aspect of the current detection device of the present invention is characterized in that the representative temperature point is a temperature point at which a change in the resistance value of the switch with respect to at least the ambient temperature is large.

  In another aspect of the current detection device of the present invention, the voltage detection circuit includes a first resistor connected in parallel to the power supply side of the switch, and a non-inverting input terminal connected to the load side of the switch. A differential amplifier having an inverting input terminal connected to the downstream side of the first resistor, an emitter terminal connected between the first resistor and the inverting input terminal of the differential amplifier, and a collector terminal being the current And a transistor having a gate terminal connected to the output terminal of the differential amplifier. The transistor is grounded via a measuring resistor.

  In another aspect of the current detection device of the present invention, when the ambient temperature detected by the temperature sensor is lower than the lowest temperature among the two or more representative temperature points, the lowest temperature representative temperature point is selected. A current value obtained from the voltage-current conversion table is used as the load current.

  In another aspect of the current detection device of the present invention, the switch is a power MOSFET of an n-channel semiconductor switch.

  According to a first aspect of the power supply apparatus of the present invention, there is provided a power source, a switch for energizing or interrupting a load current supplied from the power source to a load via a harness, and the current detection according to any one of the above aspects. An operation switch for commanding energization or interruption of the load current to the harness, and a command receiving unit that receives a command from the operation switch and outputs the command to the current detection device. The detection device receives a command of the operation switch from the command receiver and controls the switch, and controls the switch to be turned off when an overcurrent is detected by the current detection device.

  According to a first aspect of the current detection method of the present invention, there is provided a current detection method for measuring a predetermined voltage that varies with a load current energizing the switch and calculating the load current from the measured voltage. A voltage-current conversion table composed of voltage-to-current data for converting the measurement voltage into the load current for each of two or more ambient temperatures set in advance as representative temperature points of Detecting the measurement voltage and the ambient temperature, obtaining the two representative temperature points sandwiching the detected ambient temperature, and the voltage-current conversion table for each of the detected measurement voltage and the two representative temperature points; To obtain two current values at each of the two representative temperature points, and linearly interpolate the two current values to calculate the load current at the detected ambient temperature And wherein the Rukoto.

  Another aspect of the current detection method of the present invention is characterized in that the voltage-current conversion table reduces the number of data of the voltage versus current data when a change in the load current with respect to the measurement voltage is small.

  Another aspect of the current detection method of the present invention is characterized in that the representative temperature point is a temperature point at which a change in resistance value of the semiconductor switch with respect to at least the ambient temperature is large.

  According to another aspect of the current detection method of the present invention, when the ambient temperature is lower than the lowest temperature among the two or more representative temperature points, the current detection method is obtained from the voltage-current conversion table for the lowest temperature representative temperature point. The measured current value is used as the load current.

  According to the present invention, a data table for temperature correction is created only at two or more predetermined temperature points, and a current detection device for correcting current detection values with high accuracy at a wide range of ambient temperatures using the data table is provided. A power supply device and a current detection method can be provided.

1 is a block diagram illustrating a schematic configuration of a current detection device according to a first embodiment of the present invention. It is a graph which shows an example of the correlation of a measurement voltage and load current. It is a graph which shows an example of the change of ON resistance with respect to ambient temperature. It is a block diagram which shows schematic structure of the electric current detection apparatus which concerns on 2nd Embodiment of this invention. It is a graph which shows an example of the limit overcurrent characteristic with respect to power MOSFET. It is a graph which shows the relationship between ambient temperature and a temperature coefficient in the electric current detection method of 3rd Embodiment. It is a block diagram which shows the structure of the power supply apparatus which concerns on embodiment of this invention. It is a flowchart explaining the flow of a process of the power supply device which concerns on embodiment of this invention. It is a flowchart explaining the method of calculating a load current integrated value. It is a flowchart explaining the flow of the process at the time of forced interruption | blocking. It is a block diagram which shows the structure of the conventional field current correction control apparatus. It is a temperature correction map used with the conventional field current correction control apparatus. It is a correction table used with the conventional field current correction control apparatus. It is a block diagram of the power converter device provided with the means to detect the main current of the conventional IGBT. It is a block diagram which shows the structure of the conventional switching apparatus. It is a graph which shows the smoke generation characteristic of the conventional harness.

  A configuration of a current detection device, a power supply device including the current detection device, and a current detection method according to a preferred embodiment of the present invention will be described below in detail with reference to the drawings. In addition, about each structural part which has the same function, the same code | symbol is attached | subjected and shown for simplification of illustration and description. In the following, a case where a semiconductor switch is used as a switch for energizing / cutting off current will be described as an example. However, the present invention is not limited to this, and the present invention can also be applied when other opening / closing means are used.

(First embodiment)
The configuration of the current detection device and the current detection method according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of a current detection device 100 according to the present embodiment. In the figure, in a system in which a load 40 is connected to a power source 10 via a harness 20 and a power MOSFET 30 of a semiconductor switch provided in the middle thereof, a load current I _load supplied to the load 40 is measured with high accuracy. The structure of the electric current detection apparatus 100 of embodiment is shown.

The power MOSFET 30 is an n-channel power MOSFET and is configured to turn on / off the power supply from the power supply 10 to the load 40 under the control of the driver circuit 50. As such a system, for example, the power source 10 can be a battery mounted on a vehicle, and the load 40 can be an on-vehicle electrical component. When an H level drive voltage is output from the driver circuit 50 to the gate terminal of the power MOSFET 30, the power MOSFET 30 is turned on and the load current I _load is supplied to the load 40. On the other hand, when the drive voltage output from the driver circuit 50 is changed from the H level to the L level, the power MOSFET 30 is switched from the on state to the off state, and the load current I _load to the load 40 is interrupted.

  The current detection device 100 of this embodiment includes a voltage detection circuit 110, a temperature sensor 120, and a temperature correction unit 130. The voltage detection circuit 110 includes a differential amplifier 111, a transistor 112, a first resistor 113, and a second resistor 114. The transistor 112 is a pnp type, and has an emitter terminal connected to the power supply 10 via a first resistor 113 and a collector terminal grounded via a second resistor 114.

  The differential amplifier 111 has a non-inverting input terminal connected to the source side (load 40 side) of the power MOSFET 30 and an inverting input terminal connected to the downstream side of the first resistor 113, that is, the emitter terminal of the transistor 112. Thus, the voltage at the non-inverting input terminal is equal to the voltage at the source side of the power MOSFET 30, and the voltage at the inverting input terminal is equal to the voltage at the emitter terminal of the transistor 112. The output terminal of the differential amplifier 111 is connected to the gate terminal of the transistor 112.

In the voltage detection circuit 110 configured as described above, the output of the differential amplifier 111 is adjusted so that the voltage applied to the inverting input terminal of the differential amplifier 111 is equal to the voltage applied to the non-inverting input terminal. Thus, the emitter-collector current of the transistor 112, that is, the current flowing through the first resistor 113 is controlled. When the voltage of the power supply 10 is V0, the drain-source voltage of the power MOSFET 30 is Vds, the resistance value of the first resistor 113 is Rs, and the current flowing through the first resistor 113 is Is.
V0−Vds = V0−Rs · Is (1)
Is established.

Thus, the current Is is given by the following equation.
Is = Vds / Rs (2)
From equation (2), it can be seen that the current Is flowing through the first resistor 113 is proportional to the drain-source voltage Vds. This current Is flows from the emitter side to the collector side of the transistor 112 and is consumed by the second resistor 114.

Meanwhile, when the on-resistance of the power MOSFET 30 Rds and (ON), the following equation holds between the drain-source voltage Vds and the load current _{I load.}
Vds = I _load · Rds (ON) (3)
From the equations (2) and (3), the load current I _load and the current Is are
Is = I _load · (Rds (ON) / Rs)
Or I _load = Is · (Rs / Rds (ON)) (4)
Holds. That is, it can be seen that a current Is proportional to the load current I _load flows through the first resistor 113.

The current detection device 100 according to the present embodiment is configured to detect the load current I _load by detecting the current Is. Hereinafter, the current Is will be referred to as a measurement current Is. The measurement current Is is detected by detecting the collector side voltage of the transistor 112 and converting it into a current value. The collector side voltage of the transistor 112 corresponds to the voltage on the opposite side of the second resistor 114 from the ground side. When this voltage (hereinafter referred to as measurement voltage) is Vt and the resistance value of the second resistor 114 is Rt, the measurement current Is is Is = Vt / Rt (5)
Given in.

From equations (4) and (5),
I _load = (Vt / Rt) · (Rs / Rds (ON))
= Vt · (Rs / {Rds (ON) · Rt)} (6)
Is obtained. Thus, when the resistances Rds (ON), Rs, and Rt are determined, the load current I _load can be obtained by detecting the measurement voltage Vt.

However, the on-resistance Rds (on) of the power MOSFET 30 varies greatly with changes in ambient temperature. An example of the correlation between the measured voltage Vt given by the equation (6) and the load current _Iload is shown in FIG. Here, with respect to the load current I _{load on} the horizontal axis, the vertical axis indicates an AD conversion value AD_Vt obtained by AD conversion of the measurement voltage Vt by a predetermined AD converter, and is indicated by an AD converter unit (LSB). . Since the on-resistance Rds (on) varies depending on the ambient temperature, FIG. 2 shows the correlation between the load current I _load and the AD conversion value AD_Vt of the measured voltage Vt for each different ambient temperature T.

The AD conversion value AD_Vt shown on the vertical axis in FIG. 2 can be converted into [V] units and used as the digital value Vt of the measurement voltage. Alternatively, the AD conversion value AD_Vt in LSB units may be used as it is. In the following description, the measurement value Vt of a digital value converted into [V] units will be used. The correlation between the load current I _load and the measurement voltage Vt as described above is created in advance for each ambient temperature as a voltage-current conversion table in a predetermined correlation formula or data table format, and is used to calculate the load current from the measurement voltage Vt. I _load can be calculated.

However, in order to be able to calculate the load current _Iload with high accuracy, conventionally, it has been necessary to create a voltage-current conversion table at a number of temperature points with different ambient temperatures T. Therefore, there is a problem that the data amount of the voltage-current conversion table becomes enormous. For example, when the voltage-current conversion table is created by changing the temperature point every 5 ° C. in the temperature range of ambient temperature −40 ° C. to 140 ° C., the data amount of the voltage-current conversion table for one temperature point 37 times as much data is required, and the amount of data becomes enormous.

  Therefore, in the current detection method of this embodiment, a small number of representative temperature points are selected in advance as the ambient temperature, and only the voltage-current conversion table at this representative temperature point is created and used. A method for selecting the representative temperature point of the ambient temperature will be described below.

  The on-resistance Rds (ON) of the power MOSFET 30 shows a non-linear change with respect to a change in the ambient temperature. FIG. 3 shows an example of changes in the on-resistance Rds (ON) with respect to the ambient temperature T when the horizontal axis is the ambient temperature T and the vertical axis is the on-resistance Rds (ON). In the figure, the slopes of broken lines A and B indicate temperature coefficients TC_Rds (ON) at ambient temperatures T1 and T2, respectively.

  As shown in FIG. 3, the temperature coefficient TC_Rds (ON) of the on-resistance Rds (ON) changes with the ambient temperature T, and shows a change represented by a substantially quadratic curve with respect to the ambient temperature T. Therefore, in this embodiment, a temperature range in which the temperature coefficient TC_Rds (ON) can be linearly interpolated with the ambient temperature is selected in advance, and a representative temperature point of the ambient temperature is appropriately selected based on this temperature range. As the representative temperature point, it is preferable to select a temperature point having a large change in on-resistance Rds (ON) with respect to at least the ambient temperature. As an example, −40 ° C., −25 ° C., 25 ° C., 125 ° C., and 140 ° C. can be selected as representative temperature points when the power MOSFET 30 is targeted. These representative temperature points are indicated by a one-dot chain line in FIG.

  For each representative temperature point of the ambient temperature selected in this way, a voltage-current conversion table composed of voltage-to-current data for converting the measured voltage into the load current is created in advance and used in the current detection device 100. I am doing so. The voltage-current conversion table can reduce the number of data of voltage versus current data when the change of the load current with respect to the measured voltage is small.

In the current detection method of the present embodiment, the load current I _load at the ambient temperature T is calculated with high accuracy using the voltage-current conversion table corresponding to each representative temperature point created in advance as follows. First, representative temperature points T1 and T2 sandwiching the detected ambient temperature T are obtained. Next, using the voltage-current conversion table corresponding to the representative temperature points T1 and T2, load currents I _load 1 and I _load 2 at each representative temperature point are obtained from the detected measurement voltage Vt. Further, the load current I _load 1 and I _load 2 are linearly interpolated to calculate the load current I _load at the ambient temperature T.

The load current I _load can be calculated using the following equation.
I _load = I _load 1+
(I _load 2−I _load 1) × {(T−T1) / (T2−T1)} (7)
As a result, the load current I _load can be calculated with high accuracy.

In order to calculate the load current I _load with high accuracy using the current detection method of the present embodiment, a temperature correction unit 130 is provided in the current detection device 100 of the present embodiment. The temperature correction unit 130 includes a calculation unit 131, a memory 132, a first AD conversion unit 133, and a second AD conversion unit 134. In the temperature correction unit 130, a microcomputer is used as the calculation means 131 in order to correct the influence of the change in the on-resistance Rds (ON) due to the ambient temperature by performing digital calculation processing. The voltage-current conversion table corresponding to each representative temperature point is created in advance and stored in the memory 132.

  The measurement voltage Vt input from the voltage detection circuit 110 to the temperature correction unit 130 is converted into a digital value AD_Vt by the first AD conversion unit 133 and input to the calculation unit 131. Further, the ambient temperature T of the power MOSFET measured by the temperature sensor 120 is also converted into a digital value AD_T by the second AD conversion unit 134 and input to the calculation unit 131. The digital values AD_Vt and AD_T output from the AD conversion means 133 and 134 are all in LSB units, but are converted into the measurement voltage Vt in [V] units and the ambient temperature T in [° C] units by the calculation means 131, respectively. The The calculation means 131 performs the following calculation processing using the digital measurement voltage Vt [V] and the ambient temperature T [° C.].

Based on the ambient temperature T, the calculation means 131 selects a representative temperature point T1 on the low temperature side and a representative temperature point T2 on the high temperature side sandwiching the ambient temperature T. When the representative temperature points T1 and T2 are selected, the voltage-current conversion table corresponding to each representative temperature point is read from the memory 132, and the load currents I _load 1 and I _load for the measured voltage Vt are read from the respective voltage-current conversion tables. 2 is determined. Using these load currents I _load 1 and I _load 2, the load current I _load at the ambient temperature T is calculated from the equation (7).

As described above, according to the current detection device 100 and the current detection method of the present embodiment, the voltage-current conversion table representing the correlation between the measurement voltage Vt and the load current _Iload corresponds to a representative temperature point selected in advance. It is sufficient to prepare only what to do, and the data amount of the voltage-current conversion table can be greatly reduced. Further, since the amount of data to be stored is reduced, the capacity required for the memory 132 is also reduced, and the load current can be estimated with high accuracy at low cost.

(Second Embodiment)
A current detection apparatus and a current detection method according to the second embodiment of the present invention will be described below with reference to FIG. FIG. 4 is a block diagram illustrating a configuration of the current detection device 200 according to the second embodiment. The current detection device 200 according to the present embodiment further includes an abnormality determination unit 240 in addition to the current detection device 100 according to the first embodiment. The abnormality determination unit 240 determines whether or not the load current I _load calculated by the calculation unit 131 exceeds a load current limit value set for protecting the power MOSFET 30 and the harness 20.

In the present embodiment, the semiconductor limit overcurrent characteristic provided for protecting the power MOSFET 30 and the wire limit overcurrent characteristic provided for protecting the harness 20 are stored in the memory 132 in advance. The abnormality determination unit 240 reads the semiconductor limit overcurrent characteristic and the wire limit overcurrent characteristic from the memory 132, and selects the lower one of the two as the load current limit value. Then, the load current I _load inputted from the operation unit 131 determines whether more than the load current limit, if it is determined that more than the load current limit value, requests the interruption of the load current I _load to the driver circuit 50 Output a signal. Thus, the driver circuit 50 controls the power MOSFET30 to interrupt the load current _{I load.}

  As described above, according to the current detection device 200 of the present embodiment, the load current can be estimated with high accuracy using the voltage-current conversion table with a small amount of data, as in the first embodiment. In addition, if it is determined that the load current exceeds a predetermined limit value, it is possible to block the load current and prevent damage to the power MOSFET and the harness.

(Third embodiment)
A current detection device and a current detection method according to the third embodiment of the present invention will be described below. In the current detection method of the present embodiment, the data amount of the voltage-current conversion table is reduced by reducing the representative temperature point on the low temperature side of the ambient temperature where the allowable current amount increases based on the protection characteristics of the power MOSFET 30 and the harness 20. Further reduction is made.

  As a protection characteristic of the power MOSFET 30, a semiconductor limit overcurrent characteristic that limits the time for which energization is permitted is defined by the magnitude of the current. An example of the semiconductor limit overcurrent characteristic set in the power MOSFET 30 is shown in FIG. As shown in the figure, the semiconductor limit overcurrent characteristic of the power MOSFET 30 changes depending on the ambient temperature T, and the line of the semiconductor limit overcurrent characteristic moves to the higher current side as the ambient temperature decreases. Therefore, for example, even when the current value is the same, the time during which energization is permitted becomes longer as the ambient temperature becomes lower. Even if the energization time is the same, the current value at which energization is permitted increases as the ambient temperature decreases.

  The above limit overcurrent characteristics are set similarly for the harness 20, and the wire limit overcurrent characteristics that limit the time for which the harness is energized are defined by the magnitude of the current. In the current detection device 200 of the second embodiment, the abnormality determination unit 240 uses the lower one of the semiconductor limit overcurrent characteristic and the wire limit overcurrent characteristic as the load current limit value.

In the semiconductor limit overcurrent characteristic and the wire limit overcurrent characteristic, as illustrated in FIG. 5, when the ambient temperature becomes low, the allowable current value increases rapidly. Therefore, when the ambient temperature is low, there is a sufficiently large margin for the current limit value compared to the case of normal temperature or high temperature. Therefore, when the ambient temperature is low, even if the temperature coefficient TC_Rds (ON) is not accurately corrected at the ambient temperature, the load current I _load is the current limit value given by the semiconductor limit overcurrent characteristic or the wire limit overcurrent characteristic. There is no risk of exceeding.

Therefore, in the current detection method of the present embodiment, when the ambient temperature is lower than the predetermined temperature Tc, the load current I _load is corrected using the temperature coefficient TC_Rds (ON) when the ambient temperature is Tc. To do. That is, the temperature coefficient TC_Rds (ON) changes with respect to the ambient temperature T as shown in FIG. In FIG. 6, Tc = 0 ° C. is taken as an example. Therefore, in the current detection method and current detection apparatus of the present embodiment, the ambient temperature Tc is used as a representative temperature point, a voltage-current conversion table corresponding to this temperature Tc is created in advance and stored in the memory 132, and the temperature When the ambient temperature detected by the sensor 120 is equal to or lower than Tc, the current obtained from the voltage-current conversion table corresponding to the ambient temperature Tc is set as the load current _Iload .

In the current detection method and the current detection device of the present embodiment, when the ambient temperature is equal to or lower than Tc, the load current I _load is calculated using the voltage-current conversion table corresponding to the ambient temperature Tc. Need not be set at a temperature lower than the temperature Tc, and the data amount of the voltage-current conversion table can be further reduced.

  An embodiment of the power supply apparatus of the present invention will be described with reference to FIG. FIG. 7 is a block diagram showing the configuration of the power supply apparatus according to the embodiment of the present invention. The power supply apparatus 300 of this embodiment further includes an operation switch 350 and a command receiving unit 360 in addition to the power supply 10, the power MOSFET 30, the driver circuit 50, and the current detection device 301.

The operation switch 350 is provided for a driver or the like to command the power MOSFET 30 to be turned on (energized) / off (cut off), and the command receiving unit 360 displays the command content of the operation switch 350 as a current detection device. The data is always output (with a predetermined cycle tc) to the calculation means 331 of 301. In addition to detecting the load current _Iload , the current detection device 301 of the present embodiment controls the power MOSFET 30 in accordance with the command content from the command receiving unit 360. The flow of processing in the current detection device 301 will be described with reference to the flowchart of FIG.

The processing in the current detection device 301 is executed at a cycle tc. The period tc can be set to 2 milliseconds, for example. First, the calculation means 331 inputs the command content of the operation switch 350 from the command receiving unit 360 (step S1), and determines the command content of the operation switch 350 (step S2). If the command content of the operation switch 350 is an energization command for the power MOSFET 30, the process proceeds to step S3. If the command content is a shut-off command, the process proceeds to step S4. In step S4, the arithmetic means 331 outputs a signal requesting the driver circuit 50 to cut off the load current _Iload , and the driver circuit 50 automatically controls the power MOSFET 30 to be turned off. Thereafter, the process proceeds to step S10.

On the other hand, in step S3, it is determined whether or not the load current I _load is forcibly cut off. If the load current I _load is not forcibly cut off, the process proceeds to step S5. In step S5, the calculation means 331 outputs a signal requesting energization of the load current I _load to the driver circuit 50, and the driver circuit 50 automatically controls the power MOSFET 30 to be turned on. Thereafter, the process proceeds to step S7, and processing such as calculation of the load current _Iload is performed. The process in step S7 will be described in detail with reference to the flowchart of FIG.

In the present embodiment, in order to prevent smoke from the harness 20, the current passing through the harness 20, that is, the load current I _load is monitored using a current integrated value obtained by integrating or integrating the current in a predetermined period. Similar to the semiconductor limit overcurrent characteristic shown in FIG. 5, the wire limit overcurrent characteristic for protecting the harness restricts the time during which a certain amount of current can be applied, and the current increases as the current increases. The possible time is shortened. Therefore, by monitoring so that the current integrated value obtained by integrating the current in the predetermined period (t s) does not exceed the predetermined current integration threshold, the load current I _load does not exceed the limit of the wire limit overcurrent characteristic. Can be made.

9, in step S71, the measurement voltage Vt and the ambient temperature T are input from the voltage detection circuit 110 and the temperature sensor 120, respectively. In step S72, the load current I is calculated from the measurement voltage Vt and the ambient temperature T using the voltage-current conversion table. Calculate _load . In step S73, the calculated load current I _load is stored in the memory 132 and the load current history is updated. The memory 132 stores the load current I _load for the past ts time, and every time the latest load current I _load is calculated, the oldest value is discarded and the latest value is stored. In step S74, the load current stored in the memory 132 is integrated or integrated to calculate an integrated current value. The period ts for integrating the load current can be set to 60 seconds, for example.

  The current integrated value calculated in step S7 is output to the abnormality determination unit 340, and the abnormality determination unit 340 performs the process of step S8. In step S8, the current integration value is compared with a current integration threshold value determined in advance based on the wire limit overcurrent characteristics. If the current integration value exceeds the current integration threshold value, the process of step S9 is performed. On the other hand, when the current integration value does not exceed the current integration threshold, the process proceeds to step S10.

In step S9, a signal requesting the driver circuit 50 to shut off the load current _Iload is output. Thus, power MOSFET30 is automatically controlled forced off by the driver circuit 50 to interrupt the load current _{I load.} Then, it progresses to step S10.

On the other hand, when it is determined in step S3 that the load current I _load is forcibly cut off, the process for the case of forcible cut-off is performed in step S6. The processing contents in step S6 will be described in detail with reference to the flowchart shown in FIG. First, in step S61, the ambient temperature is input from the temperature sensor 120. In step S62, it is determined whether or not the ambient temperature is lower than a predetermined return temperature. If it is determined that the ambient temperature is lower than the predetermined return temperature, the process proceeds to the next step S63 to perform a recovery process from the forced shut-off. On the other hand, if it is determined that the ambient temperature is equal to or higher than the predetermined return temperature, the process is terminated without performing the return process from the forced shutdown.

In step S63, in order to return from the forced interruption of the load current _{I load,} and outputs a signal for requesting the energization of the load current _{I load} to the driver circuit 50, the driver circuit 50 is automatically controlled on again the power MOSFET 30. When the process of step S6 is completed, the process proceeds to step S10.

In step S10, the process in the current detection device 301 is made to wait for a time tc until the next cycle is reached. As described above, according to the power supply device of the present embodiment, the load current _{I load} with the driver or the like power MOSFET30 energizing / blocked to be able to operate the load current _{I load} when power MOSFET30 is on It is possible to prevent the harness 20 from emitting smoke by monitoring the current integration value. Further, after the power MOSFET 30 is forcibly cut off to prevent the harness 20 from emitting smoke, the power MOSFET 30 is automatically turned on to automatically supply power to the load 40 when the ambient temperature decreases again and falls below the return temperature. It becomes possible to carry out efficiently.

  In addition, the description in this Embodiment shows an example of the electric current detection apparatus concerning this invention, a power supply apparatus provided with the same, and an electric current detection method, It is not limited to this. The detailed configuration and detailed operation of the current detection device and the like in the present embodiment can be changed as appropriate without departing from the spirit of the present invention.

10 Power supply 20 Harness 30 Power MOSFET
40 load 50 driver circuit 100, 200, 301 current detection device 110 voltage detection circuit 111 differential amplifier 112 transistor 113 first resistor 114 second resistor 120 temperature sensor 130, 330 temperature correction unit 131, 331 arithmetic unit 132 memory 133 first AD Conversion means 134 Second AD conversion means 240, 340 Abnormality determination unit 300 Power supply device 350 Operation switch 360 Command receiving unit

Claims (14)

A current detection device for detecting the load current connected in parallel to a switch for turning on / off a load current supplied to a load from a power source via a harness,
Current measurement resistors;
A voltage detection circuit for detecting a voltage drop due to the current measurement resistor and outputting the voltage drop as a measurement voltage;
A temperature sensor for detecting the ambient temperature of the switch;
A temperature correction unit that calculates the load current by inputting the measurement voltage and the ambient temperature from the voltage detection circuit and the temperature sensor, respectively.
The temperature correction unit is
First AD conversion means for AD converting the measurement voltage input from the voltage detection circuit;
A second AD converting means for AD converting the ambient temperature input from the temperature sensor;
A voltage-current conversion table comprising voltage-to-current data for converting the measurement voltage created in advance for each of the two or more ambient temperatures set in advance as representative temperature points into the load current is stored. Memory to
Two representative temperature points sandwiching the ambient temperature of the digital value input from the second AD conversion means are obtained, the measured voltage of the digital value input from the first AD conversion means, and the two representative temperatures input from the memory Two current values at each of the two representative temperature points are obtained from the voltage-current conversion table for each of the points, and the load current at the detected ambient temperature is calculated by linearly interpolating the two current values. A current detecting device comprising: an arithmetic means; When the load current is input from the computing means, it is determined whether a predetermined overcurrent limit condition is satisfied based on the load current, and when it is determined that the overcurrent limit condition is not satisfied, the switch The current detection device according to claim 1, further comprising an abnormality determination unit that controls the power off. The determination of the overcurrent limiting condition is determined to be satisfied when a current integral value obtained by integrating or integrating the load current or the square value of the load current in a latest fixed period is equal to or less than a predetermined current integration threshold. The current detection device according to claim 2, wherein when the current integration value exceeds the current integration threshold, it is determined that the current integration value is not satisfied. The current integration threshold is calculated based on a threshold calculated based on a predetermined limit overcurrent characteristic set to protect the switch and a wire limit overcurrent characteristic set to protect the harness. The current detection device according to claim 3, wherein the current detection device has a lower value of any one of the other threshold values. 5. The voltage-current conversion table according to claim 1, wherein when the change in the load current with respect to the measurement voltage is small, the number of data of the voltage versus current data is reduced. The current detection device described. The current detection device according to claim 1, wherein the representative temperature point is a temperature point at which a change in the resistance value of the switch with respect to at least the ambient temperature is large. The voltage detection circuit includes:
A first resistor connected in parallel to the power supply side of the switch;
A differential amplifier having a non-inverting input terminal connected to the load side of the switch and an inverting input terminal connected to the downstream side of the first resistor;
An emitter terminal is connected between the first resistor and the inverting input terminal of the differential amplifier, a collector terminal is grounded via the current measuring resistor, and a gate terminal is connected to the output terminal of the differential amplifier. The current detection device according to claim 1, further comprising a transistor. When the ambient temperature detected by the temperature sensor is lower than the lowest temperature among the two or more representative temperature points, a current value obtained from the voltage-current conversion table for the lowest temperature representative temperature point is obtained. The current detection device according to claim 1, wherein the load current is used. The current detection device according to claim 1, wherein the switch is a power MOSFET of an n-channel semiconductor switch. Power supply,
A switch for energizing or interrupting a load current supplied from the power source to a load via a harness;
The current detection device according to any one of claims 2 to 9,
An operation switch for commanding energization or interruption of the load current to the harness;
A command receiving unit that receives a command from the operation switch and outputs the command to the current detection device,
The current detection device controls the switch by inputting a command of the operation switch from the command receiver, and controls the switch to be turned off when an overcurrent is detected by the current detection device. Power supply device to do. A current detection method for measuring a predetermined voltage that varies with a load current energizing a switch and calculating the load current from the measured voltage,
A voltage-current conversion table including voltage-current data for converting the measurement voltage into the load current is created in advance for each of two or more ambient temperatures set in advance as representative temperature points of the switch. ,
Detecting the measured voltage and the ambient temperature;
Find the two representative temperature points sandwiching the detected ambient temperature,
Obtaining two current values at each of the two representative temperature points from the detected measurement voltage and the voltage-current conversion table for each of the two representative temperature points;
A current detection method comprising: linearly interpolating the two current values to calculate the load current at the detected ambient temperature. The current detection method according to claim 11, wherein the voltage-current conversion table reduces the number of data of the voltage versus current data when a change in the load current with respect to the measurement voltage is small. The current detection device according to claim 11, wherein the representative temperature point is a temperature point at which a change in resistance value of the semiconductor switch with respect to at least the ambient temperature is large. When the ambient temperature is lower than the lowest temperature among the two or more representative temperature points, a current value obtained from the voltage-current conversion table for the lowest temperature representative temperature point is used as the load current. The current detection method according to any one of claims 11 to 13.

Images