JP2013012902A - Load drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely detect a current in both on and off command periods.SOLUTION: In an on command period of a PWM driving signal, a control device 13 applies a current detected by a current detection circuit 14 and a supply voltage detected by a supply voltage detection circuit 15 to a voltage equation to calculate a resistance value and an inductance value of an on period current path. Resistance values and inductance values of paths other than a return path 12 are subtracted from those values to determine a resistance value and an inductance value of an off period current path. In an off command period, a resistance value R and an inductance value L of the off period current path, a forward voltage Vf of a diode 7, and the preceding current value determined in the preceding calculation are applied to the voltage equation to calculate a load current flowing through a linear solenoid 2 in succession.

Description

  The present invention relates to a load driving circuit including an output transistor and a return diode, and more particularly to a load driving circuit having a function of detecting a load current.

  FIG. 8 shows a conventional configuration in which an inductive load such as a linear solenoid is PWM driven by an output transistor for high side driving. The linear solenoid 2 is connected between the terminals 1a and 1b of the load driving circuit 1, and the terminals 1c and 1d are connected to the power supply lines 3 and 4 for use. In the load driving circuit 1, an output transistor 5 and a shunt resistor 6 are connected in series between a terminal 1c and a terminal 1a, and the terminal 1b is connected to a power supply line 4 (ground). A reflux diode 7 is connected in parallel to the series circuit of the shunt resistor 6 and the linear solenoid 2. The voltage detection circuit 8 amplifies the voltage of the shunt resistor 6 and outputs it to the control device 9. The control device 9 generates a PWM drive signal and applies it to the output transistor 5 via the drive circuit 10.

  In this configuration, current flows in the order from the power supply line 3 to the output transistor 5, the shunt resistor 6, and the linear solenoid 2 during the PWM command signal on command period, and during the PWM command signal off command period, the diode 7, shunt resistor 6, The current flows back through the path of the linear solenoid 2.

  In this configuration, since the current continues to flow through the shunt resistor 6 during both the on command period and the off command period of the PWM drive signal, power loss at the shunt resistor 6 increases and heat is generated. The heat generated by the shunt resistor 6 hinders high-density mounting. Further, the shunt resistor 6 generally used has a characteristic that the rate of change in resistance value (temperature change rate) due to temperature change is large. For this reason, when the temperature of the shunt resistor 6 changes with the lapse of time of PWM drive, there is a problem that current detection with high accuracy cannot be performed.

  On the other hand, the linear solenoid drive circuit described in Patent Document 1 includes a MOS transistor that is always turned on instead of a shunt resistor, and a sense MOS transistor connected in parallel to the MOS transistor. Currents in both the on command period and the off command period are detected based on the flowing current. Moreover, the solenoid drive circuit described in Patent Document 2 uses the ON resistance of the MOS transistor as the shunt resistance.

JP 2006-203415 A JP 2000-58320 A

  However, in the configurations described in Patent Documents 1 and 2, it is necessary to interpose not only a driving transistor but also a current detecting transistor in series with a solenoid as a load. For this reason, the number of components increases, resulting in an increase in circuit scale and cost. Further, the loss of the current detection transistor increases as the load current increases.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to detect the current in both the ON command period and the OFF command period with high accuracy without interposing a current detection element in the return path. It is to provide a load driving circuit.

  According to the first aspect of the present invention, the inductive load is driven by the power supply voltage applied through the first and second power supply lines and the current flowing through the load is detected. An output transistor and a load are connected in series between the first and second power supply lines, and the output transistor is turned on / off by a drive signal composed of an on command and an off command given from the drive circuit. A diode that circulates current during the off command period is connected in parallel to the load.

  Of the path through which current flows during the ON command period of the drive signal (hereinafter referred to as ON period current path), the ON period current detection means detects current during the ON command period outside the return path formed by the load and the diode. Is provided. The on-period current detection means cannot detect the return current flowing during the off-command period.

  Therefore, the off period current calculation means obtains the current flowing through the load during the off command period by calculation. For this reason, power supply voltage detection means for detecting the power supply voltage is provided. The off-period current calculation means inputs the detection current and the detected power supply voltage from the on-period current detection means and the power supply voltage detection means in the on command period. Then, the detected current and the detected power supply voltage are applied to the voltage equation of the on-period current path, and the resistance value and the inductance value of the on-period current path are calculated using a suitable one from various processing methods based on the processing capability.

  A path through which current flows during an off command period of the drive signal (hereinafter referred to as an off-period current path) is different from an on-period current path. Therefore, the resistance value and the inductance value of the off-period current path are obtained by subtracting the resistance value and inductance value of the path other than the return path (that is, the off-period current path) from the calculated resistance value and inductance value, respectively. This process is completed until the next off command period starts.

  The off-period current calculation means is configured to turn off the resistance value and inductance value of the off-period current path calculated above in the voltage equation of the off-period current path, the forward voltage of the diode, and the off-command period during the off-command period (for example, on-command The current flowing through the load is sequentially calculated by applying the detection current at the end of the period.

  According to this means, the resistance value and the inductance value of the on-period current path can be calculated by inputting and solving at least three detection currents and detected power supply voltages in the on-command period into the voltage equation of the on-period current path. The resistance value and inductance value of the off-period current path can be calculated by preparing the values of the inductance component and resistance component existing in the outer path of the return path as data in advance. As a result, the load current in both the on command period and the off command period can be detected and calculated with high accuracy without interposing a current detection element in the return path, and power loss can be reduced compared to the conventional configuration.

  According to the means described in claim 2, the on-period current detection means and the off-period current calculation means execute detection and calculation of the current flowing through the load at a predetermined sampling period. The drive circuit switches the drive signal from the on command to the off command in synchronization with the sampling period. As described above, when the sampling timing and the drive signal change timing from on to off are synchronized, the current at the start time of the off command period can be obtained by sampling at the end time of the on command period. By using this detected current as the initial value current in the off command period, the load current in the off command period can be accurately calculated.

  According to the means described in claim 3, the off-period current calculating means obtains the calculated current at the end of the off-command period obtained as a result of sequential calculation over the off-command period, and at the start of the next on-command period. Compare with the detected current. When there is a difference between the two, learning control is performed to correct at least one of the resistance value and inductance value of the off-period current path and the forward voltage of the diode and to store the correction value so as to reduce the difference. By using the previously stored correction value in the next off command period, even if there is an error in the constant used to calculate the load current in the off command period, the calculated current value can be brought closer to the true value and higher Calculation accuracy is obtained.

  According to the means described in claim 4, the temperature detecting means for detecting the temperature correlated with the temperature of the diode (for example, the ambient temperature of the diode) is provided. The off-period current calculation means has characteristic information indicating the relationship between the diode temperature, forward voltage, and forward current. The off-period current path calculated current (for example, the previously calculated value), the temperature detected by the temperature detection means, and the above-mentioned Based on the characteristic information, the forward voltage of the diode applied to the voltage equation of the off-period current path is obtained. As a result, the forward voltage of the diode that varies depending on the temperature and forward current and has characteristic variations can be obtained accurately, so that the load current in the off command period can be calculated more accurately.

  According to the means described in claim 5, the forward voltage detecting means for detecting the forward voltage of the diode is provided. The off-period current calculation means applies the detected forward voltage to the voltage equation of the off-period current path. As described above, since the forward voltage of the diode changes due to temperature, forward current, variation, and the like, the load current in the off command period can be calculated more accurately by applying the actually detected forward voltage.

  According to the means described in claim 6, the output transistor is constituted by a MOS transistor, and the on-period current detection means is provided with a shunt resistor. The off-period current calculation means subtracts the resistance value of the first and second power supply lines, the resistance value of the on-resistance of the MOS transistor, and the resistance value of the shunt resistance from the calculated resistance value of the on-period current path. Find the resistance value of the path. These resistance values are variously changed when the load driving circuit is employed, and can be measured or calculated in advance. Thereby, the load current in the off command period can be accurately calculated.

The block diagram of the load drive circuit which shows the 1st Embodiment of this invention The figure which shows each waveform of the applied voltage and current of a linear solenoid 2 equivalent diagram The figure which shows the current waveform of the linear solenoid in the 2nd Embodiment of this invention. FIG. 1 equivalent view showing a third embodiment of the present invention (A) is a figure which shows the forward voltage-current characteristic of a diode, (b) is a figure which shows the characteristic information memorize | stored in memory. FIG. 1 equivalent view showing a fourth embodiment of the present invention 1 equivalent diagram showing the prior art

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. 1 to 3.
FIG. 1 shows the configuration of a high-side drive load drive circuit, and the same reference numerals are given to portions corresponding to the load drive circuit shown in FIG. The load driving circuit 11 is mounted on an electronic control unit (ECU) of a vehicle, for example, and PWM drives a hydraulic control linear solenoid 2 (corresponding to an inductive load) connected between output terminals 11a and 11b. The load current flowing through the linear solenoid 2 is detected (including calculation). The power terminals 11c and 11d are connected to power lines 3 and 4 (first and second power lines) connected to a battery (not shown).

  Inside the load driving circuit 11, an N-channel MOS transistor 5 (hereinafter referred to as the output transistor 5) and a shunt resistor 6 are connected in series between the power supply terminal 11c and the output terminal 11a. The drive circuit 10 outputs a PWM drive signal in which an on command period and an off command period having a commanded duty ratio are repeated at a PWM cycle. The output transistor 5 is driven by this PWM drive signal.

  Since the output transistor 5 is a high-side drive element, the drive circuit 10 includes a boost power supply (not shown) such as a charge pump circuit. The drive circuit 10 applies a voltage Vcp higher than the power supply voltage by at least the gate-source voltage VGS to the gate of the output transistor 5 during the ON command period. Thereby, during the ON command period, a load current flows through an ON period current path from the power supply line 3 to the power supply line 4 via the output transistor 5, the shunt resistor 6 and the linear solenoid 2.

  Between the output terminals 11 a and 11 b, a reflux diode 7 is connected so that the terminal 11 a side is a cathode and is parallel to the linear solenoid 2. During the off command period, a load current flows through the return path 12 (off period current path) composed of the linear solenoid 2 and the diode 7.

  The voltage detection circuit 8 amplifies the voltage of the shunt resistor 6 and outputs it to the control device 13 as a detection current. The shunt resistor 6 and the voltage detection circuit 8 constitute a current detection circuit 14 (on-period current detection means). The shunt resistor 6 is provided outside the return path 12 in the on-period current path, that is, between the output transistor 5 and the return path 12 so that no loss occurs in the shunt resistance 6 during the off command period. The current detection circuit 14 can detect the load current flowing through the linear solenoid 2 only during the ON command period.

  The power supply voltage detection circuit 15 is composed of, for example, a voltage dividing resistor, and detects the power supply voltage between the power supply lines 3 and 4. This detected power supply voltage is required when calculating the resistance value and inductance value of the on-period current path, as will be described later.

  The control device 13 is composed of a microcomputer, and a plurality of channels of A / D converters 16 and PWM drive signals that receive the voltage output from the current detection circuit 14 and the voltage output from the power supply voltage detection circuit 15 as inputs. In addition to a control program and a non-volatile memory 17 for storing data. The control device 13 corresponds to off-period current calculation means, and executes detection and calculation of load current and output of a PWM drive signal in synchronization with a predetermined sampling period.

  Next, the operation of the present embodiment will be described with reference to FIGS. 2 and 3 show waveforms of applied voltage and current of the linear solenoid 2. The white dots shown in the figure are the detected value and the calculated value.

  The control device 13 feedback-controls the duty ratio of the PWM drive signal so that the load current flowing through the linear solenoid 2 becomes equal to the command value. For this reason, the control device 13 needs to detect (calculate) the load current not only during the on command period of the PWM drive signal but also during the off command period. However, since the current detection circuit 14 is arranged outside the return path 12 so as not to cause a loss during the off command period as described above, the current cannot be directly detected during the off command period.

  Therefore, the control device 13 calculates the resistance value and the inductance value of the on-period current path using the detected current and the detected power supply voltage during the on-command period. Then, the resistance value and inductance value of the return path 12 (off-period current path) are subtracted from the detected resistance value and inductance value of the on-period current path by subtracting the resistance value and inductance value of paths other than the return path 12, respectively. Ask. The load current during the off command period is calculated using the obtained resistance value and inductance value. This will be specifically described below.

(A) ON command period (Fig. 2)
The on-period current path is an RL circuit, and its voltage equation can be expressed by the following equation (1). Here, i is the load current, V is the power supply voltage, R is the resistance of the on-period current path, and L is the inductance of the on-period current path.

The resistance R includes the resistance component of the linear solenoid 2, the ON resistance of the output transistor 5, the shunt resistance 6, and the resistance of the wire harness that constitutes the power supply lines 3 and 4. The inductance L includes an inductance component of the linear solenoid 2 and the like. When the current i is solved from this voltage equation, equation (2) is obtained. A is a constant determined by conditions.

In order to obtain the resistance value R and the inductance value L in the equation (2), the current values i0, i1, i2 at three different times t0, t1, t2 in the ON command period and the voltage values V0, V1 at the times t0, t1. (3) and (4) are used to express (2) in a discrete manner.

  For example, the on-period is applied to the equations (3) and (4) by applying the detected current values i0, i1, i2, and the power supply voltage values V0, V1 at times t0, t1 shown in FIG. Calculate the resistance and inductance values of the current path. Since the control device 13 is constituted by a microcomputer, various calculation methods such as numerical calculation, analytical solution, approximate calculation, and table reference can be used.

  In order to calculate the load current during the off command period, it is necessary to acquire only the resistance value and the inductance value included in the return path 12 that is the off period current path. Therefore, the resistance value and inductance value of paths other than the return path 12 in the on-period current path are measured or calculated in advance and stored in the memory 17 as data. The resistance of the path other than the reflux path 12 includes the ON resistance of the output transistor 5, the shunt resistance 6, the resistance of the wire harness, and the like. The inductance of the path other than the return path 12 includes the inductance of the wire harness, but is usually sufficiently smaller than the inductance of the linear solenoid 2.

  The control device 13 subtracts the resistance value and the inductance value stored in the memory 17 from the resistance value and inductance value of the on-period current path calculated from the expressions (3) and (4), respectively, to thereby determine the resistance of the reflux path 12. Find the value and inductance value. The calculation processing so far needs to be completed before the off command period starts.

(B) Off command period (Fig. 3)
The return path 12 which is an off-period current path is also an RL circuit, and a voltage equation thereof can be expressed by the following equation (5). Here, i is the load current, Vf is the forward voltage of the diode 7, R is the resistance of the off-period current path, and L is the inductance of the off-period current path.

The resistance R is mainly a resistance component of the linear solenoid 2, and the inductance L is mainly an inductance component of the linear solenoid 2. When the current i is solved from this voltage equation, equation (6) is obtained. B is a constant determined by conditions.

For each sampling period, the control device 13 substitutes the resistance value R and inductance value L of the off-period current path, the forward voltage Vf of the diode 7 and the previous current value calculated in the previous sampling period into the equation (6), The load current flowing through the linear solenoid 2 is sequentially calculated from t1 to t6. For example, the detected current values i1 and i2 at times t1 and t2 shown in FIG. 3 can be obtained by calculating Expressions (7) and (8), respectively. I0 applied to the equation (7) is a detected current at the end of the ON command period, that is, at the start of the OFF command period.

  Time t6 is not only the end of the off command period but also the start of the on command period. Therefore, the control device 13 can directly detect the load current by the current detection circuit 14 after changing the PWM drive signal to the ON command at time t6. The calculated current value at time t6 can be used, for example, for learning control described in the second embodiment.

  According to the present embodiment described above, the shunt resistor 6 of the current detection circuit 14 is arranged outside the return path 12 in the on-period current path, so that no current flows through the shunt resistor 6 during the off command period, and load driving is performed. Loss generated in the circuit 11 can be reduced. Moreover, since the heat generation of the shunt resistor 6 is reduced, a change in the resistance value of the shunt resistor 6 due to the heat generation can be suppressed, and the current detection accuracy can be increased. Furthermore, high-density mounting is possible.

  The arrangement of the shunt resistor 6 as described above makes it impossible to directly detect the load current during the off command period. Therefore, the control device 13 calculates the resistance value and the inductance value of the on-period current path by applying the detected current and the detected power supply voltage to the voltage equation of the on-period current path in the on-command period. The resistance value and inductance value of the off-period current path are calculated by subtracting the resistance value and inductance value of the current path. In the off command period, the load current is sequentially calculated by applying the resistance value and inductance value of the off period current path, the forward voltage of the diode 7 and the current at the start of the off command period to the voltage equation of the off period current path. To do. As a result, the ON resistance of the output transistor 5, the shunt resistance 6, the resistance of the wire harness, and the like are removed from the constant of the return path 12 used for calculating the current during the OFF command period, so that the load current during the OFF command period is accurately calculated. be able to.

  Since the sampling timing of current detection and power supply voltage detection and the on / off change timing of the PWM drive signal are synchronized, the detection current at the start time of the off command period can be obtained by sampling at the end time of the on command period. By using this detected current as the initial value current in the off command period, the load current in the off command period can be accurately calculated.

(Second Embodiment)
Next, a second embodiment will be described with reference to FIG. FIG. 4 shows a current waveform of the linear solenoid 2. The dot on the broken line shown in the off command period is a calculated current by the control device 13 described in the first embodiment, and the solid line shown in the off command period is a conventional configuration in which the shunt resistor 6 is provided in the return path 12. This is the detected current (actual load current).

  The control device 13 can detect an accurate load current by the current detection circuit 14 during the ON command period. However, in the off command period, an error may occur in the calculated load current due to a difference between the resistance value and the inductance value used as constants of the off period current path, the forward voltage of the diode 7, and the like. Therefore, the control device 13 obtains an error of the calculated load current by comparing the current value ia calculated at the end of the off command period with the current value ib detected at the start of the on command period.

  The control device 13 corrects at least one of the resistance value and inductance value of the off-period current path and the forward voltage of the diode 7 so as to reduce this error, and stores the correction value in the memory 17. For example, when ia> ib, the resistance correction value ΔR is increased so as to increase the resistance value of the off-period current path, and when ia <ib, the resistance correction value ΔR is decreased so as to decrease the resistance value of the off-period current path. Make corrections to reduce. When determining the resistance value of the off-period current path in the next on-command period, the control device 13 adds the resistance correction value ΔR stored in the memory 17 to the resistance value obtained from the equations (3) and (4). To do.

  As another example, when ia> ib, the forward voltage correction value ΔVf is increased so as to increase the forward voltage Vf of the diode 7, and when ia <ib, the forward voltage Vf of the diode 7 is decreased. Correction is performed to reduce the voltage correction value ΔVf. According to the present embodiment, even when there is an error in the constant used to calculate the load current during the off command period, such as an error in the resistance component of the wire harness, the calculated current value can be brought close to the true value, and the calculation accuracy Can be further enhanced.

(Third embodiment)
FIG. 5 shows the configuration of the load drive circuit according to the third embodiment, and the same parts as those in FIG. The load drive circuit 21 includes a thermistor 22. The thermistor 22 is temperature detecting means for detecting at least a temperature correlated with the temperature of the diode 7, preferably the temperature of the diode 7 itself, and is desirably arranged in the vicinity of the diode 7.

  The control device 23 includes a conversion circuit that converts the resistance of the thermistor 22 into a voltage and supplies the voltage to the A / D converter 16. The A / D converter 16 inputs the converted voltage and performs A / D conversion. The memory 17 includes a control program, resistance values and inductance values of the off-period current path, correction values learned as necessary, thermistor correction information for obtaining the temperature from the conversion values of the A / D converter 16, diodes 7 stores characteristic information indicating the relationship between temperature, forward voltage, and forward current.

  FIG. 6A shows the forward voltage-current characteristics of the diode 7 at three different temperatures T1, T2, and T3 (T1> T2> T3). In general, the voltage-current characteristics in the forward direction of a diode have a negative temperature coefficient, and the forward voltage decreases with increasing temperature. If the temperature and forward current of the diode 7 are determined, the forward voltage Vf of the diode 7 is determined.

  As shown in FIG. 6B, the memory 17 stores forward characteristic information indicating the relationship among the temperature, forward voltage, and forward current of the diode 7 in a table format, for example. In the figure, specific voltage values are omitted. Since there are variations in the characteristics of the diode, it is preferable to store the characteristic information in the memory 17 after measuring the characteristic information of the diode 7 in advance. In this case, all data may be measured, but simply, a plurality of selected data may be measured, and non-selected data may be approximated based on the measured data.

  The calculation method of the load current in the off command period is as described in the first embodiment except for the application of the forward voltage of the diode 7. The control device 23 A / D-converts the conversion voltage related to the thermistor 22 at a predetermined time interval, for example, every PWM cycle, and detects the temperature of the diode 7. Then, the forward voltage Vf of the diode 7 is obtained based on the detected temperature of the diode 7, the current of the return path 12 obtained in the previous calculation, and the characteristic information stored in the memory 17. The controller 23 linearly substitutes the resistance value R and inductance value L of the off-period current path, the forward voltage Vf of the diode 7 obtained as described above, and the previous current value obtained in the previous calculation into the equation (6). The load current flowing through the solenoid 2 is sequentially calculated.

  According to this embodiment, even if there is a forward voltage variation due to temperature or a variation in forward voltage for each element in the diode 7, an accurate forward voltage can be obtained and used to load current during the off command period. Can be calculated accurately.

(Fourth embodiment)
FIG. 7 shows the configuration of the load drive circuit according to the fourth embodiment, and the same parts as those in FIG. The load drive circuit 31 includes a voltage detection circuit 32 (forward voltage detection means) that receives the voltage between the cathode and anode of the diode 7 as an input.

  The control device 33 performs A / D conversion on the output voltage of the voltage detection circuit 32 for each sampling period in the off command period, and applies the obtained detection forward voltage Vf to the equation (6). With this configuration, even when there is a variation in forward voltage due to temperature or a variation in forward voltage for each element, the load current in the off command period can be calculated using an accurate forward voltage.

(Other embodiments)
As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to embodiment mentioned above, A various deformation | transformation and expansion | extension can be performed within the range which does not deviate from the summary of invention.
In each of the above embodiments, the resistance value and the inductance value of the on-period current path are calculated using the detected values at times t0, t1, and t2 including the start time of the on-command period. A value may be used. Further, it may be calculated by applying four or more different detected values to the equation (2).

It is good also as a structure which combined 2nd Embodiment and 3rd Embodiment. Moreover, it is good also as a structure which combined 2nd Embodiment and 4th Embodiment.
The shunt resistor 6 may be provided between the return path 12 and the power supply line 4 in the on-period current path. Further, a sense MOS transistor for the output transistor 5 may be used as the on-period current detection means.
The load is not limited to a linear solenoid as long as it is inductive.

  In the drawing, 2 is a linear solenoid (inductive load), 3 is a first power supply line, 4 is a second power supply line, 5 is an output transistor, 6 is a shunt resistor, 7 is a diode, 10 is a drive circuit, 11 and 21 , 31 is a load drive circuit, 13, 23 and 33 are control devices (off period current calculation means), 14 is a current detection circuit (on period current detection means), 15 is a power supply voltage detection circuit (power supply voltage detection means), 22 Is a thermistor (temperature detection means), and 32 is a voltage detection circuit (forward voltage detection means).

Claims (6)

In a load driving circuit for driving an inductive load by a power supply voltage applied through first and second power supply lines and detecting a current flowing through the load,
An output transistor interposed in series with the load between the first and second power supply lines;
A drive circuit for applying a drive signal comprising an on command and an off command to the output transistor;
A diode that is connected in parallel to the load and circulates the current flowing through the load during an off command period of the drive signal;
On-period current detection means for detecting a current flowing in the on-command period, provided outside the return path formed from the load and the diode among the current paths in the on-command period of the drive signal;
Power supply voltage detecting means for detecting the power supply voltage;
In the on-command period, the resistance value and inductance of the on-period current path are applied by applying the detection current and the detected power supply voltage input from the on-period current detection means and the power supply voltage detection means to the voltage equation of the on-period current path. A resistance value and an inductance value of a path other than the return path are subtracted from the resistance value and the inductance value, respectively, to obtain a resistance value and an inductance value of an off-period current path. The current flowing through the load is sequentially calculated by applying the resistance value and inductance value of the off-period current path, the forward voltage of the diode, and the detected current before transitioning to the off-command period to the voltage equation of the period current path. A load driving circuit comprising an off-period current calculation means. The on-period current detection means and the off-period current calculation means execute detection and calculation of a current flowing through the load at a predetermined sampling period,
2. The load drive circuit according to claim 1, wherein the drive circuit switches the drive signal from an on command to an off command in synchronization with the sampling period.   The off period current calculation means has a difference between the calculated current at the end of the off command period obtained as a result of the sequential calculation over the off command period and the detected current at the start of the next on command period A learning control for correcting at least one of a resistance value and an inductance value of the off-period current path and a forward voltage of the diode and storing the correction value so as to reduce the deviation. The load driving circuit according to claim 1 or 2. Temperature detecting means for detecting a temperature having a correlation with the temperature of the diode;
The off-period current calculation means has characteristic information indicating the relationship between the temperature, forward voltage, and forward current of the diode, the calculated current of the off-period current path, the temperature detected by the temperature detection means, and the characteristic information 4. The load drive circuit according to claim 1, wherein a forward voltage of the diode applied to the voltage equation of the off-period current path is obtained based on A forward voltage detecting means for detecting a forward voltage of the diode;
The load drive circuit according to claim 1, wherein the off-period current calculation unit applies the detected forward voltage to a voltage equation of the off-period current path. The output transistor is composed of a MOS transistor,
The on-period current detection means includes a shunt resistor,
The off-period current calculation means subtracts the resistance value of the first and second power supply lines, the resistance value of the on-resistance of the MOS transistor, and the resistance value of the shunt resistor from the calculated resistance value of the on-period current path. The load drive circuit according to claim 1, wherein a resistance value of the off-period current path is obtained.

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