JP3596415B2 - Inductive load drive circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an inductive load driving circuit for driving an inductive load by supplying a current to an inductive load such as a motor or a solenoid, and particularly to an inductive load driving circuit having a function of detecting an overcurrent. Circuit.
[0002]
[Prior art]
2. Description of the Related Art A load driving circuit that drives a load by performing current control and current detection with high accuracy and supplying power to the load has been known.
Some of such load drive circuits have a function of detecting an overcurrent of a current flowing through the load. For example, the load driving circuit includes a first switching unit including a power MOSFET or the like that conducts / cuts off a current path to the load. One that detects an overcurrent by using a current mirror circuit constituted by a second switching means composed of a power MOSFET or the like that supplies a smaller current than the first switching means. The first switching means and the second switching means are controlled by the same drive command signal, and the second switching means has a current proportional to the first switching means (for example, the first switching means: the second switching means = 1000: 1).
[0003]
In the load drive circuit having the overcurrent detection function configured as described above, for example, when an abnormality such as a ground short (ground short) occurs in the load and an overcurrent flows through the first switching means, the second switching is performed. The current of the means becomes, for example, 1/1000 (1/1000) of the overcurrent of the first switching means, and the abnormality is detected by flowing the current through a resistor or the like.
[0004]
On the other hand, such a load drive circuit includes, for example, an inductive load drive circuit for drive-controlling (such as PWM (Pulse Width Modulation) control) an inductive load such as a motor or a solenoid.
Then, the inductive load has a characteristic that when a current to be supplied fluctuates sharply, a flyback voltage (back electromotive force) is instantaneously generated at both ends thereof. That is, assuming that the inductance of the inductive load (for example, about several tens [mH]) is L, a voltage V (= −L (di / di / dt)) occurs.
[0005]
For this reason, when the first switching means is turned off based on the drive command signal to stop energizing the inductive load, a flyback voltage is instantaneously generated at both ends of the inductive load due to the stop of energizing, and the first switching means is turned off. The potential V1 may be lower than the ground potential (0 [v]). At this time, the second switching means is also turned off based on the drive command signal, but since the second potential V2 does not drop below the ground potential, the first potential V1 is lower than the second potential V2, A large current flows through the detection resistor, and an overcurrent is erroneously detected.
[0006]
To solve such a problem, there is an inductive load drive circuit configured to prevent an erroneous detection of an overcurrent by providing a filter that delays the detection of the overcurrent for a predetermined time. FIG. The inductive load driving circuit 1a shown in FIG. 2 detects an overcurrent that flows through a first transistor 51 composed of an n-channel power MOSFET and is larger than a first specified value.
[0007]
Then, based on the drive command signal Sb output from the gate drive circuit 55, the first transistor 51 transfers the current from the power supply line LV to which the output (power supply voltage) Vc from the DC power supply (not shown) is supplied to the inductive load. The first energizing path for supplying to the LL is energized and cut off. Note that the gate drive circuit 55 outputs a drive command signal Sb in accordance with the control command signal Sa output by the control logic 57, and the control logic 57 performs current control of the inductive load LL. The control command signal Sa is output.
[0008]
When the first potential V1 at the current output terminal of the first transistor 51 becomes lower than the second potential V2 at the current output terminal of the second transistor 53 composed of an n-channel type power MOSFET, the output signal of the first comparator 61 changes. It becomes high level, and the third transistor 63 composed of an npn-type transistor is driven. As a result, a current flows through the second conduction path including the second transistor 53, the third transistor 63, and the resistor 65, and a potential difference generated between both ends of the resistor 65 due to the current is a constant voltage power supply set for overcurrent determination. When the output voltage of the second comparator 67 is exceeded, the output signal of the second comparator 67 becomes high level. The output signal of the second comparator 67 is input to the gate drive circuit 55 via the filter 71. When the high-level signal is input, the gate drive circuit 55 stops outputting the drive command signal Sb. Thereby, the energization in the first energization path is stopped, and the first transistor 51 is protected from overcurrent.
[0009]
At this time, the filter 71 outputs an output signal to the gate drive circuit 55 when a certain period (for example, several μsec to several tens μsec) has elapsed since the output signal of the second comparator 67 was input. Is configured.
In other words, the inductive load drive circuit having the overcurrent detection function shown in FIG. 2 is provided with the filter 71 to delay the detection time of the overcurrent so that the instantaneous voltage fluctuation does not determine the overcurrent. Is configured. For this reason, it is possible to prevent an erroneous determination of an overcurrent due to an instantaneous voltage fluctuation generated by the flyback voltage of the inductive load.
[0010]
[Problems to be solved by the invention]
However, in the conventional inductive load drive circuit as shown in FIG. 2, during a delay period in which the output signal of the second comparator 67 is delayed by the filter 71, an overcurrent flows through the conduction path. As a result, the first transistor (first switching means) 51 may be damaged.
[0011]
Here, the semiconductor device (such as a power MOSFET) used as the first switching means becomes more expensive as the current carrying capacity is larger. It is desirable to use a semiconductor element having a small capacity as the switching means. For this reason, in an actual inductive load drive circuit, a semiconductor element having a capacity slightly larger than the rated current of the load is often used as the switching means.
[0012]
When detecting an overcurrent in an inductive load drive circuit using a switching means having a small margin with respect to the rated current as described above, if a delay process of signal output is performed, an overcurrent flowing during the delay period causes The possibility that the switching means is damaged increases.
[0013]
The present invention has been made in view of such a problem, and when detecting an overcurrent of a current supplied to an inductive load such as a motor or a solenoid, suppresses erroneous detection due to a flyback voltage and accurately detects the overcurrent. It is another object of the present invention to provide an inductive load driving circuit that can prevent the switching means from being damaged by an overcurrent.
[0014]
[Means for Solving the Problems]
According to the inductive load driving circuit of the present invention (claim 1), it is not possible to erroneously determine an overcurrent due to a flyback voltage generated by stopping the supply of current to the inductive load, and the overcurrent is accurately detected. be able to. In addition, the processing for detecting the overcurrent can be performed quickly, and the first switching means can be protected from the overcurrent, so that the first switching means is less likely to be damaged by the overcurrent.
[0015]
When the control command signal is not output, the first switching means is turned off and no current flows, so that no overcurrent flows in the first energizing path. Therefore, there is no problem caused by stopping the overcurrent detection. .
Here, as the switching means in the above-described inductive load driving circuit, for example, a bipolar transistor or a field effect transistor (FET) can be used. It is preferable to use a first switching means and a second switching means composed of an n-channel MOSFET for flowing a current smaller than the current flowing by the first switching means.
[0016]
That is, since the MOSFET has a smaller resistance in the current path than the bipolar transistor and can perform high-speed switching, the MOSFET has excellent switching characteristics of a large current, and conducts and cuts off the current path from the DC power supply to the load. Suitable for MOSFETs are classified into an n-channel type and a p-channel type depending on the type of carriers (holes or electrons). Since the n-channel type is less expensive than the p-channel type, the load using the n-channel type MOSFET is low. The drive circuit can be realized at low cost.
[0017]
In addition, since the first switching means and the second switching means can be simultaneously driven and controlled by one command signal (drive command signal), overcurrent can be detected by comparing the first potential with the second potential. It becomes. In addition, a current proportional to the current flowing in the first current path can flow in the second current path, and the current flowing in the second current path is small at this time. The consumption is reduced.
[0018]
Next, according to the third aspect of the present invention, since the current flowing through the second switching means is proportional to the current flowing through the first switching means, the inductive load driving circuit includes: A current proportional to the first current path flows. Then, when an overcurrent exceeding the first specified value flows through the first current path, the current flowing through the second current path exceeds the second specified value set according to the first specified value, An overcurrent in the first current path can be detected based on the current flowing in the second current path.
[0019]
As described above, in addition to the comparison between the first potential and the second potential, the current value in the first current path is determined based on the current flowing in the second current path to detect an overcurrent, so that the first potential and the second potential are detected. The overcurrent can be detected more accurately as compared with the overcurrent detection based only on the comparison with the second potential.
[0020]
Therefore, according to the present invention (claim 3), the overcurrent in the first energization path can be detected more accurately, so that the first switching means can be more reliably protected.
Further, according to the inductive load drive circuit of the present invention (claim 4), the influence of the flyback voltage is suppressed by adding the overcurrent detection stop means without newly developing the overcurrent detection means. Therefore, an inductive load drive circuit that can suppress erroneous detection of overcurrent can be realized at low cost.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an inductive load drive circuit for performing drive control of an inductive load. The inductive load drive circuit has an overcurrent detection function.
[0022]
As shown in FIG. 1, the inductive load driving circuit according to the present embodiment converts the current from the power supply line LV supplied with the output (for example, power supply voltage 12 [v]) Vc from a DC power supply (not shown) into an inductive load. A first transistor 11 composed of an n-channel type power MOSFET for energizing / disconnecting a first energizing path for supplying to the LL, and an n for energizing / disabling a second energizing path for supplying current from the power supply line LV to the resistor 25 A second transistor 13 composed of a channel type power MOSFET, a gate drive circuit 15 for outputting a drive command signal Sb for driving the first transistor 11 and the second transistor 13, and a control for driving and controlling the inductive load LL And a control logic 17 for outputting the command signal Sa.
[0023]
The control logic 17 is configured by a microcomputer using a process using a CMOS transistor, and operates by power supply from a power supply device (for example, an output voltage of 5 [v]) (not shown), and performs complicated control processing. A control command signal Sa for controlling the inductive load LL is output.
[0024]
Further, the gate drive circuit 15 includes a charge pump, and outputs a drive command signal Sb capable of driving the first transistor 11 and the second transistor 13 according to a control command signal Sa output from the control logic 17. . That is, the gate drive circuit 15 is a circuit that converts a low-potential signal (control command signal Sa) into a high-potential signal (drive command signal Sb), and in accordance with the control command signal Sa, A high-potential drive command signal Sb is output.
[0025]
Further, the first transistor 11 has a gate connected to the output terminal of the drive command signal Sb in the gate drive circuit 15, a drain connected to the power supply line LV, and a source connected to the inductive load LL. Then, when the drive command signal Sb goes to a high level, the first transistor 11 is turned on, and a current flows through the first current path from the power supply line LV to the inductive load LL.
[0026]
Therefore, in the inductive load drive circuit 1, when the control logic 17 sets the control command signal Sa to the high level, the gate drive circuit 15 sets the drive command signal Sb to the high level, whereby the first transistor 11 is turned on. As a result, power is supplied from the power supply line LV to the inductive load LL through the first power supply path.
[0027]
The second transistor 13 has a gate connected to the output terminal of the drive command signal Sb in the gate drive circuit 15, a drain connected to the power supply line LV, and is turned on when the drive command signal Sb goes to a high level. Further, a small current proportional to the first transistor 11 flows.
[0028]
In addition to the above configuration, the inductive load driving circuit 1 has an inverting input terminal (-) connected to the source of the first transistor 11 and a non-inverting input terminal (+) connected to the source of the second transistor 13. A first comparator (hereinafter, referred to as a first comparator) 21 and an npn-type transistor having a collector connected to the source of the second transistor 13 and a base connected to the output terminal of the first comparator 21. A non-inverting input terminal (+) is connected to the third transistor 23, a resistor 25 having one end connected to the emitter of the third transistor 23 and the other end grounded, and a connection point between the emitter of the third transistor 23 and the resistor 25. A second comparator (hereinafter, referred to as a second comparator) 27 having an output terminal connected to the gate drive circuit 15, and an inverting input of the second comparator 27. Child (-) cathode is connected to, and a constant voltage power source 29 for the negative electrode is grounded and.
[0029]
When the potential of the source of the first transistor 11 (hereinafter, referred to as a first potential) V1 becomes lower than the potential of the source of the second transistor 13 (hereinafter, referred to as a second potential) V2, the first comparator 21 outputs. The output signal Sc becomes high level, and the third transistor 23 is turned on. Then, a current flows from the power supply line LV to the second conduction path leading to the ground (ground) via the second transistor 13, the third transistor 23, and the resistor 25.
[0030]
Here, for example, when an abnormality such as a ground short (ground short) occurs in the inductive load LL, an overcurrent flows through the first transistor 11 and the first potential V1 becomes the ground potential (0 [v]). , The first potential V1 becomes lower than the second potential V2. Therefore, the first comparator 21 detects an overcurrent in the first conduction path by comparing the first potential V1 with the second potential V2.
[0031]
When an overcurrent flows in the first current path, the first comparator 21 drives the third transistor 23 to cause a current to flow in the second current path. At this time, the current flowing in the second current path is , The magnitude is proportional to the current flowing through the first current path. In addition, since a potential difference proportional to the current flowing through the second current path occurs at both ends of the resistor 25, the voltage across the resistor 25 has a magnitude proportional to the current flowing through the first current path.
[0032]
At this time, the constant voltage power supply 29 is configured by a constant voltage power supply that outputs a voltage equal to the voltage value obtained by multiplying the resistance value of the resistor 25 by the second specified value of the current in the second current path. . The second specified value is a value of a current flowing through the second current path when a current equal to the first specified value flows through the first current path. The first specified value is an index of an overcurrent in the current flowing through the first transistor 11, and a current larger than the first specified value is an overcurrent.
[0033]
Then, the second comparator 27 outputs a high-level signal to the gate drive circuit 15 when the voltage across the resistor 25 becomes higher than the output voltage of the constant voltage power supply 29. That is, the second comparator 27 detects the current flowing in the first current path based on the current flowing in the second current path, and detects the overcurrent by making the current flowing in the first current path larger than the first specified value. The detection is notified to the gate drive circuit 15.
[0034]
Therefore, in the inductive load driving circuit 1, the first comparator 21 compares the first potential V1 with the second potential V2, and furthermore, the second comparator 27 performs the first based on the current flowing through the second current path. By detecting the current flowing in the current path, an overcurrent flowing in the first transistor 11 is detected.
[0035]
As described above, not only the comparison of the potentials at the current output terminals of the transistors, but also the detection of the overcurrent by detecting the current flowing through the first energizing path enables the overcurrent to be detected with higher accuracy. . Further, since the current flows through the second conduction path only when the first comparator 21 drives the third transistor 23, the power consumption required for detecting the overcurrent is smaller than when the current always flows through the second conduction path. Can be suppressed.
[0036]
Then, the gate drive circuit 15 to which the signal from the second comparator 27 has been input stops the output of the drive command signal Sb to a low level regardless of the state of the control command signal Sa, and turns off the first transistor 11. To Thereby, the energization in the first energization path is stopped, and the first transistor 11 is protected from overcurrent.
[0037]
Further, the inductive load drive circuit 1 includes an overcurrent detection stop circuit 31 that stops overcurrent detection based on the control command signal Sa. The overcurrent detection stop circuit 31 includes an inverter circuit 33 for inverting a signal level, a resistor 35, and a detection stop transistor 37 formed of an npn transistor.
[0038]
First, when the input signal input to the input terminal is at a high level (for example, a potential of 5 [v]), the inverter circuit 33 outputs a signal of a low level (for example, a ground potential of 0 [v]). When the signal is at a low level, a high-level signal is output. The input terminal of the inverter circuit 33 is connected to the output terminal of the control command signal Sa in the control logic 17.
[0039]
The detection stop transistor 37 has a base connected to the output terminal of the inverter circuit 33 via the resistor 35, a collector connected to the base of the third transistor 23, and an emitter grounded.
Therefore, in the overcurrent detection stop circuit 31, when the control command signal Sa is at a low level, the output signal of the inverter circuit 33 is at a high level, and the detection stop transistor 37 is turned on. As a result, the base potential of the third transistor 23 is maintained at the low level, and the third transistor 23 is forcibly maintained in the off state regardless of the operation of the first comparator 21. Therefore, current does not flow through the second conduction path, and the second comparator 27 does not output a high-level signal.
[0040]
When the control command signal Sa is at a high level, the output signal of the inverter circuit 33 is at a low level, and the detection stop transistor 37 is turned off. As a result, the base potential of the third transistor 23 is determined by the first comparator 21, and when the first comparator 21 detects an overcurrent, the third transistor 23 is turned on and a current flows through the second current path.
[0041]
Therefore, the overcurrent detection stop circuit 31 stops the detection of the overcurrent by the second comparator 27 by forcibly turning off the third transistor 23 when the control command signal Sa becomes low level.
Therefore, in the present inductive load drive circuit 1, the first potential V1 is lower than the second potential V2 due to the flyback voltage (back electromotive force) generated when the power supply is stopped in the drive control of the inductive load LL. Even if the first comparator 21 detects an overcurrent, the operation of the overcurrent detection stop circuit 31 prevents the second comparator 27 from detecting the overcurrent, thereby preventing erroneous detection of the overcurrent due to the flyback voltage. be able to.
[0042]
In this embodiment, the control logic 17 corresponds to the control means in the claims, the gate drive circuit 15 corresponds to the drive means, the first transistor 11 corresponds to the first switching means, and the first transistor 11 corresponds to a control terminal of the first switching means, the second transistor 13 corresponds to the second switching means, and the gate of the second transistor 13 corresponds to the control terminal of the second switching means. Corresponds to overcurrent detection means, the second comparator 27 and the constant voltage power supply 29 correspond to protection means, the overcurrent detection stop circuit 31 corresponds to overcurrent detection stop means, and the third transistor 23 corresponds to third switching means. , The resistor 25 corresponds to the second current detection means, and the output signal Sc of the first comparator 21 corresponds to the overcurrent detection signal. To.
[0043]
As described above, according to the inductive load drive circuit 1 of the present embodiment, the overcurrent detection is not performed when the control command signal Sa is not output, so that the flyback generated by stopping the power supply to the inductive load LL. The voltage does not cause erroneous determination of an overcurrent, and the overcurrent can be accurately detected. In addition, the power supply stop processing of the first power supply path at the time of overcurrent detection can be executed quickly, and the first transistor can be protected from overcurrent, so that the first transistor is less likely to be damaged by the overcurrent.
[0044]
When the control command signal Sa is not output, the first transistor 11 is turned off and no current flows. Therefore, no overcurrent flows in the first current path. Absent. As for the flyback voltage generated at the start of energization to the inductive load LL, the rising speed of the drive command signal Sb is relatively slow because the gate drive circuit 15 generates the drive command signal Sb using the charge pump. Therefore, the flyback voltage is reduced, and there is no effect on overcurrent detection.
[0045]
Further, according to the inductive load drive circuit of the present embodiment, the first transistor 11 and the second transistor 13 can be simultaneously driven and controlled by the drive command signal Sb, so that the first potential V1 and the second potential V2 are , The overcurrent can be detected. Further, since the current flowing through the second current path is a small current, it is possible to suppress power consumption when performing overcurrent detection.
[0046]
Further, in addition to comparing the first potential V1 and the second potential V2, the current value in the first current path is determined based on the current flowing in the second current path to detect an overcurrent. The overcurrent can be detected more accurately as compared with the overcurrent detection based only on the comparison with the two potentials.
[0047]
Further, the inductive load drive circuit of the present embodiment can use the first comparator 21 conventionally used as it is, and additionally includes an overcurrent detection stop circuit 31 in the conventional inductive load drive circuit. Therefore, an inductive load driving circuit capable of suppressing erroneous detection of overcurrent can be realized at low cost.
[0048]
As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, A various aspect can be employ | adopted.
For example, the output voltage of the power supply device that supplies power to the control logic 17 is not limited to 5 [v], but may be any voltage value that can drive the control logic 17. The power supply voltage supplied to the power supply line LV is not limited to 12 [v], but may be any voltage value according to the inductive load LL.
[0049]
As a method of stopping the overcurrent detection, for example, a signal cutoff switching unit that opens and shorts a signal path connecting the first comparator 21 and the third transistor 23 is provided. The on / off state of the signal cutoff switching means may be controlled.
[0050]
Further, in the above embodiment, the load drive circuit using the n-channel MOSFET as the first transistor and the second transistor has been described. However, these transistors may be configured using the p-channel MOSFET. Bipolar transistors may be used. Further, in the above embodiment, the first transistor and the second transistor are provided as high-side switches provided on the higher potential side than the load in the conduction path. The present invention can be applied to a circuit.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an inductive load driving circuit according to an embodiment.
FIG. 2 is a schematic configuration diagram of a conventional inductive load driving circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Inductive load drive circuit, 11 ... 1st transistor, 13 ... 2nd transistor, 15 ... Gate drive circuit, 17 ... Control logic, 21 ... 1st comparator, 23 ... 3rd transistor, 25 ... Resistance, 27 ... 2 Comparator, 29 constant-voltage power supply, 31 overcurrent detection stop circuit, 33 inverter circuit, 35 resistor, 37 detection stop transistor, LL inductive load, LV power supply line.

Claims (4)

First switching means provided on a first current path from the DC power supply to the inductive load, for energizing / disconnecting the first current path based on a drive command signal input to a control terminal;
Control means for outputting a control command signal for driving and controlling the inductive load,
Driving means for outputting a drive command signal for driving the first switching means in response to the control command signal from the control means;
A second switching path is provided in a second current path for supplying a current from the DC power supply to a predetermined load, and a control terminal is connected to a control terminal of the first switching means to flow a current proportional to the first switching means. Means,
A first potential at a current output terminal of the first switching means is compared with a second potential at a current output terminal of the second switching means, and when the first potential is lower than the second potential, Overcurrent detection means for detecting an overcurrent larger than a first prescribed value flowing through the first switching means;
When an overcurrent flowing through the first switching means is detected, the output of the drive command signal by the driving means is stopped, thereby stopping the energization in the first energization path to protect the first switching means. Means,
Comprising an inductive load drive circuit that drives the inductive load and detects overcurrent.
An inductive load drive circuit comprising: an overcurrent detection stop means for stopping detection of overcurrent by the overcurrent detection means when the control command signal is not output from the control means. The first switching means comprises an n-channel MOSFET,
The second switching means is composed of an n-channel MOSFET that allows a current smaller than that of the first switching means to flow;
The inductive load drive circuit according to claim 1, wherein: A third switching unit that is provided downstream of the second switching unit in the second energization path and energizes the second energization path when an overcurrent is detected by the overcurrent detection unit;
Second current detecting means for detecting a current flowing through the second current path, wherein the protection means sets a current detected by the second current detecting means in accordance with the first specified value. Stopping the output of the drive command signal by the drive unit when exceeding a second specified value;
The inductive load drive circuit according to claim 1 or 2, wherein: The overcurrent detection means is configured to output an overcurrent detection signal when detecting an overcurrent flowing through the first switching means,
The overcurrent detection stop unit stops the detection of the overcurrent by controlling the overcurrent detection signal in preference to the overcurrent detection unit,
4. The inductive load drive circuit according to claim 1, wherein:

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