JP2007027465A - Driving circuit for linear solenoid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a circuit for driving a linear solenoid which has a diagnosing function and a superior response property. <P>SOLUTION: The driving circuit comprises: a first switching means 1 having a diagnosing unit 11 for detecting at least an overcurrent, and a switch 12 which is controlled to turn on and off, based on a first inputted control signal CS1, and turns on when an eddy current is detected by the diagnosing result of the diagnosing unit 11; and a second switching means 2 controlled to turn on and off, based on a second pulsewidth-modulated control signal CS2. The first and second switching means 1, 2 are taken as high-side and low-side switches, respectively, to form an asynchronous half bridge 10, thereby driving a linear solenoid 20 connected between the low side of the first switching means 1 and the high side of the second switching means 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a linear solenoid driving circuit having a function of detecting a failure of the linear solenoid and its driving circuit.

  A configuration as shown in FIG. 3 is known as a drive circuit for a solenoid or a solenoid having a diagnostic function for detecting a failure of the drive circuit. This is a series connection of a switching circuit T0 with a diagnostic function having one end connected to the power supply voltage VD side (high side) and a solenoid 200 having one end connected to the ground side (low side). Further, a flywheel diode FD is connected in parallel with the solenoid 200 in order to regenerate a current generated by the induced electromotive force of the solenoid 200 when the switching circuit T0 is turned off.

  A solenoid drive circuit configured as shown in FIG. 3 is described in, for example, Patent Document 1 shown below. The solenoid drive circuit disclosed in Patent Document 1 has the following configuration. Transistors (P-channel metal-oxide semiconductor field effect transistors) with one end connected to the power supply voltage side, linear solenoids with one end connected to the ground side, and resistors connected to the other ends The element (symbol R1) is connected in series. The resistance element (R1) is provided with a current detection circuit in parallel. The current detection circuit detects a current flowing through a series circuit of a transistor and a linear solenoid by measuring a voltage between terminals of the resistance element (R1). The measurement result of the current detection circuit is further integrated by the integration circuit and input to the A / D port of the microcomputer. That is, the resistance element (R1), the current detection circuit, and the integration circuit are means for taking a diagnostic function. Therefore, these, together with the transistor, correspond to the switching circuit T0 with a diagnostic function shown in FIG. The point that a flywheel diode is provided in parallel with the linear solenoid is similar to the configuration shown in FIG.

  As described in Patent Document 1, when a current detection circuit or an integration circuit is provided, the scale of the circuit increases. Therefore, Patent Document 2 shown below proposes an intelligent power switch (IPS) that is a switching circuit with a diagnostic function in order to reduce the size of the circuit and reduce the cost. This IPS includes an N-channel MOSFET (reference numeral 41), a charge pump, and a current detection unit.

  In the drive circuit described in Patent Document 1, a P-channel MOSFET is used as a switching element. However, power P-channel MOSFETs that drive actuators such as solenoids are few and therefore expensive. This is generally the same when a single switching element is incorporated in an integrated circuit. The N channel type is superior in electrical characteristics such as on-resistance and switching speed. For this reason, an N-channel MOSFET is often used as the switching means as in the configuration described in Patent Document 2.

  Most power MOSFETs are of an enhancement type in which a drain current flows by applying a voltage between the gate and the source. In other words, for the n channel, the gate potential may be higher than the source, and for the p channel, the gate potential may be lower than the source. Therefore, if an appropriate voltage is applied between the gate and the source by configuring a source-grounded circuit, the power MOSFET functions as a good switch. When a P-channel MOSFET is used on the high side, it is easy to switch off if the gate voltage is equivalent to the high-side voltage such as the power supply voltage, and turned on if the gate voltage is equivalent to the low-side voltage such as ground. Can be configured. However, when an N-channel MOSFET is used on the high side, even if the gate voltage is equal to the power supply voltage, the source voltage is high, so that a potential difference necessary for turning on the transistor does not occur between the source and the source. Therefore, a booster circuit that boosts the gate voltage of the N-channel MOSFET is required. For this reason, the IPS described in Patent Document 2 has a charge pump as a booster circuit.

Japanese Unexamined Patent Publication No. 2000-114039 (15th to 18th paragraphs, FIG. 1) JP 2003-179472 A (10th to 17th paragraphs, FIG. 1)

  As described above, the configuration shown in FIG. 3 is well known and used as a solenoid drive circuit. However, in the configuration shown in FIG. 3, after turning off the switching circuit T0, the regenerative current flows to the solenoid via the flywheel diode. For this reason, the interruption of the current flowing through the solenoid becomes worse. This affects the responsiveness of the solenoid. Any simple on / off switching application may be used, but this is a problem in applications where the linear solenoid is precisely controlled. As a countermeasure, there is a method of using a Zener diode instead of the flywheel diode. However, in this case, heat generation of the Zener diode becomes a problem.

  In addition, in order to configure a switching circuit with a diagnostic function on a small scale and at low cost, there are the following problems when using IPS. As described above, when an N-channel FET built in IPS is used as a high-side switch, it is necessary to incorporate a booster circuit in order to ensure a gate-source voltage. This booster circuit is constituted by a charge pump using a capacitor in an integrated circuit such as IPS. Since it takes time to charge the capacitor in the charge pump, the switching speed of the IPS is approximately 1 to 5 kHz. Therefore, there is a problem in responsiveness when switching control of a linear solenoid at a frequency of about 15 kHz or more is performed in an application in which mechanical vibration is detected and suppressed as in a vibration isolator of an automobile engine. is there.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a drive circuit for a linear solenoid that has a diagnostic function and can ensure high responsiveness.

In order to achieve the above object, a drive circuit for a linear solenoid according to the present invention has the following features.
That is, at least a diagnostic unit that detects the occurrence of an overcurrent, and a switch that is controlled to open and close based on the input first control signal, and that is opened when the occurrence of an overcurrent is detected by the diagnostic result of the diagnostic unit And a second switching means that is controlled to open and close based on a second control signal that has been subjected to pulse width modulation.
The first switching means is a high-side switch, the second switching means is a low-side switch, and an asymmetric half bridge is configured. The low-side side of the first switching means, the high-side side of the second switching means, A linear solenoid connected between the two is driven.

According to this configuration, the linear solenoid is controlled by closing the switch portion of the first switching means on the high side by the first control signal and controlling the opening and closing of the second switching means on the low side by the second control signal. be able to.
When a failure such as a short circuit occurs at both ends of the linear solenoid, an overcurrent flows through the first switching means, so the diagnosis unit can detect this overcurrent. When the diagnosis unit detects an overcurrent, the switch unit is opened, and thus the overcurrent to the short-circuit portion is suppressed.
The linear solenoid is driven by closing the switch portion of the first switching means and opening / closing the low-side second switching means by a second control signal. Therefore, the response of the linear solenoid depends on the switching performance of the second switching means on the low side.

  The second switching means provided as the low-side switch has many varieties, can be used at low cost, and can use an N-channel MOSFET for power having excellent electrical characteristics such as on-resistance and switching speed. When an N-channel MOSFET is used as a low-side switch, it is needless to say that voltage operations such as step-up and step-down are unnecessary. Therefore, voltage conversion means such as a charge pump is not necessary. That is, since the obstruction factor for the high-speed switching of the second switching means is almost eliminated, the linear solenoid can be driven with good responsiveness. Further, since the second switching means is controlled to be switched by the second control signal subjected to pulse width modulation, the current flowing through the linear solenoid can be precisely controlled.

The first switching means and the second switching means constitute an asymmetric half bridge. Since it is an asymmetric half bridge, diodes connected in opposite directions are provided on the sides where the first and second switching means are not provided. That is, the first switching means is connected in series with a flywheel diode whose forward direction is from the low side of the second switching means toward the first switching means. The second switching means is connected in series with a flywheel diode whose forward direction is from the second switching means toward the power supply voltage side. Therefore, the induced current generated by the linear solenoid is regenerated to the low side of the power supply and the second switching means via these flywheel diodes. Therefore, the responsiveness of the linear solenoid is not affected.
As a result, according to the present invention, it is possible to provide a drive circuit for a linear solenoid that has a diagnostic function and can ensure high responsiveness.

  Furthermore, it is preferable that a resistor is provided in parallel with the second switching means on the low side of the asymmetric bridge.

  As described above, in the linear solenoid drive circuit according to the present invention, the second switching means is switched at a high speed by the pulse width-modulated second control signal. In other words, the current supply to the linear solenoid is precisely controlled by turning the second switching means on and off while the first switching means is on. The first switching means has at least a function of detecting an overcurrent as a diagnostic function, but may be unloaded, that is, may have an open detection function. When the first switching means is in the on state and the second switching means is in the off state, it is equivalent to no load when viewed from the first switching means, and open detection is performed. If a resistor is provided in parallel with the second switching means, the connection is maintained through this resistor even if the second switching means is turned off. Therefore, open detection is not performed by the first switching means. As a result, a linear solenoid drive circuit having a good diagnostic function can be obtained.

  Here, the terminal voltage on the high side of the resistor may be output as a second diagnosis result.

When the first switching means is on and the second switching means is off, the terminal voltage on the high side of the resistor is the on-resistance of the first switching means, the impedance of the linear solenoid, and the resistance of the resistor. It becomes the partial pressure value by the value. Since the on-resistance of the first switching means is usually very small, it becomes a partial pressure value with respect to the impedance of the linear solenoid. That is, it becomes a value having a constant voltage from the low side of the second switching means.
When the first switching means is in the on state and the second switching means is in the on state, the on resistance of the second switching means is also very small, so the voltage value on the high side of the second switching means is substantially the second switching means. The voltage on the low side. The terminal voltage on the high side of the resistor connected in parallel with this also becomes the voltage on the low side of the second switching means.
When the first switching means is in the on state and the second switching means is in the off state, when a disconnection occurs in the linear solenoid or the like, the terminal voltage on the high side of the resistor becomes substantially the voltage on the low side of the second switching means. That is, the resistor is equivalent to being pulled down to the low side of the second switching means.
Thus, the terminal voltage on the high side of the resistor functions well as an indication of the diagnostic result of the open detection of the linear solenoid or the drive circuit. Further, when the impedance is gradually increased in the process leading to the disconnection, not the complete disconnection or the like, more detailed estimation diagnosis can be performed by the value of the terminal voltage. Therefore, when this terminal voltage is output as the second diagnosis result, a linear solenoid drive circuit having a good diagnosis function can be obtained.

  The resistor may be composed of a plurality of resistance components, and a voltage value divided by the resistance components may be output as a second diagnosis result.

  Generally, an actuator such as a linear solenoid is driven at a high voltage as an electronic circuit having a power supply voltage of about 12V or more. On the other hand, a control system circuit such as a microcomputer is driven with a low voltage of 5 V or less. The terminal voltage indicating the second diagnosis result is a voltage of a part of a so-called power circuit having a power supply voltage of 12 V or higher. Therefore, there is a possibility that a voltage value of 5 V or more can be taken. In this case, the second diagnosis result cannot be directly connected to the control system circuit. Therefore, when the resistor is constituted by a plurality of resistor parts and the value obtained by dividing the terminal voltage of the resistor by the resistor parts is taken as the second diagnosis result, it can be satisfactorily transmitted to the control system circuit.

In addition, the first control signal and the second control signal are output, and the control unit is configured to input the diagnosis result and the second diagnosis result output from the first switching unit. The operating state of the half bridge circuit and the linear solenoid may be determined.
That is, when the control means determines operating states of the asymmetric half bridge circuit and the linear solenoid based on the first control signal, the second control signal, the diagnosis result, and the second diagnosis result. Good.

Generally, the diagnostic result output of the first switching means is one signal line in order to reduce the wiring scale. For example, when the first switching means is constituted by an integrated circuit, the number of diagnostic result output signals is small so that the number of terminals of the envelope of the integrated circuit is not increased. For example, when the first switching means diagnoses an overcurrent, a short circuit, and a disconnection (open) of the asymmetric half bridge circuit and the linear solenoid, it is necessary to notify these states with one signal line. When a short circuit occurs, an overcurrent flows, so there is no problem even if the overcurrent and the short circuit are notified with the same logical value. Therefore, it is necessary to notify at least that overcurrent, disconnection (open), and normal state can be distinguished.
In many cases, the diagnosis result is input to the control means and used for various determinations in the control means. Since the control means outputs the first control signal for controlling the first switching means, the state may be expressed by a combination of the first control signal and the diagnosis result.
For example, when there is no problem of overcurrent and disconnection and the operation is normal, the same logical value as that of the first control signal is output as the diagnosis result. When an overcurrent is detected, a low (L) level logic value is output regardless of the logic value of the first control signal. When open is detected, a high (H) level logic value is output regardless of the logic value of the first control signal. The same applies when the resistor connected in parallel to the second switching means diagnoses the disconnection of the asymmetric half bridge circuit and the linear solenoid.
In this way, the control means logically determines the asymmetric half bridge circuit and the linear solenoid based on the first control signal and the second control signal, the diagnosis result output from the first switching means, and the second diagnosis result. The operating state can be determined. As a result, a linear solenoid drive circuit having a good diagnostic function can be obtained.

Embodiments of the present invention will be described below with reference to the drawings, taking as an example a drive circuit for a linear solenoid in a vibration isolator for an automobile engine. FIG. 1 is a block diagram schematically showing the configuration of a linear solenoid drive circuit according to the present invention.
The drive circuit for the linear solenoid according to the present invention is provided in an ECU (Electronic Control Unit) 100 together with other circuits. The ECU 100 includes an MPU (Micro Processing Unit) 4 as control means, and outputs control signals CS1 and CS2 for driving the linear solenoid 20. Although details will be described later, in the present embodiment, the second control signal CS2 is a control signal obtained by pulse width modulation (PWM), and the linear solenoid 20 is precisely controlled by this signal.

  The drive circuit includes an IPD (Intelligent Power Device) 1 having a diagnostic function for detecting at least the occurrence of an overcurrent, and a power MOSFET 2. IPD1 corresponds to the first switching means of the present invention. The power MOSFET 2 corresponds to the second switching means of the present invention and is an N-channel type.

As shown in the figure, the IPD 1 and the power MOSFET 2 constitute an asymmetric half bridge 10. Since it is an asymmetric half bridge, diodes connected in opposite directions are provided on the sides where the IPD 1 and the power MOSFET 2 are not provided. That is, IPD1 is connected in series with flywheel diode 3a whose forward direction is from the ground side toward IPD1. The power MOSFET 2 is connected in series with a flywheel diode 3b having a forward direction from the power MOSFET 2 toward the power supply voltage VDD.
The linear solenoid 20 is an inductive load, and the inductive load has a property of causing a current to flow by an induced electromotive force even after the supply of current is interrupted. The advantage of the bridge circuit is that the regenerative current is easily regenerated. That is, the induced current generated in the linear solenoid 20 is regenerated to the power source and the ground via the flywheel diode 3.
In addition, an electrolytic capacitor C1 for stabilizing the power supply is disposed in the vicinity of the asymmetric half bridge 10. As this electrolytic capacitor, a capacitor having a large capacity of about several hundred μF to 1,000 μF (Micro Farad) is used. By increasing the capacity, the power source impedance is kept low, and it is possible to accurately respond to the duty ratio of the PWM control signal waveform applied to the bridge circuit.

  The power supply to the ECU 100 is performed from the battery 30 that outputs the voltage VB through the fuse 40 and an ignition switch (IGSW) 50. The voltage VB supplied via the fuse 40 is switched by the N-channel MOSFET 5 (power supply opening / closing means) in the ECU 100 and transmitted to the linear solenoid drive circuit.

  The moment when the FET 5 transitions to the ON state by switching is electrically excessive. The impedance of the electrolytic capacitor C1 for stabilizing the power supply is the reciprocal of the capacitance. Since the capacitance of the electrolytic capacitor C1 is very large, the impedance between the power source and the ground in the transient state is very small. For this reason, a large transient current, so-called inrush current, flows between the power source and the ground. In order to suppress this inrush current, precharge means 6 is provided.

  The precharge means 6 includes a resistor 6a and a diode 6b. Inrush current also flows at the moment when the IGSW 50 is turned on. The resistor 6a is an inrush current preventing resistor for reducing the inrush current by providing an impedance with respect to the transient current. The diode 6b supplies electric charge from the battery B until the electrolytic capacitor C1 is charged. Usually, a forward voltage drop occurs in the diode, so the electrolytic capacitor C1 is theoretically charged to a voltage 0.6 to 0.7 V lower than the battery voltage VB. The time for which the electrolytic capacitor C1 is charged to a steady value is theoretically infinite. Therefore, the charging time may be considered based on the time constant τ that can be calculated from the resistance value of the resistor 6a, the impedance of the diode 6b, and the electrolytic capacitor C1. For example, after τ seconds after the start of charging, it reaches 63.2% of the steady value of the terminal voltage when the electrolytic capacitor C1 is fully charged. And, 5τ seconds after the start of charging, it reaches 99.3% of the steady value. Since these are numerical values derived from the theoretical calculation of the transient phenomenon, the charging time may be set based on the time constant τ.

  The regulator 7 is a semiconductor integrated circuit that steps down the battery voltage VB, which is usually about 12V, to a voltage VCC of 5V or 3.3V, which is an operating voltage of an electronic circuit such as the MPU4. When the IGSW 50 is turned on, the electrolytic capacitor C1 is charged (precharged) as described above, and the power supply voltage VCC of the MPU 4 is generated by the regulator 7. When the MPU 4 is supplied with the power supply voltage VCC, the MPU 4 starts to operate according to the program. A reset circuit (not shown) that operates with the power supply voltage VCC may be provided, and the power supply voltage VCC may be reset for a certain period of time after being supplied to the reset circuit and the MPU 4. When the power supply voltage VCC is applied or the reset is released, the MPU 4 performs its own initialization (initialization). When the initial setting is completed, the power supply control signal CS0 is output at the H (high) level. When the N-channel MOSFET 5 is turned on by the power control signal CS0, the voltage VB is supplied from the battery 30 to the asymmetric half bridge 10 and the electrolytic capacitor C1 through the fuse 40 and the FET 5.

  Here, if the predetermined charging time calculated based on the time constant τ described above is shorter than the initial setting time of the MPU 4, it may be considered that the charging of the electrolytic capacitor C1 is completed when the initial setting is completed. For example, if the time of 2τ has elapsed, it has reached about 87% of the steady state, so it may be considered that the battery is sufficiently charged. At least, the uncharged electrostatic capacitance of the electrolytic capacitor C1 is reduced by precharging, and the impedance of the electrolytic capacitor C1 is surely larger than before the start of charging. Therefore, even if the MPU 4 completes the initial setting and immediately outputs the power control signal CS0 to turn on the FET 5, the inrush current can be reliably reduced. Of course, the power supply control signal CS0 may be output to turn on the FET 5 after a predetermined time corresponding to, for example, 5τ has elapsed after the MPU 4 is powered on.

  When the FET 5 is turned on, the electrolytic capacitor C1 is charged to the power supply voltage VDD that is substantially close to the voltage VB. Since the resistance value of the fuse 40 and the on-resistance between the drain and source of the FET 5 are very small, a large voltage drop does not occur. When the FET 5 is turned on, the electrolytic capacitor C1 is already charged to a voltage value of about 0.6 to 0.7 V lower than the voltage VB via the precharge means 6. Therefore, the electrolytic capacitor C1 is charged to almost the voltage VDD without a new large inrush current.

The MPU 4 receives a detection signal from a sensor 60 provided on an object mechanically controlled by the linear solenoid 20, such as an automobile engine. The sensor 60 is, for example, a vibration sensor, and provides information such as the magnitude, direction, and frequency of mechanical vibration to the MPU 4.
The MPU 4 processes the given mechanical vibration information based on the program, and outputs a control signal for driving the linear solenoid 20 so as to absorb this mechanical vibration.

  The drive circuit of the linear solenoid is composed of an asymmetric half bridge in which the IPD (first switching means) 1 is a high side switch and the N-channel power MOSFET (second switching means) 2 is a low side switch. The MPU 4 outputs a first control signal CS1 for switching control of the IPD 1 and a second control signal CS2 for controlling the FET2. As described above, the MPU 4 operates with the power supply voltage VCC of about 5 V, for example, and the first control signal CS1 and the second control signal CS2 to be output are also outputs within the range of the voltage VCC. Since it is necessary to apply an operating current to the linear solenoid 20 using the voltage VDD, the operating voltage of the asymmetric half bridge 10 is the voltage VDD. Therefore, in order to turn on / off the FET 2, it is necessary to raise the signal level of the second control signal CS2. For this reason, a pre-driver 8 is provided. The second control signal CS2a having the signal level of the voltage VCC output from the MPU 4 is input to the pre-driver 8, and the second control signal CS2b having the signal level of the voltage VDD is output and input to the gate of the FET2.

  Note that the same can be said for the IPD 1. Depending on the configuration of the IPD 1, the first control signal CS1 also requires level conversion by the pre-driver. In the present embodiment, since the IPD 1 employs a configuration that can be directly controlled by the control signal CS1 having the signal level of the voltage VCC, no pre-driver is provided.

  Here, the configuration of the IPD 1 will be described with reference to FIG. The IPD 1 is a high-side switch that can be directly driven from a logic circuit such as an MPU, and is a semiconductor integrated circuit having at least a diagnostic function for detecting occurrence of an overcurrent. IPS (Intelligent Power Switch) is also synonymous. As shown in FIG. 2, the IPD 1 is controlled to open and close based on a diagnostic unit 11 that performs self-diagnosis and an input first control signal CS1. And a switch unit (power MOSFET) 12 that is opened when the occurrence of an overcurrent is detected by the diagnostic result of the diagnostic unit 11 and a diagnostic result output unit 13 that outputs the diagnostic result of the diagnostic unit 11. Yes.

  The diagnosis unit 11 includes an overcurrent detection unit 11a, an overheat detection unit 11b, and an open detection unit 11c. The overcurrent detection unit 11a monitors the current flowing through the asymmetric half bridge 10 by detecting the current flowing through the switch unit 12. For example, an overcurrent is detected when an abnormality occurs in which the terminals at both ends of the linear solenoid 20 are short-circuited or when a failure occurs such that the high-side of the linear solenoid 20 is short-circuited to another potential member (for example, the ground of the power supply). The overheat detector 11b detects overheating of the IPD 1 due to overcurrent or long-time use. When overcurrent or overheating is detected, the first control signal CS1 input via the input I / F unit 17 is controlled by the protection unit 18. As a result, the ON time of the switch unit 12 is reduced, and the current supplied through the switch unit 12 is reduced. Here, the reduction of the on-time includes, for example, switching control in which on / off control is performed more finely during the on-time. As described above, when overcurrent and overheat are detected, the IPD 1 controls to reduce or stop the output current in any case.

  The open detection unit 11c detects the opening of the load connected to the IPD 1 by detecting the voltage at the output terminal of the IPD 1 mainly when the switch unit 12 is in the OFF state. Under normal conditions, a circuit is formed that continues from the power supply voltage VDD to the ground through the open detection unit 11c, the output terminal of the IPD 1, the asymmetric half bridge 10, and the linear solenoid 20. Since the impedance of the asymmetric half bridge 10 and the linear solenoid 20 is low, the impedance of the open detection unit 11 c can be set to a value sufficiently higher than the impedance of the asymmetric half bridge 10 and the linear solenoid 20. In this case, the equivalent circuit is the electric voltage VDD-open detection unit 11c-output terminal-ground. Accordingly, the output terminal of the IPD 1 is at the L level. However, if the asymmetric half bridge 10 or the linear solenoid 20 is disconnected or deteriorated, the impedance becomes very large. In this case, the equivalent circuit is voltage VDD−open detection unit 11c−output terminal−high impedance− (ground). As a result, the voltage at the output terminal of the IPD 1 becomes the H level, or at least a voltage that cannot be said to be the L level. Accordingly, the open detection unit 11c detects the voltage at the output terminal of the IPD 1 to detect disconnection or deterioration occurring in the asymmetric half bridge 10 or the linear solenoid 20.

  The diagnosis result detected by the diagnosis unit 11 is input to the diagnosis result output unit 13, and the diagnosis result output unit 13 outputs the diagnosis result DS1 from the IPD 1. The diagnosis result DS1 is output as a signal level in the range of the voltage VCC so that it can be input to the MPU 4 as it is. The IPD 1 of this example has only one output terminal that outputs the diagnosis result DS1. The logical value of the first control signal CS1 is also input to the diagnosis result output unit 13 via the input I / F unit 17. The diagnosis result DS1 is output at the following signal level based on the diagnosis result by the diagnosis unit 11 and the first control signal CS1.

  When the diagnosis unit 11 does not detect any of overcurrent, overheat, and open, the diagnosis result DS1 is output at the same logic level as the first control signal CS1. That is, when the first control signal CS1 is at the H level, the output is at the H level, and when the first control signal CS1 is at the L level, the output is at the L level.

  When the diagnosis unit 11 detects either overcurrent or overheat, the diagnosis result DS1 is output at the logic level L regardless of the logic level of the first control signal CS1. That is, it indicates that the switch unit 12 cannot be turned on due to a restriction when the first control signal CS1 is at the H level, which should turn the switch unit 12 on.

  When the diagnosis unit 11 detects open, the diagnosis result DS1 is output at the logic level H regardless of the logic level of the first control signal CS1. That is, when the first control signal CS1 is at the L level, the output terminal of the IPD 1 that should be at the L level when the switch unit 12 is turned off indicates that the output terminal is at the H level.

Since the MPU 4 grasps the logic level of the first control signal CS1, the operations of the asymmetric half bridge circuit 10 and the linear solenoid 20 are logically performed based on the first control signal and the diagnosis result DS1 output from the IPD 1. Determine the state.
The signal information processing inside the IPD 1 as described above is performed within the range of the voltage VCC, which is a signal level of CMOS or TTL, similarly to the MPU 4, and the diagnosis result DS1 is also output at the same signal level. For this reason, the IPD 1 includes a regulator 16 that steps down the input voltage VDD, and generates a voltage VS corresponding to the power supply voltage VCC.

  Since the IPD 1 in this example receives the first control signal CS1 from the MPU 4 as it is, it has a driver 14 for driving the switch unit 12 that switches the voltage VDD. It is not sufficient for the driver 14 to boost the first control signal CS1 to the voltage level of the voltage VDD. That is, the switch unit 12 is configured using an N-channel power MOSFET that is advantageous in terms of electrical characteristics. As described above, in order to obtain a sufficient gate-source voltage for the N-channel MOSFET used as the high-side switch, a voltage higher than the voltage VDD is required. For this reason, the IPD 1 has a charge pump 15 as a boosting means.

  The charge pump 15 is a booster circuit using charging / discharging of a capacitor. Since it takes time to charge the capacitor, the switch unit 12 of the IPD 1 has a switching characteristic of approximately 1 to 5 kHz. Therefore, there is a problem in responsiveness when the linear solenoid is subjected to switching control at a frequency of about 15 kHz or more so as to detect the vibration of the object and cancel the vibration like a vibration isolator.

Therefore, in this embodiment, the asymmetric half bridge 10 is configured by using the IPD 1 as a high-side switch and the N-channel MPSFET 2 as a low-side switch, and the EFT 2 is controlled to be opened and closed based on the second control signal CS 2 that has been subjected to pulse width modulation. I have to.
In the asymmetric half bridge 10, diodes 3 (3 a, 3 b) connected in the reverse direction are provided as flywheel diodes on the sides symmetrical to the respective switch means.

Here, when the first control signal CS1 for the IPD1 as the high-side switch is fixed to the H level and the second control signal CS2 for the FET2 as the low-side switch is pulse width modulated, the current supply to the linear solenoid 20 is precisely controlled. can do. When the second control signal CS2 is in the L state, the FET 2 is turned off. At this time, the IPD 1 may detect open. Of course, since the MPU 4 knows that the second control signal CS2 is being output in the L state, the open detection of the IPD 1 may be ignored. In the present embodiment, a resistor R is provided in parallel with the FET 2 on the low side of the asymmetric bridge 10 so that the exclusion process by the MPU 4 can be omitted.
When the second control signal CS2 is in the L state, the FET 2 is turned off, but the connection to the ground is maintained through the resistor R. The constant of the resistor R is appropriately determined from the power supply voltage VDD, the resistance constant of the open detection circuit 11c of the IPD1, the electrical characteristics such as the open detection voltage, and the like. In other words, a value may be set such that the impedance of the resistor R is too high and the IPD 1 does not detect open.

  When the MPU 4 includes an A / D converter (analogue to digital converter), the terminal voltage on the high side of the resistor R may be input to the MPU 4 as the second diagnosis result DS2. Of course, an A / D converter and a comparator may be provided separately from the MUP 4 and the result may be output to the MPU 4.

  In the present embodiment, the resistor R is composed of a plurality of resistors (resistive components) R1 and R2. Then, the voltage value divided by the resistors R1 and R2 is output to the MPU 4 as the second diagnosis result DS2. This may be regarded as a voltage conversion function between the asymmetric half bridge 10 that operates at the power supply voltage VDD and the MPU 4 that operates at the power supply voltage VSS.

  The MPU 4 is a control means to which the first control signal CS1 and the second control signal CS2 are output, and the diagnosis result DS1 and the second diagnosis result DS2 output from the IPD 1 are input. Therefore, the MPU 4 can logically determine the operation states of the asymmetric half bridge 10 and the linear solenoid 20 based on the first control signal CS1, the second control signal CS2, and the diagnosis result DS1. Further, the operating states of the asymmetric half bridge 10 and the linear solenoid 20 can be determined based on the second diagnosis result DS2.

  As described above, according to the present invention, it is possible to provide a drive circuit for a linear solenoid that has a diagnostic function and can ensure high responsiveness.

The block diagram which shows typically the structure of the drive circuit of the linear solenoid which concerns on this invention 1 is a block diagram schematically showing the configuration of the IPD in FIG. Block diagram schematically showing a general drive circuit of a linear solenoid equipped with a switching circuit with a diagnostic function

Explanation of symbols

1 IPD (first switching means)
2 Power MOSFET (second switching means)
3 Flywheel diode 4 MPU (control means)
DESCRIPTION OF SYMBOLS 10 Asymmetric half bridge 11 Diagnosis part 11a Overcurrent detection part 12 Switch part 20 Linear solenoid CS1 1st control signal CS2 2nd control signal DS1 Diagnostic signal (diagnosis result)
DS2 diagnostic signal (second diagnostic result)
R resistor R1 resistor (resistor component)
R2 resistor (resistor component)

Claims (5)

A diagnostic unit that detects at least the occurrence of an overcurrent, and a switch unit that is controlled to open and close based on the input first control signal, and that is opened when the occurrence of an overcurrent is detected based on the diagnosis result of the diagnostic unit; First switching means comprising:
A second switching means that is controlled to open and close based on a pulse width modulated second control signal,
The first switching means is a high-side switch, the second switching means is a low-side switch, and an asymmetric half bridge is configured.
A drive circuit for a linear solenoid that drives a linear solenoid connected between a low side of the first switching means and a high side of the second switching means.   The linear solenoid drive circuit according to claim 1, wherein a resistor is provided in parallel with the second switching means on a low side of the asymmetric bridge.   The linear solenoid drive circuit according to claim 2, wherein a terminal voltage on a high side of the resistor is output as a second diagnosis result.   The linear solenoid drive circuit according to claim 2, wherein the resistor includes a plurality of resistor parts, and a voltage value divided by the resistor parts is output as a second diagnosis result. The first control signal and the second control signal are output, and the diagnosis result output from the first switching means and the control means to which the second diagnosis result is input,
The control means logically determines operating states of the asymmetric half bridge and the linear solenoid based on the first control signal, the second control signal, the diagnosis result, and the second diagnosis result. The linear solenoid drive circuit according to claim 3 or 4.

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