JP2011056971A - On-vehicle load control circuit - Google Patents

Abstract

A vehicle-mounted load control circuit capable of dealing with a temporary voltage drop due to a momentary disconnection and a problem of reverse connection of a vehicle-mounted battery by a simple circuit method.
[Effect] Since the on-vehicle load control circuit 100 can provide the delay action of the protection circuit by the capacitor C1 connected to the input side of the constant voltage circuit 21, it is not necessary to add a new capacitor, and the circuit configuration is reduced. Simplification is achieved. Further, since the gate voltage of the power MOSFET (Tr5) is applied through the diode element D1 provided in the constant voltage circuit 21, it is not necessary to add a new diode element, and this also simplifies the circuit configuration. Is planned.
[Selection] Figure 1

Description

  The present invention relates to an in-vehicle load control circuit that can solve a temporary voltage drop due to a momentary interruption and a problem of reverse connection of an in-vehicle battery with a simple circuit configuration.

  In recent years, electric devices mounted on automobiles have appeared in various forms such as an internal combustion engine ignition device, various motors, illumination lamps, and audio. And these electric equipments are provided with the vehicle-mounted load control circuit which drives the said electric equipment as a load.

  For example, Japanese Patent Laid-Open No. 6-245396 (Patent Document 1) introduces an in-vehicle load control circuit in the case where the load is an audio deck. The in-vehicle load control circuit 100a is connected in parallel to the in-vehicle battery Vb, the ignition switch Ig inserted in the anode-side power line Lp, and the ignition switch Ig in parallel with the in-vehicle battery Vb, as shown in FIG. Alternator (the power generator in the claims), the constant voltage circuit 21 connected to the power supply line Lp via the diode element D1, the capacitors C1 and C2 π connected to the constant voltage circuit 21, and the constant voltage The control circuit 22 is supplied with a constant voltage from the circuit 21 and an audio deck AD (a load in the claims) driven in accordance with a drive signal from the control circuit 22.

  In the in-vehicle load control circuit 100a having such a configuration, when the ignition key is turned by the operator, the ignition switch Ig is turned on, and the voltage of the in-vehicle battery Vb temporarily drives a cell motor (not shown). When the internal combustion engine is started according to the operation of the cell motor, the alternator Alt starts power generation according to the operation of the internal combustion engine. The output power of the alternator Alt is controlled to the required power supply voltage by the constant voltage circuit 21, and the control circuit 22 is driven by the power supply voltage to appropriately control the audio deck AD in the subsequent stage.

[Problems when instantaneous interruption occurs]
Here, when the vehicle is traveling, the conduction state at the ignition switch Ig may be temporarily interrupted (instantaneous interruption) due to vibration of the vehicle body or the like. In addition, since vibration is transmitted to the connector provided in the middle of the vehicle body mounting cable, the potential on the anode side also temporarily drops due to momentary interruption. Such a momentary electrical interruption affects the output voltage of the constant voltage circuit 21, thereby causing a problem of destabilizing the operation of the control circuit 22 and the load AD.

  Therefore, in the in-vehicle load control circuit 100a according to Patent Document 1, the diode element D1 that prevents the charge accumulated in the capacitor C1 from flowing back to the anode-side power line Lp and the input side of the constant voltage circuit are provided. A capacitor C1 that smoothes the voltage waveform is provided, whereby the capacitor C1 suppresses a step-by-step variation in the amount of charge due to a momentary interruption, thereby realizing stable operation of the control circuit 22 and the audio deck AD.

[In-vehicle battery reverse connection problem]
As a further problem, if the polarity is reversed by mistake when connecting the on-vehicle battery, when the ignition switch Ig is turned on, a reverse voltage is applied to the on-vehicle load control circuit, resulting in a large current. This causes a phenomenon that flows and breaks down, and a phenomenon that internal circuit elements break down due to a reverse voltage. For this reason, generally, a test standard has been established for a unit equipped with an in-vehicle load control circuit to determine whether or not it can withstand reverse battery connection. As a countermeasure in this case, as shown in FIG. 3, a method of inserting a diode element D3 into the power supply line Lp is generally used. However, in a load control circuit unit that handles a large current, the diode element D3 generates a large amount of heat and causes a problem that efficiency is lowered.

  Therefore, Japanese Patent No. 4003255 (Patent Document 2) introduces a vehicular electrical apparatus (the vehicular load control circuit in the claims) that solves the problem of reverse connection of the on-vehicle battery. The vehicular electrical apparatus is a device that controls the headlamp Lt as a load, and as shown in FIG. 4, a protection circuit is provided between the anode-side power line Lp and the cathode-side power line Ln. Yes. The protection circuit includes a gate resistor Rg, a power MOSFET, and a capacitor Cm having a small capacity of about 0.1 μF. Among these, the power MOSFET is arranged so that the forward direction of the parasitic diode Dm faces the cathode terminal of the in-vehicle battery Vb, and is connected between the cathode side power supply lines Ln. The gate resistor Rg has one end connected to the gate of the power MOSFET and the other end connected to the power line Lp on the anode side. Further, the capacitor Cm is connected between the gate and the source of the power MOSFET. In addition, about another structure, since it bears the function substantially the same as the structure demonstrated in FIG. 2, it attaches | subjects the same code | symbol in the same figure, and abbreviate | omits description.

  When the on-vehicle battery Vb is reversely connected to the vehicular electrical device apparatus provided with the protection circuit, the power MOSFET is turned off because the gate voltage falls below the threshold voltage. The power MOSFET in this technology uses an element that can withstand the reverse bias of the on-vehicle battery, and the reverse bias applied voltage is cut off by the protection circuit. As a result, the vehicle electrical device apparatus can reduce unnecessary power consumption of the vehicle-mounted battery Vb, and the control circuit connected to the subsequent stage of the protection circuit is scheduled to be designed by cutting off the reverse bias. Eliminates damage caused by unapplied voltage and heat.

  Further, in the technique of Patent Document 2, the negative transient surge is reduced by delaying the off timing of the power MOSFET by the delay action of the gate resistor Rg and the capacitor Cm and guiding the negative transient surge to the subsequent stage of the power MOSFET. ing.

JP-A-6-245396 Japanese Patent No. 4003255

  However, in the technique according to Patent Document 2, since the capacitor Cm that provides a delay action is provided, there is a problem that the circuit configuration becomes complicated and the cost increases with the addition of the electric element.

  Further, even in the technique according to Patent Document 2, since the constant voltage circuit 21 is generally installed in the previous stage of the control circuit 22, the diode element D1 is placed before and after the constant voltage circuit 21 as shown in FIG. , Capacitors C1 and C2 are usually provided. In order to suppress the fluctuation of the gate voltage, it is known to provide a diode element D2 in the gate signal line Lg as shown in FIG. In this case, since the diode element D2 is newly added, there arises a problem that the circuit configuration is further complicated and the cost is increased.

  In view of the above problems, an object of the present invention is to provide an in-vehicle load control circuit that can cope with a temporary voltage drop due to a momentary interruption and a problem of reverse connection of an in-vehicle battery with a simple circuit system.

  In order to solve the above problems, the present invention has the following configuration of an in-vehicle load control circuit. That is, the power control unit includes an in-vehicle battery and an ignition switch, and a load control unit that is connected to the subsequent stage of the power control unit and controls a load. The load control unit has an anode on the anode side. A diode element connected to the power supply line, a capacitor connected between the cathode side power supply line and the cathode of the diode element, a contact point of the capacitor and the diode element, and a load control unit provided in the load control unit When connected to a constant voltage circuit interposed between the circuit and a gate signal line with a gate resistor interposed therebetween, the forward side of the parasitic diode faces the cathode terminal of the in-vehicle battery. A power MOSFET inserted in the power supply line, and one end of the gate signal line is connected to the gate of the power MOSFET. , And the other end is connected to the contact point between the capacitor and the diode element.

  According to the on-vehicle load control circuit according to the present invention, the gate voltage of the power MOSFET configured as the protection circuit is applied via the diode element provided in the constant voltage circuit, so that it is not necessary to add a new diode element. This simplifies the circuit configuration.

  In addition, since the gate voltage is maintained above the threshold voltage of the power MOSFET for the protection circuit for a predetermined time by the capacitor for preventing instantaneous interruption connected to the input side of the constant voltage circuit, the in-vehicle load control circuit is newly A countermeasure for negative transient surge can be realized with a simple configuration without adding a capacitor.

The figure which shows the structure of the vehicle-mounted power converter circuit which concerns on embodiment. The figure which shows the structure of the vehicle-mounted power converter circuit which concerns on the prior art example 1. FIG. The figure which shows the structure of the vehicle-mounted power converter circuit which concerns on the prior art example 2. FIG. The figure which shows the structure of the vehicle-mounted power converter circuit which concerns on the prior art example 3. FIG. The figure which shows the structure of the vehicle-mounted power converter circuit which concerns on the prior art example 4. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the in-vehicle load control circuit 100 includes a power supply control unit 10 and a load control unit 20. Further, the in-vehicle load control circuit 100 includes a power supply control unit 10 using an anode-side power line Lp (hereinafter simply referred to as a power line Lp) and a cathode-side power line Ln (hereinafter simply referred to as a power line Ln). The load control unit 20 is connected, and a plurality of load control units 30 and 40 are connected in parallel between the power supply line Lp and the power supply line Ln. In the present embodiment, the load 30 is a motor and the load control unit 20 is a motor driver. However, the meaning of the term of the load control unit described in the claims is not limited to the motor driver, and assumes various forms such as a control circuit for an in-vehicle illumination light or an audio control circuit. Yes. In addition, the anode side does not simply indicate the power line on the anode side, but includes the entire range from the contact point or gate to the power line on the anode side. The cathode side does not simply indicate the power line on the cathode side, but includes the entire range from the contact point or gate to the power line on the cathode side.

  The power supply control unit 10 includes an in-vehicle battery Vb, a power generation device Alt, and an ignition switch Ig. As illustrated, the power generation device Alt is connected in parallel to the in-vehicle battery Vb, and the ignition switch Ig is connected between the power supply lines Lp. Further, the subsequent stage of the ignition switch Ig is connected to the power generation device Alt via the ON-time power supply line Ls.

  When the vehicle-mounted battery Vb is arranged in an appropriate space of the vehicle and is correctly connected, the anode terminal is connected to the power supply line Lp and the cathode terminal is connected to the power supply line Ln. Further, when the reverse connection is made by some kind of hook, the polarities in both power supply lines are inverted accordingly. In the present embodiment, it is assumed that the in-vehicle battery Vb is correctly connected to both power supply lines unless there is a notice of “reverse connection”.

  The power generation device Alt may employ a dynamo or the like in addition to the alternator Alt used in the present embodiment. The alternator Alt is composed of a generator composed of a magnetic coil and a regulator IC that controls the output voltage.

  The ignition switch Ig is turned on / off by the operator's operation, thereby permitting or not permitting the power supply to the regulator IC of the alternator Alt and the load control units 20, 30, 40. The regulator IC is connected to the power supply line Lp via the power supply line Ls when ON, and is activated when the ignition switch Ig is turned on.

  The load control units 30, 40... Are connected in parallel to the load control unit 20 as shown in the figure. Any of the load control units 30, 40,... Has an inductive element such as a motor in the circuit. When the ignition switch Ig is turned off, the inductive element generates a “negative transient surge” which will be described later, and the load control unit 20 is also affected by the surge.

  When the ignition switch Ig is turned on by the operator, the power supply control unit 10 having such a configuration applies a battery voltage to each of the load control units 20, 30, 40. In the alternator Alt, a built-in regulator IC is activated. Further, when the cell motor is driven and the engine is started, the alternator Alt drives the generator by the timing belt and outputs the supply voltage to the load control unit. The supply voltage is controlled to be a constant value by the regulator IC.

  The load control unit 20 includes a diode element D1, capacitors C1 and C2, a constant voltage circuit 21, a control circuit 22, a power conversion circuit 23, a gate resistor Rg, and a power MOSFET (Tr5). The load control unit 20 is connected to the subsequent stage of the power supply control unit 10 through the power supply lines Lp and Ln, and plays a role of controlling the motor M in the present embodiment.

  The diode element D1 has an anode connected to the power supply line Lp and a cathode connected to the capacitor C1 and a contact on the input side of the constant voltage circuit 21. The diode element D1 prevents the electric charge accumulated in the capacitor C1 from being discharged to the anode side, and even if a voltage drop occurs in the power supply line Lp due to a momentary interruption, the input voltage to the constant voltage circuit 21 is rapidly reduced. To prevent. Further, the diode element D1 also plays a role of reducing the gate voltage fluctuation range by rectifying the waveform of the voltage when the voltage on the anode side suddenly fluctuates due to instantaneous interruption or the like. That is, the diode D1 used in the present embodiment serves both as a circuit configuration as a measure against instantaneous interruption and as a protection circuit.

  The capacitors C1 and C2 are π connected with the constant voltage circuit 21 in between. Among these, the capacitor C1 is connected between the power supply line Ln and the cathode of the diode element D1, and the capacitor C2 is connected to the power supply line Ln and the output side of the constant voltage circuit 21.

  The electric capacity of the capacitor C1 is such that an element having a predetermined electric capacity is used so that the load control circuit (the control circuit 22 and the power conversion circuit 23) can stably operate even when the voltage applied to the constant voltage circuit 21 is momentarily interrupted. In the present embodiment, an element of about 100 μF to 1000 μF is used. Further, as a result, the electric capacity is set so that the gate voltage is higher than the threshold voltage of the power MOSFET (Tr5) for a certain period of time. The capacitor C2 is also one of the components of the circuit as a measure against instantaneous interruption, and specifically, the output voltage of the constant voltage circuit 21 is smoothed.

  These capacitors C1 and C2 generally employ electrolytic capacitors because of their relatively large electric capacities, but this is not the only case where the electric capacities can be kept low. It is possible to appropriately use a film capacitor, a ceramic capacitor, or the like.

  The constant voltage circuit 21 is inserted between the contact of the capacitor C1 and the diode element D1 and the load control circuit (control circuit 22, power conversion circuit 23), adjusts the input voltage, and serves as a power supply voltage for the control circuit 22. Generate and output the output voltage used.

  The control circuit 22 operates with the above-described power supply voltage, and appropriately includes an electrical element such as a microcomputer. The microcomputer generates a predetermined control signal and outputs it to the power conversion circuit 23 by arithmetic processing executed in cooperation with the CPU and the memory circuit. In the present embodiment, the load control circuit includes the control circuit 22 and the power conversion circuit 23. However, the variation of the load control circuit is not limited to this, and various modifications can be made. It is done.

  The power conversion circuit 23 according to the present embodiment is a full-bridge circuit composed of power MOSFETs (Tr1 to Tr4), and drives the power MOSFETs (Tr1 to Tr4) according to the state of the control signal, so that the motor in the subsequent stage 30 is operated appropriately. Of course, the power conversion circuit is not limited to the form shown in the figure, and can be modified according to the configuration of the load, such as a half-bridge circuit or an inverter circuit.

  The power MOSFET (Tr5) is a power transistor, and an element that can withstand an applied voltage when the in-vehicle battery Vb is reversely connected is used. As shown in the figure, the power MOSFET (Tr5) is connected between the power supply lines Ln so that the forward direction of the parasitic diode D5 faces the cathode terminal of the in-vehicle battery Vb. For example, if an N-channel power MOSFET is used as the power MOSFET (Tr5), the power MOSFET has a source connected to the power conversion circuit 23 via one power supply line Ln and a drain connected to the other power supply line Ln. Connected to the cathode of the in-vehicle battery Vb. In the figure, a Zener diode ZD is connected between the gate and the source of the power MOSFET in order to prevent the gate voltage from rising and breaking the gate oxide film.

  The on-time of the power MOSFET is proportional to the electric capacity of the capacitor C1 and the voltage across the capacitor C1, and inversely proportional to the current value passing through the constant voltage circuit 21. Since the capacitance of the capacitor C1 is relatively large as a measure against instantaneous interruption, the power MOSFET (Tr5) may pass a negative transient surge unless the resistance value of the gate resistance Rg is extremely small. The ON state is maintained for a possible period. Note that if the capacitance of the capacitor C1 according to the present embodiment is set so as to satisfy the measure against instantaneous interruption as described above, as a result, there is also a condition for eliminating the “problem of negative transient surge at the time of Ig off” described later. Satisfied. However, as an interpretation of this technical idea, the capacitance of the capacitor C1 is determined based on the condition that the load control circuit operates stably even when the voltage applied to the constant voltage circuit 21 is momentarily interrupted, and the gate voltage is a power MOSFET ( It also includes that both of the conditions for a certain period of time higher than the threshold voltage of Tr5) are satisfied.

  The gate resistor Rg is inserted in the gate signal line Lg, and one end of the gate signal line Lg is connected to the gate of the power MOSFET (Tr5), and the other end is connected to a contact point between the diode element D1 and the capacitor C1. Yes. The resistance value of the gate resistor Rg is selected within a predetermined range so as to be a gate voltage required for the power MOSFET (Tr5).

  When the supply voltage of the in-vehicle battery Vb is applied from the power supply control unit 10 to the load control unit 20 having such a configuration, the supply voltage is adjusted to an appropriate voltage value by the constant voltage circuit 21. The output voltage adjusted by the constant voltage circuit 21 is input to the control circuit 22 as a power supply voltage to operate an electrical element such as a microcomputer. At this time, the microcomputer performs arithmetic processing according to the processing procedure defined by the program, generates a plurality of control signals corresponding to the power MOSFETs (Tr1 to Tr4), and outputs the control signals. In the power conversion circuit 23, the power MOSFETs (Tr1 to Tr4) are driven by the control signal, and the motor 30 is controlled.

  Further, the load control unit 20 controls the supply voltage input from the power supply control unit 10 as follows. That is, the supply voltage input from the power supply control unit 10 is applied to the gate of the power MOSFET (Tr5) via the diode element D1 and the gate resistance Rg. At this time, the diode element D1 rectifies the high frequency component of the supply voltage, and the gate resistor Rg adjusts the gate voltage. In parallel with this, the supply voltage input from the power supply controller 10 is guided to the constant voltage circuit 21 via the diode element D1. This supply voltage is used as the input voltage of the constant voltage circuit 21, and the capacitor C1 is charged with electric charge according to the value of the input voltage to smooth the input voltage. The output voltage of the constant voltage circuit 21 is smoothed by the capacitor C2. Here, as described in “Problems at the time of occurrence of instantaneous interruption”, when an instantaneous interruption occurs due to the vibration of the vehicle, the voltage value of the power supply line Lp decreases step by step, but the diode element D1 is connected to the capacitor C1. In order to prevent the discharge of the charged charges, the input voltage to the constant voltage circuit 21 is maintained in a stable state by the diode element D1 regardless of the voltage value of the power supply line Lp. Since the diode element D1 is not inserted into the power supply line Lp, it does not cause heat generation or decrease in efficiency as shown in FIG. 3 (prior art).

  Furthermore, when the in-vehicle battery Vb is reversely connected by some kind of defect, as described in “Problems of reverse connection of in-vehicle battery”, various problems associated with the discharge current occur in the conventional technology. However, in the load control unit 20 according to the present embodiment, for example, assuming that the in-vehicle battery Vb is 12V, an element that can withstand the applied voltage 12V is selected for the power MOSFET (Tr5) at the design stage. When the in-vehicle battery Vb is reversely connected, the power supply line Lp and the power supply line Ln receive an applied voltage having a reverse polarity to the original polarity, so that the power MOSFET (Tr5) is turned off unless the polarity is corrected correctly. State. At this time, since the power MOSFET (Tr5) uses an element that can withstand the applied voltage from the in-vehicle battery Vb, the power supply to the subsequent stage can be cut off from the power MOSFET (Tr5). Therefore, the power MOSFET (Tr5) prevents unnecessary discharge of the in-vehicle battery Vb and application of voltage, and prevents damage to the load control circuit such as the control circuit 22 or the power conversion circuit 23.

[Problem of negative transient surge at Ig off]
In addition, when the vehicle-mounted battery is connected in the correct direction, the following problem also occurs. In this state, when the ignition switch Ig is turned off (hereinafter referred to as Ig off), inductive elements such as the load control circuits 30 and 40 generate an induced electromotive force in response thereto. A temporary large voltage is generated with a positive polarity on the cathode side. Such a phenomenon is called a negative transient surge, and when a vehicle-mounted battery having a rated voltage of 12V is connected, the potential on the cathode side temporarily reaches several hundred volts. Therefore, when a negative transient surge occurs, there is a problem in the in-vehicle load control circuit that electrical elements such as power MOSFETs and microcomputers used for load control are destroyed.

  In order to avoid such a problem, in the present embodiment, when Ig is turned off, the power MOSFET (Tr5) passes a negative transient surge during the on-state due to the delay action of the capacitor C1. Thereafter, the negative transient surge is led to the subsequent stage from the protection circuit and is appropriately consumed by the load or the like, but the voltage value of the negative transient surge is sufficiently suppressed for the following reason. That is, in the load control circuit in which the negative transient surge has occurred, a current flows through a low impedance circuit component such as a parasitic diode in the power MOSFET (Tr1 to Tr4). Accordingly, since the load control circuit has a low load as described above, a large current instantaneously flows when a negative transient surge occurs. Since this large current increases the voltage drop at the output impedance of the surge source, the surge reverse voltage applied to each of the load control circuits is reduced, so that the surge reverse voltage causes the components of the load control circuit to be reduced. Reduced to a level that can be protected.

  Therefore, the withstand voltage of the power MOSFET according to the present embodiment does not need to be examined for negative transient surge, and it is sufficient to support the reverse bias of the on-vehicle battery, so that it can withstand the reverse bias (about 12V). It is possible to select a small element that can be obtained.

  As described above, the protection circuit according to the present embodiment includes the diode element D1, the capacitor C1, the gate resistor Rg, and the power MOSFET (Tr5). On the other hand, a circuit related to measures against instantaneous interruption is configured by a diode element D1, capacitors C1 and C2, and a constant voltage circuit 21. In other words, the capacitor C1 and the diode element D1 serve as both a component of the circuit and a component of the protection circuit for measures against instantaneous interruption.

  According to the in-vehicle load control circuit 100 according to the present embodiment, the gate voltage of the power MOSFET (Tr5) configured as the protection circuit is applied via the diode element D1 provided in the constant voltage circuit 21, and therefore a new Therefore, it is unnecessary to add a diode element, and the circuit configuration can be simplified.

  In addition, since the gate voltage is maintained above the threshold voltage of the power MOSFET (Tr5) for the protection circuit by the capacitor C1 for preventing instantaneous interruption connected to the input side of the constant voltage circuit 21, the vehicle load The control circuit can realize a countermeasure against negative transient surge with a simple configuration without adding a new capacitor.

  Furthermore, the in-vehicle load control circuit 100 according to the present embodiment simplifies the circuit configuration, and then “problems at the time of momentary interruption”, “problems of reverse connection of the in-vehicle battery”, and “when the Ig is off”. It solves all the problems of “Negative Transient Surge”. Then, by appropriately selecting the electric capacity of the capacitor C1 and the withstand voltage performance of the power transistor Tr5 described above, a circuit capable of clearing a requirement test such as the JASO standard can be studied, and the safety of the automobile is ensured.

  In addition, this invention should not be limited to the matter described by embodiment mentioned above. For example, the gate signal line Lg in the present embodiment has one end connected to the contact point between the diode D1 and the constant voltage circuit 21, but the one end is connected to the constant voltage circuit 21 and the capacitor C2. Even if it is connected to this contact, the same effect as described above can be obtained.

DESCRIPTION OF SYMBOLS 100 Vehicle-mounted load control circuit 10 Power supply control part 20 Load control part 21 Constant voltage circuit 22 Control circuit 23 Power conversion circuit 24 Load Tr5 Power MOSFET
C1 Capacitor D1 Diode element Rg Gate resistance Alt Power generator Vb On-board battery Ig Ignition switch

Claims (1)

A power control unit comprising an in-vehicle battery and an ignition switch, and a load control unit connected to a subsequent stage of the power control unit to control a load,
The load control unit includes a diode element having an anode connected to a power line on the anode side, a capacitor connected between the power line on the cathode side and the cathode of the diode element, and a contact point between the capacitor and the diode element. When connected to a constant voltage circuit interposed between the load control circuit provided in the load control unit and a gate signal line inserted with a gate resistor, the forward direction of the parasitic diode is the in-vehicle A power MOSFET inserted in the cathode-side power line so as to face the cathode terminal of the battery,
One end of the gate signal line is connected to the gate of the power MOSFET, and the other end is connected to a contact point between the diode element and the capacitor.

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