Patent Abstract:
A power supply device is provided for a vehicle having an idling-stop function, the power supply device including a boosting converter circuit with small loss that compensates for a voltage drop of a battery during starting of the engine and performing a protection function against a case in which the polarities of the battery are mistakenly connected in reverse. A series circuit including two MOSFETs serially connected to one another and an inductor is connected to the ends of a DC power source. A diode is connected to the connection point between the two MOSFETS serially connected to one another and the inductor, and a capacitor is connected in parallel to the two MOSFETS serially connected to one another. The two MOSFETs are serially connected such that the polarities of respective body diodes thereof are opposite to each other.

Full Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a power supply device for a vehicle, and more particularly, to a power supply device for a vehicle to be mounted in an idling-stop vehicle which temporarily stops the engine automatically when the vehicle comes to a stop, such as at a traffic light. 
     2. Description of the Related Art 
     In recent years, idling-stop vehicles that temporarily stop the engine automatically when the vehicles come to a stop, such as at a traffic light, have been used to reduce fuel consumption and emissions. 
     In a vehicle of this type, the engine is automatically stopped based on predetermined idling determination information such as the vehicle speed or the degree of opening of the accelerator when the vehicle is presumed to have stopped, and then automatically started by the starter in order to prepare the vehicle to start moving when an engine start condition indicating that the driver wants to start moving is satisfied. 
     In general, since the starter for starting an engine consumes a large amount of power, a phenomenon of a temporary drop in the voltage of a battery output system at the moment of starting the engine may occur. 
     Such a phenomenon becomes significant especially when a battery used as the power source is heavily discharged due to street driving in which stopping and starting of movement are frequently repeated. 
     When such a voltage drop occurs, problems, such as resetting of microcomputers used in electrical equipment in the vehicle, thereby losing memory contents, such as contents that have been learned up to that time, or temporary dimming of the instrument lighting or other lighting, thereby severely impairing the quality feeling of the vehicle, may occur. 
     Therefore, a configuration has been disclosed in which a boosting circuit for voltage compensation is provided in an idling-stop vehicle in order to prevent a voltage drop in the battery output system during restarting of the engine, and the boosting circuit is operated during a period in which the starter is operating upon starting of the engine (see, for example, Japanese Unexamined Patent Application Publication No. 2005-237149). 
     In addition, since a battery can be replaced by the owner, there may be a possibility of the polarities thereof being erroneously connected. Therefore, a protection circuit that prevents current from flowing when a reverse connection is made has been disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2-197441. 
     A method for forming a protection circuit that prevents current from flowing when the polarities of a battery are mistakenly connected in reverse in a circuit that compensates, by using a boosting converter, for an output voltage drop due to a large power consumption of the starter during restarting of the engine as described above will be explained with reference to  FIGS. 7 and 8 . 
       FIG. 7  illustrates a configuration including a battery  1  provided as a DC power source, a first load  6 , a first capacitor  2 , a boosting converter circuit  3 , a control circuit  4  which controls the boosting converter circuit  3  and a connector  5  to which the output voltage of the boosting converter circuit  3  is supplied, wherein the connecter  5  is connected to a second load (not shown). 
     The first load  6  includes a starter  61 , an engine  62 , and a generator  63 . The starter  61  is supplied with DC voltage from the battery  1  during starting of the engine in order to start the engine  62 . When the engine starts, power is generated by the generator  63  by using rotation as a power source in order to charge the battery  1 . 
     The boosting converter circuit  3  includes an inductor  31 , a first semiconductor switching element  32  defined by a field-effect transistor or other suitable semiconductor element, a first diode  34  and a second capacitor  35 . The inductor  31  and the first semiconductor switching element  32  are connected in series to the ends of the battery  1 . The anode of the first diode  34  is connected to the connection point between the inductor  31  and the first semiconductor switching element  32 , and the cathode of the first diode  34  is connected to an output terminal of the connector  5 . The second capacitor  35  is connected to the ends of the connector  5 . 
     With automobiles, it is often the case that the battery  1  can be replaced by the user. Therefore, it is necessary to provide, in the power supply device for a vehicle, a protection circuit that prevents current from flowing in the reverse direction when the user mistakenly connects the polarities of the battery  1  in reverse. In order to provide such a function, a relay switch  8  shown in  FIG. 7  or a third diode  9  shown in  FIG. 8 , for example, may be used to enable conduction only when a forward current flows. However, there is a problem in that when the output current of the power supply device for a vehicle is extremely large, the forward power loss of the third diode  9  or the power consumption of the relay switch  8  becomes too large to ignore, which causes the battery life to be shortened. 
     In addition, since the vehicle weight is large for large vehicles that are equipped with power steering devices, a high power is required for a motor used in the power steering device, and therefore the size of the motor must be increased. In order to prevent such an increase, a voltage greater than the output voltage (12 V) of an existing lead acid battery may be required. However, even in this case, a large current flows, and the loss cannot be ignored in an existing power supply device using a diode or a relay switch. 
     SUMMARY OF THE INVENTION 
     To overcome the problems described above, a power supply device for a vehicle according to a preferred embodiment of the present invention preferably includes a boosting converter circuit connected to a DC power source, a voltage detection circuit arranged to detect an output voltage of the DC power source, and a control circuit arranged to drive the boosting converter circuit in accordance with the output voltage detected by the voltage detection circuit so as to set the output voltage to a predetermined value. In the boosting converter circuit, a series circuit including at least one inductor and two semiconductor switching elements serially connected to one another is preferably connected to the ends of the DC power source. The boosting converter circuit preferably includes at least one rectifying element connected to a connection point between the at least one inductor and the two semiconductor switching elements serially connected to one another. The boosting converter circuit preferably includes at least one capacitor connected in parallel to the two semiconductor switching elements serially connected to one another. The two semiconductor switching elements are preferably serially connected such that the polarities of respective body diodes thereof are opposite to each other. 
     In the power supply device for a vehicle, preferably, the control circuit controls the boosting converter circuit such that the output voltage of the boosting converter circuit becomes the output voltage of the DC power source when a load connected to the DC power source is in an overloaded state and the output voltage of the DC power source is transiently dropped. 
     In the power supply device for a vehicle, preferably, a load of the boosting converter circuit is a power steering device, and the control circuit controls the output voltage of the boosting converter circuit in accordance with rotation angle information of steering in the power steering device. 
     In the power supply device for a vehicle, preferably, both of the two semiconductor switching elements are N-channel MOSFETs, and drain terminals thereof or source terminals thereof are connected to each other. 
     In the power supply device for a vehicle, preferably, the semiconductor switching element on a low-voltage side of the two semiconductor switching elements is controlled by the control circuit and the semiconductor switching element on a high-voltage side is configured as a self-driven type element including a diode arranged to apply a bias voltage to a control terminal. 
     According to various preferred embodiments of the present invention, in the power supply device for a vehicle including the boosting converter circuit that compensates a voltage drop of the battery due to a transient increase in load and supplies a voltage higher than the battery supply voltage, a circuit that prevents current from flowing in the reverse direction when the polarities of the battery are mistakenly connected in reverse can be provided with a low loss. 
     In addition, a mechanical switch, such as a relay switch, is no longer required when two FET body diodes are arranged such that the polarities thereof are opposite to each other, such that spark generation and noise generation are prevented. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a first preferred embodiment of the present invention. 
         FIG. 2  is a circuit diagram showing a case in which a battery is correctly connected in the first preferred embodiment of the present invention. 
         FIG. 3  is a circuit diagram showing a case in which a battery is reversely connected in the first preferred embodiment of the present invention. 
         FIG. 4  is a circuit diagram illustrating a second preferred embodiment of the present invention. 
         FIG. 5  is a circuit diagram illustrating a third preferred embodiment of the present invention. 
         FIG. 6  is a circuit diagram illustrating a fourth preferred embodiment of the present invention. 
         FIG. 7  is a circuit diagram of a power supply device for a vehicle for preventing reverse connection of a battery according to the related art. 
         FIG. 8  is a circuit diagram of another power supply device for a vehicle for preventing reverse connection of a battery according to the related art. 
         FIG. 9  is a circuit diagram illustrating a modification of the first preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be explained in detail with reference to the drawings. The same or similar components and elements are denoted by the same reference characters, and the explanation thereof will essentially not be repeated. 
     First Preferred Embodiment 
       FIG. 1  is a circuit diagram illustrating a configuration of a power supply device for a vehicle according to a first preferred embodiment of the present invention. 
     In  FIG. 1 , the power supply device for a vehicle preferably includes a battery  1  provided as a DC power source, a first load  6 , a first capacitor  2 , a boosting converter circuit  3 , a control circuit  4  which controls the boosting converter circuit  3 , and a connector  5  to which the output voltage of the boosting converter circuit  3  is supplied. A second load (not shown) is connected to the connecter  5 . 
     The first load  6  preferably includes a starter  61 , an engine  62 , and a generator  63 . The starter  61  is supplied with DC voltage from the battery  1  during starting of the engine in order to start the engine  62 . When the engine starts, power is generated by the generator  63  by using rotation as a power source, and charges the battery  1 . 
     The boosting converter circuit  3  preferably includes an inductor  31 , a first semiconductor switching element  32 , and a second semiconductor switching element  33  defined by a field-effect transistor (MOSFET) or other suitable semiconductor element, a first diode  34 , a second capacitor  35 , a second diode  36 , a bias resistor  37 , and a discharge resistor  38 . The inductor  31 , the second semiconductor switching element  33 , and the first semiconductor switching element  32  are preferably connected in series to the ends of the battery  1 . The drains of the first semiconductor switching element  32  and the second semiconductor switching element  33  are preferably connected such that the polarities of respective body diodes  321  and  331  are opposite to each other. Preferably, the anode of the first diode  34  is connected to the connection point between the inductor  31  and the second semiconductor switching element  33 , and the cathode of the first diode  34  is connected to an output terminal of the connector  5 . The second capacitor  35  is preferably connected to the ends of the connector  5 . 
     The second diode  36  with the anode thereof connected to the connection point between the first capacitor  2  and the inductor  31  and the cathode thereof connected to the gate terminal of the second semiconductor switching element  33  via the bias resistor  37 , and the discharge resistor  38  connected between the gate and the source of the second semiconductor switching element  33 , are preferably provided. The control circuit  4  monitors an input voltage supplied from the battery  1  and an output voltage by using an output voltage detection circuit  7  to control on/off of the first semiconductor switching element  32  such that an output voltage to be supplied to the second load has a predetermined value. 
     When the load connected to the battery  1  (DC power source) is in an overloaded state and the voltage of the DC power source transiently drops, the control circuit  4  controls the boosting converter circuit  3  such that the output voltage of the boosting converter circuit  3  has the voltage of the DC power source. 
       FIG. 2  is a circuit block diagram showing a case in which the polarities of the battery  1  are correctly connected. The first load  6  including the starter  61 , the engine  62 , and generator  63  in  FIG. 1  is not shown since the first load  6  has no direct role in the operation. 
     When DC voltage is supplied from the battery  1  and the control circuit  4  applies the voltage to the gate terminal of the first semiconductor switching element  32  to turn on the first semiconductor switching element  32 , current flows in the inductor  31 , thereby generating the voltage between the ends of the inductor  31 . This turns on the second diode  36 , and the voltage is applied to the gate terminal of the second semiconductor switching element  33  via the bias resistor  37 , thereby also turning on the second semiconductor switching element  33 . In this manner, a current flows in a closed loop from the positive terminal of the battery  1  to the inductor  31 , the second semiconductor switching element  33 , the first semiconductor switching element  32 , and to the negative terminal of the battery  1 . 
     Subsequently, when the first semiconductor switching element  32  is turned off by a control signal from the control circuit  4 , energy accumulated in the inductor  31  during an ON period is released via the first diode  34  to charge the second capacitor  35 . In this manner, a current flows in a closed loop from the positive terminal of the battery  1  to the inductor  31 , the first diode  34 , the second capacitor  35 , and to the negative terminal of the battery  1 . 
     Next, in  FIG. 3 , a case in which the polarities of the battery  1  are mistakenly connected in reverse is assumed.  FIG. 3  is a circuit block diagram showing the case where the polarities of the battery  1  are connected in reverse. 
     When the battery  1  is reversely connected, the body diode  321  of the first semiconductor switching element  32  is biased in the forward direction, and thus is turned on. However, the body diode  331  of the second semiconductor switching element  33  is biased in the reverse direction, and thus is not turned on. That is, the two semiconductor switching elements ( 32  and  33 ) are used as a switch of the boosting converter circuit  3 , and are serially connected such that the polarities of the body diodes ( 321  and  331 ) thereof are opposite to each other, whereby current can be prevented from flowing in the boosting converter circuit  3  when the polarities of the battery  1  are mistakenly connected in reverse. Consequently, damage and malfunction of the load connected to the output of the boosting converter circuit  3  are prevented. 
     In this case, the second semiconductor switching element  33  is preferably configured as a self-driven type element in which the second semiconductor switching element is not controlled by the control circuit  4  since the second diode  36  is present, and is always turned on when the battery  1  is correctly connected thereto and always turned off when the polarities of the battery  1  are mistakenly connected in reverse. 
     In addition, to compensate for a transient drop of the supply voltage of the battery  1  upon starting of the starter  61  as described above, the output voltage of the boosting converter circuit  3  may preferably be set so as to be equal or substantially equal to or greater than the supply voltage of the battery  1 . 
     Furthermore, as shown in  FIG. 9 , when the power supply device for a vehicle is used in the power steering device of a vehicle having a heavy vehicle weight, since stress is required to be controlled in accordance with the steering wheel angle that the driver has made, the control circuit  4  may preferably control, as appropriate, the output voltage of the boosting converter circuit  3  by receiving the steering rotation angle information from the second load. 
     Second Preferred Embodiment 
       FIG. 4  is a circuit diagram illustrating a configuration of a power supply device for a vehicle according to a second preferred embodiment of the present invention. 
     The second preferred embodiment differs from the first preferred embodiment in that the on/off control for the second semiconductor switching element  33  is preferably performed in the control circuit  4 . When the control circuit  4  is configured so as to detect the voltage between the ends of the inductor  31 , the control circuit  4  can perform the on/off control for the first semiconductor switching element  32  and the second semiconductor switching element  33 . 
     Other features are substantially the same as in the first preferred embodiment, and explanations thereof are omitted. 
     Third Preferred Embodiment 
       FIG. 5  is a circuit diagram illustrating a configuration of a power supply device for a vehicle according to a third preferred embodiment of the present invention. 
     The third preferred embodiment differs from the second preferred embodiment in that the connection order of the first semiconductor switching element  32  and the second semiconductor switching element  33  is reversed. With a configuration in which the control circuit  4  performs the on/off control for the first semiconductor switching element  32  and the second semiconductor switching element  33 , preferably, the first semiconductor switching element  32  may be disposed on the high-voltage side and the second semiconductor switching element  33  may be disposed on the low-voltage side, as shown in  FIG. 5 . 
     Other features are substantially the same as in the first preferred embodiment, and explanations thereof are omitted. 
     Fourth Preferred Embodiment 
       FIG. 6  is a circuit diagram illustrating a configuration of a power supply device for a vehicle according to a fourth preferred embodiment of the present invention. 
     The fourth preferred embodiment differs from the second preferred embodiment in that the fourth preferred embodiment preferably includes a P-channel FET as the second semiconductor switching element  33  while the second preferred embodiment includes an N-channel FET as the second semiconductor switching element  33 . With a configuration in which the control circuit  4  performs the on/off control for the first semiconductor switching element  32  and the second semiconductor switching element  33 , the same operation can be achieved by configuring the power supply device such that a negative potential is applied to the gate terminal when a P-channel FET is used as the second semiconductor switching element  33 . 
     Other features are substantially the same as in the first preferred embodiment, and explanations thereof are omitted. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.

Technology Classification (CPC): 5