JP3555239B2 - Power generator for vehicles - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an exciting current control device for an automotive alternator that PWM controls an exciting current.
[0002]
[Prior art]
2. Description of the Related Art In a conventional vehicular power generating apparatus, an output terminal of a vehicular alternator with a built-in rectifier (hereinafter, also simply referred to as a generator) is connected to a battery and an electric load through a power supply control switch means (hereinafter, also referred to as a transfer switch). A circuit configuration for supplying power is known. The merit of charging the battery through such a transfer switch is that the battery can be separated from the generator by cutting the transfer switch as necessary, whereby the generator can be separated from another battery (hereinafter, referred to as a second battery). Or when only the second battery supplies power to, for example, a vehicle electric load, the effect of saving the capacity of the cut battery for, for example, starting the engine can be obtained.
[0003]
When power is supplied to the second battery through the second switch means (second transfer switch), the conduction of both transfer switches is switched and the power generation voltage of the generator is switched. Two batteries with the rated voltage can be charged.
As such a transfer switch, an electromagnetic relay, a reverse connection of a pair of vertical channel MOSFETs, a bipolar transistor connected in series with a backflow prevention diode, or the like can be employed. The reason why the above-mentioned pair of vertical channel MOSFETs are reverse-connected is that in the conventional MOSFET, the well region is short-circuited to the source region on the surface in order to fix the potential of the well region where the inversion channel layer is formed. When the short-circuit connection is performed in this manner, in the operation mode in which the vertical channel MOSFET is operated as an electric source region, a parasitic diode formed between the well region and the substrate is forward-biased and the MOSFET cannot be cut off current. It is because it becomes.
[0004]
The reason for connecting a reverse current prevention diode to the bipolar transistor in series is that, in a potential state where the pn junction between the emitter and the base is reverse-biased, the breakdown voltage of the pn junction is small and the breakdown easily occurs to cut off the current. It is not possible.
That is, when the transfer operation from the generator to the battery is controlled by the transfer switch, when the generated voltage decreases or disappears, the bypass current through the parasitic diode in the conventional MOSFET or the emitter of the bipolar transistor as described above. Since the breakdown current of the pn junction between the bases may flow from the battery to the generator or the second battery, conventionally, a pair of MOSFETs is connected in series as described above, or a backflow prevention diode is connected in series to the bipolar transistor. Or
[0005]
[Problems to be solved by the invention]
However, when the above-described transfer switch is configured by an electromagnetic relay, there are problems such as the physical size, life, and operation speed of the device. Further, when a pair of series-connected MOSFETs are used as transfer switches and when a backflow prevention diode is connected in series to a bipolar transistor, an increase in power loss, an increase in accommodation space, an increase in device size, and an increase in functions requiring cooling are caused. .
[0006]
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a vehicular power generation device that supplies power to a battery through a transfer switch, and that greatly simplifies the configuration and also achieves a reduction in loss. The purpose is.
[0007]
[Means for Solving the Problems]
First of the present invention, Seventh and eighthA vehicle alternator configured to supply an output current rectified by a built-in rectifier to a battery from an output terminal, a semiconductor switch unit interposed between the output terminal and the battery, and the semiconductor switch Control means for controlling a portion of the semiconductor switch portion, wherein the semiconductor switch portion has a first conductivity type well region having a gate electrode formed on the surface thereof via a gate insulating film, and the gate electrode is formed on the surface of the well region. A vehicular power generating device including a MOSFET (insulated gate field effect transistor) having a source region and a drain region of a second conductivity type that are electrically connected to each other by an inversion channel layer,
A power generating device for a vehicle, comprising: a high-resistance portion connecting one of the source region and the drain region to the well region.
[0008]
The resistance value of the high resistance portion is different from the resistance value of the diode connected in parallel with the high resistance portion and having a normal pn junction between the well region and the source region or the drain region at the time of reverse bias. And However, means for selectively doping (for example, ion-implanting) conductive particles such as gold into the pn junction constituting the diode to form a conductive path and reducing the resistance value of the junction at the time of reverse bias. In this case, the conductive path corresponds to the high-resistance portion in the present invention.
[0009]
The resistance value of the high-resistance portion is determined under the operating conditions in which, of the pair of parasitic diodes of the MOSFET, the parasitic diode that is not bypassed by the high-resistance portion is forward-biased and the rated maximum on-voltage is applied to the gate electrode. , The bypass current through the parasitic diode is set to be at least smaller than the channel current.
[0010]
The present invention1ConfigurationIsFurther, one of the source region and the drain region is connected to a high-order end of the second battery.
The present invention2The configuration of the above1Further, the second battery has a lower rated voltage than the battery and is connected to the output terminal of the generator through a second MOSFET, and one end of the high-resistance portion is connected to the battery side of the MOSFET. It is characterized by being connected.
[0011]
The present invention3The configuration of the above2In the configuration of the above, further, when the generator performs power generation capable of charging the battery, the control section intermittently charges the second MOSFET at a predetermined duty ratio to charge the second battery from the generator. At least during the conduction period of the second MOSFET, the MOSFET is cut off.
[0012]
The present invention4The configuration of3In any one of the above structures, the MOSFET is made of single crystal SiC.
The present invention5The configuration of the above4In the above configuration, the MOSFET is mounted on the generator.
The present invention6The configuration of the above4In the above configuration, the MOSFET is mounted on the same circuit board as the control unit.
A seventh configuration of the present invention further includes a high-resistance portion connecting one of the source region and the drain region to the well region, wherein the MOSFET is made of single-crystal SiC, It is characterized by being mounted on.
An eighth configuration of the present invention further includes a high-resistance portion connecting one of the source region and the drain region to the well region, wherein the MOSFET is made of single-crystal SiC, And mounted on the same circuit board.
[0013]
[Action and effect of the invention]
First of the present invention, Seventh and eighthIn this configuration, a MOSFET is employed as a semiconductor switch section (also referred to as a transfer switch) provided between a generator and a battery, and one of a source region and a drain region of the MOSFET and a well region are connected to a high resistance section. Are electrically connected.
[0014]
With this configuration, the potential fluctuation of the gate electrode acts on the well region through the gate capacitance between the well region and the gate electrode without short-circuiting either the source region or the drain region and the well region. In this case, it is possible to prevent the MOS transistor characteristics from deteriorating due to the potential fluctuation of the well region in the same direction.
[0015]
Further, according to the present embodiment, when a potential state occurs in which a parasitic diode (hereinafter, also referred to as a non-bypass parasitic diode) which is not bypassed in the high-resistance portion of the MOSFET is forward-biased, the current flowing through the non-bypass parasitic diode occurs. The bias current can be made sufficiently small as needed, and problems caused by the bias current, such as problems such as battery discharge or overcharge, can be solved.
[0016]
The present invention1In the configurationFurtherSince one of the source region and the drain region is connected to the higher end of the second battery, the following operation and effect can be obtained.
First, when the cathode of the non-bypass parasitic diode is connected to the high end of the second battery, when the capacity of the second battery is insufficient, or when the rated voltage of the second battery is lower than that of the battery, The problem that the forward bias current flows from the battery to the second battery side and the battery becomes insufficient in capacity or the second battery is overcharged is suppressed by the high resistance portion.
[0017]
Further, when the cathode of the non-bypass parasitic diode is connected to the high end of the battery, the problem that the battery is overcharged from the generator through the non-bypass parasitic diode is suppressed by the high resistance portion. Further, even when the battery capacity is insufficient or when the rated voltage of the battery is lower than that of the second battery, the capacity of the second battery is not insufficient and the battery is not overcharged.
[0018]
The present invention2In the configuration of1Further, the second battery has a lower rated voltage than the battery and is connected to the output terminal of the generator through the second MOSFET, and one end of the high-resistance portion of the MOSFET is connected to the battery-side source or drain region of the MOSFET. During the high-voltage generation from the generator through the non-bypass parasitic diode, the battery prevents the battery from being constantly charged and becoming overcharged by the non-bypass parasitic diode, and the low-voltage power generation of the generator or When power generation is stopped, a forward bias current flows from the battery to the second battery through the non-bypass parasitic diode of the MOSFET, so that there is no shortage of battery capacity or overcharge of the second battery.
[0019]
The present invention3In the configuration of2Further, when the generator performs battery-chargeable power generation, the second MOSFET is intermittently charged at a predetermined duty ratio to charge the second battery from the generator, and at least during the conduction period of the second MOSFET. Turn off the MOSFET.
With this configuration, the second battery having a low rated voltage can be charged even during high-voltage power generation in which the generator can charge a battery having a high rated voltage. At this time, since the difference between the generated voltage and the rated voltage of the second battery is mainly consumed by the internal impedance of the generator, a large voltage is applied between the source region and the drain region of the second MOSFET and the second voltage is applied. A sudden increase in the heat generated by the two MOSFETs is suppressed. Further, since the MOSFET is cut off when the second MOSFET is turned on, a current flows from the battery to the second battery, thereby preventing a rapid increase in heat generation of the second MOSFET for the same reason as described above.
[0020]
The present invention4In the configuration of the above,3Any ofOr seventh or eighthFurther, in the configuration described above, since the MOSFET is made of single crystal SiC, the following effects can be obtained. That is, by using a single-crystal SiC semiconductor having an excellent breakdown field strength as the MOSFET, the withstand voltage layer having a high resistance of the MOSFET can be thinned. The output of the vehicle alternator can be significantly improved, and the size of the MOSFET can be reduced and the cooling structure thereof can be simplified.
[0021]
The present invention5In the configuration of4th or 7thFurther, since the SiC semiconductor can be used at a high temperature, the MOSFET can be built in the generator. In this case, the device configuration can be simplified.
The present invention6In the configuration of4th or 8thFurthermore, since the MOSFET is made of SiC having low on-resistance and low heat generation, the MOSFET can be mounted on the same circuit board as the control means, and the device configuration can be made more compact.
[0022]
【Example】
(Example 1)
One embodiment of the present invention will be described with reference to the circuit diagram of FIG.
Reference numeral 1 denotes a vehicle AC generator including a three-phase synchronous generator including a three-phase full-wave rectifier (not shown). The generator 1 includes a charging line 2 and a MOSFET (semiconductor switch unit according to the present invention) 3. , Is connected to a high end of a starter battery (battery in the present invention) 5 through a charging line 4, and further connected to a high end of a starter 51 through a start switch 50.
[0023]
The charging line 2 is connected to the higher end of a battery (second battery according to the present invention) 6 for supplying normal electric load, and further connected to the higher end of a normal electric load 61 through a load switch 60.
The MOSFET 3 is an N-channel insulated gate field effect transistor controlled by the controller 7, and has a generator-side main electrode D, a battery-side main electrode S, and a gate electrode G. Naturally, when charging the battery 5, the battery-side main electrode S becomes a source electrode, and the generator-side main electrode D becomes a drain electrode. DD is a parasitic diode formed of a PN junction formed between an N-type region connected to the generator-side main electrode D and the P-well region 3p, and DS is an N-type junction connected to the battery-side main electrode S. It is a parasitic diode formed of a PN junction formed between the region and the region.
[0024]
Although not shown, the controller 7 includes a microcomputer, a booster circuit, and an output buffer circuit, and is supplied with a power supply voltage from the battery 5 or the second battery 6. The booster circuit incorporates a switching capacitor circuit or the like and outputs a voltage V5 or V6 to a predetermined power supply voltage (at least the rated voltage of the battery 5 + the threshold voltage Vt of the MOSFET 3 + a few volts or more) to the output buffer circuit. This output buffer circuit is a power amplifier circuit and can be constituted by, for example, a low power consumption CMOS inverter or a complementary (complementary) common emitter bipolar transistor circuit in which the CMOS inverter is bipolarized. It is well known that this type of booster circuit is used to control the opening and closing of the enhancement type MOSFET 3, and illustration and further description are omitted.
[0025]
In this embodiment, the P-well region 3p and the generator-side main electrode D are connected by the high resistance portion r. Therefore, when the parasitic diode DD is not in a forward bias state, the P-well region 3p and the generator-side main electrode D are not connected. The electric resistance between the resistance D and the resistance D is equal to the parallel combined resistance of the reverse bias resistance of the parasitic diode DD and the high resistance part r. In this embodiment, the resistance value of the high resistance portion r is set to a value smaller than the reverse bias resistance by one digit or more.
[0026]
Hereinafter, the operation of this circuit will be described.
Normally, the MOSFET 3 is shut off, and when the start switch 50 is turned on, the starter 51 is started by power supply from the battery 5. Since the capacity required for starting the starter 51 is not large, the battery 5 can have a small capacity. However, in order to prevent the starter 51 from being unable to start, it is necessary to keep the charge state of the battery 5 always higher than a certain capacity, that is, the terminal voltage of the battery 5 must be higher than a certain voltage value.
[0027]
When the starter 51 starts the engine and the engine speed increases, the generated voltage of the generator 1 increases, and the generator 1 charges the second battery 6. Normally, the electric load 61 is not required to be driven reliably as in the starter 51, and is therefore driven by the second battery 6. The output voltage of the generator 1 is controlled by a regulator (not shown) built in the generator 1. That is, the terminal voltage of the second battery 6 is compared with a predetermined reference voltage, and the field current of the generator 1 is controlled so that they match.
[0028]
Next, control of the MOSFET 3 by the controller 7 will be described with reference to the flowchart of FIG. First, the voltages V5 and V6 are read (100), and it is checked whether the terminal voltage V5 of the battery 5 is lower than a predetermined reference voltage Vref (101). If not, it is checked whether or not the terminal voltage V6 of the second battery 6 is higher than V5 (102). If not, the MOSFET 3 is cut off at step 106 and the process proceeds to step 108; Is turned on and the routine proceeds to step 108. In step 108, the process returns to step 100 after a predetermined time delay for adjusting the routine traveling time.
[0029]
Also, instead of steps 101 and 102, the state of charge of the battery 5 is monitored, and the process proceeds to step 104 to charge the battery 5 until the amount of electricity discharged by starting the starter is recovered. When the vehicle is stopped, the process proceeds to step 106, and the battery 5 can be disconnected from the electric load.
As a result, the starting battery 5 can be charged by turning on the MOSFET 3 only when necessary, and when it is not necessary to turn off the MOSFET 3, the electric load (light or the like) is turned off when the vehicle is stopped or the like. Even if it is forgotten, the discharge of the battery 5 can be prevented, and reliable starting can be realized.
[0030]
What is particularly important in this embodiment is that the potential of the P well region 3p is set by the high resistance portion r. In this way, even if a high-speed potential change of the P-well region 3p (due to the influence of the gate electrode potential through the capacitance) occurs, there is a limit to the high-speed tracking due to the limitation of the CR time constant. Thus, the potential fluctuation of the P well region 3p can be suppressed. Moreover, when the generated voltage of the generator 1, that is, the potential V6 of the charging line 2 is higher than the potential V5, the forward bias current through the parasitic diode DS can be reduced, and the overcharge of the battery 5 can be suppressed.
(Example 2)
Another embodiment will be described with reference to FIG.
[0031]
This embodiment differs from the first embodiment in that the high resistance portion r connects the battery side main electrode S and the P well region 3p to short-circuit the parasitic diode DS in the embodiment of FIG. In this way, charging of the battery 5 through the parasitic diode DD of the MOSFET 3 during power generation of the generator 1 is completely prohibited. Further, when the voltage of the second battery 6 drops, the current flowing from the battery 5 to the second battery 6 through the parasitic diode DD is greatly reduced, thereby eliminating the shortage of the capacity of the battery 5 except during an extremely long period of unattended state. be able to.
(Example 3)
Another embodiment in which the generated voltage of the generator 1 is switched between high and low levels will be described with reference to FIG.
[0032]
This embodiment differs from the embodiment of FIG. 1 in that a second MOSFET 8 is interposed between the charging line 2 and the second battery 6 and the load switch 60, and the lower end of the battery 5 is connected to the higher end of the second battery 6. Is different from the first embodiment. Therefore, in this embodiment, the electric load 51 has a rated voltage of 24V. Note that the gate electrode of the second MOSFET 8 also receives a control voltage from the controller 7, and the battery-side main electrode S of the second MOSFET 8 is connected to the second battery 6 and the switch 60 via the charging line 9, and the battery-side main electrode S of the second MOSFET 8 Are short-circuited to the P-well region 8p.
[0033]
Further, the controller 7 reads the voltage V2 of the charging line 2, the terminal voltage V5 of the battery 5, and the terminal voltage V6 of the second battery 6, and intermittently controls the field current control transistor 11 built in the generator 1. . The generator 1 has a field current control transistor 12 for controlling a field current supplied to the field winding 11 and a three-phase armature winding 13.
[0034]
Hereinafter, the control operation of the controller 7 will be described with reference to the flowcharts of FIGS.
First, the voltages V2, V5, and V6 are read (200), and it is checked whether or not the terminal voltage V5 of the battery 5 is lower than a predetermined reference voltage Vref1 (201). It is checked whether it is larger than V5 (202). If V2 is larger than V5, the MOSFET 3 is turned on and the second MOSFET 8 is turned off (204), and the process proceeds to step 214. If V2 is equal to or less than V5, the process directly proceeds to step 214.
[0035]
On the other hand, if V5 is equal to or higher than the reference voltage Vref1 in step 201, it is checked whether V6 is lower than the reference voltage Vref2 (208), and if it is lower, it is checked whether V2 is higher than Vref (210). If V2 is larger than V6, the MOSFET 3 is turned off and the second MOSFET 8 is turned on (212), and the process proceeds to step 214. If V6 is equal to or higher than the reference voltage Vref2, the process proceeds to step 214. Is less than or equal to V6, the routine proceeds to step 214.
[0036]
In steps 214 to 226, the field current of the generator 1 is controlled.
In step 214, it is checked whether the MOSFET 3 is on and the second MOSFET 8 is off. If YES, the voltage V2 is compared with a predetermined reference voltage VH (the reference voltage Vref1 or slightly higher). When the voltage V2 is larger than the predetermined reference voltage VH + the predetermined small value a (for example, about 0.1 V), the transistor 12 is turned off (220), and the voltage V2 becomes the predetermined reference voltage VH-the predetermined small value a (for example, If less than about 0.1 V), the transistor 12 is turned on (224), and the voltage V2 is equal to or lower than the predetermined reference voltage VH + the predetermined small value a (for example, about 0.1 V) and the predetermined reference voltage VH-the predetermined voltage. If it is larger than the small value a (for example, about 0.1 V), the process directly returns to step 200.
[0037]
Similarly, if the MOSFET 3 is turned off and the second MOSFET 8 is turned on in step 214, the voltage V2 is compared with a predetermined reference voltage VL (the reference voltage Vref2 or slightly higher). When the voltage V2 is larger than the predetermined reference voltage VL + the predetermined small value a (for example, about 0.1 V), the transistor 12 is turned off (226), and the voltage V2 becomes the predetermined reference voltage VL-the predetermined small value a (for example, If less than about 0.1 V), the transistor 12 is turned on (224), and the voltage V2 is equal to or less than the predetermined reference voltage VL + the predetermined small value a (for example, about 0.1 V) and the predetermined reference voltage VL-the predetermined voltage. If it is larger than the small value a (for example, about 0.1 V), the process directly returns to step 200.
[0038]
This embodiment is characterized in that the potential control of the battery 5 and the second battery 6 can be performed by the MOSFET 3 and the second MOSFET 8, so that the control of the power generation output voltage V2 of the generator 1 may be rough and the field current control transistor 12 It is not necessary to frequently perform the intermittent switching, and it is possible to suppress noise and efficiency reduction due to the frequent intermittent switching.
Further, both the terminal voltage V5 of the battery 5 and the terminal voltage V6 of the second battery 6 can be controlled to a desirable level. What is important is that a high resistance portion r is provided in the MOSFET 3 on the high voltage side. That is, the problem that the parasitic diodes DD of both MOSFETs 3 and 8 generate an excessively large generated voltage and the battery 5 and the second battery 6 are overcharged is solved. The high-resistance portion r can prevent a problem that a charging current flows from the battery 5 through the high-resistance portion r and the parasitic diode DD of the MOSFET 3 when the second MOSFET 8 is conducting. In the present embodiment, the battery 5 and the second battery 6 are connected in series, but it is obvious that both can be arranged separately.
(Example 4)
An embodiment in which two types of batteries are charged without switching the generated voltage of the generator 1 will be described with reference to the flowchart of FIG. In this embodiment, the voltage generated by the generator 1 is controlled to be substantially constant at which the battery 5 can be charged.
[0039]
In this embodiment, steps 210 and 212 in FIG. 5 are replaced with steps 310, 312 and 314, and steps 214, 218 and 226 in FIG. 5 are omitted.
In step 208, it is checked whether or not V6 is smaller than the reference voltage Vref2 (208). If it is higher than the reference voltage Vref2, the process proceeds to step 208. If it is smaller, it is checked whether or not V2 is larger than V6 (210). If V2 is equal to or lower than V6, the process proceeds to step 216. If V2 is larger than V6, the MOSFET 3 is turned off, the second MOSFET 8 is turned on (310), and the process waits for a predetermined time (312).
[0040]
By doing so, the output current from the generator 1 charges the second battery 6 through the second MOSFET 8. In addition, since the reactance of the generator 1 is very large and the current change is suppressed, the flow of a large current through the second MOSFET 8 is suppressed. If a predetermined short time has elapsed in step 312, the MOSFET 3 is turned on and the second MOSFET 8 is turned off (314), and the process proceeds to step 216.
[0041]
That is, in this embodiment, PWM control of a constant duty ratio is performed by software in steps 310, 312, and 314. Of course, the delay time ΔT can be changed according to, for example, V6.
In this way, the generator 1 can charge the second battery 6 without switching the generated voltage, and can drive an electric load having a different rated voltage. What is important is that a high resistance portion r is provided in the MOSFET 3 on the high voltage side. That is, the problem that the parasitic diodes DD of both MOSFETs 3 and 8 generate an excessively large generated voltage to overcharge the battery 5 and the second battery 6 is solved. The high-resistance portion r can prevent a problem that a charging current flows from the battery 5 through the high-resistance portion r and the parasitic diode DD of the MOSFET 3 when the second MOSFET 8 is conducting.
[0042]
A manufacturing example of the high-resistance portion r of the MOSFET 3 which is a feature of the present invention described above will be described with reference to FIG.
n⁺N on the substrate 91⁻A breakdown voltage layer 92 and a p-well region 93 are sequentially grown epitaxially, and n⁺A region 94 is formed by ion implantation, a thick silicon oxide film 95 is formed on the surface, a U-groove 96 is trenched, and a gate insulating film 97 is formed on the surface of the U-groove 96 by thermal oxidation. A gate electrode 98 made of polysilicon is formed.⁺A surface main electrode 99 made of aluminum is formed on the surface of the region 94, and a low-phosphorus-doped polysilicon film 90 extending to the opening on the p-well region 93 and the surface main electrode 99 is formed as a high resistance portion r. The substrate is single crystal 6H-SiC, and the epitaxial layers 92 and 93 are SiC homoepitaxial layers.
[0043]
The high resistance portion r can be easily formed by a method of increasing the reverse bias leak current of the junction by ion-implanting conductive particles into the pn junction between the regions 93 and 94. In FIG. 8, the low-phosphorus-doped polysilicon film 90 may be formed only on the opening K of the p-well region 93, and the surface main electrode 99 may extend thereover.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a vehicular power generating device according to a first embodiment.
FIG. 2 is a flowchart showing an operation of a controller 7 of FIG.
FIG. 3 is a circuit diagram of a vehicle power generator according to a second embodiment.
FIG. 4 is a circuit diagram of a vehicle power generator according to a third embodiment.
FIG. 5 is a flowchart showing the operation of the controller 7 of FIG.
6 is a flowchart showing an operation of the controller 7 of FIG.
FIG. 7 is a flowchart showing the operation of another embodiment of the controller 7 of FIG. 4;
FIG. 8 is a cross-sectional view illustrating an example of a MOSFET 3.
[Explanation of symbols]
1 is a vehicle alternator (generator), 3 is a semiconductor switch unit (MOSFET), 5 is a battery, 6 is a second battery, 7 is a controller, and 8 is a second MOSFET. 91 is a substrate (one of a source region and a drain region), 93 is a well region, and 94 is n⁺A region (the other of the source region and the drain region), 98 is a gate electrode, 90 and r are high resistance portions, D is one of a source region and a drain region, S is the other of the source region and the drain region, and G is a gate electrode.

Claims (8)

A vehicle alternator for supplying an output current rectified by the built-in rectifier to the battery from an output terminal, a semiconductor switch disposed between the output terminal and the battery, and controlling the semiconductor switch; Control means, wherein the semiconductor switch unit includes a first conductivity type well region having a gate electrode formed on the surface thereof via a gate insulating film, and an inversion channel layer formed on the surface of the well region by the gate electrode. A power generation device for a vehicle including a MOSFET (insulated gate field effect transistor) including a source region and a drain region of a second conductivity type that are conducted to each other,
Have a high resistance portion that connects the source region and either said well region of the drain region,
One of the source region and the drain region is connected to a higher end of a second battery . The second battery has a lower rated voltage than the battery, is connected to the output terminal of the generator through a second MOSFET, and further has one end of the high resistance portion connected to the battery side of the MOSFET. 2. The vehicle power generator according to claim 1 . The control means intermittently charges the second MOSFET at a predetermined duty ratio from the generator to the second battery when the generator performs power generation capable of charging the battery, and at least the second MOSFET 3. The power generator for a vehicle according to claim 2 , wherein the MOSFET is shut off during a conduction period of the power supply. The power generator for a vehicle according to any one of claims 1 to 3 , wherein the MOSFET is made of single crystal SiC. The vehicle power generator according to claim 4, wherein the MOSFET is mounted on the generator. The vehicle power generator according to claim 4, wherein the MOSFET is mounted on the same circuit board as the control means. An automotive alternator for supplying an output current rectified by the built-in rectifier to the battery from an output terminal, a semiconductor switch disposed between the output terminal and the battery, and controlling the semiconductor switch. Control means, wherein the semiconductor switch unit comprises a first conductivity type well region having a gate electrode formed on the surface thereof via a gate insulating film, and an inversion channel layer formed on the surface of the well region by the gate electrode. A power generating device for a vehicle including a MOSFET (insulated gate field effect transistor) having a source region and a drain region of a second conductivity type that are conducted to each other,
  A high-resistance portion connecting one of the source region and the drain region to the well region;
  The power generation device for a vehicle, wherein the MOSFET is made of single crystal SiC and is mounted on the power generator. An automotive alternator for supplying an output current rectified by the built-in rectifier to the battery from an output terminal, a semiconductor switch disposed between the output terminal and the battery, and controlling the semiconductor switch. Control means, wherein the semiconductor switch unit comprises a first conductivity type well region having a gate electrode formed on the surface thereof via a gate insulating film, and an inversion channel layer formed on the surface of the well region by the gate electrode. A power generating device for a vehicle including a MOSFET (insulated gate field effect transistor) having a source region and a drain region of a second conductivity type that are conducted to each other,
  A high-resistance portion connecting one of the source region and the drain region to the well region;
  The power generation device for a vehicle, wherein the MOSFET is made of single crystal SiC and is mounted on the same circuit board as the control unit.

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