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A power supply apparatus comprised of a bridge circuit made up of rectification diodes and MOSFETs for rectifying an output of a generator through a full-wave rectifier circuit comprised of rectification diodes and parasitic diodes of the MOSFETs and obtaining a supply voltage of a fuel injection ap

A power supply apparatus comprised of a bridge circuit made up of rectification diodes and MOSFETs for rectifying an output of a generator through a full-wave rectifier circuit comprised of rectification diodes and parasitic diodes of the MOSFETs and obtaining a supply voltage of a fuel injection apparatus, the power supply apparatus being comprised of an FET control section which turns ON/OFF the MOSFETs to step up the output voltage of the generator and a transistor provided for each MOSFET, which is set in an ON-state for a period during which a reverse voltage is applied to a parasitic diode of each MOSFET and set in an OFF-state for a period during which a forward voltage is applied to the parasitic diode of each MOSFET, wherein a control voltage for turning ON the MOSFET is given between the gate and source of the corresponding MOSFET for a period during which each transistor is in an OFF-state.

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What is claimed is: 1. A power supply apparatus which gives a supply voltage to a fuel injection apparatus of an internal combustion engine, comprising: n (n: integer of 2 or greater) input terminals to which a single-phase or multi-phase AC voltage is input from a magneto AC generator driven by sa

What is claimed is: 1. A power supply apparatus which gives a supply voltage to a fuel injection apparatus of an internal combustion engine, comprising: n (n: integer of 2 or greater) input terminals to which a single-phase or multi-phase AC voltage is input from a magneto AC generator driven by said internal combustion engine; m (m: integer of 2 or greater and not greater than n) MOSFETs with ones of drains and sources commonly connected and the others connected to m input terminals of said n input terminals; parasitic diodes formed between the drains and sources of said m MOSFETs and 2n-m rectification diodes provided so as to constitute together a diode bridge full-wave rectifier circuit which rectifies an AC voltage given to the n input terminals; and an FET control section which performs control, when the rotational speed of said internal combustion engine is equal to or lower than a set value, so that MOSFETs, to the drain-source parasitic diodes of which a reverse voltage is applied out of said m MOSFETs are turned ON/OFF at a frequency higher than the output frequency of said generator, wherein said FET control section comprises: a low-speed drive signal supply circuit which gives, when the rotational speed of said internal combustion engine is equal to or lower than a set value, each MOSFET a drive signal varying between an ON level which turns ON each MOSFET and an OFF level which turns OFF each MOSFET at a frequency higher than the output frequency of said generator; and a control voltage supply circuit provided with a control voltage supply control switch which is ON/OFF-controlled by the drain-source voltage of each MOSFET so as to be set in an OFF-state when a forward voltage is applied to the parasitic diode of each MOSFET and set in an ON-state when a reverse voltage is applied to the parasitic diode of each MOSFET, which gives a control voltage equal to or higher than said ON-level between the gate and source of each MOSFET for a period during which said control voltage supply control switch is in an OFF-state, and a DC voltage output from said diode bridge full-wave rectifier circuit is given to the fuel injection apparatus of said internal combustion engine as a supply voltage. 2. A power supply apparatus which gives a supply voltage to a fuel injection apparatus of an internal combustion engine, comprising: n (n: integer of 2 or greater) input terminals to which a single-phase or multi-phase AC voltage is input from a magneto AC generator driven by an internal combustion engine; m (m: integer of 2 or greater and not greater than n) N-channel type MOSFETs with sources commonly connected and drains connected to m input terminals of said n input terminals; parasitic diodes formed between the drains and sources of the m MOSFETs and 2n-m rectification diodes provided so as to constitute together a diode bridge full-wave rectifier circuit which rectifies an AC voltage given to the n input terminals; and an FET control section which performs control, when the rotational speed of said internal combustion engine is equal to or lower than a set value, so that MOSFETs, to the drain-source parasitic diodes of which a reverse voltage is applied out of said m MOSFETs are turned ON/OFF at a frequency higher than the output frequency of said generator, wherein said FET control section comprises: a low-speed drive signal supply circuit which gives, when the rotational speed of said internal combustion engine is equal to or lower than a set value, a drive signal varying between an ON level which turns ON each MOSFET and an OFF level which turns OFF each MOSFET at a frequency higher than the output frequency of said generator between the gate and source of each MOSFET; and a control voltage supply circuit which gives a control voltage equal to or higher than said ON-level between the gate and source of each MOSFET for a period during which a forward voltage is applied to both ends of the parasitic diode of each MOSFET, said control voltage supply circuit comprises: an NPN transistor provided for each MOSFET, a collector and a base thereof being connected to an output terminal on a positive electrode side of said rectifier circuit through a first resistor and a second resistor, an emitter thereof being connected to a part having the same potential as that of a source of the corresponding MOSFET; a single transistor control diode or a plurality of transistor control diodes connected in series between a base of each transistor and a drain of the corresponding MOSFET with anode(s) of said diode(s) facing the base of each transistor; and a backflow prevention diode connected between a collector of each transistor and a gate of the corresponding MOSFET with an anode of said diode facing the collector of the transistor, the number of said transistor control diodes is set so that a voltage between the base of the corresponding transistor and the source of each MOSFET is higher than a base-emitter voltage of the corresponding transistor when a reverse voltage is applied to the parasitic diode of each MOSFET and a voltage between the base of the corresponding transistor and the source of each MOSFET is lower than the base-emitter voltage of the corresponding transistor when a forward voltage is applied to the parasitic diode of each MOSFET, and a DC voltage output from said diode bridge full-wave rectifier circuit is given to the fuel injection apparatus of said internal combustion engine as a supply voltage. 3. The power supply apparatus for a fuel injection apparatus according to claim 1, further comprising a voltage adjusting signal supply circuit which gives, when the output voltage of said rectifier circuit exceeds a set value, a voltage adjusting signal equal to or higher than an ON-level between the gates and sources of said m MOSFETs. 4. The power supply apparatus for a fuel injection apparatus according to claim 2, further comprising a voltage adjusting signal supply circuit which gives, when the output voltage of said rectifier circuit exceeds a set value, a voltage adjusting signal equal to or higher than an ON-level between the gates and sources of said m MOSFETs.