Patent ID: 7307355

Claim:
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.