Control device of vehicle mounted alternator

Claim 1

A control device for a vehicle-mounted, self-excited alternator having an armature coil (101) and a field coil (102), and including a rectifier (2) for rectifying an a.c. output of said alternator, and for supplying a field current to said field coil and a charging current to a vehicle-mounted storage battery (5), a high voltage electric load (6) of said vehicle being energizable by a first voltage which is substantially higher than a second voltage, said second voltage being a terminal voltage of said storage battery, and a changeover switch (8) for selectively connecting an output of said rectifier to one of said storage battery and said high voltage electric load, said control device comprising: field current detection means (312) for detecting field current flowing through said field coil; and a field current limiter (4) for cutting off said field current when the field current exceeds a predetermined value, wherein said field current limiter comprises reference means (401, 402) for providing a fixed reference value, a comparator (403) for comparing the field current detected by said field current detection means with said fixed reference value, and control means responsive to an output of said comparator to control a voltage regulator to cut-off the field current when the field current detected is larger than said reference value, said field current limiter further comprising a resistor (407) through which said field current flowing through said field coil is input to said comparator (403); and wherein said voltage regulator receives an input from said storage battery, said input being indicative of said terminal voltage of said storage batter, said changeover switch exclusively connecting the rectifier output to the battery for the charging thereof in a first position, and exclusively connecting the rectifier output to the high voltage electric load in a second position.