Patent ID: 7294983

Claim:
A motor drive circuit comprising an output unit that has a first drive transistor for controlling continuity between a first power supply and a drive output terminal and a second drive transistor for controlling continuity between a second power supply and said drive output terminal and performs power supply from said drive output terminal to a motor according to conditions of said first drive transistor and said second drive transistor, a first control unit that turns on and off said first drive transistor corresponding to a first switching signal and delivers voltage corresponding to said first power supply from said drive output terminal when said first drive transistor is in a conduction state and a second control unit that controls the action of said second drive transistor corresponding to a second switching signal and a mode signal, wherein said second control unit comprises an on-off control section that selectively delivers on-voltage for making said second drive transistor be in a conduction state and off-voltage for making it to be in a cut-off state according to said second switching signal, a constant voltage control section that generates a conduction control signal to be input to a control terminal of said second drive transistor based on the voltage of said drive output terminal set at a required target voltage and a switching section that selects either said on-voltage delivered by said on-off control unit or the output from said constant voltage control section to deliver said output to said second drive transistor as said conduction control signal corresponding to said mode signal when making said second drive transistor be in said conduction state and said switching section selects said on-voltage of said on-off control section as said conduction control signal to deliver voltage corresponding to said second power supply from said drive output terminal when said mode signal corresponds to a saturation output mode and selects the output of said constant voltage control section as said conduction control signal to set said voltage of said drive output terminal at said target voltage when said mode signal corresponds to a constant voltage output mode.