OVER-CURRENT DETECTION CIRCUIT OF SINGLE PHASE LOAD SUBJECTED TO PWM VOLTAGE CONTROL BY MOS TRANSISTOR

摘要

PPROBLEM TO BE SOLVED: To provide an over-current detection circuit capable of accurately detecting an over-current state of a load current even when an on-time of a MOS transistor is short in the case that the MOS transistor is used to apply PWM voltage control to a single phase load such as a single phase DC motor. PSOLUTION: The over-current detection circuit uses a subtractor circuit to detect a source-drain voltage of the PMOS transistor. When the PMOS transistor is conductive, the detected source-drain voltage is A/D-converted and the result is directly compared with an over-current discrimination reference voltage to detect an over-current. Simultaneously, the source-drain voltage is sampled and held when the PMOS transistor is conductive, and a sampled-held value is given to the subtractor circuit in place of a drain voltage to prevent an output of the subtractor circuit from highly swinging when the PMOS transistor is nonconductive. PCOPYRIGHT: (C)2004,JPO&NCIPI