Default-phase signal detection circuit for three-phase power

The invention discloses a default-phase signal detection circuit for three-phase power, which comprises an optical-coupling device, a single-phase full-bridge rectifier, a resistor, a capacitor and an impedor, wherein three-phase power needing detection is connected with three optical-coupling detection circuits through three voltage-reducing impedors respectively; the absence of three phase currents is detected through the optical-coupling detection circuits; three detection output signals are combined into a total switch output signal; and the signal is taken as a basis for judging whether the three-phase power has default phase. The default-phase signal detection circuit for three-phase power can effectively detect whether the three-phase power has default phase, and outputs control signals to cut off power in case of default phase so as to protect power. The circuit has the advantages of simplicity, reliability, manufacturing easiness and wide applicable power voltage range.