A voltage comparator, comprising a first branch, a second branch and a third branch; wherein: the first branch comprises a first transistor, a second transistor and a third transistor; wherein a source of the first transistor is connected to a power supply, a gate of the first transistor is connected to a drain of the first transistor, and the drain of the first transistor is connected to a drain of the second transistor; a gate of the second transistor is connected to a first input terminal, and a source of the second transistor is connected to a drain of the third transistor; a source of the third transistor is grounded, and the drain of the third transistor is connected to a gate of the third transistor; the second branch comprises a fourth transistor, a fifth transistor and a sixth transistor; wherein a source of the fourth transistor is connected to the power supply, a gate of the fourth transistor is connected to a drain of the fourth transistor, and the drain of the fourth transistor is connected to a drain of the fifth transistor;a gate of the fifth transistor is connected to a second input terminal, and a source of the fifth transistor is connected to a drain of the sixth transistor; a source of the sixth transistor is grounded, and the drain of the sixth transistor is connected to a gate of the sixth transistor; and the third branch comprises a seventh transistor and an eighth transistor; wherein a source of the seventh transistor is connected to the power supply, a gate of the seventh transistor is connected to the drain of the first transistor, a drain of the seventh transistor is connected to an output terminal of the voltage comparator and a drain of the eighth transistor; the seventh transistor and the first transistor form a current mirror; a gate of the eighth transistor is connected to the drain of the sixth transistor, the drain of the eighth transistor is connected to the output terminal of the voltage comparator, a source of the eighth transistor is grounded; the eighth transistor and the sixth transistor form a current mirror, and the voltage comparator further comprising a first resistor, wherein one terminal of the first resistor is connected to the second input terminal, and the other terminal of the first resistor is grounded. the first branch comprises a first transistor, a second transistor and a third transistor; wherein a source of the first transistor is connected to a power supply, a gate of the first transistor is connected to a drain of the first transistor, and the drain of the first transistor is connected to a drain of the second transistor; a gate of the second transistor is connected to a first input terminal, and a source of the second transistor is connected to a drain of the third transistor; a source of the third transistor is grounded, and the drain of the third transistor is connected to a gate of the third transistor; the second branch comprises a fourth transistor, a fifth transistor and a sixth transistor; wherein a source of the fourth transistor is connected to the power supply, a gate of the fourth transistor is connected to a drain of the fourth transistor, and the drain of the fourth transistor is connected to a drain of the fifth transistor;a gate of the fifth transistor is connected to a second input terminal, and a source of the fifth transistor is connected to a drain of the sixth transistor; a source of the sixth transistor is grounded, and the drain of the sixth transistor is connected to a gate of the sixth transistor; and the third branch comprises a seventh transistor and an eighth transistor; wherein a source of the seventh transistor is connected to the power supply, a gate of the seventh transistor is connected to the drain of the first transistor, a drain of the seventh transistor is connected to an output terminal of the voltage comparator and a drain of the eighth transistor; the seventh transistor and the first transistor form a current mirror; a gate of the eighth transistor is connected to the drain of the sixth transistor, the drain of the eighth transistor is connected to the output terminal of the voltage comparator, a source of the eighth transistor is grounded; the eighth transistor and the sixth transistor form a current mirror, and the voltage comparator further comprising a first resistor, wherein one terminal of the first resistor is connected to the second input terminal, and the other terminal of the first resistor is grounded.