A boost converter includes a comparator having first and second gain stages that operate in compare and auto-zero modes. The comparator measures voltage drop across a P-channel transistor to determine when current through an inductor reaches zero. When the inductor current reaches zero, the P-channel transistor becomes inactive to prevent a reduction in efficiency caused by allowing negative inductor current to draw current from a load. The comparator is then placed in a low power state. When the comparator is not in a compare mode, the comparator can operate in an auto-zero mode to cancel offset when measuring the input of the comparator.