An online monitoring unit and a control circuit for ultra-wide voltage range applications are disclosed. Compared with a conventional online monitoring unit, present invention eliminates a need to reserve delay units, replaces flip-flops in the conventional online monitoring unit with a latch, and uses a transition detector with fewer transistors than that of a shadow latch in the conventional online monitoring unit, thereby reducing an area and a power consumption of the online monitoring unit significantly and improving an energy efficiency of online monitoring techniques. In addition, in the ultra-wide voltage range applications, a time borrowing property of the latch adopted by the present invention can be utilized to prevent a timing error caused by process-voltage-temperature (PVT) variations, thus enabling a minimization of a timing margin and ensuring a higher power efficiency. The present invention also discloses a control circuit for use with the online monitoring unit.