Abstract: A step up converter with overcurrent protection is disclosed. The step up converter can precisely limit the output current of the upstream device. Current from the input terminal of the converter is detected and compared with a predetermined maximum current to get a comparison value which is delivered to a close-loop regulator. The overcurrent protection is achieved by the regulator outputting a control signal to fulfill the conduction or resistance increase of a resistive element of the protection circuit. Furthermore, detection of the temperature or the output voltage may trigger shut off of the protection circuit to implement a protection function.