A series regulator with an over current protection circuit regulates output current by controlling an output transistor. A current sense transistor output depends on the conductivity of the output transistor. A current limiting transistor controls the conductivity of the output transistor. A current supply provides current to a constant current source and a converter output of a current to voltage converter. The converter output is connected to a control electrode of the current limiting transistor. A first differential transistor couples the current sense transistor to the constant current source and a second differential transistor couples the current supply to the constant current source. The current sense transistor controls the second differential transistor to vary a control current. When the control current matches a threshold value, the current limiting transistor limits maximum current flow through the output transistor.