| FP133 is a main rail current detection and over current protection IC. It is including a current shunt comparator and shutdown comparator with a precision shunt regulator like FP431.
The current shunt comparator has the any gain adjustable function for rail current detection using three external resistors, and inter-connecting to a shutdown comparator for driving a protection circuit like a photo-coupler to shutdown the primary side PWM IC when over current is occurred.
And the voltage shunt regulator has a 2.5V reference for switching power supply secondary output voltage feedback.
FP133 is used with a few external parts for O.C.P. and output voltage feedback function and good active point during wide temperature range in secondary main rail power supply of SPS or isolated fly-back DC-DC converter application field.