The NCP1237 is a new generation of the NCP12xx fixed-frequency current-mode controllers featuring Dynamic Self-Supply (DSS) pin to pin compatible with the previous generation. The DSS function greatly simplifies the design of the auxiliary supply and the VCC capacitor by activating the internal start-up current source to supply the controller during transients. Due to its proprietary Soft-Skip mode combined with frequency foldback the controller exhibits excellent efficiency in light load condition while still achieving very low standby power consumption. This Soft-Skip feature also dramatically reduces the risk of acoustic noise which enables the use of inexpensive transformers and capacitors in the clamping network. The NCP1237