Controller, Fixed Frequency, Current Mode, for Flyback Converters

NCP1234 is a new fixed-frequency current-mode controller featuring Dynamic Self-Supply (DSS). This device is pin-to-pin compatible with the previous NCP12xx families. The DSS function greatly simplifies the design of the auxiliary supply and the VCC capacitor by activating the internal startup current source to supply the controller during transients. Due to frequency foldback, the controller exhibits excellent efficiency in light load condition while still achieving very low standby power consumption. Internal frequency jittering, ramp compensation, and a versatile latch input make this controller an excellent candidate for converters where component cost is the key constraint. It features a timer-based fault detection that ensures the detection of overload independently of an auxiliary winding, and an adjustable compensation to help keep the maximum power independent of the input voltage.