The 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.

FEATUREs
Fixed−Frequency Current−Mode Operation with Built−In Ramp Compensation
65 kHz or 100 kHz Oscillator Frequency version
Frequency Foldback then Skip Mode for Maximized Performance in Light Load and Standby Conditions
Timer−Based Overload Protection with Latched (option A) or Auto−Recovery (option B) Operation
High−voltage Current Source with Dynamic Self−Supply, Simplifying the Design of the VCC Capacitor
Frequency Modulation for Softened EMI Signature, including during Frequency Foldback mode
Adjustable Overpower Compensation
Latch−off Input for Severe Fault Conditions, Allowing Direct Connection of an NTC for Overtemperature Protection (OTP)
VCC Operation up to 28 V, with Overvoltage Detection
±500 mA Peak Source/Sink Current Drive Capability
4.0 ms Soft−Start
Internal Thermal Shutdown
Pin−to−Pin Compatible with the Existing NCP12xx Series
These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS Compliant