The NCP1238 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 V
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. Internal frequency jittering, ramp compensation, and a versatile latch input make this controller an excellent candidate for converters where ruggedness and components cost are the key constraints. In addition, the controller includes a new high voltage circuitry that combines a startup current source and a brown-out / line OVP detector able to sense the input voltage either from the rectified ac line or the dc filtered bulk voltage. Finally, due to a careful design, the precision of critical parameters is well controlled over the entire temperature range (-40°C to +125°C), enabling easier design and increased safety (e.g. ±5% for the peak current limit, ±7% for the oscillator).

• Timer-Based Overload Protection with AutoRecovery (Option B) or Latched (Option A) Operation
• Frequency Jittering
• Frequency Foldback transitioning into Soft-Skip
• High-Voltage Current Source with DSSwith Built-in Brown-out and Line Overvoltage Protections
• Fixed-Frequency Current-Mode Operation with Built-in Ramp Compensation
• Adjustable Overpower Compensation
• Latch-off Input for Severe Fault Conditions, with Direct Connection of an NTC for Overtemperature Protection (OTP)
• Protection Against Winding Short-Circuit
• 65 kHz Oscillator (100 kHz and 133 kHz Versions Available Upon Request)
• V
• Operation up to 28 V
• Increased Precision on Critical Parameters
• 1.0 A Peak Current Drive Capability
• 4.0 ms Soft-Start
• Internal Thermal Shutdown with Hysteresis
• These Devices are Pb-Free, Halogen free/BFR free and are ROHS compliant