NCP1238: Controller, Fixed Frequency, Current Mode, for Flyback Converters

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 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. 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).

Features
  • 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 DSS with 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)
  • VCC 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
Benefits
  • Overload protection independent of the auxiliary voltage
  • Reduced EMI Signature
  • Improved Performance in Standby
Applications
  • Ac-dc Adapters for Notebooks, LCD, and Printers
  • Offline Battery Chargers
  • Consumer Electronic Power Supplies
  • Auxiliary/Housekeeping Power Supplies
Design & Development Tools (1)
Document TitleDocument ID/SizeRevisionRevision Date
Flyback Current Mode Loop Compensation Design WorksheetFLYBACK DWS.XLS.ZIP (3516kB)10Dec, 2014
Data Sheets (1)
Document TitleDocument ID/SizeRevisionRevision Date
Fixed Frequency Current Mode Controller for Flyback ConvertersNCP1238/D (271.0kB)3
Application Notes (2)
Document TitleDocument ID/SizeRevisionRevision Date
32 W, 32 V Universal Input AC-DC Printer Adapter using the NCP1237AND8454/D (331.0kB)1Feb, 2010
Stability Analysis in Multiple Loop SystemsAND8327/D (213.0kB)0
Package Drawings (1)
Document TitleDocument ID/SizeRevision
SOIC 7 CASE OUTLINE751U (62.0kB)E
Order Information
ProductStatusCompliancePackageMSL*ContainerBudgetary Price/Unit
NCP1238AD65R2GActivePb-free Halide freeSOIC-7751U1Tape and Reel2500$0.6667
NCP1238BD65R2GActivePb-free Halide freeSOIC-7751U1Tape and Reel2500$0.6667
Specifications
ProductTopologyControl Modefsw Typ (kHz)Stand-by ModeUVLO (V)Short Circuit ProtectionLatchSoft StartVCC Max (V)Drive Cap. (mA)
NCP1238AD65R2GFlybackCurrent Mode65Yes9.5YesYesYes281000 / 1000
NCP1238BD65R2GFlybackCurrent Mode65Yes9.5YesYesYes281000 / 1000
Fixed Frequency Current Mode Controller for Flyback Converters (271.0kB) NCP1238
Flyback Current Mode Loop Compensation Design Worksheet NCP1129
32 W, 32 V Universal Input AC-DC Printer Adapter using the NCP1237 NCP1288
Stability Analysis in Multiple Loop Systems NCP1055
SOIC 7 CASE OUTLINE NCL30060
NCP1238