Diodes Incorporated

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SoftStart with Smart Jitter for EMI Management

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The AP31251 is a current mode PWM controller which is optimized for high performance, low standby power and cost effective offline flyback converters.

The PWM switching frequency at normal operation is internally fixed (about 65kHz). In middle load, the IC will enter green mode to improve system efficiency with the help of frequency foldback. A minimum switching frequency (about 20kHz) is set to avoid the audible noise. In no load or light load, the IC will enter the burst mode to minimize standby power. Furthermore, the frequency dithering function is built-in to reduce EMI emission.

Internal slope compensation allows more stable Peak-Current Mode control over wide range of input voltage and load conditions. Internal line compensation ensures constant output power limit over entire universal line voltage range.

Comprehensive protection features are included, such as cycle-bycycle current limit (OCP), VCC Over Voltage Protection (VOVP),
internal OTP, Over Load Protection (OLP) and pins’ fault protection. The versatile latch functions can be implemented using a minimal number of external components.


  • Very Low Start-Up Current
  • Current Mode Control
  • Non-Audible-Noise Green-Mode Control
  • Internal Slope Compensation
  • Soft Start during Startup Process
  • Frequency Fold Back for High Average Efficiency
  • Secondary Winding Short Protection with FOCP
  • Soft Switching (Soft Driver and Smart Jitter) for Reducing EMI
  • VCC Maintain Mode
  • Useful Pin Fault Protection:
    SENSE Pin Floating
    CTRL Pin Short to Ground
    FB/Opto-Coupler Open/Short
  • Comprehensive System Protection Feature:
    VCC Over Voltage Protection (VOVP)
    Over Load Protection (OLP)
  • Optional Latch Mode for VOVP, OLP and CTRL Pin Protection
  • Mini Size Package of SOT26
  • Pin to Pin Compatible with AP3105NA
  • Moisture Sensitivity: MSL Level 3 per J-STD-020
  • Terminals: Finish – Matte Sn Plated Leads, Solderable per M2003 JESD22-B102, Method 208
  • Weight: 0.016 grams (Approximate)
  • Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
  • Halogen and Antimony Free. “Green” Device (Note 3)
  • For automotive applications requiring specific change control (i.e. parts qualified to AEC-Q100/101/200, PPAP
    capable, and manufactured in IATF 16949 certified facilities), please contact us or your local Diodes representative. https://www.diodes.com/quality/product-definitions/


  • Switching AC-DC Adapter/Charger
  • ATX/BTX Auxiliary Power
  • Set-Top Box (STB) Power Supply
  • Open Frame Switching Power Supply

Product Specifications

Product Parameters

Operation Mode CCM/DCM
HV Start-UpCircuit N/A
Vcc_MAX(V) 30
UVLOThresholdon/off (V) 15.8/7.6 V
Gate OutputCurrent (mA) -1 mA
Maximum OscillationFrequency (kHz) 65 (CCM mode) kHz
Release Date 201810

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