Diodes Incorporated
SO 8

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Primary Side Regulated power switcher

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The AP3981C is a high performance power switchers integrated with a primary side regulation controller and an N-channel power MOSFET. It can be used for battery charger and adaptor applications, accurate Constant Voltage (CV) and Constant Current (CC) can be achieved without an opto-coupler and secondary control circuitry.

The AP3981C operates in Pulse Frequency Modulation (PFM) mode and peak current Amplitude Modulation (AM) mode to form a fine tune frequency curve within the whole power range. Therefore, the AP3981C can achieve high average efficiency and improve audible noise.

The AP3981C provides comprehensive protections without additional circuitry. It contains VCC over voltage protection, output over voltage protection, output under voltage protection, output short circuit protection, cycle-by-cycle current limit, open loop protection, and internal over temperature protection, etc.

The AP3981C is available in SO-8 package.


  • Primary Side Control for Eliminating Opto-Coupler
  • Built-In 650V Power MOSFET
  • 75mW No-Load Input Power
  • Flyback Topology in DCM Operation
  • External Adjustable Line Compensation for CC
  • Fixed Internal Cable Compensation
  • Multiple Segment AM/PFM Control Mode to Improve Audio Noise and Efficiency
  • Frequency Jitter to Improve System EMI
  • Capacitive Load Start-Up Capability
  • Valley-On for the Higher Efficiency and Better EMI Behavior
  • Multiple Protections:
    • Secondary-Side Over Voltage Protection (SOVP)
    • Secondary-Side Under Voltage Protection (SUVP)
    • Output Short Circuit Protection (SCP)
    • Transformer Saturation Protection (TSP) via Primary Peak Current Limitation
    • Internal Over Temperature Protection (OTP)
  • SO-8 Package
  • Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
  • Halogen and Antimony Free. “Green” Device (Note 3)


  • Routers
  • Set-Top Box (STB) Power Supply
  • Network Adaptors

Product Specifications

Product Parameters

Switch MOS
BVDSS (Min) (V) 650
OperatingCurrent (µA) 650
StandbyPower (Max) (mW) 75
CableCompensation 4%
Power Rating (W) 12 W
Release Date 201905

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