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Primary Side Regulated power switcher

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The AP3981B is a high performance power switcher 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 AP3981B 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 AP3981B can achieve high average efficiency and improve audible noise.

The AP3981B 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 OTP, etc.

The AP3981B is available in SO-7 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-7 Package
  • The Recommended Output Power is up to 7.5W
  • 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

BVDSS (Min) (V) 650 V
Collector DC Current (A) 1 A
StartupCurrent (µA) 3 µA
OperatingCurrent (µA) 650 µA
UVLOThresholdon/off (V) 16/6.8 V
Power Rating (W) 7.5 W
StandbyPower (Max) (mW) 75 mW
CableCompensation 4%

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Orderable Part Number Buy from Distributor / Contact Sales Request Samples


Authorized Distributor Quantity Inventory Date Countries/Regions Buy Online
RS Components - Spain 3925 10/4/2022 Spain Contact Sales
RS Components - UK 3925 10/4/2022 England Buy Now
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Authorized Distributor Quantity Inventory Date Countries/Regions Buy Online
Digi-Key Electronics 17198 10/4/2022 Europe, Asia, North America Buy Now
Mouser Electronics Inc. 55932 10/4/2022 South America, North America, Asia, Europe, Middle East Buy Now
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