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The AP3981D2 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 optocoupler and secondary control circuitry.

The AP3981D2 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, AP3981D2 can achieve high-average efficiency and improve audible noise.

The AP3981D2 provides comprehensive protections without additional circuitry. It contains VCC overvoltage protection, output overvoltage protection, output undervoltage protection, output short-circuit protection, cycle-by-cycle current limit, open-loop protection, and internal OTP, etc.

The AP3981D2 is available in SO-8.


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


• Primary Side Control for Eliminating Optocoupler
• Built-In 650V Power MOSFET of AP3981D2
• 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 Overvoltage Protection (SOVP)
• Secondary-Side Undervoltage Protection (SUVP)
• Output Short-Circuit Protection (SCP)
• Transformer Saturation Protection (TSP) via Primary Peak
Current Limitation
• Internal Overtemperature Protection (OTP)
• SO-8 Package
• Totally Lead-Free & Fully RoHS Compliant (Notes 1 & 2)
• Halogen and Antimony Free. “Green” Device (Note 3)

Product Specifications

Product Parameters

Collector DC Current 4 A
Startup Current 3 µA
Operating Current 650 µA
UVLO Threshold on/off 16/6.8 V
Power Rating 18 W
Standby Power 75 mW
Cable Compensation 0.04

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Orderable Part Number Authorized Distributor Quantity Inventory Date Buy Online Region
AP3981D2S-13 Digi-Key Electronics 3867 1/19/2020 Buy Now United States
AP3981D2S-13 Mouser Electronics Inc. 3850 1/19/2020 Buy Now United States