Diodes Incorporated AP3981D2EV1

Overview

AP3981D2 from Diodes Incorporated is a primary-side regulated (PSR) flyback power switcher integrating a 650V N-channel MOSFET and controller in SO-8 package. It delivers accurate constant voltage (2.4V FB threshold) and constant current (700mV VCS_H typ.) regulation without optocoupler or secondary-side circuitry, enabling compact, low-noise AC/DC adapters for consumer electronics. Key specs include 75mW no-load input power, valley-on switching, and multi-segment AM/PFM control.

For engineers reviewing the AP3981D2 datasheet, AP3981D2 pinout, AP3981D2 application, or AP3981D2 equivalent, this device is selected for cost-sensitive, low-audio-noise, isolated offline power supplies requiring high average efficiency across universal input (90–264VAC), tight CV/CC tolerance, and comprehensive fault protection - especially where transformer auxiliary winding sensing is feasible.

Technical Context

The AP3981D2 implements primary-side regulation via auxiliary winding sampling during tONS, using programmable sample ratio (50–80% of tONS) and dual-threshold VCS detection (180mV/700mV) to distinguish load conditions and enable seamless CV-to-CC transition. Its three-segment peak current control adjusts VCS_REF across 2–100% load to maintain switching frequency above 20kHz and suppress audible noise.

Valley-on turn-on is triggered when tOFF < 32µs (typ.), reducing switching losses and EMI; combined with ±2% VCS jitter over 12-cycle dithering, it improves conducted and radiated EMI performance. Line compensation uses internal 55Ω RLINE and external RFB1 to offset propagation delay-induced CC error across input voltage range.

Key Specifications

Pinout & Package

AP3981D2 is housed in a standard SO-8 package with exposed thermal pad (pin 4 connected to SOURCE, pins 5–8 tied internally to DRAIN). The layout supports high-voltage isolation between primary (DRAIN/SOURCE) and control (FB/VCC/GND) domains.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar primary-side regulated flyback controller applications.

Compared with MP6004DJ-LF-Z and LNK364PG, the AP3981D2 delivers superior light-load efficiency, lower audible noise through valley-on and frequency jitter, and tighter CC regulation via adjustable line compensation - making it optimal for cost-sensitive, low-noise, adapter-class PSR designs up to 15W.

Availability

AP3981D2 is available at Aetrix Electronics and suitable for router power supplies, set-top box adapters, network adaptors, and smart home hub power systems requiring stable component supply, RoHS-compliant packaging, and long-term lifecycle support.

Supply support for AP3981D2 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Diodes Incorporated is a global semiconductor company specializing in discrete, analog, and mixed-signal solutions for power management, signal integrity, and connectivity applications.

The AP3981D2 belongs to Diodes' PSR AC/DC controller product line, designed specifically for cost-optimized, low-noise, optocoupler-free offline power supplies targeting consumer and networking markets.

FAQ

What is the minimum recommended auxiliary winding turns ratio for reliable CV regulation?

The AP3981D2 requires sufficient auxiliary winding voltage to maintain VCC > 6.8V across full load and line range. For 12V output, a typical N_AUX/N_SEC ratio of 0.25–0.35 ensures stable VCC generation and accurate FB sampling during tONS, validated in Diodes' reference design DER-642.

How does the AP3981D2 achieve constant current without secondary current sensing?

It measures tONS/tSW ratio during the secondary conduction period - which correlates directly with output current - and regulates VCS threshold dynamically. At 40–100% load, tONS/tSW = 0.5 fixes output current; at light load, VCS_L (180mV) sets lower peak current to maintain regulation.

Can the AP3981D2 drive a transformer with >500mH magnetizing inductance?

Yes - its maximum off-time of 2ms supports low-frequency operation down to ~500Hz, accommodating high-inductance transformers used in low-power, high-isolation designs. However, valley-on may not trigger below 20kHz, so efficiency gains diminish at very light loads.

What is the role of the RLC resistor in the line compensation circuit?

RLC (55Ω internal) forms a voltage divider with external RFB1 to inject line-proportional voltage into the VCS reference. This offsets the fixed propagation delay (~150ns) that causes CC drift at high line voltage, ensuring ±3% current accuracy from 90VAC to 264VAC.