Diodes Incorporated AP3981D2S-13

Overview

AP3981D2-13 from Diodes Incorporated is a primary-side regulated (PSR) flyback power switch integrating a 650V N-channel MOSFET and PWM controller in SO-8 package. It delivers accurate constant voltage (2.4V FB threshold) and constant current (0.75/0.5 t_ONS/t_SW ratio) regulation without optocoupler or secondary-side circuitry, enabling compact, low-noise AC/DC adapters for consumer electronics.

For engineers reviewing the AP3981D2-13 datasheet, AP3981D2-13 pinout, AP3981D2-13 application, or AP3981D2-13 equivalent, key selection considerations include its valley-on switching (26–38 µs valid off time), multi-segment AM/PFM control for audible noise suppression, 75mW no-load input power, integrated line compensation (45–65 Ω R_LINE), and comprehensive protection suite including SOVP (3.3–3.9V), SUVP (1.22–1.48V), SCP (680–820mV), and OTP (130–160°C).

Technical Context

The AP3981D2-13 implements primary-side regulation via auxiliary winding sampling during t_ONS, using programmable sample ratio (45–55% at light load, 75–85% at full CC) to reject ringing and diode drop effects. Its dual-mode control combines PFM for light-load efficiency and peak current amplitude modulation across three load segments to maintain switching frequency above 20kHz and avoid audible noise.

Valley-on turn-on is triggered when t_OFF < 26–38 µs, reducing switching losses and introducing natural jitter; this is augmented by active VCS reference dithering (±2% every 2 cycles over 12-cycle period) to improve conducted EMI. Line compensation is achieved through internal R_LC (55Ω) and external R_FB1, adjusting VCS threshold proportionally to bus voltage during primary conduction.

Key Specifications

Pinout & Package

AP3981D2-13 is housed in a standard SO-8 package with exposed thermal pad (θ_JA = 65°C/W, θ_JC = 3°C/W on FR-4 with 1in² copper). Drain pins (5,6,7,8) are internally paralleled for low-inductance high-current routing; SOURCE (Pin 4) serves as MOSFET source return and current sense reference.

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 AP3981D2-13 uniquely integrates line compensation, valley-on timing, and dual-ratio t_ONS/t_SW control-enabling tighter CV/CC regulation, lower audible noise, and faster startup in 12–20W universal-input adapters without secondary sensing.

Availability

AP3981D2-13 is available at Aetrix Electronics and suitable for router power supplies, set-top box adapters, network adaptors, and USB-C wall chargers requiring stable component supply, long-term lifecycle support, and RoHS-compliant manufacturing.

Supply support for AP3981D2-13 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 manufacturer specializing in discrete, analog, and mixed-signal ICs for power management, signal integrity, and connectivity applications.

The AP3981D2-13 belongs to Diodes' PSR AC/DC controller product line, engineered specifically for cost-sensitive, low-noise, optocoupler-free flyback converters in consumer adapter and networking power supplies.

FAQ

What is the maximum continuous drain current rating of the integrated MOSFET in AP3981D2-13?

The integrated N-channel MOSFET supports 4A continuous drain current (I_D) at T_A = +85°C, validated under recommended operating conditions (V_CC = 10–28V, ambient ≤+85°C) with SO-8 thermal performance (θ_JA = 65°C/W). This rating assumes proper PCB copper area and airflow per Diodes' layout guidelines in DS41421 Rev. 2.

How does AP3981D2-13 achieve constant current regulation without secondary-side sensing?

AP3981D2-13 regulates output current by controlling the t_ONS/t_SW ratio during secondary conduction - fixed at 0.75 during startup and 0.5 under normal CC operation - while maintaining constant peak primary current (V_{CS_H} = 560–700mV). The FB pin samples auxiliary winding voltage timing to infer secondary current, eliminating need for shunt resistors or optocouplers.

Does AP3981D2-13 support quasi-resonant (QR) operation?

No - AP3981D2-13 implements valley-on switching, not full QR control. It detects drain voltage minima only within a defined window (t_VAL-ON = 26–38µs after t_OFF begins) and forces turn-on if valley is detected; otherwise, it defaults to fixed-frequency PFM. This differs from QR controllers that continuously search for valleys across multiple cycles.

What protection features trigger auto-recovery versus latched shutdown?

All protections - V_CC OVP, SOVP, SUVP, SCP, TSP, and OTP - trigger auto-recovery mode: the IC halts switching, discharges V_CC below 6.1–7.5V (V_OPR(MIN)), then restarts automatically when V_CC rises above 14.5–17.5V (V_{TH_ST}). No latched shutdown occurs; recovery is fully autonomous once fault condition clears.