Diodes Incorporated AP3981BEV2

Overview

AP3981BEV2 from Diodes Incorporated is a primary-side regulated (PSR) flyback power switcher integrating a 650V N-channel MOSFET and controller in SO-7 package. It delivers accurate constant voltage (2.4 V ±0.05 V FB threshold) and constant current (t_ONS/t_SW = 0.5 above SUVP) without opto-coupler or secondary-side circuitry, targeting ≤7.5W AC/DC adapters for routers and STB power supplies.

For engineers reviewing the AP3981BEV2 datasheet, AP3981BEV2 pinout, AP3981BEV2 application, or AP3981BEV2 equivalent, key selection criteria include its valley-on switching (t_VAL-ON = 26–38 µs), multi-segment AM/PFM control for audible noise suppression, 75 mW no-load input power, and comprehensive protection suite including SOVP (FB = 3.3–3.9 V), SUVP (FB = 1.22–1.48 V), and SCP (FB = 680–820 mV).

Technical Context

The AP3981BEV2 implements primary-side regulation via auxiliary winding sampling during t_ONS, with dual-mode control: PFM dominates at light load while peak-current amplitude modulation (AM) adjusts V_{CS_REF} across three load segments to maintain switching frequency >20 kHz and suppress audible noise. Its valley-on detection triggers turn-on at drain voltage minima to reduce switching losses and improve EMI.

Protection logic is tightly coupled to FB pin monitoring: SOVP, SUVP, and SCP each use distinct voltage thresholds and time delays (e.g., SUVP requires 116–140 ms low-FB condition), while transformer saturation is detected via cycle-by-cycle V_CS limiting (V_{CS_MAX} = 720–880 mV) and internal OTP (T_OTP = +125 to +155 °C) with +27 to +33 °C hysteresis.

Key Specifications

Pinout & Package

AP3981BEV2 is housed in a 7-pin SOIC (SO-7) package with gull-wing leads, optimized for high-voltage isolation and thermal dissipation in compact AC/DC adapters. Pin 1 is NC; pins 5 and 6 are paralleled DRAIN terminals; pin 4 is SOURCE; pin 7 is GND; pin 2 is FB (multi-function sampling/control); pin 3 is VCC (bias supply).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP6004GQ-Z and LNK3206P, AP3981BEV2 offers superior system-level integration-its built-in cable compensation, valley-on switching, and 75 mW no-load power enable smaller magnetics, fewer passives, and direct compliance with latest energy standards without design trade-offs.

Availability

AP3981BEV2 is available at Aetrix Electronics and suitable for router power supplies, set-top box adapters, and network adaptors requiring stable component supply, full RoHS compliance, and lead-free manufacturing support.

Supply support for AP3981BEV2 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 ICs for power management, signal integrity, and connectivity applications.

The AP3981B belongs to Diodes' PSR AC/DC controller product line, designed specifically for cost-sensitive, space-constrained offline adapters needing high efficiency, low EMI, and robust protection without secondary-side feedback components.

FAQ

What is the maximum recommended output power for AP3981BEV2?

The AP3981BEV2 is rated for up to 7.5 W output power in flyback topology with DCM operation. This limit is defined by thermal constraints (θ_JA = 77 °C/W), MOSFET R_DS(ON) (7.8–9.3 Ω), and peak current capability (V_{CS_H} = 560–700 mV). Exceeding this requires derating or enhanced heatsinking per Diodes' AN-41422 thermal guidelines.

How does the AP3981BEV2 achieve constant current without secondary sensing?

It uses primary-side t_ONS/t_SW ratio control: during secondary conduction, the auxiliary winding voltage reflects output voltage, and t_ONS duration is measured to derive load current. At >40% load, t_ONS/t_SW is fixed at 0.5; below SUVP, it shifts to 0.75 for capacitive start-up-enabling precise CC without shunt regulators or optocouplers.

What protections are implemented on the FB pin and how do they function?

The FB pin hosts four protections: SOVP (trip at 3.3–3.9 V for ≥3 cycles), SUVP (trip at 1.22–1.48 V for 116–140 ms), SCP (trip at 680–820 mV for 58–70 ms), and FB-negative protection (low/high thresholds at 11–17 mV and 27–45 mV). All trigger auto-recovery mode-IC stops switching until VCC drops to ≤7.5 V and fault clears.

Can AP3981BEV2 support universal AC input (85–265 VAC) with consistent CC accuracy?

Yes-external line compensation via R_FB1 corrects for propagation delay-induced current error across input range. The internal R_LINE (45–65 Ω) and formula-driven VLC adjustment ensure <±5% CC variation from 85 to 265 VAC, validated in Diodes' DS41422 Rev. 2 application circuits.