Diodes Incorporated AP3981CEV3

Overview

AP3981CEV3 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 (t_ONS/t_SW = 0.5 above SUVP) without opto-coupler or secondary-side circuitry, achieving ≤75mW no-load input power and valley-on switching for improved efficiency and EMI. It targets compact AC/DC adapters for routers and STB power supplies.

For engineers reviewing the AP3981CEV3 datasheet, AP3981CEV3 pinout, AP3981CEV3 application, or AP3981CEV3 equivalent, key selection criteria include its integrated 650V MOSFET (R_DS(ON) = 2.8–3.5Ω), PFM/AM multi-segment frequency control, SOVP/SUVP/SCP protections with auto-recovery, and external line compensation via FB pin - all critical for cost-sensitive, low-noise, isolated CV/CC charger designs.

Technical Context

The AP3981CEV3 implements primary-side regulation using auxiliary winding sampling during t_ONS, where FB pin serves as a multi-function terminal for CV feedback, CC t_ONS detection, line voltage sensing, and negative-voltage protection. Its valley-on operation triggers at t_VAL-ON = 26–38μs, reducing turn-on loss and introducing natural jitter to improve radiated/conducted EMI.

It employs a 3-segment peak current control: V_{CS_L} = 160–200mV (≤2% load), V_{CS_H} = 560–700mV (≥40% load), and interpolated V_{CS_M} in between - enabling stable >20kHz switching across full load range to suppress audible noise while maintaining high average efficiency in DCM flyback topology.

Key Specifications

Pinout & Package

AP3981CEV3 is housed in a standard SO-8 package with exposed drain pads (pins 5–8) for thermal dissipation and integrated MOSFET source connection (pin 4). The IC uses GND-referenced control architecture with multi-function FB pin enabling PSR without secondary feedback components.

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 LNK364PG, AP3981CEV3 uniquely integrates line/cable compensation, valley-on, and multi-segment AM/PFM in a single SO-8 package - delivering superior CV/CC accuracy, lower audible noise, and reduced component count for 5–12W universal-input adapters.

Availability

AP3981CEV3 is available at Aetrix Electronics and suitable for router power supplies, set-top box adapters, and USB-C charging solutions requiring stable component supply, RoHS-compliant packaging, and production-ready PSR integration.

Supply support for AP3981CEV3 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 AP3981CEV3 belongs to Diodes' PSR AC/DC controller product line, designed specifically for cost-sensitive, low-noise, isolated CV/CC flyback converters in consumer and networking power adapters.

FAQ

What is the purpose of the FB pin's multi-function capability?

The FB pin serves four verified roles: sampling auxiliary winding voltage for CV regulation at end of t_ONS, detecting t_ONS duration for CC control, measuring line voltage for external compensation via R_FB1, and monitoring negative voltage for fault protection. This integration eliminates separate sensing networks and reduces BOM count by three components versus conventional PSR controllers.

How does the 3-segment AM/PFM control improve system performance?

The 3-segment control adjusts V_CS threshold across load: low (160–200mV) below 2%, medium (interpolated) from 2–40%, high (560–700mV) above 40%. This maintains switching frequency above 20kHz across full load range, preventing audible coil noise while preserving >78% average efficiency at 20% load - confirmed in Diodes' DS41619 Rev.2 typical performance curves.

Can AP3981CEV3 support universal AC input with tight CC regulation?

Yes - its integrated line compensation circuit uses R_FB1 to inject line-proportional voltage into V_{CS_REF}, correcting primary peak current variation caused by propagation delay. With proper R_FB1 selection (e.g., 1.2MΩ for 85–265VAC), CC deviation is reduced from ±15% to ±5% across full input range, as validated in Section 10 of DS41619.

What protection features trigger auto-recovery versus latched shutdown?

SOVP, SUVP, SCP, OTP, and transformer saturation protection all use auto-recovery: the IC stops switching and restarts when VCC drops to 6.1–7.5V (UVLO threshold). Only VCC OVP causes immediate shutdown without restart until VCC falls below 29.5V - confirmed in Absolute Maximum Ratings and Protection Function sections of DS41619 Rev.2.