STMicroelectronics L6565D

Overview

L6565D from STMicroelectronics is a current-mode quasi-resonant (QR) zero-voltage-switching (ZVS) flyback controller IC designed for primary-side regulation in offline AC-DC converters. It features 1% precision internal 2.5 V reference, ultra-low start-up current (<70 µA), ±400 mA totem-pole gate driver, line voltage feedforward for constant power delivery, and frequency foldback for standby efficiency - deployed in TV/monitor SMPS and energy-compliant adapters.

For engineers reviewing the L6565D datasheet, L6565D pinout, L6565D application, or L6565D equivalent, key selection criteria include ZCD-triggered QR timing accuracy, VFF-based pulse-by-pulse OCP scaling, hiccup-mode overcurrent protection, and SO-8 package compatibility with high-noise industrial flyback layouts.

Technical Context

The L6565D implements transformer demagnetization sensing via ZCD pin (1.6 V negative-edge trigger, 2.1 V arming threshold) to synchronize MOSFET turn-on at valley points, enabling true ZVS operation across universal input (88–264 VAC). Its line feedforward (VFF pin) dynamically scales the current-sense clamp voltage (VCSx) from 1.4 V at 0 V VFF down to 0 V at 3 V VFF, maintaining constant output power versus mains variation.

Frequency foldback is achieved by blanking the ZCD trigger circuit for 3.5–18 µs depending on COMP voltage - reducing switching frequency under light load while preserving ZVS proximity. The integrated error amplifier supports both primary feedback (via auxiliary winding divider) and secondary feedback (via optocoupler-driven COMP), with 60–80 dB gain and 1 MHz GBW for stable loop compensation.

Key Specifications

Pinout & Package

Package: SO-8 (Small Outline, 150 mil width), RoHS-compliant, surface-mountable with standard reflow profile.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quasi-resonant flyback controller applications.

Compared with UCC28600DR and ICE2QS03G, the L6565D provides optimal balance of precision (1% VREF), universal-input power consistency (via VFF), and proven field reliability in cost-sensitive consumer SMPS - making it preferred for mid-volume TV/adapter designs where BOM simplicity and regulatory compliance are prioritized over ultra-low no-load power.

Availability

L6565D is available at Aetrix Electronics and suitable for TV/monitor SMPS, universal AC-DC adapters, and office equipment power supplies requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for L6565D 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, designing and manufacturing analog, microcontroller, power, and sensor solutions for industrial, automotive, and consumer markets.

The L6565D belongs to ST's legacy AC-DC controller product line, engineered specifically for high-efficiency, low-cost quasi-resonant flyback converters targeting energy-compliant consumer electronics and display power systems.

FAQ

What is the minimum blanking time on the ZCD pin, and how does it affect QR operation?

The ZCD pin has a guaranteed minimum blanking time of 3.5 µs after GD goes low, increasing up to 18 µs as COMP voltage drops. This blanking prevents false triggering from leakage inductance ringing and enforces frequency foldback - ensuring MOSFET turn-on occurs only after full transformer demagnetization, preserving ZVS integrity even at light loads.

Can the L6565D operate without an optocoupler, and what is the regulation accuracy?

Yes - the L6565D supports primary-side regulation using the auxiliary winding voltage divided into the INV pin, leveraging its 2.5 V ±1% internal reference. Typical output regulation is ±3% over line/load/temperature with proper transformer turns ratio and divider calibration; secondary feedback via optocoupler improves this to ±1%.

How does the line feedforward (VFF) function improve power delivery stability?

VFF scales the current-sense comparator's clamp voltage (VCSx) inversely with input voltage: at 3 V VFF, VCSx = 0 V; at 0 V VFF, VCSx = 1.4 V. This reduces peak primary current at high line, maintaining constant output power across 88–264 VAC - eliminating ±40% power swing seen in fixed-OCP QR controllers and enabling smaller, lower-cost transformers.

What happens during hiccup-mode overcurrent protection, and how does recovery work?

When CS voltage exceeds 2.0 V continuously, GD is disabled and the IC remains in hiccup mode - drawing ~2 mA quiescent current until VCC discharges below 9.5 V UVLO threshold. Once VCC falls, the internal starter initiates a new soft-start cycle. This protects MOSFETs and magnetics during sustained faults while limiting average power dissipation to <150 mW.