STMicroelectronics VIPER25LN

Overview

VIPER25LN from STMicroelectronics is an integrated quasi-resonant off-line SMPS controller with 800 V avalanche-rugged power MOSFET, current-mode PWM control, and on-chip ZCD-based valley switching. It delivers up to 20 W in open-frame designs at 50 °C ambient, supports adjustable current limiting via ZCD pin, features hysteretic thermal shutdown at 155 °C typical, and achieves <50 mW standby power at 265 Vac - used in auxiliary supplies for LCD TVs, LED drivers, and utility meters.

For engineers reviewing the VIPER25LN datasheet, VIPER25LN pinout, VIPER25LN application, or VIPER25LN equivalent, key selection considerations include its 800 V drain rating, QR valley-sensing operation, dual OCP thresholds (0.7 A primary + 1.2 A secondary), burst-mode activation below 0.6 VFB, and brown-in/brown-out protection with 50 mV hysteresis - all critical for low-EMI, energy-compliant flyback converters.

Technical Context

The VIPER25LN integrates a high-voltage start-up circuit drawing current directly from the DRAIN pin, enabling self-biased operation without auxiliary winding during startup. Its ZCD pin performs four concurrent functions: zero-current detection for QR timing, adjustable current limit setpoint (via RLIM), voltage feed-forward (via RFF), and digital-strobed overvoltage protection (VOVP = 4.2 V).

Control logic implements soft-start (tSS = 3.5 ms), frequency foldback (FOSClim = 136 kHz for 'L' variant), valley-skipping above FOSClim, and burst mode triggered by FB voltage falling below 0.6 V. Fault recovery uses safe auto-restart with reduced 0.6 mA start-up current and VDD restart threshold of 4.5 V to limit thermal stress.

Key Specifications

Pinout & Package

Package: SO16N (16-pin small outline, exposed metal pad for thermal dissipation). DRAIN pins (13–16) are internally bonded to the metal frame and must be connected to large copper areas for heat transfer. GND pins (1–2) serve as both control ground and power section source reference.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar off-line QR flyback controller applications.

Compared with ICE2QS03G and LNK364PG, VIPER25LN offers higher voltage robustness (800 V), true valley-switching for lower EMI and loss, and flexible current limiting - making it optimal for 15–20 W industrial and metering applications demanding reliability and regulatory compliance.

Availability

VIPER25LN is available at Aetrix Electronics and suitable for smartphone adapters, LCD TV auxiliary supplies, and utility power meter SMPS requiring stable component supply, long-term lifecycle assurance, and traceable manufacturing origin.

Supply support for VIPER25LN 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, specializing in power management, microcontrollers, and analog ICs for industrial, automotive, and consumer markets.

VIPER25LN belongs to ST's VIPer™ high-voltage offline converter family, designed specifically for compact, low-standby-power flyback power supplies targeting energy-efficient consumer and industrial equipment.

FAQ

What is the purpose of the ZCD pin in VIPER25LN?

The ZCD pin serves four simultaneous functions: it detects transformer demagnetization for quasi-resonant valley switching, sets the primary overcurrent limit via RLIM resistor, provides voltage feed-forward for line regulation via RFF, and triggers digital-strobed overvoltage protection at 4.2 V. Its multi-function architecture eliminates external components required in discrete controller solutions.

How does VIPER25LN achieve <50 mW standby power?

VIPER25LN achieves sub-50 mW standby by combining burst-mode operation (triggered below 0.6 VFB), ultra-low quiescent current (270 µA in UVLO), and automatic disabling of the HV start-up circuit once VDD reaches 14 V. The IC enters deep-sleep state with minimal internal biasing, reducing total system consumption even with auxiliary winding leakage.

Can VIPER25LN replace VIPER22A in existing designs?

VIPER25LN is not a drop-in replacement for VIPER22A due to differences in pinout (VIPER22A has 8 pins, VIPER25LN has 16), higher voltage rating (800 V vs. 730 V), and added features like ZCD-based QR control and dual OCP. Layout and feedback network redesign are required; however, it enables higher power density and better efficiency in new designs.

What thermal management is required for 20 W operation?

For 20 W open-frame operation at 50 °C ambient, VIPER25LN requires ≥100 mm² of 35 µm copper connected to DRAIN pins (13–16) to achieve RTH-JA = 85 °C/W. Thermal vias under the exposed pad and minimal trace length between DRAIN pins and transformer primary are essential to maintain junction temperature below 125 °C under full load.