STMicroelectronics VIPER25LD

Overview

VIPER25LD from STMicroelectronics is an off-line quasi-resonant (QR) flyback controller IC with integrated 800 V avalanche-rugged power MOSFET, adjustable current limiting via ZCD pin, hysteretic thermal shutdown at 150 °C, and <50 mW standby power at 265 Vac - designed for compact, low-noise AC/DC adapters and auxiliary supplies in consumer and industrial equipment.

For engineers reviewing the VIPER25LD datasheet, VIPER25LD pinout, VIPER25LD application, or VIPER25LD equivalent, key selection considerations include its QR valley-switching operation, dual overcurrent protection (primary-side 0.7 A limit + secondary 1.2 A OCP), brown-in/brown-out hysteresis (50 mV), and SO-16N package with thermally enhanced DRAIN pins for open-frame 12 W designs.

Technical Context

The VIPER25LD implements a current-mode PWM controller with zero-current detection (ZCD) circuitry to enable valley-switching in discontinuous conduction mode (DCM), reducing switching losses and EMI. Its internal oscillator supports frequency foldback and valley-skipping above 136 kHz (VIPER25L variant), with burst-mode activation below 0.6 V on FB pin to meet <50 mW no-load requirements.

Power-up sequencing includes soft-start (3.5 ms), high-voltage start-up via DRAIN pin (60–100 V turn-on threshold), and auto-restart with reduced charging current (0.6 mA) after fault clearance. Brown-out protection uses a dedicated BR pin with 0.45 V threshold and 50 mV hysteresis, while overvoltage protection (OVP) triggers at 4.2 V on ZCD with 2.2 µs digital strobe filtering.

Key Specifications

Pinout & Package

Package: SO-16N (10.3 × 10.3 mm, 1.27 mm pitch), with pins 13–16 internally connected to metal frame for thermal dissipation. Copper area under DRAIN pins required per datasheet layout guidelines.

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 LNK306P, VIPER25LD delivers superior EMI performance and system integration via its 800 V QR architecture and single-pin ZCD configuration - making it optimal for compact, certified adapters and auxiliary supplies where board space and regulatory test margin are critical.

Availability

VIPER25LD is available at Aetrix Electronics and suitable for smartphone adapters, LCD TV auxiliary supplies, no-el-cap LED drivers, and utility power meter PSUs requiring stable component supply, long-lifecycle support, and full traceability.

Supply support for VIPER25LD 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.

VIPER25LD belongs to the VIPerPlus family of high-voltage offline controllers - engineered specifically for cost-sensitive, space-constrained AC/DC conversion in sub-20 W applications demanding high reliability and regulatory compliance.

FAQ

What is the purpose of the ZCD pin in VIPER25LD?

The ZCD pin serves four concurrent functions: (1) zero-current detection for QR valley switching, (2) adjustable drain current limit set-point via R_LIM, (3) line-voltage feed-forward via R_FF to maintain constant power, and (4) overvoltage protection input with 4.2 V threshold and 2.2 µs digital strobe filtering - all implemented without external comparators or timers.

How does VIPER25LD achieve <50 mW standby power?

VIPER25LD achieves <50 mW standby power through burst-mode operation (activated below 0.6 V on FB pin), ultra-low quiescent current (270 µA in UVLO), and automatic disable of the HV start-up generator once VDD reaches 14 V - eliminating continuous high-voltage bias current during no-load conditions.

Can VIPER25LD replace VIPER22A in existing designs?

VIPER25LD is not a direct replacement for VIPER22A due to differences in pinout (VIPER22A has 8-pin DIP/SO-8), current limit (0.7 A vs. 0.45 A), and lack of built-in soft-start in VIPER22A. Layout redesign and ZCD/FB resistor recalibration are required; however, its 800 V rating and QR capability offer improved efficiency and EMI in upgraded designs.

What thermal design guidance applies to VIPER25LD's SO-16N package?

VIPER25LD's SO-16N requires ≥100 mm² copper pour under pins 13–16 (DRAIN) to achieve R_TH-JA = 85 °C/W. Without this, junction temperature may exceed 150 °C at 12 W open-frame operation. The datasheet specifies minimum 35 µm copper thickness and recommends thermal vias to inner ground planes for sustained 10 W+ operation.