STMicroelectronics VIPER25HD

Overview

VIPER25HD from STMicroelectronics is an off-line quasi-resonant (QR) flyback controller IC with integrated 800 V avalanche-rugged power MOSFET, designed for AC-DC primary-side regulation in low-to-mid power SMPS. It delivers up to 12 W in open-frame designs at 50 °C ambient, features adjustable current limiting via ZCD pin, <50 mW standby power at 265 Vac, and built-in brown-in/brown-out protection. Used in auxiliary supplies for LCD TVs, LED drivers, and utility meters.

For engineers reviewing the VIPER25HD datasheet, VIPER25HD pinout, VIPER25HD application, or VIPER25HD equivalent, key selection criteria include its 800 V drain rating, QR valley-switching control, dual overcurrent protection levels, hysteretic thermal shutdown at 150–160 °C, and SO-16N package with DRAIN pins thermally connected to metal frame.

Technical Context

The VIPER25HD implements a current-mode PWM controller with zero-current detection (ZCD) circuitry enabling true quasi-resonant operation-synchronizing MOSFET turn-on to transformer demagnetization valleys to minimize switching losses and EMI. Its internal oscillator supports frequency foldback and valley-skipping modes, with FOSClim set to 225 kHz (typ.) for the 'H' variant.

It integrates high-voltage startup from DRAIN (60–100 V start threshold), on-board soft-start (4.2 ms), burst-mode operation below 0.6 V FB, and dual-level overcurrent protection: first-level adjustable via ZCD current (0.7 A typ.), second-level fixed at 1.2 A. Brown-out hysteresis (50 mV) and overvoltage protection (3.8–4.6 V strobed threshold) are digitally filtered for noise immunity.

Key Specifications

Pinout & Package

VIPER25HD is housed in a SO-16N (Small Outline, 16-pin, narrow) package with exposed DRAIN pins (13–16) thermally connected to the metal frame for enhanced heat dissipation. Copper area under DRAIN pins is mandatory per layout guidelines.

Key Features

Applications

Equivalent & Alternatives

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

Compared with VIPER25HD, STVIPER06HS trades 800 V ruggedness for lower conduction loss and reduced system cost in benign line environments, while ICE2QS03G offers topology flexibility and higher power headroom at the expense of integration and component count.

Availability

VIPER25HD is available at Aetrix Electronics and suitable for adapter power supplies, auxiliary power for displays, LED driver power stages, and utility meter SMPS requiring stable component supply, long lifecycle support, and compliance with global energy efficiency standards.

Supply support for VIPER25HD 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, MCU, power, and sensor solutions for automotive, industrial, and consumer markets.

VIPER25HD belongs to ST's VIPer™ high-voltage AC-DC converter family, engineered specifically for compact, low-BOM-count offline SMPS targeting energy-efficient auxiliary and adapter applications up to 20 W.

FAQ

What is the purpose of the ZCD pin in VIPER25HD?

The ZCD (Zero-Current Detection) pin serves three critical functions: it senses transformer demagnetization for quasi-resonant valley switching, sets the adjustable drain current limit via an external resistor to GND, and hosts the overvoltage protection circuit. Its internal arming and triggering thresholds (0.8 V and 0.6 V) ensure noise-immune timing, while blanking time (2.5–6.3 µs) suppresses leakage ringing artifacts.

How does VIPER25HD achieve <50 mW standby power?

VIPER25HD achieves sub-50 mW standby power through burst-mode operation triggered when FB voltage falls below 0.6 V, reducing switching frequency to hundreds of Hz; ultra-low quiescent current (270 µA in UVLO, 400 µA during fault); and automatic disabling of the high-voltage starter once VDD reaches operating range. These features collectively minimize all dynamic and static losses during no-load conditions.

Can VIPER25HD operate without an auxiliary winding?

No - VIPER25HD requires an auxiliary winding to sustain VDD after startup. The internal HV starter only charges the VDD capacitor until the auxiliary winding generates sufficient voltage (~14 V) to maintain operation. Without it, VDD collapses below 8.0 V, causing UVLO shutdown. The CVDD capacitor must be sized using Equation 1 from DS6205 to bridge the startup gap before auxiliary voltage stabilizes.

What thermal design considerations apply to the SO-16N package?

The SO-16N package relies on DRAIN pins (13–16) connected to a minimum 100 mm² copper pour (35 µm thick) for thermal performance. With this layout, R_TH-JA drops from 120 °C/W (standard board) to 85 °C/W, enabling 12 W continuous output at 50 °C ambient. Thermal vias under the DRAIN pads and internal layer copper planes further reduce junction-to-ambient resistance and prevent thermal shutdown under sustained load.