STMicroelectronics VIPER35HD

Overview

VIPER35HD from STMicroelectronics is a quasi-resonant high-voltage offline converter IC integrating an 800 V avalanche-rugged power MOSFET, embedded HV start-up circuitry, soft-start, and multifunction ZCD pin for zero-current detection, OCP threshold setup, output OVP, and feed-forward compensation. It delivers up to 22 W in open-frame designs at 50 °C ambient and supports isolated flyback topology with optocoupler feedback. Used in auxiliary power supplies and low-power AC/DC adapters.

For engineers reviewing the VIPER35HD datasheet, VIPER35HD pinout, VIPER35HD application, or VIPER35HD equivalent, key selection criteria include its 800 V drain rating, quasi-resonant current-mode control, <30 mW no-load consumption, brown-out hysteresis, and thermal shutdown with 30 °C hysteresis - all critical for energy-efficient, compact, and reliable offline SMPS design.

Technical Context

The VIPER35HD implements a current-mode PWM controller with valley-synchronized quasi-resonant (QR) operation, using internal ZCD logic to detect transformer demagnetization and trigger MOSFET turn-on at minimum drain-source voltage. Its frequency foldback limits switching to 136 kHz (L-type) or 225 kHz (H-type), enabling EMI reduction and transformer size optimization.

It integrates HV start-up via DRAIN pin (VDRAIN_START = 60–100 V), soft-start (tSS = 4.2 ms), burst-mode regulation (VFBbm = 0.56–0.64 V), and multi-level protection including cycle-by-cycle OCP (IDlim adjustable via ZCD), output OVP (VOVP = 3.8–4.6 V), short-circuit auto-restart, and hysteretic thermal shutdown (TSD = 150–160 °C, THYST = 30 °C).

Key Specifications

Pinout & Package

Package: SO-16 Narrow (SO 16 N), surface-mount, with pins 13–16 connected to metal frame for enhanced thermal dissipation. Pin 4 (N.A.) must be tied to GND for noise immunity; pins 9–12 (N.C.) must remain floating to ensure safe creepage/clearance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quasi-resonant offline converter applications.

Compared with ICE3B0565J and LNK364PG, the VIPER35HD uniquely combines 800 V ruggedness, true quasi-resonant valley switching, and a multifunction ZCD pin - enabling higher efficiency, lower EMI, and fewer external components in optocoupler-feedback flyback designs up to 22 W.

Availability

VIPER35HD is available at Aetrix Electronics and suitable for smartphone chargers, STB auxiliary supplies, industrial sensor power modules, and personal care adapters requiring stable component supply, long-term lifecycle support, and compliance with global energy standards.

Supply support for VIPER35HD 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, power, MCU, and sensor solutions for industrial, automotive, and consumer markets.

The VIPER™ family targets highly integrated, energy-efficient AC/DC conversion - specifically engineered to replace discrete HV MOSFET + controller combinations in sub-25 W offline power supplies.

FAQ

What is the difference between VIPER35HD and VIPER35LD?

The VIPER35HD is the 'H-type' variant with a 225 kHz internal frequency limit (FOSClim), optimized for extended quasi-resonant operation and smaller transformer size. The VIPER35LD is the 'L-type' with 136 kHz limit, prioritizing EMI filter minimization. Both share identical pinout, protection features, and SO-16 package - only oscillator frequency differs.

Can VIPER35HD operate without an optocoupler?

No - VIPER35HD requires optocoupler-based feedback for closed-loop regulation. Its FB pin sources current into the optocoupler LED and lacks primary-side sensing capability. For primary-side regulation, ST offers the VIPer0P or SRK100x families, which do not support the same ZCD functionality or integrated HV start-up.

How is output overvoltage protection implemented on VIPER35HD?

OVP is implemented via the ZCD pin using an external resistor divider (ROVP/RLIM) that scales output voltage to the ZCD input. When this scaled voltage exceeds VOVP = 3.8–4.6 V, the IC enters auto-restart mode. Unlike dedicated OVP pins, this method shares the ZCD node with current limiting and feed-forward functions - requiring careful divider design to avoid interaction.

What thermal derating applies to VIPER35HD in SO-16 package?

In standard FR4 PCB layout (100 mm² copper), RthJA is 80 °C/W. With 1.5 W max power dissipation (PTOT), junction temperature rise is ~120 °C above ambient - limiting continuous operation to ≤30 °C ambient for full 150 °C TJ rating. Heatsinking pins 13–16 to large copper planes reduces RthJA and enables 50 °C ambient operation at full load.