STMicroelectronics VIPER35LE

Overview

VIPER35LE from STMicroelectronics is a quasi-resonant high-performance offline high-voltage converter IC integrating an 800 V avalanche-rugged power MOSFET, embedded HV start-up circuit, soft-start, and multifunction ZCD pin for zero-current detection, OCP threshold setup, output OVP, and feed-forward compensation. It supports isolated flyback topology with optocoupler feedback and delivers up to 22 W in open-frame designs at 50 °C ambient.

For engineers reviewing the VIPER35LE datasheet, VIPER35LE pinout, VIPER35LE application, or VIPER35LE equivalent, key selection considerations include its 136 kHz frequency limit (L-type), <30 mW no-load consumption at 230 VAC, brown-out hysteresis (50 mV), thermal shutdown (150–160 °C), and quasi-resonant valley-skipping operation for EMI reduction and efficiency optimization in auxiliary power supplies.

Technical Context

The VIPER35LE implements a current-mode PWM controller with integrated zero-current detection logic synchronized to transformer demagnetization, enabling valley-switching turn-on to minimize switching losses. Its ZCD pin serves four concurrent functions: quasi-resonant timing reference, drain current limit (IDlim) programming via external resistor, output overvoltage protection (OVP) threshold setting, and feed-forward compensation scaling.

Brown-out protection uses a dedicated BR pin with independent switch-on/switch-off thresholds (0.45 V ±40 mV hysteresis) and disable voltage (50–150 mV), while thermal shutdown features 30 °C hysteresis and auto-restart recovery. The device operates in burst mode below 0.6 V on FB, reducing no-load power to <30 mW - compliant with stringent energy-saving standards like Energy Star.

Key Specifications

Pinout & Package

Package: SO-16 narrow (SO 16 N), surface-mount, with pins 13–16 internally connected to the metal frame for enhanced thermal dissipation. Pin 4 (N.A.) is mechanically tied to the controller die pad and must be grounded for noise immunity.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ICE3BR1765J and LNK364PG, VIPER35LE offers superior universal-input capability (800 V), integrated multifunction ZCD for single-pin protection tuning, and deterministic soft-start - making it optimal for high-reliability, low-EMI industrial and premium consumer auxiliary supplies.

Availability

VIPER35LE is available at Aetrix Electronics and suitable for smartphone/tablet chargers, STB power supplies, industrial metering systems, and personal care appliance adapters requiring stable component supply, long-term lifecycle support, and compliance with global energy-efficiency regulations.

Supply support for VIPER35LE 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 microcontrollers, power ICs, sensors, and analog solutions for automotive, industrial, and consumer markets.

VIPER35LE belongs to ST's VIPer™ family of high-voltage offline converters - engineered specifically for compact, efficient, and highly integrated AC-DC power supplies in auxiliary and low-to-mid power applications.

FAQ

What is the difference between VIPER35LE and VIPER35HE?

VIPER35LE is the 'L' version with a 136 kHz internal frequency limit and 3.5 ms soft-start time, optimized for EMI-sensitive applications and smaller EMI filters. VIPER35HE ('H' version) has a 225 kHz limit and 4.2 ms soft-start, enabling extended quasi-resonant operation and reduced transformer size - but with higher EMI risk if layout is not carefully controlled.

Can VIPER35LE operate without an optocoupler?

No - VIPER35LE requires optocoupler-based feedback for regulation, as it lacks primary-side sensing or auxiliary winding voltage regulation capability. The FB pin expects current-mode feedback from a phototransistor; open-loop operation will trigger burst mode or OLP shutdown.

How is the drain current limit (IDlim) set using the ZCD pin?

IDlim is programmed by connecting a resistor between ZCD and GND. A 10 µA ZCD sink current sets IDlim = 1.0 A (typ.), while 55 µA yields ~0.8 A and 105 µA yields ~0.65 A - enabling precise OCP tuning across line/load variations without additional components.

What thermal derating applies when using VIPER35LE on a standard FR4 board?

With 100 mm² of 35 µm copper on a single-sided FR4 board, RthJA is 80 °C/W. At 1.5 W dissipation, junction temperature rise is 120 °C - so maximum ambient must be limited to 30 °C to stay within the 150 °C TJ limit. Adding thermal vias or double-sided copper reduces RthJA and enables higher power density.