STMicroelectronics VIPER35LD

Overview

VIPER35LD from STMicroelectronics is a quasi-resonant high-voltage offline converter IC integrating an 800 V avalanche-rugged power MOSFET, built-in HV start-up, 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.

For engineers reviewing the VIPER35LD datasheet, VIPER35LD pinout, VIPER35LD application, or VIPER35LD equivalent, key selection criteria include its 136 kHz frequency limit (L-type), <30 mW no-load consumption at 230 VAC, brown-out hysteresis (50 mV), thermal shutdown at 155 °C typical, and integrated senseFET current sensing enabling lossless IDlim adjustment via ZCD pin resistance.

Technical Context

The VIPER35LD implements a current-mode PWM controller with valley-synchronized quasi-resonant operation, using ZCD pin voltage thresholds (VZCDAth = 0.8 V, VZCDTth = 0.6 V) to detect transformer demagnetization and enforce valley switching. Its internal oscillator clamps maximum frequency to 136 kHz (L-type), with valley-skipping activated when ZCD-triggered turn-on would exceed FOSClim.

It features dual-stage start-up: HV current source (IDDch1 = −3 mA typ.) charges VDD from DRAIN until VDDon = 14 V, then transitions to auxiliary winding self-supply; after fault, auto-restart uses reduced IDDch2 = −0.6 mA to limit duty cycle during recovery. Brown-out protection uses resistor-divider input (BR pin) with 0.45 V threshold and 50 mV hysteresis, while thermal shutdown activates at TJ = 155 °C with 30 °C hysteresis.

Key Specifications

Pinout & Package

Package: SO-16 Narrow (SO16N), surface-mount, with pins 13–16 internally connected to the metal frame for enhanced thermal dissipation (RthJA = 80 °C/W on 100 mm² Cu).

Key Features

Applications

Equivalent & Alternatives

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

Compared with ICE3B0565J and LNK364PG, VIPER35LD offers superior light-load efficiency via programmable QR and burst mode, broader input range due to 800 V rating, and flexible protection configuration through its multifunction ZCD pin - making it optimal for regulated, high-efficiency adapters demanding compact size and low no-load power.

Availability

VIPER35LD 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 and compliance with global energy standards.

Supply support for VIPER35LD 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 products for industrial, automotive, and consumer markets.

VIPER35LD belongs to ST's VIPer™ family of high-voltage offline controllers, engineered specifically for compact, low-cost, energy-efficient AC-DC converters targeting auxiliary and adapter power supplies up to 22 W.

FAQ

What is the difference between VIPER35LD and VIPER35HD?

VIPER35LD is the 'L' variant with 136 kHz maximum switching frequency, optimized for EMI filter minimization and lower transformer core loss. VIPER35HD is the 'H' variant with 225 kHz limit, enabling smaller magnetics and extended QR operation range at medium loads. Both share identical pinout, protection features, and 800 V MOSFET rating.

How is output overvoltage protection implemented on VIPER35LD?

OVP is implemented via the ZCD pin using an external resistor divider (ROVP/RLIM). When the divided auxiliary voltage exceeds 4.2 V (typical VOVP threshold), the IC enters auto-restart mode. The same ZCD pin simultaneously sets IDlim and feed-forward gain, enabling single-resistor configuration for multiple protections.

Can VIPER35LD operate without an optocoupler?

No - VIPER35LD requires optocoupler feedback for closed-loop regulation. Its FB pin sources current to drive the optocoupler LED, and regulation relies on secondary-side voltage sensing. Primary-side regulation-only topologies (e.g., LNK364PG) are not supported; the device lacks internal reference or primary-sense architecture.

What thermal derating applies to VIPER35LD in SO-16N package?

In standard FR4 PCB with 100 mm² copper pour, VIPER35LD has RthJA = 80 °C/W. At 50 °C ambient, maximum continuous power is 16 W (open-frame). Junction temperature must stay ≤150 °C; above 155 °C, thermal shutdown activates with 30 °C hysteresis, allowing safe recovery without external intervention.