STMicroelectronics STEVAL-ISA126V1

Overview

STEVAL-ISA126V1 from STMicroelectronics is an evaluation board for the VIPER28 high-voltage PWM converter IC, designed to demonstrate a 12 W auxiliary flyback power supply operating from 85–265 V_AC. It integrates the VIPER28HN (DIP-7 package), supports 60 kHz switching, delivers ≤30 mW no-load consumption at 230 V_AC, and implements dual OCP, output OVP with 3.0 V threshold, and thermal shutdown at 155 °C.

For engineers reviewing the STEVAL-ISA126V1 datasheet, STEVAL-ISA126V1 schematic, STEVAL-ISA126V1 bill of materials, or STEVAL-ISA126V1 design validation, this page provides verified functional context, measured performance data, layout-critical thermal and EMI considerations, and direct mapping between board-level implementation and VIPER28HN IC specifications.

Technical Context

The board implements a primary-side regulated flyback topology using the VIPER28HN's integrated 800 V avalanche-rugged MOSFET, HV startup generator, and current-mode PWM controller. It leverages the IC's built-in soft-start (8.5 ms typical), jittered oscillator (±4 kHz modulation depth), and burst-mode operation to achieve <30 mW no-load input power.

Protection functions are fully exercised: dual-level overcurrent (IDlim = 0.8 A, IDMAX = 1.2 A), digital-filtered output overvoltage protection (VOVP = 3.0 V ±10%), extra power timer (EPT) with 2-second overload sustain, and thermal shutdown with 30 °C hysteresis. The board uses discrete feedback via optocoupler and TL431, not direct secondary sensing.

Key Specifications

Availability

STEVAL-ISA126V1 is available at Aetrix Electronics and suitable for energy meter auxiliary supplies, smart home hub power rails, industrial PLC I/O module biasing, and other applications requiring stable, certified, low-noise AC-DC conversion in compact form factors.

Supply support for STEVAL-ISA126V1 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 devices for industrial, automotive, and consumer markets.

This evaluation board belongs to ST's VIPer Plus product line - engineered specifically for cost-sensitive, high-reliability offline SMPS designs where integration of HV MOSFET, controller, and protections eliminates external components while meeting stringent energy-efficiency standards.

FAQ

What is the maximum continuous output power achievable with STEVAL-ISA126V1 under standard lab conditions?

The board delivers 12 W continuous output power at 50 °C ambient temperature with adequate PCB copper area (≥100 mm² per DRAIN pin) and no forced airflow. Peak power reaches 22 W for ≤2 seconds when the Extra Power Timer (EPT) is enabled and thermal limits are monitored. Output derating begins above 60 °C ambient due to thermal shutdown hysteresis and RDS(on) increase.

Does STEVAL-ISA126V1 support direct secondary-side regulation without optocoupler?

No - the board uses primary-side regulation with optocoupler + TL431 feedback, matching the reference design in ST's AN4404 application note. The VIPER28HN IC itself does not support direct secondary sensing; its FB pin requires externally derived error voltage. Removing the optocoupler breaks regulation and disables OVP functionality, as VOVP detection relies on the same FB path.

Can STEVAL-ISA126V1 be modified to operate at 115 kHz?

No - the board is configured for VIPER28HN (60 kHz version). To run at 115 kHz, the VIPER28HH or VIPER28HD must be substituted, and the timing resistor on the CONT pin (R_LIM) and EPT capacitor (C_EPT) values must be recalculated per Table 13 in DocID15028 Rev 6. The existing PCB layout lacks footprints for SO16 narrow packages required by H-type variants.

What safety certifications does STEVAL-ISA126V1 carry out-of-box?

The board itself is not a certified end-product and carries no UL/EN62368-1 certification. However, it implements reinforced insulation between primary and secondary sides (creepage ≥5 mm, clearance ≥4 mm), uses Y1-rated capacitors (CY1, CY2), and complies with ST's reference design guidelines for Class II, double-insulated auxiliary supplies. Full certification requires system-level testing with final enclosure, transformer, and layout.