STMicroelectronics STEVAL-ISA124V1

Overview

STEVAL-ISA124V1 from STMicroelectronics is an evaluation board for the VIPER17HN high-voltage PWM controller IC, designed to demonstrate a 5 W flyback converter with no optocoupler feedback. It integrates an 800 V avalanche-rugged power MOSFET, 115 kHz switching frequency, <30 mW standby power at 265 VAC, and built-in protections including OVP, brown-out, thermal shutdown, and auto-restart - validated for auxiliary power supply in LCD TV and audio systems.

For engineers reviewing the STEVAL-ISA124V1 datasheet, STEVAL-ISA124V1 schematic, STEVAL-ISA124V1 application, or STEVAL-ISA124V1 equivalent, this board enables rapid validation of VIPER17-based offline SMPS designs meeting IEC 62368-1 and Energy Star Level VI requirements without external feedback components.

Technical Context

The board implements a primary-side regulated (PSR) flyback topology using the VIPER17HN's integrated CONT pin sensing for output voltage monitoring via auxiliary winding, eliminating optocoupler and TL431. Burst-mode operation below 0.45 V on FB pin ensures <30 mW no-load consumption, while jittered 115 kHz oscillator reduces EMI peak amplitude by spreading spectral energy across ±8 kHz bandwidth at 250 Hz.

Protection logic is fully embedded: brown-out triggers at 0.45 V on BR pin with 50 mV hysteresis; overvoltage protection samples CONT pin 2.2 µs after MOSFET turn-off for noise immunity; thermal shutdown activates at 155 °C with 30 °C hysteresis; and safe auto-restart limits fault repetition rate via reduced 0.6 mA HV startup current.

Key Specifications

Availability

STEVAL-ISA124V1 is available at Aetrix Electronics and suitable for LCD TV auxiliary power supplies, audio system standby rails, and industrial SMPS requiring stable component supply, regulatory-compliant low-power operation, and rapid PSR flyback prototyping.

Supply support for STEVAL-ISA124V1 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, delivering intelligent power, analog, MEMS, and microcontroller solutions for automotive, industrial, and consumer applications.

The VIPER™ family targets highly integrated, low-component-count offline AC-DC converters - specifically engineered for cost-sensitive, space-constrained auxiliary and adapter power supplies with stringent no-load and EMI requirements.

FAQ

What input voltage range does STEVAL-ISA124V1 support?

The board accepts 85–265 VAC input, validated per ST's typical power table for open-frame 5 W operation. Its VIPER17HN controller features a high-voltage startup circuit drawing current directly from the DRAIN pin above 80 VDC, enabling reliable start-up across global mains voltages without auxiliary bias winding during initial power-up.

How is output voltage regulated without an optocoupler?

Regulation uses primary-side sensing: the CONT pin monitors voltage from the transformer's auxiliary winding during MOSFET off-time. When sampled voltage exceeds 3.0 V (VOVP threshold) four consecutive times, OVP triggers. Feedback loop stability is maintained via FB pin current sourcing (−200 µA typical) into a resistor divider, enabling precise 12 V ±5% output tolerance under line/load transients.

Does STEVAL-ISA124V1 include thermal protection?

Yes - the VIPER17HN IC integrates hysteresis thermal shutdown activating at 155 °C (typical) with 30 °C hysteresis. During overtemperature, the device enters safe auto-restart mode with reduced 0.6 mA HV startup current, limiting average power dissipation and preventing thermal runaway without external thermistors or shutdown circuitry.

Can STEVAL-ISA124V1 be modified for higher output power?

No - the board is optimized for 5 W per ST's validated open-frame rating (Table 2). Increasing output power requires re-designing transformer turns ratio, snubber, heatsinking, and safety clearance; the VIPER17HN's 24 Ω RDS(on) and 1 W package power dissipation limit practical continuous output to 5 W at 50 °C ambient without derating or forced cooling.