Monolithic Power Systems Inc. EVHF920-S-00D

Overview

EVHF920-S-00D from Monolithic Power Systems is an evaluation board for the HF920GSE off-line flyback regulator IC with integrated 900V MOSFET, delivering triple isolated outputs (13.5V/300mA, 8V/50mA, 8V/50mA) across 85–350VAC input. It implements frequency jittering and programmable switching (up to 150kHz), supports frequency doubling mode, and meets EN55022 conducted EMI and CISPR22 RE Class B with proper transformer design - optimized for smart power meter applications requiring three independent, safety-isolated supplies.

For engineers reviewing the EVHF920-S-00D datasheet, EVHF920-S-00D pinout, EVHF920-S-00D application, or EVHF920-S-00D equivalent, this board provides validated reference design, PCB layout guidance, transformer specifications, and test waveforms for rapid integration into AC-DC power systems with stringent EMC and isolation requirements.

Technical Context

The EVHF920-S-00D implements a primary-side regulated flyback topology using the HF920GSE IC, which integrates a 900V avalanche-rated MOSFET and proprietary control logic for stable regulation without optocoupler feedback on secondary outputs. Its PRO pin enables external hysteresis-based protection with auto-restart recovery, while FB pin receives optocoupler-coupled feedback from the main 13.5V output to maintain ±3% regulation under line/load transients.

It features dual-stage EMI filtering (X-cap CX1 + common-mode choke LX1), series-connected bulk capacitors (C6/C8) with voltage-balancing resistors, and triple-insulated transformer windings (N1–N6) supporting 4500VAC isolation between primary and secondaries - enabling reinforced insulation per IEC61000-4-5 and IEC62053 standards for revenue-grade metering.

Key Specifications

Availability

EVHF920-S-00D is available at Aetrix Electronics and suitable for smart electricity meters, industrial energy monitoring systems, and grid-edge IoT gateways requiring stable component supply, certified reference designs, and fast-turn prototyping support.

Supply support for EVHF920-S-00D 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

Monolithic Power Systems (MPS) is a fabless semiconductor company specializing in high-performance analog and power ICs, with expertise in DC-DC conversion, LED drivers, motor drivers, and AC-DC controllers - headquartered in Kirkland, WA, and serving global industrial, automotive, and computing markets.

The HF920 product line delivers high-voltage flyback controllers for revenue-grade metering and industrial AC-DC power supplies, emphasizing safety isolation, low no-load consumption, and robust EMI performance without compromising thermal efficiency.

FAQ

What is the role of the PRO pin on the EVHF920-S-00D board?

The PRO pin connects to an external resistor divider that monitors bulk capacitor voltage. When overvoltage is detected, it triggers hysteresis-based shutdown with automatic restart after fault clearance - providing precise, adjustable overvoltage protection independent of the main FB loop.

How is GND2 connected and why is it tied to the L-line?

GND2 is electrically connected to the AC Line (L) terminal via JP1, establishing a referenced ground for the 8V/50mA output used by power line communication (PLC) modems. This configuration enables zero-crossing detection and PLC signal coupling without additional level-shifting circuitry.

Does the board support frequency doubling mode, and how is it enabled?

Yes - frequency doubling is activated by placing a 1nF capacitor (C19) between FSET and GND. This mode increases switching frequency to improve transient response and reduce output ripple in magnetizing-critical applications like PLC supply rails.

What transformer specifications are required for full compliance?

The board requires the EE16 FX0553 transformer with N1:N2:N3:N4:N5 = 22:120:13:15:9:9 turns, 2.2mH primary inductance ±5%, triple-insulated windings, and 4500VAC isolation between primary and all secondaries - as documented in Section 12 of the reference design guide.

Can the EVHF920-S-00D be used without the optocoupler U1?

No - U1 (EL817B) is essential for closed-loop regulation of the 13.5V output. Removing it disables feedback to the FB pin, causing unregulated output voltage drift and potential OVP activation; the design does not support primary-side sensing-only operation.

What safety certifications has the EVHF920-S-00D board achieved?

The board itself is an engineering prototype and has not undergone agency certification (UL, CE, etc.). However, its design complies with IPC-2221 creepage/clearance rules and supports end-product certification when implemented with approved transformers, Y-caps (CY1/CY2), and safety-rated components per IEC62368-1 and IEC61000-4-5.

How is over-load protection implemented on this board?

Over-load protection uses time-based detection: the HF920GSE monitors peak current through R21/R22 and initiates foldback current limiting if sustained overload exceeds 120ms. Recovery occurs automatically after load removal and VCC re-stabilization, avoiding latch-off behavior.