Monolithic Power Systems Inc. EVHF920-S-00B

Overview

EVHF920-S-00B from Monolithic Power Systems is an evaluation board for the HF920GS off-line flyback regulator IC, integrating a 900V monolithic MOSFET. It delivers dual isolated 16.5V outputs (300mA and 100mA) across 85–350VAC input, supports frequency programming up to 150kHz, enables frequency doubling mode, and meets EN55022 conducted EMI with jittering-optimized for smart power meter designs using EF20 transformer core.

For engineers reviewing the EVHF920-S-00B datasheet, EVHF920-S-00B pinout, EVHF920-S-00B application, or EVHF920-S-00B equivalent, this board provides validated reference design for PLC-coupled power supplies, magnetic field–resistant AC-DC conversion, and dual-output metering power architectures requiring low-noise VCC biasing, time-based OLP, and robust short-circuit recovery.

Technical Context

The EVHF920-S-00B implements a primary-side regulated flyback topology using the HF920GS controller in SOIC-14 package, with integrated 900V MOSFET and programmable switching frequency via external resistor R15 (160kΩ). It employs a custom EF20 transformer (L_m = 2.8mH ±5%, N1:N2:N3:N4:N5 = 25:120:13:19:19) enabling strong anti-interference against external magnetic fields-critical for metering environments.

Its dual-output configuration isolates GND2 from system ground and ties it to the L line for PLC signal coupling, while GND1 serves as MCU/LCD supply return. Protection features include over-temperature shutdown, VCC UVLO, output over-voltage protection, time-based over-load protection, and auto-recovery short-circuit response-all verified per test waveforms on page 6–8 of the Rev. 1.0 document.

Key Specifications

Availability

EVHF920-S-00B is available at Aetrix Electronics and suitable for smart electricity meter development, industrial energy monitoring systems, and PLC-based grid communication modules requiring stable component supply, rapid prototyping validation, and EMC-compliant reference design reuse.

Supply support for EVHF920-S-00B 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 design centers in the US, China, and Taiwan, and manufacturing partners across Asia.

The HF920GS product line targets high-reliability AC-DC conversion in utility-grade metering applications, emphasizing magnetic immunity, wide-input operation, and integrated safety protections-enabling single-chip solutions for Class I and Class II meter designs.

FAQ

What is the purpose of connecting GND2 to the L line on EVHF920-S-00B?

GND2 is intentionally tied to the L (line) terminal to establish a common-mode reference for power line communication (PLC) circuitry. This configuration enables clean coupling of PLC signals onto the AC mains while maintaining isolation between the MCU supply (GND1) and PLC interface, as confirmed in the Circuit Description section (page 12) and schematic Figure 1.

Does EVHF920-S-00B support frequency doubling mode, and how is it enabled?

Yes-frequency doubling mode is supported via capacitor C19 (1nF), connected between PRO and GND pins of U2 (HF920GS). This external setup activates a special operating mode that doubles the base switching frequency, enhancing performance in magnetically noisy environments such as substations or motor-driven loads, as stated in the DESCRIPTION section (page 1).

What transformer specifications are mandatory for replicating EVHF920-S-00B's performance?

The EF20 core with 2.8mH ±5% primary inductance (pins 2–3), winding ratio N1:N2:N3:N4:N5 = 25:120:13:19:19, and Class B insulation wire (Φ0.22mm/0.15mm/0.28mm) is mandatory. Deviations affect magnetic immunity, regulation accuracy, and EMI behavior-verified in Transformer Specification (pages 10–11) and Circuit Description (page 12).

How does the board achieve EN55022 compliance with minimal filtering components?

EN55022 compliance is achieved through three integrated techniques: (1) frequency jittering built into HF920GS to spread spectral energy; (2) optimized PCB layout with minimized high-di/dt loops and controlled return paths; and (3) targeted use of CX1 (4.7nF X-cap) and CY1/CY2 (1nF Y-caps), as demonstrated in conducted EMI test plots (page 8).

Is EVHF920-S-00B agency-certified for safety standards like UL or IEC 61000-4-x?

No-per the Warning on page 2, the engineering prototype has not undergone agency certification (UL, CE, IEC). Users must implement isolation transformers during testing and perform full safety qualification-including creepage/clearance verification, transformer insulation testing, and surge immunity per IEC 61000-4-5-before deployment in certified meter products.

Can the 16.5V outputs be reconfigured for different voltages?

Yes-output voltage is set by resistive divider networks: R14/R18 for VOUT1 and R19/C13/U3 feedback path for VOUT2. Adjusting these values changes regulation points, but transformer turns ratios (N2/N1, N3/N1) and controller FB threshold (2.5V reference) constrain practical range; redesign requires recalculation of snubber, current sense, and loop compensation.

What is the role of FR1 (10Ω fuse resistor) in the input stage?

FR1 serves dual functions: (1) limits inrush current during AC power-up to prevent rectifier diode stress and capacitor charging spikes; and (2) acts as a sacrificial open-circuit element during catastrophic failure (e.g., MOSFET short, transformer fault), protecting upstream wiring and distribution infrastructure-as described in Circuit Description (page 12).