Monolithic Power Systems Inc. HF81GS

Overview

HF81GS from Monolithic Power Systems is a two-terminal X-capacitor bleeder IC that functions as a smart high-voltage switch in series with discharge resistors to eliminate standby power loss while ensuring automatic, safe X-capacitor discharge upon AC removal. It blocks current at 230 VAC (supply current ≤15 µA), activates discharge when AC is unplugged (detection time ≤25 ms), and integrates a 1000 V internal JFET for differential surge immunity. It is used in AC/DC front-ends requiring EuP Lot 6 and Energy Star V2.0 compliance.

For engineers reviewing the HF81GS datasheet, HF81GS pinout, HF81GS application, or HF81GS equivalent, key selection criteria include zero-crossing detection timing, 1000 V L1–L2 rating, dual-pin redundancy per terminal, creepage ≥4 mm, and compatibility with X-capacitors up to 5 µF and total series resistance down to 150 kΩ.

Technical Context

The HF81GS operates without external bias, deriving power directly from the AC line via internal charge-pump circuitry. Its core function relies on zero-crossing detection to reset an internal timer; absence of crossings for >25 ms triggers latch activation and discharge transistor turn-on.

It implements dual-pin redundancy per AC terminal (L1 and L2) to maintain safety integrity under single-point failure-open-circuit or short-circuit between opposite terminals results in benign behavior equivalent to omitting the device entirely. The 1000 V rated internal JFET and ≥4 mm creepage support IEC 60950-1 compliance in high-surge environments.

Key Specifications

Pinout & Package

HF81GS is housed in an SOIC-8 package with 1.27 mm pitch, JEDEC MS-012 AA compliant, featuring dual pins per AC terminal for redundancy and ≥4 mm creepage on PCB layout.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar X-capacitor bleeder applications.

Compared with ST8002BTR and ICE3B0565J, HF81GS offers true two-terminal operation, 1000 V rating, and lowest supply current (15 µA), making it uniquely suited for pre-fuse, ground-free, ultra-low-power X-capacitor discharge in space-constrained AC/DC front-ends.

Availability

HF81GS is available at Aetrix Electronics and suitable for energy-efficient appliances, server power supplies, and industrial AC/DC converters requiring stable component supply, long-term lifecycle support, and safety-certified X-capacitor discharge functionality.

Supply support for HF81GS 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 global design centers and manufacturing partnerships focused on energy efficiency and reliability.

The HF81GS belongs to MPS's safety and power management product line, engineered specifically for ultra-low-power, high-voltage AC/DC front-end applications where regulatory compliance, surge resilience, and no-load consumption are critical.

FAQ

What is the maximum X-capacitor value supported by HF81GS?

HF81GS supports X-capacitors up to 5 µF, as validated in Table 1 of the datasheet. At this value, a total series resistance of 150 kΩ achieves a 0.75 s RC time constant, ensuring discharge to 37% voltage within 1 second per IEC 60950-1, even with ±5% resistor and ±20% capacitor tolerances.

Can HF81GS be placed before the input fuse?

Yes - HF81GS is certified for use before or after the input fuse per IEC 60950-1. When the X capacitor exceeds 0.1 µF and is placed pre-fuse, HF81GS must also be positioned pre-fuse to satisfy safety discharge requirements, and the MOV should likewise be placed pre-fuse for surge levels >1.5 kV.

How does HF81GS handle single-point failures?

HF81GS uses dual pins for L1 (pins 2 & 3) and L2 (pins 6 & 7). If one pin opens, the other maintains continuity. If pins from opposite terminals short, the device behaves identically to a direct short - equivalent to removing HF81GS entirely - preserving system safety without introducing new hazards.

What is the role of the NC pins (1, 4, 5, 8)?

Pins 1, 4, 5, and 8 are internally not connected and must remain unconnected on the PCB. They serve no electrical function but provide mechanical symmetry and package compatibility. Routing traces or soldering to these pins may compromise creepage distance or thermal performance.

Does HF81GS require external timing components?

No - HF81GS contains fully integrated zero-crossing detection, timer, latch, and high-voltage switching circuitry. No external capacitors, resistors, or clock sources are needed. Its operation is self-contained and powered solely from the AC line across L1 and L2.

What is the significance of the 1000 V rating?

The 1000 V rating applies to the L1–L2 terminals and reflects the breakdown voltage of the internal JFET. It enables robust operation in 265 VAC systems with high transient margins, supports placement before MOVs, and eliminates need for external series voltage clamping in most 1.5 kV surge environments.

How does HF81GS reduce power loss compared to fixed resistors?

During AC operation, HF81GS blocks current through the external bleed resistors, reducing their power loss to zero. Only 15 µA quiescent current flows through the IC itself - cutting typical 100–400 mW resistor losses entirely, which directly enables compliance with EuP Lot 6 and Energy Star V2.0 standby power limits.