FM2145 FMSH +-6.5V Ground Fault Protection IC

The FMSH FM2145 is an analog ic. Description The FM2145 is a low power controller for AC outlet ground fault interrupters. Contained internally are a 26V zener shunt regulator, an op amp, and an SCR driver. With the addition of two sense transformers, a bridge rectifier, an SCR, a relay, and a few additional components, the FM2145 will detect and protect against both hot wire to ground and neutral wire to ground faults.

Key Specifications

Features

• ‹ No potentiometer required
• ‹ Direct interface to SCR
• ‹ Supply voltage derived from AC line —26V shunt
• ‹ Adjustable sensitivity
• ‹ Grounded neutral fault detectio
• ‹ Meets U.L. 943 standards
• ‹ 450µA quiescent current
• ‹ Ideal for 120V or 220V systems

Design Notes

• The trip threshold is specified over a tolerance band, not at a single point. Design the sense resistor against the worst-case ends of that band, or nuisance tripping will appear at temperature extremes.
• These circuits are usually supplied from a capacitive dropper or a resistive divider off the mains. Verify the supply current budget against the datasheet before adding load.
• Package choice drives creepage. For mains-referenced parts, use the widest package the layout allows and keep the specified clearance to the low-voltage side.
• Check the temperature coefficient of the threshold if the product must hold accuracy over an outdoor temperature range.

Common Questions

What is the trip threshold?

the threshold above. The threshold is specified over a tolerance band, so size the sense element against the band ends rather than the typical value.

What does this device do?

the function described above. It integrates the control loop that would otherwise need a board of discrete parts.

Which packages are offered?

the package listed above. For mains-referenced circuits choose the package that meets the creepage requirement of the layout.

How is it powered?

Typically from a capacitive dropper or resistive divider off the mains rail. Check the supply current budget in the datasheet before adding any load to that rail.