Resettable fuses go on the line side

Designed for use in line voltage applications, the LVR series of PolySwitch resettable devices are rated at 240V AC, and are available in hold currents from 50 to 400mA.

Designed for use in line voltage applications, the LVR series of PPTC (polymeric positive temperature coefficient) PolySwitch resettable devices are rated at 240V AC, permitting maximum voltages up to 265V AC, and are available in hold currents from 50 to 400mA.

The thermally active devices can help protect against both overcurrent and overtemperature faults on the primary side of power supplies and transformers.

The LVR device was developed to help prevent damage to control boards and components by limiting current in the event of a load-side short-circuit or overdraw, or improper incoming voltage.

Unlike a single-shot current fuse, the resettable LVR device can help protect against conditions where faults may cause a rise in temperature with only a slight increase in current draw.

When installed on the primary side of the circuit, in proximity to potential heat-generating components such as magnetics, FETs, or power resistors, the LVR device can help provide both overcurrent and overtemperature protection with a single installed component.

The properties of the LVR device offer distinct benefits in transformer protection designs.

The surface temperature of the LVR device in the high resistance state is well within the range most transformer winding insulation ratings.

This low temperature operation, combined with small size, low resistance and good thermal shock tolerance, allows the LVR device to be mounted in direct contact with the transformer windings for a faster response to potential fault conditions.

"For many years, circuit designers have relied on PPTC devices for secondary-side protection.

This development makes possible, for the first time, resettable PPTC circuit protection on the primary side of power circuitry", said Steve Zalewski, Industrial Market Manager for Tyco Electronics Power Components.

"Higher voltage ratings and the thermal characteristics of the LVR series PolySwitch device make it a logical and innovative solution for power supply and charger designs", he added.

The LVR devices are available in straight-lead or kinked-lead configurations, and can be supplied in tape-and-reel packaging for compatibility with high-volume assembly.

UL, CSA, and TUV certifications are currently pending.

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