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issue: January 2003 APPLIANCE Magazine

Electronics Report
Circuit Protection Devices

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Tyco Electronics (Harrisburg, PA, U.S.) introduces a new Raychem Circuit Protection product series, the LVR series of PolySwitch¨ resettable devices.

Tyco's new LVR series of PolySwitch¨ resettable 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 T†V certifications are currently pending.

Designed for use in line voltage applications, the LVR series PPTC (polymeric positive temperature coefficient) devices are rated at 240 V a.c., permitting maximum voltages of up to 265 V a.c., and are available in hold currents from 50-400 mA. The thermally active devices reportedly 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 reportedly 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 is said to help provide protection with a single installed component.

According to Steve Zalewski, Worldwide Industrial Market manager for Tyco Electronics Power Components, LVR devices have been designed for a large variety of appliance applications, including white goods, HVAC systems, metering equipment, security systems, and portable tools. "They are often used as a resettable solution to help protect on the primary side of the power supply, on a.c. fans and motors in the event of stalls and overloads, and on input and output lines such as solenoids, valves, and sensors, where there is a chance of 120- or 240-V a.c. faults," he explains. "Basically, any product having either a control board, fan, motor, or input/output lines and needing protection from overcurrent or overtemperature conditions is a possible application for the LVR product family."

PPTC devices are a proven technology that offer a resettable solution to help protect batteries, telecom lines, computer ports, and industrial equipment, says Mr. Zalewski, but the operating voltage has typically been limited to 72 V and lower. "The LVR device is the first PPTC product family rated for operation at 240 V a.c., with a maximum of 265 V a.c.," he explains. "This higher voltage rating opens up PPTC technology to a wide range of new product areas - many products running on 100-240 V a.c. power levels. The small size and low surface temperature in the high-resistance (tripped) state of the LVR device give the designer flexibility to put the protection where they need it."

Mr. Zalewski adds that engineers need to note that a PTC device is not a fuse; it is a non-linear thermistor that limits current. It goes into a high-resistance state, but a small trickle current does continue to flow. "The LVR devices have rated maximum interrupt voltage and current and should only be used in applications where these are not exceeded," he warns. "Mounting where the PTC device is constrained, such as rigid potting materials or in an environment where the PTC material is exposed to certain silicon-based oils or aggressive solvents, can adversely impact performance. The designer must independently evaluate the suitability of - and test each product selected for - [his or her] own application."


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