Tyco Electronics introduced a new Raychem Circuit Protection product series, the LVR series of PolySwitch® resettable devices. 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 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 is said to 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 reportedly help provide both overcurrent and overtemperature protection with a single installed component.
The properties of the LVR device are said to offer distinct benefits in transformer protection designs. The surface temperature of the LVR device in the high resistance state is said to be well within the range of most transformer winding insulation ratings. This low temperature operation, combined with small size, low resistance, and good thermal shock tolerance, reportedly allows the LVR device to be mounted in direct contact with the transformer windings for a faster response to potential fault conditions.
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 TÜV certifications are pending.