The PTC circuit protection thermistors can be used as an alternative to fixed resistors

By Heather Hamilton, contributing

Ametherm has released a series of ceramic PTC circuit protection
thermistors with high voltage ratings paired with low available resistance. The
CL20 Series is an alternative solution to fixed resistors and are optimized for
inrush current limiting in pre-charge circuits, degaussing circuits, heater
applications, and overcurrent protection.

Claimed to provide the industry’s
highest voltage rating with the lowest available resistance, the thermistors
boast voltage ratings up to 1,200 VDC and maximum energy ratings to 600 J. The
thermistors offer five resistance values at 25°C from 7.0 W to 100.0 W with
tolerance down to 25%. This accommodates a variety of pre-charge times, said
the company, and the resistance values do not change over the −40°C to 110°C
operating temperature range.

In high-voltage applications, the
CL20 thermistors offer stability and reliability and can withstand hundreds of
hits of maximum inrush current without degrading, said the company. They also
don’t need time to reset, which prevents large inrush current during repeated
use because their resistance remains in a high state.

The series boasts a dissipation
constant of 22.5 mW/°C, a heat capacity of 2.0 J/°C to 3.4 5J/°C, a transition
temperature of 120°C, and a thermal time constant of 65 s. Switch and continuous
currents range from 450 mA to 1750 mA and 225 mA to 850 mA, respectively.

The thermistors feature easy PCB
mounting, a diameter of 22 mm, and straight leads. Most of the devices also come
with optional outside or inside kinked leads. Smaller versions are available with
diameters ranging from 6 mm to 20 mm. The device specification table can be
found here.

The CL20 Series is available
direct or through distributors such as Digi-Key and Mouser. Samples and production quantities are
available now, with a factory lead time of 10 weeks. Volume pricing in the U.S.
begins at $1.14 each in quantities of 1,000.