New PTC Thermistors by Ametherm Offer Industry’s Highest Voltage Rating and Lowest Resistance for Pre-Charge Circuits

New PTC Thermistors provide an alternative to fixed resistors and are optimized for inrush current limiting in pre-charge circuits, degaussing circuits, heater applications, in addition to over-current protection.

CARSON CITY, Nev. — November 15, 2018 — Ametherm introduced today a new series of ceramic PTC circuit protection thermistors that combine the industry’s highest voltage rating with lowest available resistance. The CL20 Series PTC Thermistors provide an alternative to fixed resistors and are optimized for inrush current limiting in pre-charge circuits, heater applications, in addition to over-current protection.


The PTC thermistors released today deliver voltage ratings up to 1200 VDC and maximum energy ratings to 600 J. The devices offer five resistance values at 25 °C from 7.0 W to 100.0 W — with tolerance down to 25% — to accommodate a variety of pre-charge times. These resistance values remain unchanged over the operating temperature range of -40 °C to +110 °C.


Providing stability and reliability in high-voltage applications, the CL20 Series of PTC thermistors can withstand hundreds of hits of maximum inrush current without degrading. PTC thermistors do not require reset time and therefore will not result in large inrush current during repetitive use, as their resistance remains in a high state.

Devices in the CL20 Series of PTC thermistors feature a dissipation constant of 22.5 mW/°C, heat capacity from 2.0 J/°C to 3.45J/°C, transition temperature of +120 °C and a thermal time constant of 65 s. Switch and continuous currents for these PTC thermistors range from 450 mA to 1750 mA and 225 mA to 850 mA respectively. They also offer easy PCB mounting, have a diameter of 22 mm, straight leads, and most come with optional outside or inside kinked leads. Ametherm also offers smaller PTC circuit protection devices with diameters from 6 mm to 20 mm.

Ametherm Part #CL20 7R0120CL20 100120CL20 200120MCL20 500100CL20 101130
Resistance @ 25 C7.0 Ω ±25%10.0 Ω ±25%20.0 Ω ±25%50.0 Ω ±25%100.0 Ω ±25%
Transition temp.120 °C120 °C120 °C120 °C120 °C
Max. voltage350 Vrms480 Vrms680 Vrms680 Vrms1200 VDC
Switch current @ 25 °C1.600 A0.800 A0.600 A0.450 A1.750 A
Cont. current @ 25 °C0.850 A0.400 A0.300 A0.225 A0.650 A
Heat capacity2.0 J/°C2.0 J/°C2.25 J/°C2.4 J/°C3.45 J/°C
Dissipation constant22.50 mW/°C22.50 mW/°C22.50 mW/°C22.50 mW/°C22.50 mW/°C
Thermal time constant65.0 s65.0 s65.0 s65.0 s65.0 s
Max. energy250 J250 J500 J600 J600 J
Max. body temp.172 °C174 °C172 °C178 °C180 °C
Diameter22 mm22 mm22 mm22 mm22 mm

The CL20 Series of PTC thermistors are available direct or through distributors such as Digi-Key and Mouser. Samples and production quantities are available now, with factory lead times of 10 weeks. Volume pricing for US delivery starts at $1.14 per piece in 1,000-piece quantities.

For more information on Ametherm’s products or to request a sample, visit Or call 800-808-2434 (toll free in the United States) or 775-884-2434 from outside the U.S. and Canada. Follow Ametherm online at

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About Ametherm

Ametherm, headquartered in Carson City, Nevada, was founded in 1994 and specializes in thermistors for temperature sensing and inrush current limiting in industrial, automotive, green energy, AMS (avionics, military and space), and many other markets. Ametherm’s devices are some of the highest rated in the industry and are available in customized versions to meet the needs of specific applications. For more information, visit or call 800-808-2434.

Ametherm Contact:
Lori Morton
+1 775 884 2434

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