Selection Criteria for Thermometrics CL-Products

1.

I max - Thermometrics CLs are rated for maximum steady state current. The maximum steady current is mainly

determined by the acceptable life of the final products for which the thermistor becomes a component. The

differential equation Pdt = HdT + δ(T – TA)dt reduces to Power = I2R = δ(T – TA). An example in the case of a 100

watt power supply with an efficiency rating of 80%, 100% load is calculated to be 125 watts. The maximum input

current is calculated from the minimum supply voltage. For a standard 120V supply, this could be rated as low at

110V. Therefore, input current would be calculated by 125 watts/110 V = 1.14 Amps. Selection of the CL should

have an I max rating of at least 1.14 Amps.

2.

The second step of selection of the CL is to understand the desired maximum inrush current allowable. This is

generally specificed by the components in line of the CL, such as the diode bridge. In the case of the diode bridge

rated at 200 Amps, one would should select a CL that would limit max surge current to 50% of the rating, therefore

limit surge to a maximum of 100 Amps. The listed maximum current flow is rated at 25°C, so derating is required if

the ambient temperture is greater than 25°C.

3.

The next selection of criteria for the CL is to understand the bulk Capacitance of the device to be protected. On

power, the bulk capacitance of the device appears as a short to the system. The designer needs to understand the

bulk capacitance at the RMS voltage rating of the system. Assuming the input capacitance is approximately 500

μFds, the selection of the CL needs to be able to absorb input energy.

Using the above criteria, the selection of the CL provides multiple solutions. One would opt for the smallest size CL to

achieve the required protection. The selection criteria is as follows:

1. I max >1.14 Amps

2. Max allowable Inrush current 100 Amps

3. Bulk Capacitance listed as 500 μfd

4. Choose smallest physical size that will allow protection for the device.

Criteria indicates that either the CL-150 or CL-160 would be suitable for the application. In the case of the CL-150 less

heat is dissipated allowing the operating resistance to drop but at a higher temperature. This increases efficiency of the

system but may lead to shorter component life.

AAS-920-325E - 10/2022

www.amphenol-sensors.com

© 2022 Amphenol Corporation. All Rights Reserved. Specifications are subject to change without notice.

Other company names and product names used in this document are the registered trademarks or

trademarks of their respective owners.

Amphenol

Advanced Sensors