Temperature Specmanship And Selecting Power Inductors

By Datatronic

How many datasheets have we, as engineers, reviewed and all of the data we need is there? Well, if your experiences are like mine, very few times if at all. And to compound the problem the data listed that pertains to your project was measured at a temperature not where you are planning to run your board.

Choosing the correct power inductor may seem like an easy task. Choose the inductance needed for your SMPS, verify temp rise on the data sheet and your off. But wait. That part is specified for a temperature rise at 25°C. Your board is going to see an ambient temperature of 75°C. Will the inductor you chose work?

Inductors are fairly simply constructed devices. You have core material and wire. Each material is affected by temperature and each of their properties change as temperature increases. So how will knowing temperature effects on core materials and wire affect how you choose an inductor? Simple, you will know what questions to ask your supplier before sampling and releasing the magic smoke in your breadboards!

Power inductor core materials can have varying stabilities over temperature. Curie temperature, Tc (above Tc, ferrite materials lose their ferromagnetic properties, thus their ability to function as an inductor), should be one of your main considerations in determining if an inductor will work in your circuit. Tc can range from as low as 105°C to above 200°C. This means if your circuit is going to run in an ambient temperature of 100°C and the inductor you chose has a Tc of 105°C there is a good chance of your inductor turning into an expensive piece of wire. Knowing the material used in the magnetic component will aid you in choosing the proper inductor that will maintain its functionality while running at temperature in your circuit.