Low ESR inductor - what's the max value?

Question

Hi,

I've started looking into smps some time ago out of curiosity.

Just about everywhere it's mentioned that the inductors used should be "low ESR", but how much is that supposed to be?

I'm looking to buy a basic set of inductors to have around when trying things out, what's a reasonable value to look for?

What's the maximum?

Any good advice on a good starterset is welcome as well ofcourse...

Thanks!

Dieter

michaelkellett · Accepted Answer

Hello Dieter,

Keeping a set of inductors is even more tricky than resistors or capacitors. There may be some types commonly used in your line of work but the range is so vast that my favourite set would be very different. The way I build up stocks of such parts is buy buying a few extra on each job - that way you accumulate the kind of parts you are likely to want.

Low series resitance depends on you application - a 1uH inductor for a power supply might have a series resistance of 200mR but so would dissipate 200mW at 1A and I would be happy with it for the power supply of a little audio recorder. If I need 20A then the 80W in the inductor would be aproblem ! Low ESR depends on you application - check specs and remember that the average DC current is what matters for heating but the peak current is what matters for saturation.

MK

Catwell · Answer

Having a set of inductors could be useful, but it may be difficult to pick what range of values you will need. That all depends on the application.

What Vout do you need?

Despite the Vin, the drop across the inductor is typically expressed by V=L*dl/dT

L = inductance

dl/dT = rate of change of the current through the inductor. Related to the limits of Iripple

Always check the current at which the inductor core saturates, this value has to be higher than the applications peak current: Ipk = Iout +Iripple/2

This should help in deciding based on the application.

Cabe

Low ESR inductor -> what's the max value?