Decide between two inductors for a DC / DC converter

Thread Starter

Glebiys

Joined Mar 11, 2019
16
Hi,

I am designing a power board based on the LM2596.

Board specifications:
1) Input - 12V
2) Outpuit 5V, 2.5A

At the output, I need to put an inductor. I examined many options and settled on two:

1. TDK - 33uH, RC 3.2A, DCR 47.4 mOhm, Isat 3.2A



2. TAITEC - 33uH, RC 6A, DCR 65 - 75mOhm, Isat 8A



What prevents to determine:
1) Is TAITEC better than TDK in terms of shielding? There will be signal lines near the inductor and I would like to minimize the influence of the inductor.
2) If TAITEC has better shielding, then in comparison with TDK it has a high DCR. 47.4mOhm vs 65mOhm. As far as I understand, the lower the DCR, the better. Is 65mOhm too high?

How to be?
 

ci139

Joined Jul 11, 2016
1,351
it would guess the option 1 has grater "flux leakage" near "air gaps" -- but it likely takes to compute it out with some 3d grid model ...
i'm not really into this topic now
/// a while ago - i noticed while rewinding iron core transformers that using the Litz wire on secondary !likely gained a better efficiency ... likely → https://www.researchgate.net/publication/2391026_Minimum_Loss_Design_of_a_100_kHz_Inductor_with_Litz_Wire , (https://www.ieee.li/pdf/viewgraphs/fundamentals_magnetics_design.pdf)
← returned by https://www.google.com/search?q=flux+density+distribution+tube+bobbin+ferrite+core+inductor+flux+leakage
 
Last edited:

crutschow

Joined Mar 14, 2008
24,710
1) Is TAITEC better than TDK in terms of shielding?
Can't tell for sure from the pictures.
You need to look at the data sheets.
2) If TAITEC has better shielding, then in comparison with TDK it has a high DCR. 47.4mOhm vs 65mOhm. As far as I understand, the lower the DCR, the better. Is 65mOhm too high?
It's a matter of efficiency.
At 2.5A, (ignoring the inductor current ripple) the TAITEC will dissipate 6.25 * 65mΩ ≈ 400mW, while the TDK will dissipate 6.25 * 47.4mΩ ≈ 300mW.
Is this 100mW difference important to the efficiency you want?
 

ronv

Joined Nov 12, 2008
3,770
Hi,

I am designing a power board based on the LM2596.

Board specifications:
1) Input - 12V
2) Outpuit 5V, 2.5A

At the output, I need to put an inductor. I examined many options and settled on two:

1. TDK - 33uH, RC 3.2A, DCR 47.4 mOhm, Isat 3.2A



2. TAITEC - 33uH, RC 6A, DCR 65 - 75mOhm, Isat 8A



What prevents to determine:
1) Is TAITEC better than TDK in terms of shielding? There will be signal lines near the inductor and I would like to minimize the influence of the inductor.
2) If TAITEC has better shielding, then in comparison with TDK it has a high DCR. 47.4mOhm vs 65mOhm. As far as I understand, the lower the DCR, the better. Is 65mOhm too high?

How to be?
I would go with the one with the higher Isat.
Have you simulated the circuit to see peak inductor current? I always worry about that.
 

ci139

Joined Jul 11, 2016
1,351
there are not many occasions where the higher R.ser of the inductor can be preferred - but some of such may be ? the voltage drop at the inductor (that would otherwise draw the supply down compromising the operation of the circuit) ? to reduce ringing of the mosfet at high dv/dt (? slow down operation to enable fly-back diodes to follow up at lower voltages) ? to limit whatsoever I/O (to/from inductor) peak current (so smaller filter caps can be used) ← but this is like a last measure to consider . . . ((the high currents need to be "stored" somewhere and routed to the inductor with minimum losses))
 

BobTPH

Joined Jun 5, 2013
2,345
I agree with @ronv. The max current the inductor sees will be higher than the continuous output current. The first one may very well go above saturation at peak current.

Bob
 
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