Buck converter relationship between Efficiency and Fsw, Inductor

William Tu1

Other Parts Discussed in Thread: LMR23630-Q1

Hi all,

I want to ask about the how efficiency and fsw, efficiency and Inductor are related on the buck converter.

1. Can efficiency can be increased when I change the fsw or Inductance?

2. I calculated based on the datasheet, I could get the minimum Inductance, Lmin, is 3uH. If I use 6uH inductor(all of other condition like DCR are same with 3uH inductor), what can be technical bad effect(except cost and layout size)?

Thank you

over 5 years ago

0 Dorian Brillet de Cande over 5 years ago

TI__Genius 14876 points

Hello William,

What is the device you are using here?

I think it would be easier for me to answer your question if I know what topology is used.

Thanks a lot!

Regards,
Dorian

0 William Tu1 over 5 years ago in reply to Dorian Brillet de Cande

Prodigy 210 points

Hi Dorian,

I'm looking on the LMR23630-Q1 device.

Datasheet : https://www.ti.com/lit/ds/symlink/lmr23630-q1.pdf?ts=1597382256957&ref_url=https%253A%252F%252Fwww.google.com%252F

0 William Tu1 over 5 years ago in reply to Dorian Brillet de Cande

Prodigy 210 points

Dorian,

Can you answer the question?

0 Tahar Allag over 5 years ago in reply to William Tu1

TI__Mastermind 32400 points

Hi William,

In buck converters, the following applies:

Reducing switching frequency helps the efficiency, but it will affect the inductor current ripple.
Increasing the inductor can have double effect, it can help on the efficiency but it will increase the size. If the size do not increase the DCR has to increase and thus the resistive losses will reduce the efficiency eventually especially at heavy loads. So boosting the inductor will help if you keep the DCR in check. But you need to follow the datasheet recommendations, because it may cause stability/bandwidth issues if you go above the datasheet recommended boundaries. The inductance also is based on the desired peak-to-peak ripple current ΔiL Since the ripple current increases with the input voltage, the maximum input voltage is always used to calculate the minimum inductance LMIN. Use Equation 13 to calculate the minimum value of the output inductor.
In addition to that saturation current, and the rated current of the inductor are as important. Check them before you select the inductor.

I hope that helps

Thanks

Tahar

0 William Tu1 over 5 years ago in reply to Tahar Allag

Prodigy 210 points

Thank you Tahar,

1. You mentioned "Reducing switching frequency helps the efficiency", is this the reason that the switching lose will be decreased if switching freq reduced?

2. Could you explain why the efficiency can increase when Inductance increases?

0 Tahar Allag over 5 years ago in reply to William Tu1

TI__Mastermind 32400 points

Hi William,

Yes, the losses increase as the fsw increases.
The inductor value (Inductance) affects the inductor current ripple. Higher inductance reduces the ripple and helps reduce the conduction losses. However, as I explained in the last post, there are conduction losses caused by the resistance. These are generated by the DC resistance (DCR) of the winding that forms the inductor. The DCR increases as the wire length increases; on the other hand, it decreases as the wire cross-section increases. If this trend is applied to the inductor parts, the DCR increases as the inductance value increases and decreases as the case size increases. Since the power loss is proportional to the square of the current, higher output current results in a greater loss. For this reason, it is important to select the appropriate inductors.

Thanks,

Tahar

0 Tahar Allag over 5 years ago in reply to Tahar Allag

TI__Mastermind 32400 points

Hu William,

I found this application note, give more details on what i explained above.it provides more equations that should help you clarify your questions even further.

https://www.ti.com/lit/an/slvaed3/slvaed3.pdf?ts=1598282946793&ref_url=https%253A%252F%252Fwww.google.com%252F

thanks

Tahar

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Buck converter relationship between Efficiency and Fsw, Inductor