Author Topic: Choosing right inductor...  (Read 504 times)

0 Members and 1 Guest are viewing this topic.

Offline 3dgeo

  • Regular Contributor
  • *
  • Posts: 213
  • Country: au
Choosing right inductor...
« on: January 14, 2019, 09:46:30 am »
Hello,

I'm making step down converter (based on "Great scotts" BMS, schematic below) for LiPo battery to replace 2 AAA batteries and my knowledge about inductors is a bit weak, so I need help.
MT3420 data sheet recommends 1-4.7uH with low DCR for higher efficiency, lowest DCR I managed to find is 4.2 mOhms@2.2uH(13x13x7 mm), but also I found 24mOhms@4.7uH(8x8x4mm). How much of an impact inductor inductance and DCR has in this particular case, load will be wireless mouse (will make separate thread on it in a few min...).

Thanks in advance.
(don't mind resistors values)
 

Offline mvs

  • Regular Contributor
  • *
  • Posts: 182
  • Country: de
Re: Choosing right inductor...
« Reply #1 on: January 14, 2019, 10:40:30 am »
MT3420 data sheet recommends 1-4.7uH with low DCR for higher efficiency, lowest DCR I managed to find is 4.2 mOhms@2.2uH(13x13x7 mm), but also I found 24mOhms@4.7uH(8x8x4mm). How much of an impact inductor inductance and DCR has in this particular case, load will be wireless mouse (will make separate thread on it in a few min...).
Power loss due DCR is P=I²R. If your mouse consumes 50mA, then it is 2.6µW vs 15µW. 
 

Offline 3dgeo

  • Regular Contributor
  • *
  • Posts: 213
  • Country: au
Re: Choosing right inductor...
« Reply #2 on: January 14, 2019, 11:11:51 am »
MT3420 data sheet recommends 1-4.7uH with low DCR for higher efficiency, lowest DCR I managed to find is 4.2 mOhms@2.2uH(13x13x7 mm), but also I found 24mOhms@4.7uH(8x8x4mm). How much of an impact inductor inductance and DCR has in this particular case, load will be wireless mouse (will make separate thread on it in a few min...).
Power loss due DCR is P=I²R. If your mouse consumes 50mA, then it is 2.6µW vs 15µW.

Thank you.

Does inductance have a huge impact on this small load? Cos that inductor is 13x13x8mm, would like something smaller if it's possible :)
 

Offline mvs

  • Regular Contributor
  • *
  • Posts: 182
  • Country: de
Re: Choosing right inductor...
« Reply #3 on: January 14, 2019, 02:21:50 pm »
Does inductance have a huge impact on this small load? Cos that inductor is 13x13x8mm, would like something smaller if it's possible :)
With lower inductance this converter may stay a bit longer in PFM mode, but I do not think that you get a huge power savings from it.
For light load scenario i usually tend to choose higher inductor values (so 4.7uH or perhaps even more) to get better regulation and lower ripple current.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf