2

I've noticed that many DC to DC converters that have have almost the same current output will have inductors that vary vastly in their rating.

For instance, I've got two separate buck-boost modules for battery charging and discharging. They have roughly the same technical specs, with one of them being slightly higher power (120 watt vs 100 watt.)

The 120W module has a 3.3uH inductor, while the 100W module has a 100uH inductor. In fact, I've got another similar module that has a 330uH inductor.

I've tried watching videos on how people select their inductors, but can't seem to figure out what exactly makes them require a low value inductor vs a high value inductor. The datasheets for the ICs will tell you what they prefer, but won't say why or much else.

My only assumption is that it has to do with the switching frequencies being different.

JRE
  • 67,678
  • 8
  • 104
  • 179
soconnoriv
  • 79
  • 5
  • 1
    Welcome! What switch frequencies are they running at? What’s the Vin and Vout range for them? – winny Mar 20 '23 at 17:57
  • Depends on the controller type. – Tim Williams Mar 20 '23 at 18:00
  • *My only assumption is that it has to do with the switching frequencies being different* <-- your assumption is likely correct. – Andy aka Mar 20 '23 at 18:01
  • 1
    What winny 1 and Andy said. The higher the switching frequency, the higher the ripple frequency, and easier it is to filter. So would need lower value caps and inductors. – SteveSh Mar 20 '23 at 18:01
  • Vin and Vout range is roughly 4-24 volts. I looked further into the specs and noticed one of the has a 1 MHz frequency while the other can go as high as 3MHz – soconnoriv Mar 21 '23 at 03:25

2 Answers2

3

The inductance depends on many factors.

  • Switching frequency
  • Ripple current
  • Max input voltage
Justme
  • 127,425
  • 3
  • 97
  • 261
1

If the switching regulator is using a lower frequency, then the inductor must have a higher value.

The current through the coil should not going to zero with time gaps, this would create a "ringing", what leads to energy loses. The minimum current must match to the inductance.

Here you can simulate a bit with different values with this StepDown example: http://schmidt-walter-schaltnetzteile.de/smps/abw_smps.html

StepDown Lückender Betrieb

MikroPower
  • 1,338
  • 2
  • 11