### Author Topic: Total current flowing through inductors in PARALLEL  (Read 1760 times)

0 Members and 1 Guest are viewing this topic.

• Contributor
• Banned!
• Posts: 42
##### Total current flowing through inductors in PARALLEL
« on: April 19, 2015, 10:28:04 am »
Hi, I need a 68uH 3A inductor and i want to connect in parallel two inductors (100uH+220uH) to obtain the value. Each inductor in rated differently: the 100uH have 2.1A current, while the 220uH one is rated 1.4A. Now i want to know if both inductors wired in parallel can substain a current of 3A. DAMN, i didn't find anything about this argument

#### PA0PBZ

• Super Contributor
• Posts: 4153
• Country:
##### Re: Total current flowing through inductors in PARALLEL
« Reply #1 on: April 19, 2015, 10:33:50 am »
I guess you are talking DC current, in that case the current will divide over the 2 inductors according to their DC resistance which is unknown at the moment.
Keyboard error: Press F1 to continue.

• Contributor
• Banned!
• Posts: 42
##### Re: Total current flowing through inductors in PARALLEL
« Reply #2 on: April 19, 2015, 11:09:05 am »
Yes, DC current. Inductors are these: http://www.futurlec.com/Power_Inductors.shtml

#### Anand

• Contributor
• Posts: 36
• Country:
##### Re: Total current flowing through inductors in PARALLEL
« Reply #3 on: April 19, 2015, 12:07:40 pm »
Measure the resistance of your inductors and you can use this rule:
http://en.wikipedia.org/wiki/Current_divider

If you can't measure it, take it from the datasheet.
If it's not in the datasheet...

Also, there is a problem when switching occurs: the lower value inductor might (or might not) take a large amount of current before the bigger one so, by combining a 100uH / 2.1A with a 220uH / 1.4A one you might get a 68uH / 2.1A inductor, not a 3A one.

Last edit:
You should make a simulation to test these things out.
I think a 100uH (15mOhm series resistance) and a 220uH (35mOhm series resistance) are a good start values.
« Last Edit: April 19, 2015, 12:34:57 pm by Anand »
trashf.

#### T3sl4co1l

• Super Contributor
• Posts: 14080
• Country:
• Expert, Analog Electronics, PCB Layout, EMC
##### Re: Total current flowing through inductors in PARALLEL
« Reply #4 on: April 19, 2015, 04:01:42 pm »
Loops between low resistance components (like inductors and transformer windings) are best avoided.  In the ideal case, where DCR = 0, the current in that loop is independent of the rest of the circuit, and in a SPICE simulation, you usually get a "singular matrix" error because it doesn't have any way to solve for that unknown current.

So, you're better off using two 33uH chokes in series.

Another point of note: if the inductors are not well shielded, the value obtained may be quite a bit different from the expected value (in series or parallel), due to coupling.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!

Smf