Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

[SOLVED] can flux from switching inductors cause interference

Status
Not open for further replies.
Z

Zak28

Advanced Member level 2
Joined
Aug 19, 2016
Messages
579
Helped
6
Reputation
12
Reaction score
6
Trophy points
18
Activity points
4,681
Can placement of boost converter feedback resistors and precision zener voltage referenes next to 2-3amp RMS switching ferrite power inductors cause interference were resistors and voltage reference would no longer function properly?

Are any transistor types placed right next to these inductors vicinity likely to incur misfunction?
 

Component "failure" is a pretty remote possibility but circuit
misbehavior is commonplace.

You can get charge pumping across any junction if there is
AC activity on the pins. This is a known design challenge in
RFICs and those are largely small signal.

EMI has two faces - aggressor and victim. The power inductor
can radiate substantial magnetic field (especially if an open
bobbin or non-closed-magnetic-path chip type). But like a
tree falling in the forest, it needs somebody listening to call
it "a sound". Otherwise it's just acoustical energy that soon
dissipates.

Placement of components and optimizing interconnect is a
big piece of the art of power electronics physical design.

There are probably clues in your definition of "properly"
that want followed up.
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
dick_freebird said:
Component "failure" is a pretty remote possibility but circuit
misbehavior is commonplace.

You can get charge pumping across any junction if there is
AC activity on the pins. This is a known design challenge in
RFICs and those are largely small signal.

EMI has two faces - aggressor and victim. The power inductor
can radiate substantial magnetic field (especially if an open
bobbin or non-closed-magnetic-path chip type). But like a
tree falling in the forest, it needs somebody listening to call
it "a sound". Otherwise it's just acoustical energy that soon
dissipates.

Placement of components and optimizing interconnect is a
big piece of the art of power electronics physical design.

There are probably clues in your definition of "properly"
that want followed up.
Click to expand...

By properly I meant far away from inductor for these varieties. What happens with 3296W trimpots right next to these inductors?

img.jpg
 
Last edited:

Circular sweep trimpots include a "free 3/4 turn inductor
in every box".

You could check the hypothesis easily enough by soldering
in a tight pair of chip resistors of appropriate (to the trim-
point) values in its place and observe the differences.
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
But isn't the inductor in the image less likely to emanate enough flux to mutually couple with the pot? Its entirely encapsulated in ferrite and its coil is likely not orientated in the same plane for mutual inductance to take place with the pot.
 

But isn't the inductor in the image less likely to emanate enough flux to mutually couple with the pot? Its entirely encapsulated in ferrite and its coil is likely not orientated in the same plane for mutual inductance to take place with the pot.
Click to expand...
Yes, I wonder why you started this thread at all?

Magnetic coupling may take place to circuits below the inductor. Furthermore the post #1 question about "resistors and voltage reference would no longer function properly" is missing the point. Surely the components won't stop functioning. If at all, you get interfering voltage induced in circuit branches. It doesn't depend on component placement but on the conductor geometry. There are very few components that may act on magnetic fields, e.g. hall sensors.
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
FvM said:
Yes, I wonder why you started this thread at all?

Magnetic coupling may take place to circuits below the inductor. Furthermore the post #1 question about "resistors and voltage reference would no longer function properly" is missing the point. Surely the components won't stop functioning. If at all, you get interfering voltage induced in circuit branches. It doesn't depend on component placement but on the conductor geometry. There are very few components that may act on magnetic fields, e.g. hall sensors.
Click to expand...

Is there a rule of thumb for voltage noise amplitude? This being for traces under the inductor along with components right beside it.
 
Last edited:

My rule of thumb is that I won't usually expect serious interferences of shielded inductors. But they have a circular air gap on the bottom and traces tangential to it can catch a certain voltage level, lets say 10 to 100 mV range. Conductor loops of the switching circuit carrying high current will also cause interferences, even more switched currents injected in the circuit ground.

Thus the general rule of thumb is to keep switching power supply circuits compact and geometrically and electrical separated from sensitive circuits like signal processing functions expected to provide mV resolution.
 

any tracks carrying current with di/dt by your pots or other tracks - can cause interference - yes...
 

Hi,

my rule fo thumb:
Careful parts placement when doing the next PCB layout.
Separate "dirty" areas from sensitive circuit.

Klaus
 
  • Like
Reactions: Zak28

    Z

    Zak28

    Points: 2
    Helpful Answer Positive Rating
Is it bad to have ground planes under these sorts of switching inductors?
 

Zak28 said:
Is it bad to have ground planes under these sorts of switching inductors?
Click to expand...

Actually it is good. The closer the ground plane to the inductor, the less interference it will produce due to more compact magnetic field lines.
 

We did not like ground planes under the SW node because
it couples all that trash right into the ground, messes up
current sense and other ground (which ground?) referred
signals etc. The SW edges should be stood off by the
inductor, not have any of their HF energy shunted to places
where it's unhelpful and probably a nuisance.
 

Hi,

A GND plane should act as stable voltage reference. To be clean it needs to be low impedance but also one should keep currents (especially those high frequency ones) low.
An inductor usually is involved in a switching node... and it needs wide traces and a big soldering pad.
This means it creates a big capacitance when this node is located next to the GND plane.
I agree that keeping out the GND plane below the switching nodes will be an improvement.
...as long as it does not the cut the GND plane into high impedance pieces...


Klaus
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top