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Inquiry on LC filter/regulator design for automotive

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spyghost

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automotive lc filter

Hi,

I am planning on building a filter/regulator in preparation for my project car. I am still in its first stage, which is constructing a filter/regulator, or voltage stabilizer for my car's electronics.

There are already a lot who have added a set of parallel capacitors between the alternator/battery to ground terminals and according to them, the effect is good.

As much as possible I wouldn't like the additional complexity of a buck-boost converter for this application, but if it is required, then I'll be putting it into place.

Here is the design... I plan on modifying the simple capacitor design by adding a series inductor. However, I have two designs in mind.

The first design involves a loop in the (+) and GND side using a single core that will be paralled into a capacitor.

The second design involves a simple inductor placed on the (+) side, which is then series to a capacitor. The rest of the car circuit is paralled with the capacitor.

I would like to get your opinions in the effectivity of this design and its possible effects. Are there other factors that I should have considered?

I also came across this page: at #12
Using an LC circuit as a power supply filter can actually multiply the power supply noise at the filter's resonant frequency. Use inductor with low Q to overcome this.

If this is the case, does that mean that the inductor would only yield to nothing?
 

Johansen

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car electronics filter regulator

The two inductor circuit shown in your post is known as a common mode choke, but it will not help if the circuit your are trying to protect forms a ground loop. (the negative output is bonded to the alternator chassis)

the lc filter has a resonant frequency, and this will pass that frequency quite well, this can be avoided by using multiple stages...

A power supply filter, mH and mF, followed by uH and uF followed by some lossy ferrite beads before powering sensitive circuitry.
 

trapoe

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The first circuit, with two windings on the same core, could be "common mode" or "differential mode" inductor, depending on the windings.
Be careful: if you connect the negative of your load to the metallic part of car you short circuit half of the winding and the circuit became like the second one, less effective than the first one.

If you don't use low loss (high Q) inductors for filtering you has a peak in frequency response at resonant frequency and there your filter can have an high gain and increase the supply noise. Usually inductor for filtering applications has lossy cores to damp oscillation and avoid peak in frequency response at resonant frequency.
 

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