Help creating a super low noise DC to DC regulator or filter for FPV

Thread Starter

bigjoncoop

Joined Feb 1, 2019
129
I've been having nothing but trouble with noise in my fpv feed on my freestyle quadcopters. I've tried creating large LC filters, low ESR capacitors every ESC, battery terminals, on the camera and video transmitters and still have problem with noise getting into my fpv feed.

Now I'm thinking I should build a dc-to-dc linear regulator with filtering on the input and on the output and see if that will solve my problem.

I'm looking some ideas how this circuit should be built. My fpv equipment can accept battery voltage so I don't have to lower it to 12 volts. Was just thinking doing so with an lm7812 would regulate the voltage to take away a lot of the noise.

Thinking of using a LM7812 circuit for the regulation and a LC filter on the output and input with a 1000uf low ESR capacitor on the end out the output filter....

Or is there a simpler way of doing this?
I need to go from 16.8 volts down to 12v or so what the max current draw 350ma.

I have Regulators, diodes, capacitors, resistors, inductors, transistors, mosfets , etc... I see a lot of circuits using LM3xx components I only have Lm358 if need be.

I just need to figure out a way to get a super clean 12-volt lowest noise possible. My camera and video transmitter can accept battery voltage.

ive included a couple example circuits. I am open to any recommendations. I just almost Fed Up with getting noise in my fpv feed no matter what I try. Keep in mind this will be powered from a 4S LiPo battery. I quadcopter can pull an excess of 120 amps for a brief moments. So there is a lot of noise going to be introduced.

Schematic_LOW-NOISE-FPV_Sheet-1_20190804125953.png
 
Last edited:

Alec_t

Joined Sep 17, 2013
11,649
Do you have a star ground system, so that no motor current shares any length of ground wire with your fpv kit?
Is all high-current wiring as physically short as possible?
 

crutschow

Joined Mar 14, 2008
25,432
I have used a common-mode choke to successfully limit noise transfer from a cryogenic cooling motor, which drew spikes of current, to some processing electronics.
The choke has to be connected in series with the motor power supply and ground lines, with healthy decoupling capacitors on the motor side of the choke..
 

Thread Starter

bigjoncoop

Joined Feb 1, 2019
129
Do you have a star ground system, so that no motor current shares any length of ground wire with your fpv kit?
Is all high-current wiring as physically short as possible?
Yea.. normally all the motors are powered from the Aio flight controller that has a built in pdb. and it has seperate pads to power the camera and video trans. everything used to be fine until recently, then I started getting a lot of noise in my fpv feed. so now since I installed a LC filter I am taking voltage from a VCC pad on my flight controller and it's going through the LC filter and then from the LC filter it's supplying voltage to the camera and the video transmitter.

and all the wires , especially the wires feeding the Motors are as short as possible.


I think I'm going to basically builds a PCB from my second example in the photo. going to get voltage directly from the battery pads into an LC filter, then into a LM7812 then into another LC filter before going to the camera and video transmitter. unless someone knows of a simpler solution with just some type of circuit I can make of a really good filter to get rid of this noise. weight is not really an issue for me on this quad-copter since it is so obnoxious already. my biggest concern is space. I literally have no extra room besides where I currently have my LC filter placed and just to get that in there I had to grease it up and pry it in... Lol. I don't think I'll have a problem running between 250ma to 350ma through the LM7812 without a heat sink. I just don't know what else to do.... i just added another 1000uf low esr cap to battery terminal
 

BobaMosfet

Joined Jul 1, 2009
1,208
There are lots of ways to get clean 12V. First, you need to identify exactly what is causing the noise. Once you know what's causing the noise, determine if it's inductive, capacitive, or both. Then either shield, filter, or isolate, including ensuring you aren't capacitively or inductively coupling that noise into your circuit that needs to be clean. Figure that out, then 12v is easy.
 

crutschow

Joined Mar 14, 2008
25,432
unless someone knows of a simpler solution with just some type of circuit
I think you should seriously consider adding a common-mode choke going to the motors as I mentioned.
That will help minimize high frequency ground currents and noise, which can be otherwise difficult to suppress.
 
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