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Noise filter for voltage regulator in PWM microcontroller circuit

Noise filter for voltage regulator in PWM microcontroller circuit

Noise filter for voltage regulator in PWM microcontroller circuit

(OP)
Schematic is located at:
http://files.engineering.com/getfile.aspx?folder=a34240a9-faba-4b64-8091-d70227087f74&file=Schematic.pdf

My electronics skills break down quickly when it comes to noise filtering.

I need to figure out what to put in the blue lined area for noise filtering.  The 12V supply will be directly from a 12V battery.  The motor being driven draws up to about 6 amps max and will be PWM driven.

I don't yet know what frequency to run the PWM at.  I will be determining that in the next few weeks.  I have a friend who developed a spreadsheet for this.  He will be visiting soon and helping me with it.  If he is willing, I will share that spreadsheet and instructions.

I also don't know how to calculate the values of a coil and probably filter capacitor to go to the regulator input voltage to filter out all the noise I will be making on the power lines by switching the motor on and off.

Can you help me with these items?  What kind of filter should I put in. How do I calculate the values based on PWM frequency?

If I am approaching this incorrectly, please let me know.  I can also upload pcb layout if that will help.  My education is an AAS in Electronics.  Total of 3 years of electronics training.  I appreciate your patience because I have many holes in my engineering skills.

Thank you,

Tim Chapman
 

RE: Noise filter for voltage regulator in PWM microcontroller circuit

You realize we can't help on school projects here...?

Quote:

Promoting, selling, recruiting and student posting are not allowed in the forums.

Keith Cress
kcress - http://www.flaminsystems.com

RE: Noise filter for voltage regulator in PWM microcontroller circuit

(OP)
It is not a school project.  I am a college graduate.  It for an ROV (underwater robot).

RE: Noise filter for voltage regulator in PWM microcontroller circuit

OK.  For filters for this kind of thing, you generally just use some RC filtering and perhaps some RF choke beads.  You also put some very short, leaded, small value caps across the motor contacts to shunt any brush arcing noise.

The RC filtering goes between the battery and the subsequent voltage regulation for the micro's power supply.

For added robustness you can put a transorb set at ~17V or so to trim off any spikes heading for the regulator.

There are no fixed values for this stuff.

I'd probably use a 100uF and a resistor that would shed a few volts at the cpu's power draw. Use something like 1000pF across the motors.  Find any RFC bead that works for you and can handle the current needed for the micro supply, thru-hole, surface mount, or whatever floats your boat, er, ROV.

Keith Cress
kcress - http://www.flaminsystems.com

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