understanding Ferrite Rings

[wopachop]

Hi everyone i have learned a ton from this forum. I have an adjustable DC-DC voltage regulator that feeds into a PWM dimmer to power LED lights. At certain dim levels im getting a buzzing sound that seems like its coming from the voltage regulator.

How can i stop that? I remembered that my RC plane uses a Ferrite ring to eliminate interference. So i borrowed one to do a quick test and installed a ferrite ring between the output of the voltage regulator and the input to the PWM dimmer. It definitely helped. But i still hear noise.

Im on DigiKey and see there are Ferrite Rings and also Ferrite Beads. Can anyone help me understand what size of Ferrite i need and also the best place to install? I dont mind using multiple Ferrite rings or beads if thats what it takes.

Here are specs to the Voltage Regulator. Im not sure if the switching frequency is important. Still very new to electronics but im having a lot of fun building and playing around.

Modules nature: non-isolated Boost Buck (SEPIC)
Rectification: Non-synchronous rectification
Input voltage: DC 3-15V
Output voltage: DC 0.5-30V
Input current: 3A (MAX)
Power: 25W (MAX)
Conversion efficiency: 95% (MAX)
Switching frequency: 150KHz
Output ripple: 40mV (max)
Load regulation: ± 0.5%
Voltage regulation: ± 2.5%
Operating Temperature: -40 ° C to +85 ° C

 

[duke37]

When you have learned about ferrite rings, you can teach me.

Ferrite rings are used to suppress voltage/current transients. They will be inportant in RC flying since the transients can be radiated and affect the radio signals.

The sound that you hear will come from some component which is vibrating, possibly a transformer. A ferrite ring will hardly affect this.

 

[wopachop]

Well the Ferrite ring i borrowed from my plane decreased the sound by roughly 75%. No clue what type of magnet is inside. I ordered 2 types of ferrite bead and 3 types of ferrite ring last night. Hoping to find a combo that works.

Unless the ferrite ring is a bad idea? How do i stop the buzzing sound that im hearing? If i use the PWM dimmer alone, i dont hear the sound. Its only when i include the voltage regulator that i hear the buzz.

 

[wopachop]

If there is a different type of filter i can use to reduce the noise im all ears. It might seem very basic to some of you guys. I really dont have a clue regarding little electrical components.

Cant wait to learn

 

[wopachop]

Still curious about stopping the buzzing noise from my voltage converter. I was talking with a guy from Germany who builds LED drivers. He was saying a Ferrite ring might reduce the efficiency to the LED device.

Is this true?

If i located the buzzing component, and covered with a thermal conduction adhesive, is that a possible solution to stop the vibration?

 

[(*steve*)]

OK, so the buzzing is mechanical, not electrical.

The goo you've used should damp the vibration, and you'll find a lot of switchmode power supplies have things glues in place).

Just be careful you don't reduce the ventilation to that component to such an extent that it overheats.

 

[wopachop]

Hi steve. I have not tried to glue anything yet. But the voltage converter came with a tiny little heat sink on top of a flat black component. When i pushed down on that, it sorta decreased the sound.

I get different frequencies of buzzing noise at different PWM levels. I dont mind using a Ferrite ring as a fix. But not if its going to reduce the voltage converter efficiency.

The Ferrite ring might be a silly idea to begin with. But it did seem to work a little.

I will experiment with RTV silicone tonight. I have some thermally conductive silicone on the way. That might be a better choice for heat dispersion.

 

[duke37]

I have looked up RTV silicone. Some of these emit acetic acid which attacks soldered joints so I would avoid them.

I use hot melt glue for fixing. It is quick and easy and can be removed if necessary.
If you want high and permanent strength, then epoxy resin would be prefered.

 

[Fish4Fun]

whopachop,

Perhaps if you provided a schematic of both the LED dimmer circuit AND the voltage regulator showing how they are connected it might shed some light on what is going on. I suspect that you have the voltage regulator feeding the dimmer circuit which can certainly cause problems. LED driver circuits use various types of current feed back to achieve constant current, one of which is "constant off time". In this scenario the PWM frequency is variable and depends entirely on the input voltage. If you reduce the input voltage to the LED driver, the PWM frequency of the driver decreases to compensate, thus negating the change of voltage in the adjustable regulator. This continues to occur until the input voltage to the LED driver drops below a certain threshold where it typically goes into "constant conduction mode", or a "fault mode". In the region between CCM or FM, the PWM frequency of the LED driver may well be in the Audio Frequency range. As the LED PWM circuit is certainly NOT designed to operate in the range, you are likely hearing "ringing". This should be an audible clue that your circuit is not functioning as designed.

If you want to dim your LED's, I would suggest you purchase an LED driver that is designed to be dimmed. These are cheap and readily available on e-bay. They simply employ a PWM input that if "absent" allows the circuit to function at the designed current; but, if present, limits the current to some portion of design current.

Fish

 

[wopachop]

Thanks everyone!! Fish im going to need to read that another 15 times to absorb it all but thanks a lot.

Just out the door but wanted to say the 12v LEDs are the flexible or rigid strips that are designed for a constant Voltage power supply. The PWM dimmer is a constant voltage dimmer. It works fine if i use an AC-DC 12v power supply. I dont hear any noise.

The problem is when i use a 12-14v battery along with the adjustable voltage regulator set to 12volts to feed into the PWM dimmer. As i adjust the dimmer i hear the noise. When i change the voltage to say 11.3v volts the noise still occurs, just at a different dimming level. I do not know if the sound is mechanical or electrical. But i did seem to reduce the sound by simply pushing down on component with the heat sink.

Not sure if you already understood all that. Just wanted to be clear im not using a Constant Current LED driver with the 12v strip lights. My goal is to take the 12-14v input and turn it into a constant 12v so that the LED strip lights dont get too hot.

Here is a pic of the voltage stabilizer. I can try to get schematics for both parts.

 

[BobK]

Switching power supplies do not like a no-load condition. By using PWM after it, you are creating periods where there is no load, and the power supply is needing to adjust quickly to that every PWM period, so it is throttling back and fortch at the PWM frequency.

I don't know if this would work, but you might try placing a small constant load on the power supply in parallel to you PWM driver.

Bob

 

[wopachop]

Wow this is all so fascinating to me. I could try that for a test Bob. We are actually in Las Vegas right now. I cant get this topic out of my head. So here i am signing onto the forum when really i should forget about it for a couple days.

My goal is to regulate an automotive battery that ranges from 12-14v. I need to turn that into a constant 12 volts to feed the PWM dimmer that controls the 12v strip lights.

 

[wopachop]

I had a couple of ideas. Sorry if my use of terms is way off. From building RC planes i learned Switching regulators are a superior technology to Linear.

1. But maybe i could find a decent Linear 12-14v input to 12v output buck/boost regulator that would not produce the noise im hearing?

2. I know you said switching regulators dont like a no-load condition, is it safe to try installing the adjustable regulator After the PWM dimmer? Would that totally kill efficiency?

3. I have some UBEC regulators for RC planes. They have a jumper to make them 6v instead of 5v. Maybe i could install two of the 6v RC regulators in series to feed into the PWM dimmer as 12v?

 

[wopachop]

Well i tried covering the adj voltage converter in hot glue. It still emits a noise. When i tough the voltage regular i can make the noise change.

Still hoping for a solution. Is there another type of noise filter i could try? Was going to use Ferrite rings until someone said it would reduce efficiency.

 

[wopachop]

Does a ferrite ring reduce efficiency when used with a voltage regulator?

 

[(*steve*)]

Can you show us a picture of your regulator that is making a noise? Preferably without the hot glue, but if you can't do that, show us what you can.

edit: Oh, OK. I see it on the bottom of page 1.

Try placing a finger on the inductors (the square black things). I'd imagine they could quite easily make a noise.

I believe that is a regulator that can step up as well as step down. I have seen figures suggesting they are actually quite inefficient (I plan some day on testing them).

The other issue is that if you have this fitted to the plastic box you've shown then you have actually created a loudspeaker. It would be best if you can ensure that vibration generated by the regulator cannot also vibrate the box.

 

[BobK]

I still think you should try my suggestion from post 11. I would like to know if it works!

Bob

 

[wopachop]

Excellent thank you!!

Yes when i push down on the little square inductors it does change/eliminate the noise.

Bob it turns out the PWM dimmer has a tiny red LED diode that is constantly on. I can try a larger load using different LED lights, im also curious if it will stop the buzz.

Thanks for all the replies and sorry if it was answered. But is using a Ferrite ring to stop the buzz sound even an option i should pursue? It did reduce the buzz sound quite significantly.

 

[(*steve*)]

The ferrite ring may stop the buzzing because it will limit the speed at which current can change.

Stopping the buzzing by touching the inductors confirms that the problem is due to the inductors (or the windings) deforming under the magnetic effects as current is switched on and off.

Bob's suggestion is meant to keep the SMPS operating in a mode that keeps these vibrations at an ultrasonic frequency. At low loads the regulator sort of switches on and off rather than running continuously. The buzzing you hear may be this modulating the ultrasonic operating frequency.

Yes, a larger load (and it's hard to quantify this) perhaps around 10% of the normal peak load?

 

[wopachop]

Think i understand. Im picturing the flow of electricity.

Is there a product that sorta "stores" energy that i could install between the Voltage Regulator and the PWM dimmer? In hopes to reduce the pulsing on and off to the voltage regulator?

I bought several different ferrite rings from DigiKey. But i never tested them. Will the Ferrite ring in fact reduce efficiency of the lighting system? Does it lose energy in the form or heat?