Hi Guys,
I am building a very simple practice amplifier with the infamous lm386 and I want to use it with a cheap ac adapter (SMPS) and a DC-DC regulator (12V). I have read somewhere that an inductor and a capacitor can help to reduce noise from the power supply. The problem is that it is not easy to find electronic parts where I live. So I wonder if I can made the inductor by myself using just cooper wire (like the one in the picture). Crazy idea? I case that it is possible, can you point me to somewhere I can learn how to calculate the coil diameter, number of loops, etc...?
I am building a very simple practice amplifier with the infamous lm386 and I want to use it with a cheap ac adapter (SMPS) and a DC-DC regulator (12V). I have read somewhere that an inductor and a capacitor can help to reduce noise from the power supply. The problem is that it is not easy to find electronic parts where I live. So I wonder if I can made the inductor by myself using just cooper wire (like the one in the picture). Crazy idea? I case that it is possible, can you point me to somewhere I can learn how to calculate the coil diameter, number of loops, etc...?
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Thanks for the link #RJM1.
Can someone share some info about this noise suppression technique?
Thanks.
Can someone share some info about this noise suppression technique?
Thanks.
the output from a DC supply should be a constant unchanging DC voltage.
but it isn't.
The DC contains AC artefacts. Some are lowish frequency, the switching frequency of the DC to DC convertor.
There are also many high frequency and very high frequency artefacts.
A filter will be fitted after the convertor. But this only attenuates the AC (noise). The effectiveness of this built in filter will depend on the current drawn from the supply.
Most DC to DC convertors will use one stage of LC filter to allow the voltage control feedback to work without instability.
Very few designers are capable of using feedback after multiple stages of LCLC filtering. One of our Forum Members is among the elite Designers that can use multi-pole filtering and still get a stable output.
As long as you fit the extra LC stage after the feedback, then you don't affect the designed stability margins.
Extra filtering provides extra attenuation of the noise. It never eliminates it.
but it isn't.
The DC contains AC artefacts. Some are lowish frequency, the switching frequency of the DC to DC convertor.
There are also many high frequency and very high frequency artefacts.
A filter will be fitted after the convertor. But this only attenuates the AC (noise). The effectiveness of this built in filter will depend on the current drawn from the supply.
Most DC to DC convertors will use one stage of LC filter to allow the voltage control feedback to work without instability.
Very few designers are capable of using feedback after multiple stages of LCLC filtering. One of our Forum Members is among the elite Designers that can use multi-pole filtering and still get a stable output.
As long as you fit the extra LC stage after the feedback, then you don't affect the designed stability margins.
Extra filtering provides extra attenuation of the noise. It never eliminates it.
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Look in most any of the lm3886 threads ?
Doing the wee coil with resistor in the middle is pretty well standard.
No need to reinvent the wheel.
Doing the wee coil with resistor in the middle is pretty well standard.
No need to reinvent the wheel.
Hi Bare, thanks for your comment. Can you point me to the forum with the "wee coil with resistor in the middle", I googled it but nothing appears 🙁
Thanks
Air cored inductors aren't going to give you much inductance (typically from a fraction of a microhenry up to maybe a millihenry for a large multilayer one). To filer noise from a switching supply you'd be better off with a ferrite-cored inductor as the addition of the core allows you to use fewer turns to achieve greater inductance. Fewer turns means lower parasitic capacitance which is one of the enemies of noise rejection in LC filters (the other being capacitor ESR).
Thank you Abraxalito, It could be hard to find a ferrite toroid here where I live, Can I use just a ring of iron for the same purpose?
I'd not recommend ferrite toroids as normally they're not gapped. Some are but they're bound to be very hard to find and not very flexible. Can you find RM cores where you are? They'd be my first choice.
A ring of iron sounds a bit hit-and-miss to build an inductor out of. Did you mean like a toroidal transformer's core?
A ring of iron sounds a bit hit-and-miss to build an inductor out of. Did you mean like a toroidal transformer's core?
I mean using a small iron toroid/ring for the core and build something similar to this: https://oscarliang.com/lc-filter-fpv/
What is a "RM Core"?, I am very ignorant on this specific topic.
You can get an idea about RM cores here - RM Series Ferrite Cores
Your link I think shows powdered iron (the black ones) and ferrite (green) cores. Which of course will work but maybe not the optimum solution for HF noise filtering. The green cores give rather too high an inductance and may well saturate, the black ones (which I'm assuming are Sendust) give too low an inductance. The writer of that article doesn't appear much interested in designing the filter.
Your link I think shows powdered iron (the black ones) and ferrite (green) cores. Which of course will work but maybe not the optimum solution for HF noise filtering. The green cores give rather too high an inductance and may well saturate, the black ones (which I'm assuming are Sendust) give too low an inductance. The writer of that article doesn't appear much interested in designing the filter.
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