Author Topic: VFE power supply filtering  (Read 223 times)

helos

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VFE power supply filtering
« on: August 08, 2017, 09:33:22 AM »
Hello guys, can someone explain me what are the differences (and advantages) of using the inductor (1mH) in the power supply filtering section, rather than a normal resistor?

Thanks

somnif

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Re: VFE power supply filtering
« Reply #1 on: August 08, 2017, 10:07:52 AM »
I'm guessing it was a size consideration. You can make a low pass filter with the inductor alone, as opposed to needing a resistor and a capacitor. 1 component vs 2, and since all its doing is smoothing the power flow, don't need to worry about frequency response as much.

(I could be wrong, I've only got a surface level understanding of most of this voodoo)

madbean

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Re: VFE power supply filtering
« Reply #2 on: August 08, 2017, 10:40:30 AM »
Two reasons -
Inductors are more efficient than resistors - they don't dissipate heat like resistors.
Inductors give you a two-pole filter instead of the one-pole filter you get with resistors.

To find out more look up LC vs RC filtering

I own madbeanpedals (duh). I am part owner of Function F(X).

helos

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Re: VFE power supply filtering
« Reply #3 on: August 09, 2017, 02:25:28 AM »
Two reasons -
Inductors are more efficient than resistors - they don't dissipate heat like resistors.
Inductors give you a two-pole filter instead of the one-pole filter you get with resistors.

To find out more look up LC vs RC filtering

Thank you very much!!  ;) ;)

helos

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Re: VFE power supply filtering
« Reply #4 on: August 09, 2017, 03:06:37 AM »
Two reasons -
Inductors are more efficient than resistors - they don't dissipate heat like resistors.
Inductors give you a two-pole filter instead of the one-pole filter you get with resistors.

To find out more look up LC vs RC filtering

Last question... does a second order low pass filter like this minimize ripple on the DC power more than a simple first order low pass would do?

Or maybe I should ask: "does a low pass filter affect the stability of the DC power minimizing the ripples? Or it just cut off the (noisy) high freq. content of the DC?"  ???

madbean

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Re: VFE power supply filtering
« Reply #5 on: August 09, 2017, 04:57:17 AM »
Last question... does a second order low pass filter like this minimize ripple on the DC power more than a simple first order low pass would do?

Or maybe I should ask: "does a low pass filter affect the stability of the DC power minimizing the ripples? Or it just cut off the (noisy) high freq. content of the DC?"  ???

Actually, I don't know. My gut says no. I'd have to look that up (or maybe we both should!)
I own madbeanpedals (duh). I am part owner of Function F(X).

helos

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Re: VFE power supply filtering
« Reply #6 on: August 09, 2017, 06:02:52 AM »

Sure, I'm searching in my engineering books  ;)

helos

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Re: VFE power supply filtering
« Reply #7 on: August 09, 2017, 11:00:28 AM »

[/quote]
Actually, I don't know. My gut says no. I'd have to look that up (or maybe we both should!)
[/quote]

I've done some simulations and I had these results:

1) LC network filtering: if you have a very little spike in the supply voltage (like 0,01volts) you can see the output voltage swinging and after a while it return steady.

2) RC network filtering: if you have a spike of the same amount (0,01volts) the output voltage is just a little perturbed but it stays pretty much close to the nominal value of 9v.

I should say that, regarding the ripple reduction, the LC is not an improvement compared to an RC... what do you think?