Single supply arrangements

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carlmart
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Re: Single supply arrangements

Post by carlmart » Tue Aug 05, 2014 4:50 pm

OK, What do you exactly mean by HF capacitors?

I will be using separate buffered Vcc/2 supplies for every channel, and also a separate Vcc/2 to feed the headphone amps, because of current demands.

Every Vcc/2 feed will use 100K resistors and a filter capacitor from the center of the split. I have seen from 22n to 10uF to filter that to ground.

And there are very strong reasons for me use a single supply, it's not a whim or anything.

That doesn't mean that in the future we may not opt for a DC-DC supply, but not for now.

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JR.
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Re: Single supply arrangements

Post by JR. » Wed Aug 06, 2014 10:14 am

carlmart wrote:OK, What do you exactly mean by HF capacitors?
Capacitors that still act like capacitors at high frequency. Caps like ceramic disc with good HF characteristic. GP larger electrolytic caps generally have a rising impedance characteristic at very high frequency.
I will be using separate buffered Vcc/2 supplies for every channel, and also a separate Vcc/2 to feed the headphone amps, because of current demands.

Every Vcc/2 feed will use 100K resistors and a filter capacitor from the center of the split. I have seen from 22n to 10uF to filter that to ground.
I would suggest using both a decent sized electrolytic cap in parallel with a modest sized ceramic or similar dielectric.

You want V/2 to be a low impedance for LF and HF, just like a ground connection.
And there are very strong reasons for me use a single supply, it's not a whim or anything.

That doesn't mean that in the future we may not opt for a DC-DC supply, but not for now.
You do not need to convince me... It's your design do whatever floats your boat.

JR
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mediatechnology
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Re: Single supply arrangements

Post by mediatechnology » Wed Aug 06, 2014 12:30 pm

Maybe that's the fishy thing you talk about.
No, it's not.
What's fishy to me (the first, most obvious thing) is that there is no DC bias current path for the non-inverting input in the second TI figure of your first post.
I don't think you're completely reading our replies to your questions.
The error was clearly stated here: viewtopic.php?f=6&t=657&start=1

John has said the same thing:
edit there is no one right way to do this, while the TI example is incomplete and will not work without a dc path for + input. /edit
Now back to the rail splitter itself...Again.

If you do provide a capacitor for RF bypass at the output of the buffered VCC/2 rail splitter the capacitor will need to have some series resistance (about 47 Ohms depending on the op amp used and the value of the C) to isolate the capacitive load from the op amp output.
Otherwise it will oscillate.

We've already answered most of your rail splitter questions.

For the second time (or is it the third?) have a look at this circuit: viewtopic.php?f=6&t=191
Look at how pin 3 of the THAT1646 is handled and how the rail splitter made from the MC33178.
The 47 Ohm isolation resistor keeps the MC33178 from oscillating due to the 1 nF load at the 1646 "ground" (V/2) pin.

Or look here for the same thing: viewtopic.php?f=6&t=261&p=5775

The circuits above provide examples of buffered rail splitters.

We also discussed the rail splitter way back here on May 20th: viewtopic.php?f=6&t=642&start=6

You are over-complicating and over-thinking this...
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