Filter Cap Directly from Rail to Rail, excluding Center Tap - diyAudio
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Old 22nd August 2007, 11:41 AM   #1
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Post Filter Cap Directly from Rail to Rail, excluding Center Tap

What is the disadvantage associated with implementing the Filter Capacitor directly from rail to rail , excluding Center Tap which is usually Ground.......
This thought came into my mind while preparing to design a SMPS for Class-D amp........

Apart from High Voltage Rating of Capacitor, which is the other thing to be taken into consideration
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Old 22nd August 2007, 12:23 PM   #2
Elvee is offline Elvee  Belgium
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Hi

The disadvantage is that your ground impedance will be dictated by whatever the center tap is made of: batteries in your example, which may be aceptable. If you try the same trick with a transformer + diodes, you'll get some nasty surprises: during the blocking periods of the diodes, the center tap will be left floating, and therefore pretty useless for most applications.
LV
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Old 22nd August 2007, 12:35 PM   #3
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Default Nice Disadvantage!!!!!

Quote:
Originally posted by Elvee
Hi
If you try the same trick with a transformer + diodes, you'll get some nasty surprises: during the blocking periods of the diodes, the center tap will be left floating, and therefore pretty useless for most applications.
LV

OK.........
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Old 22nd August 2007, 12:49 PM   #4
BWRX is offline BWRX  United States
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Default Re: Filter Cap Directly from Rail to Rail, excluding Center Tap

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Originally posted by Workhorse
What is the disadvantage associated with implementing the Filter Capacitor directly from rail to rail , excluding Center Tap which is usually Ground.......
Is this for a single ended or bridged output stage? High currents flow between the supply rails in a bridged design and between each rail and ground in a single ended design.
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Old 22nd August 2007, 01:56 PM   #5
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Default Re: Re: Filter Cap Directly from Rail to Rail, excluding Center Tap

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Originally posted by BWRX


Is this for a single ended or bridged output stage? High currents flow between the supply rails in a bridged design and between each rail and ground in a single ended design.
Its for the Half Bridge Class-D amp....so i think Split capacitor is mandatory!!
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Old 22nd August 2007, 02:17 PM   #6
mzzj is offline mzzj  Finland
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split cap for half-bridge and rail-to-rail for full-bridge.
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Old 25th August 2007, 06:03 AM   #7
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I never understood the benefits of a rail-to-rail cap in an audio amplifier.
The positive and negative half waves are 180 out of phase, meaning each rail is loaded alternately.

What is that cap supposed to do?
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Old 25th August 2007, 06:07 AM   #8
AJT is offline AJT  Philippines
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Default Re: Filter Cap Directly from Rail to Rail, excluding Center Tap

Quote:
Originally posted by Workhorse
What is the disadvantage associated with implementing the Filter Capacitor directly from rail to rail , excluding Center Tap which is usually Ground.......
This thought came into my mind while preparing to design a SMPS for Class-D amp........

Apart from High Voltage Rating of Capacitor, which is the other thing to be taken into consideration

i have done this on atx psu's that had half-bridge topology, whereas there were two 220ufd/200volt caps in series, i added a 470ufd/450 volt cap across and the power supply seemed to be able to deliver more evidenced by the pc's being overclocked, wheras before it could not.



haven't tried it on an amp though...
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Old 29th August 2007, 12:33 PM   #9
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Hi Guys,

I have tried it on a linear 300WRMS amp.....the rail sagging was lower than split cap topology........

Kanwar
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