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Re: Capacitor Question

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Fabian Russell <root@localhost.localdomain> wrote:
> On Wed, 04 Nov 2015 06:03:40 +0000, jimp wrote:
> 
>> 
>> Where's the inductor?
>> 
> 
> With a voltage regulator you don't really need an inductor
> because the regulator greatly reduces the ripple.
> 
> Besides smoothing the ripple, a large cap also insures
> that any current surges drawn by the circuit can be
> easily handled.
> 
> So you have AC --> transformer --> rectifier --> cap filter
> --> regulator --> circuit.
> 
> Some DC circuits don't require any filter or regulator at all.
> They can be fed the output from the rectifier directly.
> 
> The needs have to be determined beforehand and a suitable
> power source implemented.
> 
> My power supplies are general purpose and so I tend to over
> design them to be able to meet any needs.
> 
> Variable regulators can output a wide voltage range, but I never
> use them.  The problem is that once the voltage difference
> between the transformer output and the regulator output becomes
> too large then way too much heat is produced within the regulator.
> I always used a fixed regulator with a 5 Volt difference (recommended
> by the specs).
> 
> So I have to have lots of power supplies to meet varying voltage requirements.

It seems you are a staunch believer in the BAC (Big Ass Capacitor) method
of filter design.

This is OK for most applications as it eliminates two components and
having to put any thought into the design.

However, if your power supply is greater than 5 V where your choices
for BAC's is more limited and much more expensive, it starts to become
smarter to do a little analysis if ripple is indeed important to you.

If you do the analysis, you will find that a pi filter will provide
the same ripple rejection as your single 4700 uf capacitor with capacitor
values far less than 4700 uf. Depending on the system requirements,
it is not unusual to find the cost of two smaller capacitors and an
inductor to be quite a bit less than that of one BAC.

Also, your statement that "a large cap also insures that any current
surges drawn by the circuit can be easily handled" tells me you have
never actually done such an analysis and are just depending on the BAC
to take care of everything, which in many cases it won't.
 
In reality the surge current to the supplied device is limited by
the wiring inductance from the BAC to the regulator, the regulator,
and the wiring from the regulator to the supplied device.

That is why you put a capacitor on the output of the regulator and
a local capacitor at the supplied device.


-- 
Jim Pennino

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Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-03 22:14 +0000
  Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-03 16:35 -0600
    Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-03 22:59 +0000
      Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-03 18:10 -0600
  Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-03 22:47 +0000
    Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-03 23:07 +0000
      Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-03 23:20 +0000
        Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-03 23:42 +0000
        Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-04 02:49 +0000
          Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-03 21:40 -0600
            Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-04 04:01 +0000
              Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-04 06:03 +0000
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-04 07:07 +0000
                Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-04 20:29 +0000
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-04 20:51 +0000
                Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-04 21:08 +0000
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-04 21:53 +0000
                Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-04 22:20 +0000
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-04 22:42 +0000
                Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-04 23:07 +0000
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-05 00:28 +0000
                Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-05 00:46 +0000
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-05 00:39 +0000
                Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-05 00:58 +0000
                Re: Capacitor Question benj <none@gmail.com> - 2015-11-04 18:25 -0500
                Re: Capacitor Question benj <none@gmail.com> - 2015-11-04 18:37 -0500
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-05 00:09 +0000
                Re: Capacitor Question benj <nobody@gmail.com> - 2015-11-04 21:35 -0500
                Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-04 21:51 -0600
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-05 04:19 +0000
                Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-05 11:10 -0600
                Re: Capacitor Question "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-05 09:15 -0800
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-05 18:08 +0000
                Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-05 19:26 +0000
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-05 19:44 +0000
                Re: Capacitor Question jimp@specsol.spam.sux.com - 2015-11-05 19:56 +0000
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-05 20:53 +0000
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-05 21:52 +0000
                Re: Capacitor Question benj <none@gmail.com> - 2015-11-04 18:41 -0500
                Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-04 21:54 -0600
          Re: Capacitor Question benj <nobody@gmail.com> - 2015-11-04 02:17 -0500
            Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-04 07:30 +0000
              Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-04 07:48 -0600
              Re: Capacitor Question benj <nobody@gmail.com> - 2015-11-04 14:04 -0500
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-04 19:28 +0000
                Re: Capacitor Question benj <none@gmail.com> - 2015-11-04 18:49 -0500
                Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-04 20:41 -0600
                Re: Capacitor Question Fabian Russell <root@localhost.localdomain> - 2015-11-05 03:16 +0000
                Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-04 21:58 -0600
          Re: Capacitor Question "reber g=emc^2" <herbertglazier0@gmail.com> - 2015-11-04 12:14 -0800
            Re: Capacitor Question benj <none@gmail.com> - 2015-11-04 18:44 -0500
              Re: Capacitor Question gilber34 <fafa@invalid.com> - 2015-11-04 20:41 -0600
  Re: Capacitor Question gyansorova@gmail.com - 2015-11-05 16:34 -0800

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