Perfect DC supply?

[Outside The Box]

We take AC and transform to DC .
We add capacitors to smooth out the high points (ripple).
We add a wazoo of cap’s to further reduce the ripple (?)
My terminology is probably wrong but I think it’s called filtering?
My dumb question is: Can the ripple be eliminated? So called perfect DC.
Can the filtered DC be filtered again and again,,,, etc. to become ,,,,,,,,,,,a battery(perfect DC,( zero ripple?)).
Is straight line DC the ideal world?
To make this happen, will it be the size of a suit case before the amp circuit.
Is this a dumb question?

Thanks, Les

[931410]

Yes, you can have multiple stages of filtering for increasingly smooth DC. I doubt you ever get quite ripple free, but you can get ripple low enough it isn't really an issue. The simplest is to keep adding additional capacitance, infinite capacitance would get you zero ripple in theory. You can have more than simple cap filters by combining them with inductive coils. You can have series of cap-coil combos. You can use voltage regulation to actively filter out ripple. This without mentioning switching supplies etc.

Sounds like you need to read a good book on basic power supplies. Wish I had a current one in mind. But someone else will likely suggest one here.

[BZed]

Perfect DC. Well nothings perfect, but you can get close.

You didn't say what the output of this perfect power supply would be so its a little tough to give you an example.

What I do rather than spend a bucket load of cash on the cap of the week is to build regulated power supplies.

Lets say for example you want to build a 24VDC supply with 100ma current. For this I would go for a simple LM317 series regulator and follow the manufacturers suggestions. You could use a 24VAC output transformer @ 1 amp, a bridge rectifer and a 1000uf 50vdc cap. That would get you about 35 volts of dc with some ripple on it, maybe a volt or so. Now what the regulator does is to take that dirty 35 volts and cut off the dirty part and just pass one the clean 24VDC under the ripple. Another advantage of using a regulator is that the output impedance of the regulator is much lower than just a cap filtered supply and your amp circuit will like that a lot better. A lower impedance power supply gives the amp a much more stable source to operate from.

Regulater power supplies can be made for just about anything including high voltage, high current or both it just gets a little more complicated.

Any time I have compaired and measured an amp with first a C or CLC power supply to the same amp with a regulated supply the regulated supply always wins. The amp is more stable, lower hum, better distortion, less noise and with power amps more power.

I hope that helps.

[Outside The Box]

Yes it does,,,,,,,thanks
Lets throw one more idea in there.
How about a regulator after the filter section. Is it worth it? Does it help any?
Thanks

[metalsculptor]

The regulator usually is after the filter section except with switching regulators which usually have a filter before and after the regulator.

There is no advantage to having a filter after the regulator for hum reduction but one can supply transient demand when a slow or underpowered regulator cannot supply the transient load.

[Juhleren]

If one wants to build a regulated PS based on a linear supply for power amps which needs around 40-50VDC and around 10A peak, what are the possibilities? Any currently available boards for the DIY community and any in particular to recommend ? -I´ve seen that SKA has introduced such a board: GB150D Power Amplifier
Any other possibilities, or experiences on this subject out there?

cheers

[AndrewT]

Certainly good questions.
AC to rectified AC = pulsed DC.

Filter the pulsed DC to attenuate the High Frequency (HF) components in the supply and you get closer to DC. But it is not DC. It has some HF components remaining.

Each additional filter will attenuate the HF even more, but can never remove it in entirety.

Now apply a DC (constant) load on that filtered supply. One will find that the output current varies very slightly due to the non DC components in the filtered output. These can simply be noise and/or ripple. They will always be there.

Taking that DC load and changing it to a different DC load. What does the supply current look like? Is it a an instant step change from one DC current level to the new DC current level. No it won't be an instant step change. There will be some variation over time. These variations are HF components getting into the DC output due to load changes. These cannot be eliminated.

Both these HF aberrations (due to input variations and due to load variations) can be reduced. The trick/skill of the designer is to reduce both HF effects to levels that do not impinge on the overall performance of the load.

[AndrewT]

My post cannot be the end of the story.
Let's hear some other opinions/experiences/measurements.

[Joshua_G]

Nothing is perfect and there is no perfect DC supply. Even a battery has internal resistance, which means that its' voltage will vary with changing current load.

Ripple and HF noise can be filtered to very low values, but not eliminated completely.

The degree of filtering applied is a question of cost, size and the requirements of the circuit. That is, all else being equal (like PSRR), an RIAA pre-amp (phono-stage) will call for smoother DC than line level pre-amp.

Excellent practical DC supply can be attained by a CLC filter, followed by capacitance multiplier, followed by a shunt regulator. Better still could be different shunt regulator for each channel. This may give better DC than most batteries. Anything more than that will probably have no practical benefit.

[Outside The Box]

Thanks for the info,,,Joshua, Andrew T,90210(934110), Julheren, metalsculptor, Bzed,,,,,,,,,,,It sounds like i'm getting into the suit case department(power supply the size of a ).



The education is price-less to me,,,,,,,,,,,,,,THANKS!