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Old 22nd November 2005, 12:14 PM   #1
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Default psu capacitor problem

i'm currently building a psu which has +- 35 V rails. And i can get 50V 4700 uf Caps cheap. Would it be good to use lets say 3 of them per rails of should i buy ones with higher voltage? 63V or 80V? Which option would give me the best solution?


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Old 22nd November 2005, 12:26 PM   #2
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Well 35 volts is well within the 50 volt cap rating even allowing for mains fluctuations. As for how much capacitance you want, that depends on the load.
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Old 22nd November 2005, 05:05 PM   #3
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Default 4700uF Caps

4700uf Caps rated at 50V should do just fine. Using several smaller caps (like 4700uF) may be better than using one BIG cap as the ESR spread out over several caps will be lower.
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Old 22nd November 2005, 08:03 PM   #4
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Thanks for the fast reply. I just bought myself 40 x 50V 4700uf caps and i will use all of them in my 6-channel PSU
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Old 25th November 2005, 12:53 PM   #5
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Hi,
save the extra four caps for the bass channel (5.1) giving 24mF per rail and allowing about 8A peak current from the amp.
Into a 6ohm minimum impedance this equates to 48Vpk. Way higher than your proposed rail voltage. A 6ohm speaker with a minimum impedance of 4ohm would go to 32Vpk, that would be about your limit before the bass starts to suffer due to drooping gain.
If you plan to use 8ohms speakers exclusively, you may want to consider raising the bass channel PSU to +-45V (unloaded voltage), just far enough below 50V to allow for mains supply overvoltage.
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Old 25th November 2005, 02:13 PM   #6
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Does anybody have some idea's how i could improve a PSU any further. For now it will just bij ---- Toroid -- bridge-caps per channel.

Maybe some snubbers? Regulation? any ideas/proposals would be of help!

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Old 25th November 2005, 02:32 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
caps from rail to rail on Mains input, AC output and DC output.
Snubbers across the diodes and again at the PSU output.
Lots of hi frequency decoupling at all major loads. Some lower frequency decoupling at PSU and on board.
Keep the PSU ground and transformer centre tap separate from the star ground until you make that final wired connection.
Make your mains earth (safety ground) a permanent fixing to the metal chassis. Do not put any other ground under this same fixing nut. Put any extra ground connections under a second nut to ensure you never accidently remove your safety ground.
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Old 25th November 2005, 07:00 PM   #8
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Quote:
Originally posted by fixation
Does anybody have some idea's how i could improve a PSU any further. For now it will just bij ---- Toroid -- bridge-caps per channel.
Try a CRC supply, with R being about 0.2 to 0.3 ohms. That'll reduce your ripple by quite a bit and make the higher frequency components more benign as well.


Francois.
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Old 29th November 2005, 09:22 PM   #9
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Hi everybody

After reading through the entire topic i decided to make start building this psu. The only difference is that i have a total of 15000uf instead of 10000 uf. that won't matter will it??

I've made a universal pcb design for both Per-anders psu and CarlosFMs psu. The only difference is the 100nf cap right?

I hope you will have a look at my design and tell me what's right & wrong so i can optimize it.

The Board size is 160X110 mm and will be used with a 25-0-25 Transformer of 300 VA. It's for powering a ESP P3A( Stereo ). Will this be a good PSU for it?

all the trace are 150 mil. is this big enough?

Why all the 1000 uF caps?? simple i've got around 250 of them. And it also lowers ESR.
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Old 30th November 2005, 08:50 AM   #10
AndrewT is offline AndrewT  Scotland
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Hi,
yes i agree, many parallel caps reduce the ESR provided the long track lengths do not increase the inductance significantly. You also improve the ripple capacity very significantly which will keep the caps cooler and increase their lifetime.
I would add some large plastic film caps to the output (2u2F // 100nF) as well as smaller ceramic (47nF // 1nF // 47pF).
Then add a snubber location just in case you need it.

To gild the lily put a space between the first three caps and the last 12 for a series resistor (1r // ten times =0r1) You can then put in a shorting link or run it as CRC. Check the ripple capacity of the first three caps, they will be working very hard when in CRC mode.
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