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Old 14th January 2003, 09:00 AM   #1
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Default SS PSU without choke

I need some help to design a PSU for my future amp. I need 400V. At first everything seemed so easy. 400V / 1,41 = 283... so i figured 285V from the tranny would do the trick. But then i got the Duncan PSU-designer, and my whole (simple) world was FUBAR.

I've managed to design a very simple psu wich gives me 400,5V with 5-10mV ripple. Everything is just fine, until i change the sec. resistance of the transformer. The voltage goes berserk. Since my mains-xfmr hasn't been made yet i have NO idea what the winding-resistance will be, so how am i supposed to make a working design in theory with any kind of software or even pen and paper???

I just wan't a simple psu-design with a solid-state bridge-rectifier and a few caps and resistors. No chokes. I haven't built that much before but in my previous projects i have used pretty big lytic caps (80 000uF or so) but from what i've learned here, big caps aren't allways prefered.

When i searched this forum, all I came up with was choked psus. Does averyone build WITH chokes??
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Old 14th January 2003, 10:17 AM   #2
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Default SS PSU

Mikael,

What kind or resistance range have you been using in the program?

Jan Didden
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Old 14th January 2003, 10:31 AM   #3
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Default Re: SS PSU without choke

Quote:
Originally posted by Mikael Abdellah
I've managed to design a very simple psu wich gives me 400,5V with 5-10mV ripple. Everything is just fine, until i change the sec. resistance of the transformer. The voltage goes berserk. Since my mains-xfmr hasn't been made yet i have NO idea what the winding-resistance will be, so how am i supposed to make a working design in theory with any kind of software or even pen and paper???
Hi Mikael,
When you go into PSUD2, and edit the power trans' specification, there is a small box there marked [....]. Click on that and it will allow you to adjust in more detail. Set the voltage to about where you want it, then the current you need and the regulation. I normally use 10% for EI core transformers and 5% for torroids. It'll then calculate the secondary resistance for you.

The peak voltage = 1.414 x the RMS only ever applies in theory, with no load on the circuit, and *ideal* components, but transformers and wiring have resistances, diodes have voltage drops etc. About 1.2-1.3 is closer in reality.

I assume you're having your power trans made. When you ring for a quote, tell them the figure for regulation and max secondary resistance as well as the voltage and current of the secondaries. If you're buying a trans from a catalogue pre-made, email them for the regulation if in doubt, but the numbers I use are pretty close. Besides, there is no need for it to be exact. A couple of volts here and there isn't critical <i>provided</i> the voltage is stable and clean. My last design came out at 440V when I measured it instead or 450V, a 2% error. Who cares, when my mains voltage from the wall varies more than that?

If you give us the current requirements of your amp, and maybe a description of what it is, I'm sure someone will help you design something for your specific circuit.

Quote:
I just wan't a simple psu-design with a solid-state bridge-rectifier and a few caps and resistors. No chokes. I haven't built that much before but in my previous projects i have used pretty big lytic caps (80 000uF or so) but from what i've learned here, big caps aren't allways prefered.
Why no chokes? They make it a heck of a lot easier to get a clean supply, especially if you're not using some form of regulation.
{I can't wait to see who jumps on that one.}

All an amplifier does is modulate the power supply. If your PSU is no good, you stand little chance of having a good amplifier. Or put another way, the better your PSU, the better your amplifier can be.

Tube amps generally use smaller caps, esp in conjunction with chokes. The amount of energy stored in a cap is 1/2 x C x V^2

Quote:
When i searched this forum, all I came up with was choked psus. Does averyone build WITH chokes??
I do, always. I prefer LC if I'm using a shunt reg, and LCLC when I'm not, and LCLC->shuntreg for phono and mic preamp stages.
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Old 14th January 2003, 11:27 AM   #4
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first of all.. thank you for you replies...

the amp for the psu is a SE KT88-amp which I have designed from svetlana's specs for the 6n1p and a couple of SE 6550-amps i've found on the net.

http://213.67.45.70/se_kt88.gif

The reason i don't wan't a choke is that i can't afford it and i have'nt got enough room. The amp is allready beginning to be quite big.. physically... At least in my computer-model of it

I will have all trannys made by sowter, but i have allready asked brian 100000 stupid questions, so i don't wan't to bother him anymore.
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Old 14th January 2003, 11:57 AM   #5
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WOW!!!!!!

I just tested C-L-C and got 2mV ripple!!!!!!! I had no idea a choke could do that much..... maybe I should consider chokes after all
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Old 14th January 2003, 01:14 PM   #6
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Hi,

I am getting confused here, are you talking about chokes or inductors here?
Chris
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Old 14th January 2003, 01:34 PM   #7
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hmm... chokes i think.... i'm not very good at this yet...

I connected a 47uF cap directly to the rectifier, then i put one 20H choke and after that a HUGE cap (2200uF). It gave me incredible results on paper (screen) but I wonder how it would perform in real life. The only problem is that i see the cost for my amp shooting trough the roof.. but what the heck.. you only live once, right?
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Old 14th January 2003, 01:34 PM   #8
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Quote:
Originally posted by chris ma
Hi,

I am getting confused here, are you talking about chokes or inductors here?
Chris
Does it matter...? A choke is an inductor right?
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Old 14th January 2003, 01:57 PM   #9
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Hi Michael,

You only let the simulation run to 4.00ms right?

Try let it run to 10.00ms ....theoretically you have no ripple
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Old 14th January 2003, 01:59 PM   #10
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i've run the sim. 20 seconds... but the problem of how to specify the mains transformer remains
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