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Need help building off this schematic.


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I am sorta a noob at this stuff so I need a bit of assistance. I do know how to solder and stuff so thats not the problem.

What I am building is a power circuit that will convert 12v and 5v to 2.5v-4.3v variable with .01v fluct or less. I will be needing around 15amps, and this schematic is supposed to be enough.

Ive need as clean and stable power as possible for this project, and I've been told "design seems OK if you follow it..........Also ADD some electrolytic caps to the input and the output of that circuit plus chokes.........." If someone could help me inplement that stuff in that would be GREAT!

I just need to know what I need to get (parts not tools) and where to get them. I usually get my stuff from Jameco.com

Here is the scematic:



Thanks for all the help in advance!!!
-Jordan

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Hi

If you want a clean supply, it is probably a good idea to avoid switching regulators, despite the amount of heath the circuit will generate.
Capacitors are OK for improving the noise performance, but chokes risk destabilising the circuit; I'd avoid them.
An improvement to your circuit would be the addition of a ~1K resistor in series with the the gate of the mosfet; although not strictly necessary, it will help in reducing potential parasitic oscillations.

Lou

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Hi

If you want a clean supply, it is probably a good idea to avoid switching regulators, despite the amount of heath the circuit will generate.
Capacitors are OK for improving the noise performance, but chokes risk destabilising the circuit; I'd avoid them.
An improvement to your circuit would be the addition of a ~1K resistor in series with the the gate of the mosfet; although not strictly necessary, it will help in reducing potential parasitic oscillations.

Lou


could you possibly show me where and how to add it?

I have another design that I could use, would this be better maybe?

http://www.xtremesystems.org/forums/attachment.php?attachmentid=31748

-Jordan
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okay definatly not the second schematic...

the guy that wrote the first one told me:


If you can wait until next week, I'll have a go at drawing up a switched mode design, but its likely to be a lot more complicated than a linear supply (at a rough estimate I think I can probably do it with 4 opamps and a few resistors and capacitors and a MOSFET/transistor, unless you can find a dedicated chip to do it all for you)
IMO, a switching supply will be a bit overkill for the purpose. A simple linear regulator should provide similar performance, but with more heat output.


this circuit will be used not to power a cpu (close) but to power DDR Memory.

Ultimately what I want is this:
http://xtremesystems.org/forums/showthread.php?t=42220

but they guy wount give me a schematic :(

sooo, could someone help me with a switching design with lots of caps and chokes to keep the power nice and stable, clean, and cool?

thanks guys!

Ive been learning a lot already, been reading and reading and reading on the site. very informative! I already printed out a 50 page pdf book from here too! keep up the good work site admins!

-Jordan
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Ive got another guy giving some input now.

I dont like linear, maybe just me  ;D Switching with good filtering would be the way to go in my opinion...

What about using the PWM from a PIC to implement a full single phase PWM?

Feed a N-channel enhancement mode MOSFET as the upper FET with an invertor feeding the lower N ench FET. Feedback referenced against a LM336, output fed through a potential divider to scale it the the ref diode range before going into a ADC channel to compentsate PWM duty cycle to desired voltage. Ouput to basic LC...

You could also have LCD voltage display (or even temp. with a LM335?), RS232 communication, whatever. The whole thing in one package with a minimal amount of extra components...

Ive got a shed load of LM336's, low ESR caps, ceramics, inductors, N-channel ench MOSFETS rated from 10A - 48A. I've been planning to build one of these for a while, im planning on using a 16F877, but you have 2 PWM and 8 ADC -why not do Vtt too?

Only problem i can think of is the ADC being 10-bit, resoloution of 4 mV. Nasty thoughts of it going unstable...

Maybe just use one of the buck regulator IC's instead and add extra control?


We have decided to implement a vTT circuit too. That is just another output that will be exactly half of the vDDR voltage. So, if the main voltage was 3.0v, the vTT would need to be exactly 1.5v. I've found out that I will need 3amps on the vTT circuit, but I say call it 5amps to be safe and future proof.

Now, all we need is a schematic of this idea ^^^^^^^^

Thats where I ask for help from the pros, here  ;D

THANKS!!!

-Jordan
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What about something like this? I know it doesn have VTT, but I think that would be easy to impliment...



T = STP55NF03L
IC = TL431
C1, C3 = 3300uF/6.3V low-ESR
C2 = 100-470uF/16V low-ESR
R1 = 390ohm
R2 = 1.5Kohm
P = 1Kohm multiturn

Try to get high-quality parts, so the voltage stays as clean and stable as
possible. The mosfet (T) gets very hot, so you need to mount it on a
heatspreader; watch the isolation, it's metallic part of the case is
connected to the D pin and therefore directly to the PSU's +5V line. The
output wire should be as thick as possible, because that's the only thing
it can cause voltage drop. If well built, this circuit should provide zero
voltage drop and extremely clean power.
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