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Old 13th March 2003, 11:20 AM   #1
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Default Help with Linear PSU

Hi...

I need a psu for a project i'm currently doing - an emulation of the LC based on the designs by T.Klose at ucapps.de...

Rapid has an open frame ac/dc psu that gives 12-15v and is rated at 1.7A. This is perfect for my box, but it costs 40 quid . I really wanna keep costs down and so wondered if ne1 here has a pcb layout or schematic for a similar psu I can etch and stuff myself (as i've done with the mbhp modules)...

I know u havta be careful with the old psu building but i'm sure the knowledge on this board can point in the right direction

Peace n dumplinz

Dan
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Old 13th March 2003, 12:08 PM   #2
dhaen is offline dhaen  Europe
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Hi Dan,

Is it 85-3200 you were looking at?

How much current do you need, and how well regulated do you want it to be?

It may be possible to do it for about half that price in components, and you probably won't need a PCB.
The only fly in the ointment is that you'll have to pay P&P on a lower value order

Where abouts in London are you?

Cheers,
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Old 13th March 2003, 12:22 PM   #3
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Hey John...

Yup, t'was the 85-3200...

Current wise, around 2A is dandy - not 2 sure on how regulated it should be, tho i guess the more the better right :?

I need to get a few other parts from rapid neways, so will do it all in 1 pop....

I'm in NW London...

Nice

Dan
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Old 13th March 2003, 01:02 PM   #4
dhaen is offline dhaen  Europe
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Dan,

You'll need:
A 15-0-15v 50VA transformer such as 88-0310, or a toroidal if you want low profile.
4 schotky diodes such as 47-2538, or you could use a diode bridge, but you might need a bigger cap- depends on your actual max current.
A 10,000uF cap such as 11-2225 plus clamp.
A 78s12 fixed 2A regulator 47-3304
A suitable heatsink for 10watt dissapation.
A couple of small value caps for the input and output of the regulator, to keep it stable and quiet.


If you want a schematic I'll post one, but this is simple stuff

Disclaimer: check all numbers before ordering... I am dyslexic with numbers

Cheers,
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Old 13th March 2003, 01:14 PM   #5
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Nice1 John...

Quote:
A 10,000uF cap such as 11-2225 plus clamp.
By clamp dya mean mounting clip? Soz, newbness is rife on all things EE...

A schematic would be charmin, i'll prolly mount it all on stripboard - this should be cool ye?

Thanks again...


Dan
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Old 13th March 2003, 01:50 PM   #6
dhaen is offline dhaen  Europe
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Dan,

Clip = clamp. Have a look at the size of the components and draw it out to scale. You probably won't even need stripboard.

Also, you only need 2 schottly diodes... my mistake.

Cheers,
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Old 13th March 2003, 02:45 PM   #7
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Great Stuff John! Appreciated

For the small caps after the regulator will 4.7uF ones be okay?

Cheers

Dan
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Old 13th March 2003, 02:55 PM   #8
dhaen is offline dhaen  Europe
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Dan,

4u7 would be fine. Just to get rid of regulator noise.

You'll also need an insulation kit for the regulator. This should consist of a plastic bush and silicon washer. I find the stick-on washers are most convenient.
The heatsink has to dissapate up to 10 watts. Think about what size sink you'll need. They're rated in W/degC, so take the temperature rise that's acceptable and find a heatsink that's big enough. Leave a bit of headroom, 'cause the regulator also has some thermal resistance that we haven't taken into account, but it's "fudge-able".

Cheers,
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Old 13th March 2003, 03:06 PM   #9
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Nice, bits ordered

I'll post a pic of the psu once finished - just to make sure

Thanks again John, what a great resource the net can b eh

Dan
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Old 13th March 2003, 04:10 PM   #10
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John, soz - need to clear a few points up...

When u say fuse the xformer primary - does that mean just stuff a fuse before the xformer? I thought i'd use a 2A rated fuse after the regulator at the output...:?

Also, where would i place the power switch (which would also have an LED) - after the regulator right? Or would i get a fused power switch and thats what goes before the xformer?

Apologies for the basic q's - i'm new to all this and have only used wallplugs prior...
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