Author Topic: Dave's power supply mods.  (Read 42570 times)

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Offline electrode

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Re: Dave's power supply mods.
« Reply #75 on: February 11, 2012, 10:26:53 am »
A good tip for if you don't have the gear or experience with SMD stuff is to make your pads longer. That way you can drag the excess solder back and the bridged pins will naturally separate beautifully. One of the EEVBlog vids did this.
 

Offline sacherjj

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Re: Dave's power supply mods.
« Reply #76 on: February 11, 2012, 12:58:10 pm »
I used the SOIC footprints for the ADC and DAC's because I already have then, the MAXIM parts only exist in soic or smaller, and the atmega644 in a 40 PDIP would be huge, the next iteration of the board will probably have almost all the components in SMD, and this will be first smd's that I solder, I already have some flux syringe and an JBC soldering iron with a chisel tip, wish me luck.

I found the cheap hot air iron to make life great with SMD.  Add some GOOD tweezers.  With that, I found it almost painless to do 0402.  Squirt on solder paste.  Add some paste flux.  Use tweezers to place component close.  Use hot air iron to melt solder paste and watch the 0402 align itself with the pads.  Pretty cool.  But if you are designing the board, use bigger components!  :)
 

Offline senso

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Re: Dave's power supply mods.
« Reply #77 on: February 11, 2012, 01:23:37 pm »
At home I have my soldering iron, flux, some fine non magnetic tweezers, fine solder and solder wick, but if everything fails in the university I can ask to use an IR soldering oven, hot air station and lots of Weller soldering stations, as I have bought the pcb's from Itead I will try first in the non E-tested boards.
 

Offline senso

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Re: Dave's power supply mods.
« Reply #78 on: March 06, 2012, 02:21:22 am »
And the first pcb's finally arrived from China, 3 weeks for manufacture and shipping via slow boat, doesn't seems too bad for me, especially due to the price that I paid for them.
The silkscreen took me more time to clean than to lay out the entire pcb, and even then it has some errors/extra text that I didnt noticed.
Here are some not that good photos:



 

Offline george graves

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Re: Dave's power supply mods.
« Reply #79 on: March 06, 2012, 09:55:22 am »
Looks good.  Looks like you might have a break in the ground plane - at the ground pin of ICSP header?

Offline senso

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Re: Dave's power supply mods.
« Reply #80 on: March 06, 2012, 01:04:58 pm »
It is grounded in the top ground plane, so it is in fact grounded, not a very good ground, I usually add vias to connect top and bottom ground planes.
Its funny that only the board in the photos as all the vias tented, all the others have some tented and others are not, kinda like random..

I also soldered my first SMD and it was pretty easy  :o
Put some flux in the pads, IC on top, hold with tweezers and a tiny amount of solder in the tip is enough for all the IC, really fast, I'm for sure converted! 
 

Offline robrenz

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Re: Dave's power supply mods.
« Reply #81 on: March 06, 2012, 01:11:43 pm »
Does the back and forth wander on the header holes have a purpose?  I dont know much about PCB design, just curious.

Offline george graves

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Re: Dave's power supply mods.
« Reply #82 on: March 06, 2012, 01:16:18 pm »
Ah!  I see now.

Offline senso

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Re: Dave's power supply mods.
« Reply #83 on: March 06, 2012, 01:56:13 pm »
Does the back and forth wander on the header holes have a purpose?  I dont know much about PCB design, just curious.

They are from the Sparkfun library, they call it Lock, they are off-set by 5 mills if I'm not mistaken and their purpose is that you push the headers in the holes and due to the offsets the headers get locked in placed and aligned so they are easier to solder and you dont end with crooked headers, they are really helpful when assembling the pcbs.

I dont know if Dave sees this topic, but if you are there, are you willing to share your actual code for the uSupply?
 

Offline EEVblog

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Re: Dave's power supply mods.
« Reply #84 on: March 06, 2012, 02:20:04 pm »
I dont know if Dave sees this topic, but if you are there, are you willing to share your actual code for the uSupply?

Here is whatever is on my machine at present.
No correspondence will be entered into  :P

Dave.
 

Offline senso

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Re: Dave's power supply mods.
« Reply #85 on: March 07, 2012, 02:43:52 pm »
Thats pretty simple for now, but well its just a power supply...
My personal version as a graphic display so I will add some current plots and who knows what more.
First board is almost complete, forgot to order some of the components and ordered the MAX4080 in the wrong package  ::)

 

Offline electrode

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Re: Dave's power supply mods.
« Reply #86 on: March 07, 2012, 02:51:02 pm »
Looks really nice. The header locations look convenient too.
 

Offline senso

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Re: Dave's power supply mods.
« Reply #87 on: March 07, 2012, 09:14:23 pm »
One sanity check please, the uCurrent is only activated when the mosfet is turned on, and that only happens when 3.3v(high signal) is given to the 2n3904 transistor, I'm right or is it the other way around?
And sorry for not doing the homework, but what is the current threshold where I can safely enable it and not fry the MAX op-amp?

I dont know about how you will be distributing your code, but I will use a google code repository, so any-one that wants to take a sneak peek can go there, I will also offer pre-compiled hex files ready to program the atmega.

Is any one willing to try one board, I have 9, all of them e-tested and eye tested and seem to be fine, so far the only error is the 3.3v regulator must be inserted backwards ( swapped Vin with Vout  :-[ ), for some reason I used the wrong part and even with the datasheet open in front of me I didn't notice that.

I hope to have all soldered this week and at least some code doing an hello world.
 

Offline EEVblog

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Re: Dave's power supply mods.
« Reply #88 on: March 07, 2012, 10:44:04 pm »
FYI, I'm currently doing Rev 3, some major changes in store!
That's what happens when you leave a project for so long, you always get other ideas...
I think it's for the better though.

Dave.
 

Offline electrode

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Re: Dave's power supply mods.
« Reply #89 on: March 07, 2012, 10:46:31 pm »
Major == SMD?
 

Offline McMonster

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Re: Dave's power supply mods.
« Reply #90 on: March 07, 2012, 11:04:33 pm »
My guess is reducing BOM or going to full SMD.
 

Offline EEVblog

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Re: Dave's power supply mods.
« Reply #91 on: March 07, 2012, 11:04:52 pm »
Major == SMD?

SMD is part of it, the through hole kit just wasn't really going to be workable.
I'm removing some stuff and adding some other stuff!

Dave.
 

Offline EEVblog

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Re: Dave's power supply mods.
« Reply #92 on: March 07, 2012, 11:09:25 pm »
My guess is reducing BOM or going to full SMD.

Both, plus more.
Revising designs is half the fun ;D

Dave.
 

Offline McMonster

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Re: Dave's power supply mods.
« Reply #93 on: March 08, 2012, 12:39:56 am »
My guess is reducing BOM or going to full SMD.

Both, plus more.
Revising designs is half the fun ;D

Dave.

If revision 3 can make coffee and order pizza then I'm getting at least two.
 

Offline mtkaalund

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Re: Dave's power supply mods.
« Reply #94 on: March 08, 2012, 02:49:19 am »
Quote
If revision 3 can make coffee and order pizza then I'm getting at least two.

Would it not be easier to get a girl friend that can do tha... your right, if rev 3 can make coffee and order pizza Im also getting two ;)
"Keep buggering on" -- Winston Churchill
VIR => V = I*R, neat ;)
 

Offline markus_b

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Re: Dave's power supply mods.
« Reply #95 on: March 08, 2012, 02:56:19 am »
I've privately toyed with a variant based on a xMega. Enough ports for everything and has 12bit AD and DA on board. Reduces the BOM an awful lot. You can program these babys with Arduino too, if you want.

The other extensions I feel useful is input voltage up to 35 Volts and current up to 3 amps (3 3080 in parallel).
Markus

A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible.
 

Offline scrat

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Re: Dave's power supply mods.
« Reply #96 on: March 08, 2012, 08:43:42 am »
Could a remote output voltage sensing and/or an external analog input reference be useful?
I see them as little mods, just adding one or two opamps, and using one ADC spare channel (at least in an early revision) and the uC ADC for the reference. Choosing between internal and remote sensing is usually one of the features of a precision PSU (although it could just be an hardware ORing), while the external reference could allow one to use their PSU for testing some controller (an example? A DC motor controller).
One machine can do the work of fifty ordinary men. No machine can do the work of one extraordinary man. - Elbert Hubbard
 

Offline tom66

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Re: Dave's power supply mods.
« Reply #97 on: March 08, 2012, 09:00:55 am »
If the 3080s become expensive, maybe move to a power Darlington transistor or a P-channel MOSFET with a different driver circuit? Disadvantage - no current sense or temperature sense on die, but first current sense is done by the 317T and temperature sense could be done with an external thermistor and NPN to pull the drive signal low as an emergency cut off.

Opened up my Tagasaki power supply I got a while ago. 0-35V 0-3A. Quite interesting construction - the circuit is very similar to Dave's but no micro of course. Just two single op-amp packages, I think they were similar to 741's, and a few passive carbon resistors. Some 10W resistors x 3 for current sense. And a TL431 for voltage reference. What I found really clever though was how they were choosing taps on the transformer to reduce power dissipation in the 3 x 2N3055's (on a massive heatsink.) They used some kind of SCR devices I think but I never quite figured out how they got them to fire - I'm almost certain they weren't using any logic, probably just biasing the gate somehow so it fired when the output voltage was past a certain point...? The transformer in the power supply was easily the heaviest part, and the power supply is only capable of 105W output max.

Nowadays with modern laptop SMPS's going spare you can easily find a 20V DC power supply so there's no need to use a big bulky transformer. You could even get the laptop SMPS to follow the output by a couple of volts to significantly reduce power dissipation. There's probably a way to tap into the feedback to do this. I've done it before with an ATX supply but only increased voltage (12V -> 26V) not decreased it.
« Last Edit: March 08, 2012, 09:02:59 am by tom66 »
 

Offline george graves

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Re: Dave's power supply mods.
« Reply #98 on: March 08, 2012, 11:59:49 am »
I guess I'm starting to worry about the price!  (not too much - it looks like this kit is going to be a must-have, and a great bang for the buck!)

Will SMD increase the cost?  Decrease it?  I'd assume that you'd be doing a lot less labor with SMD as you wouldn't have to sort out all the parts and put them into a bag.

Offline EEVblog

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Re: Dave's power supply mods.
« Reply #99 on: March 08, 2012, 12:26:49 pm »
I guess I'm starting to worry about the price!  (not too much - it looks like this kit is going to be a must-have, and a great bang for the buck!)
Will SMD increase the cost?  Decrease it?  I'd assume that you'd be doing a lot less labor with SMD as you wouldn't have to sort out all the parts and put them into a bag.

Yes, SMD will be cheaper and less hassle for all involved, albeit at the expense of losing the satisfaction of having soldered it yourself for some people.

Dave.
 


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