Dave's power supply mods.

[PA3BNX]

Hello EveryBody,


My goal for foldback was simply when something unattended was running
and going bad that it switches off..

So no smoke in the device under test while away ?

I assume  that the Power Supply it self can with stand
the shortage.

If I put a a load with a big capacitor on the output of the power supply
then it should not foldback.

That's what the 3 second delay should be for.

It would be nice if you could see at what time the error function did occur.


 

[Rerouter]

that would all be possible through rolling your own code for it, say mapping one button to foldback/monitor,

[Rerouter]

well, after playing around with the design to handle a higher voltage range (30.72 - 10mV), this is a section that i feel need a second set of eyes on,

the current source is replaced with an error amp fet, driven at ~1mV, and the capacitor was to prevent oscilations at low loads, though i feel it may be an incorrect value,

the main output gain is stepped up to 15, and by pulling the fet on the gain down, it swaps back to ~10.24V, although 100K's would be more accurate, its getting into the noise for the op amp i think, and may be wrong on it,

the actual op amp model can be ignored, i havent updated it since the rev A board was released, and will need to be a rail to rail if not already,

other than that, i flipped the voltage setting portion around to try and tidy it up, and hoping for some constructive input,

[Rerouter]

And now the compliment sense line(s)

the fet once again switches between a gain of 5, and of 15, but my primary concern is, with the input clamped through 20K, even worse case, with the fet left off, would the 1.2mA passed by the diode clamp actually interfere with the reference in any measurable level? (30V/25K*5K =6V, 24V/20K = 1.2mA)

the reason why i want to clamp to the reference is, the op amp feeding the adc can possibly pass more current than its internal clamps can handle, and so want to minimise the risk,

[amspire]

Rerouter,

You have some ideas that can work, but you might be over complicating things.

First though, if you use a single LT3080, then if you want to output to go to over 30V, then you will have to reduce the current to about 250mA. Alternatively, you parallel 4 LT3080's at the cost to a slightly degraded voltage regulation due resistors you have to add to the LT3080 outputs.

Which way were you thinking of going?

Now Dave had some very particular design restrictions, that meant he absolutely had to be able to run his design from a single supply. 30V+ output sounds like you have a transformer, and once you have a transformer, getting a low current negative supply only costs some cheap diodes and capacitors (even if the transformer is just a single winding) and perhaps a 79L05 regulator. It would be nuts if you can have a negative supply, to not use it. You get much better regulation even at 0V out, the current source fed from the negative rail can sink down to 0V without any problem, you can use easy-to-get LM317's instead of LT3080, since you can offset the control voltage by -1.25V. A rail to rail opamp trying to work at 0 V does not work as well as a standard opamp with a negative rail working at 0 volts.

I haven't looked at the specs for the A/D. Does it need to be driven from a low impedance source, or can you add a series resistor to the op-amp to limit any overvoltage current?

Richard.

[Rerouter]

First though, if you use a single LT3080, then if you want to output to go to over 30V, then you will have to reduce the current to about 250mA.

was thinking of a switching pre-regulator, biased to run approximately 5V above the output of the LT3080, so that the full 1.4A would be always available, and simply use an LC filter to cut out anything above 1KHz, though that will be slightly new to me (datasheets one is 20V)

30V+ output sounds like you have a transformer, It would be nuts if you can have a negative supply, to not use it.

i have a dual 35-0-35 transformer (68W), it would help with the current source, due to the voltage limit, and the op amps, but short of the current limit, i was thinking of ways to modify Dave's kit with minimal impact, and with options that might help others who don't have access to transformers, or not willing to buy them (laptop plugpacks spit out 24-30V)

I haven't looked at the specs for the A/D. Does it need to be driven from a low impedance source, or can you add a series resistor to the op-amp to limit any overvoltage current?

it can have 1K without any noticeable offset going by the datasheet, so i guess i could loose the clamp.

suggestions for higher quality DAC / ADC? as i was planning to write up a function to measure low resistances, (2 sense lines, accurate voltage applied and current measured with ucurrent) but the current ones are far too off to manage more than relative changes.

[jgbena]

Post here you mods/ideas for Dave's design.

Alexander.

I already saw Higher voltage, but what about 0-9 Volts, and 0-3amps instead of 1?  would that also be just a matter of changing software code and losing some resolution in the voltage and current step values?

[Rerouter]

jgbenga, the LT3080 cannot supply more than 1.4A, you would need to use its big brother the LT3083, to get 3A, being how you are only aiming at such a low voltage is would almost be a direct swap in,

[kiyotewolf]

I'd love to have it have a screen saver mode, where the LCD on bottom line, spouts Dave Jones quotes.

Also, a piezo beeper, so it can play little chirps, or warnings, or even, tunes?

A way to pick colors you want on the screen, so you can change it around later.



~Paul

[Rerouter]

the colours can be picked, so far all 3 colour channels of the lcd are wired to the micro, so pwm could be implemented, as for the screen saver thing, that would be something you might have to write in yourself, as most people want a power supply to maintain its display whether its been on 30 minutes of 100 hours,

as for the buzzer, that would probably be something you would need to mod in, for a simple buzzer, an NPN driver for a buzzer off the I/O chips,

for actual tones / alarms probably better to hook in something else running on i2c to accomplish that, as the micro will be doing a fair bit of correction if you hook it on to an active load, and you probably wouldnt want to chew up its cycles with producing a tune,

[ejeffrey]

Also, a piezo beeper, so it can play little chirps, or warnings, or even, tunes?

Are you by any chance designing hand-held instruments for agilent?!

[Rutger]

Dave, I was looking at the different options for the DAC, because I was looking at the dual version of your power supply (eg with a negative output as well) and came across the following 4 channel 12 bit DAC:
   
MCP4728-E/UN  at $ 1.44 / 100 with build in voltage reference (optional).

I know you didn't want surface mount parts but with the Maxim 4080 and the voltage ref chip you have chosen that option is already gone.

The advantage of having the extra 2 channels is that you can add/drive another power supply from the same DAC. And you can save on the cost of the parts, maybe you eliminate the external voltage ref chip.

Rutger

[caroper]

... or even, tunes?
~Paul

Who needs Overload protection when you PSU can play "Smoke on the Water, Fire in the Sky"
Joking aside, that is actually a good idea, not so much the tunes, but a beep to confirm a setting or a short alarm if CC  Mode is entered or an error condition occurs.


Cheers
Chris

[kiyotewolf]

Yeah, since the whole thing is open source, (right??), then I was thinking of modding in the little things like the tunes.. (the EEVBlog theme video end diddy, .. when it shuts off..), and the display doing EEVBlog quotes..  (as it boots, "Don't turn it on, take it apart!")

I really like having little favorite themes of colors for the RGB LCD, in case you've got mood LED lighting in your lab.. .. or for other fun reasons.  (Make it play smooth jazz chip tunes while doing little glowing of reds and oranges, like a miniature fireplace.. while powering a ... <insert thing to be powered here> )



~Paul

I was fascinated watching Dave modify the code right on the screen, and how he was able to send out serial data, twiddling the bits all by himself.

[EEVblog]

I was fascinated watching Dave modify the code right on the screen, and how he was able to send out serial data, twiddling the bits all by himself.

Which of course would have been much harder to do if I followed the advice of the "software professionals" and used a for loop instead of my "shit" code that isn't good enough for production  

Dave.

[jgbena]

jgbenga, the LT3080 cannot supply more than 1.4A, you would need to use its big brother the LT3083, to get 3A, being how you are only aiming at such a low voltage is would almost be a direct swap in,

Thanks Rerouter, ill give that a look!

[senso]

Here is my take/interpretation of Daves power supply, the pcb's have been ordered and the parts are already in Portugal.
I have maintained Dave's credit in the silkscreen and this is will be a public project in the portuguese LusoRobótica forum, it uses the smd version in the dac and the adc and also an atmega644 instead of the 328p used by Dave, it is still a beta version and I plan to shrink it a bit/a lot and make some more changes to the layout.

[george graves]

Nice work!- Now many extra pins does the 644 give you over the 328?  Are you programming it as a "sanguino?"

Looks great!

[sacherjj]

I like the break out of the sense and + separately.  Allows no burden validation of current, without the uCurrent.  (Not sure if you built that in as well.)

I'm thinking about a simpler 328 based PSU, with using the onboard ADC and PWM.  I'm currently working on a 328 based 40 V and 4 A Constant Current Sink first, but imagine the ADC and PWM experience with that will help with that.  But since I only have one decent lab PSU right now, I'll probably get this kit as well if it isn't too terribly expensive. 

Although, I hate not having the mains to the inside of the box, due to parasitic power draws or separate unplugging or power switching.  But, I might think differently if it was 220v vs 110v.

[electrode]

Wow, that looks pretty nice. Good choice of microcontroller too - 12 extra pins (answering george's question) and fully Arduino compatible.

[senso]

Thanks, I will share all the files when I'am sure that there are no errors, and yes the uCurrent is also present in this power supply.
The atmega644p as said by electrode as 12 extra pins, there will be an extra board that will serve as the front panel, for now the only displays that I have are two like this:
http://www.ebay.com/itm/0-96-128X64-OLED-LED-Display-Module-PCB-Adpater-/160556409041?pt=LH_DefaultDomain_0&hash=item2561e860d1
They are pretty tiny but can be read from pretty far and I will make a large font, and I have left access to the i2c and its possible to use any 8 bits parallel display using the SPI interface to drive some shift-registers, so it can be pretty flexible, one friend of mine wants to have one small bench supply and wants to learn how to use Eagle, so probably he will design a front panel to use with regular 16x2 char displays so I can teach in with a real project and I will make one for the small oLed.
The programming is done using AvrStudio and avr-gcc but its very easy to port to Arduino, and as the design I will put everything in my Google Code page.
If some one is interested here is my blog where I still only have some programming tutorials for avr:
http://hekilledmywire.wordpress.com/

[Zad]

If you are using SMD ICs, why not use 1206/0805 passives too? If you can solder a QFP or SOIC, you can sure as hell solder an 0805!

[Rerouter]

because a lot of hobbyists aren't keen to solder SMD's unless they really have to, and SOIC's are about as basic as SMD IC packages get,

Dave made this thinking any man with a soldering iron of no notable quality could make it himself, (or herself?) without much experience, as a kit

[electrode]

I think Zad's comment was directed at senso...

I only just got into 0805s last year. Easiest way to save board space ($$$) with footprints that "even Stevie Wonder could solder".

[senso]

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.