Author Topic: Dave's power supply mods.  (Read 42546 times)

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Offline firewalker

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Dave's power supply mods.
« on: January 06, 2012, 10:26:59 pm »
Post here you mods/ideas for Dave's design.

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Offline Blue

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Re: Dave's power supply mods.
« Reply #1 on: January 07, 2012, 04:49:06 am »
Higher output voltage. E.g. 18V out...
 

Offline don.r

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Re: Dave's power supply mods.
« Reply #2 on: January 07, 2012, 04:57:46 am »
Higher output voltage. E.g. 18V out...

Higher outputs would entail losing the resolution from the MCU. You may need to step up to 16bit converters. I always like extra fixed outputs like +/- 5V and +/- 12V along with the variable. Maybe with a fixed or switch selectable current limit. Easily done with 78XX/79XX parts.
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Offline PeteInTexas

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Re: Dave's power supply mods.
« Reply #3 on: January 07, 2012, 05:04:07 am »
Voltage and current presets.  I find that I actually only use a handful of voltages that correspond with common battery combinations- 1.5, 3.0, 6.0, 9.0 and so it is annoying to have to keep turning a 10 turn pot.  With the 12-bit DAC, I can imagine it will be similarly annoying with the rotary encoder.

It would really be great to just go to the voltage you want.  A 16-key pad mod would work using the 4 encoder pins plus the 4 pins from the 4 switches.  That still leaves too much twiddling for my tastes.

Unfortunately, the 4 encoders are not going into ADC pins so a resistor matrix cannot be used for preset switches.  They still can give 16 values for the software so it is possible to portion that out between voltage and current presets.  If the 4 switches can be similarly put into only two pins, one of the saved pins can be used to toggle between the presets and the rotary encoders.  The best of both worlds!
 

Offline PeteInTexas

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Re: Dave's power supply mods.
« Reply #4 on: January 07, 2012, 05:39:43 am »
If preset switches ain't your bag, you can multiplex the four switches into 2 pins and use the 2 saved pins to toggle between 'coarse' and 'fine' encoder steps for voltage and current respectively.
 

Offline Bored@Work

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Re: Dave's power supply mods.
« Reply #5 on: January 07, 2012, 05:59:15 am »
If preset switches ain't your bag, you can multiplex the four switches into 2 pins and use the 2 saved pins to toggle between 'coarse' and 'fine' encoder steps for voltage and current respectively.

Ehm, one would do that by applying a dynamic-speed encoder profile. If you turn the encoder fast you do larger voltage or current steps (coarse). If you turn the encoder slowly you do fine steps.
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Offline ndictu

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Re: Dave's power supply mods.
« Reply #6 on: January 07, 2012, 06:15:18 am »
Ehm, one would do that by applying a dynamic-speed encoder profile. If you turn the encoder fast you do larger voltage or current steps (coarse). If you turn the encoder slowly you do fine steps.
That's a great idea, and you just need a bit more code to do that so it'll be easy.

I kind of lost track of the discussion in the main thread, anyone knows what Dave plans on using for the code? It would be best on github/other VCS, so that everyone can easily submit their modifications and they will get merged to the "official" version.

Also, few ideas:
- use the serial link to connect multiple supplies together, using one as a master control for the others
- with isolated USB link you can do all kinds of stuff: log all the values, measure power consumption, automatically sweep over the voltage range and take measurements after some settle period etc...
- using a bigger uC and duplicating most of the supply circuitry you can transform it into a dual output supply. But I would probably rather build two of these.
 

Offline Zad

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Re: Dave's power supply mods.
« Reply #7 on: January 07, 2012, 06:32:03 am »
Dave has said that there is one thing he isn't telling us about the design yet. But that could be anything ;)

One possibility is that he is using an I2C expander IC, and using that to drive a standard LCD and key switches. I think a lower power version built into an Arduino shield could potentially be a good seller via Sparkfun, Adafruit etc.

Fancy things like battery charging, preset profiles and so on are all just software and can be left to the community. Such is the benefit of Open Source. Dave mentioned in the video the potential for an opto-isolated RS232 control and logging, which is easy to connect to USB via a cheap external interface.

Offline Bored@Work

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Re: Dave's power supply mods.
« Reply #8 on: January 07, 2012, 07:09:23 am »
Dave has said that there is one thing he isn't telling us about the design yet. But that could be anything ;)

I had the impression it is more about the enclosure. And I seem to remember that in some older video he was thinking about a certain kind of enclosure for some projects.
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Offline PeteInTexas

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Re: Dave's power supply mods.
« Reply #9 on: January 07, 2012, 07:19:27 am »
If preset switches ain't your bag, you can multiplex the four switches into 2 pins and use the 2 saved pins to toggle between 'coarse' and 'fine' encoder steps for voltage and current respectively.

Ehm, one would do that by applying a dynamic-speed encoder profile. If you turn the encoder fast you do larger voltage or current steps (coarse). If you turn the encoder slowly you do fine steps.

This relies too much on ones coffee in take to finally get to the desired value.  I was thinking in the coarse mode each step cycles through the desired set of presets.  So for my 4 voltages, 3 twiddles at the most- 1 to flip to coarse mode, 2 to get to the desired voltage (you can go backwards).
 

Offline PeteInTexas

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Re: Dave's power supply mods.
« Reply #10 on: January 07, 2012, 07:38:29 am »
Ehm, one would do that by applying a dynamic-speed encoder profile. If you turn the encoder fast you do larger voltage or current steps (coarse). If you turn the encoder slowly you do fine steps.
That's a great idea, and you just need a bit more code to do that so it'll be easy.

I kind of lost track of the discussion in the main thread, anyone knows what Dave plans on using for the code? It would be best on github/other VCS, so that everyone can easily submit their modifications and they will get merged to the "official" version.

Also, few ideas:
- use the serial link to connect multiple supplies together, using one as a master control for the others
- with isolated USB link you can do all kinds of stuff: log all the values, measure power consumption, automatically sweep over the voltage range and take measurements after some settle period etc...
- using a bigger uC and duplicating most of the supply circuitry you can transform it into a dual output supply. But I would probably rather build two of these.

Good ideas but I make a distinction between a mod and a rework.  You are asking for a rework.
 

Offline Bored@Work

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Re: Dave's power supply mods.
« Reply #11 on: January 07, 2012, 07:46:42 am »
This relies too much on ones coffee in take to finally get to the desired value.

Are you able to operate a computer mouse under the influence of coffee? If yes, you should be able to operate this, too. Because dynamic profiles are the norm for mouse operations since ages.
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Offline PeteInTexas

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Re: Dave's power supply mods.
« Reply #12 on: January 07, 2012, 07:51:29 am »
This relies too much on ones coffee in take to finally get to the desired value.

Are you able to operate a computer mouse under the influence of coffee? If yes, you should be able to operate this, too. Because dynamic profiles are the norm for mouse operations since ages.

It took me a long time to perfect my mouse setting.  :-\
 

Offline Short Circuit

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Re: Dave's power supply mods.
« Reply #13 on: January 07, 2012, 08:44:39 am »
..
Ehm, one would do that by applying a dynamic-speed encoder profile. If you turn the encoder fast you do larger voltage or current steps (coarse). If you turn the encoder slowly you do fine steps.
This relies too much on ones coffee in take to finally get to the desired value.  I was thinking in the coarse mode each step cycles through the desired set of presets.  So for my 4 voltages, 3 twiddles at the most- 1 to flip to coarse mode, 2 to get to the desired voltage (you can go backwards).
Nonsense, if implemented correctly, that works marvelous. Course/fine switches on the other hand are a pain.
Always in the wrong mode, so twist, oops backtwist, toggle, twist again, toggle, fine twist.
I have a PSU that is operated like this and it sucks.
 

Offline PeteInTexas

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Re: Dave's power supply mods.
« Reply #14 on: January 07, 2012, 09:06:24 am »
This relies too much on ones coffee in take to finally get to the desired value.  I was thinking in the coarse mode each step cycles through the desired set of presets.  So for my 4 voltages, 3 twiddles at the most- 1 to flip to coarse mode, 2 to get to the desired voltage (you can go backwards).
Nonsense, if implemented correctly, that works marvelous. Course/fine switches on the other hand are a pain.
Always in the wrong mode, so twist, oops backtwist, toggle, twist again, toggle, fine twist.
I have a PSU that is operated like this and it sucks.

I'm guessing you harboring similar disdain for oscilloscopes?
 

Online Rerouter

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Re: Dave's power supply mods.
« Reply #15 on: January 07, 2012, 09:39:53 am »
For higher Voltage
(and this is only as a higher voltage modification 30.72V)
2 x http://search.digikey.com/us/en/products/MC33172N/497-7409-5-ND/1038900 op amps are pin compatible with u3 and u12

a few gain resistor changes;

2K in parrellel with R29
2K in parrellel with R31 (for a gain of 15)

10K in parrellel with R35
82K to replace R34 (for a maximum input voltage reading of approx 35.6V in, yeah not a pretty number, still working)

and for the mosfet, like a 82K resistor tieing its gate to ground, to divide input voltage by 2 (about 18V max), so its safe from 0 to 30.72V out,

For a keypad / more free pins
Hook up the keypad / existing buttons to a resistive ladder / matrix and in software make use of the adc function of the pin some of the buttons are currently on

For higher current
being how the LT3080 only requires 20mohm between regulators one could drill additional holes into the heatsink and mount regulators hooked up in parrellel, even with mod wire it would roughly be enough,
 

Offline shebu18

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Re: Dave's power supply mods.
« Reply #16 on: January 09, 2012, 12:34:51 am »
This one would be nice for a dual powersupply. A LT3080 or a L338 that supports negative voltage and a bigger micro, and one more from everythgin plus some other parts.


The biggest problem vould be the box for the PSU.
 

Offline naimis

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Re: Dave's power supply mods.
« Reply #17 on: January 09, 2012, 03:31:12 am »
mains inputs? Or am I being altogether too obvious?  ;D
 

Offline shebu18

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Re: Dave's power supply mods.
« Reply #18 on: January 09, 2012, 04:00:41 am »
After rectifing, filtering and filtering again. I think you get arround 17V, even 14 will be ok.
 

Offline caroper

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Re: Dave's power supply mods.
« Reply #19 on: January 09, 2012, 08:10:21 am »
What I have in mind is to use 2 of Dave's Boards (or something based on his design) but keep them isolated and floating so that they could be connected in Series for grater voltage or a -V_0_V+ Supply or paralleled for a larger current output. They would have to be in close tolerance but I think Dave's design has taken that into account.  I would leave the MCU on the board for the sake of reading the Encoder and driving isolated communications via SPI or TTL Serial, but not worry to much about adding any advanced functions to it. Possibly not even a display at this stage as you could use a DMM to set the Current limit and Measure the Output Voltage.

Later I would add a separate control board, with a larger processor, to take over the display and control input functions, with software to add tracking and other optional capability's such as computer control, voltage sweeps, stepped patterns etc. for bench testing of devices.

As part of the CPU board I would include a relay control to automatically configure the outputs into Independent / Serial tracking / Parallel Tracking configurations. Because it has to be isolated from the 2 power channels and independently powered it could also provide fixed outputs of 3V3. 5V and possibly 9/12V if it is driving relays. thus providing additional common supply voltages and freeing up the 2 main channels for more productive tasks.


If i were to change the current design at all it would be to simplify it rather than add features.

Even with only 10bit resolution on ADC and DAC you could control 0->1024mA in steps of 1mA and 0->20.48V in steps of 20mV, which I think would be more than adequate for most hobby bench supplies and indeed exceed the measurement capability's of most hobbyist DMM's, so I would be inclined to use PWM and on chip ADC of the MCU rather than increase the cost and complexity with the external devices. For the same reason I would argue that the inclusion of the uCurrent is also an unnecessary expense. If I were designing something that had low voltage and current requirements, such as MCU devices that draw down to the uA range in sleep mode and nA normally, I would not be wasting 10's of watts of power by testing them on a bench PSU like this one. For those applications a precision PSU of 0->6V @ 0->10mA with very fine resolution would be a good investment.


Online EEVblog

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Re: Dave's power supply mods.
« Reply #20 on: January 09, 2012, 08:33:22 am »
Even with only 10bit resolution on ADC and DAC you could control 0->1024mA in steps of 1mA and 0->20.48V in steps of 20mV, which I think would be more than adequate for most hobby bench supplies and indeed exceed the measurement capability's of most hobbyist DMM's, so I would be inclined to use PWM and on chip ADC of the MCU rather than increase the cost and complexity with the external devices. For the same reason I would argue that the inclusion of the uCurrent is also an unnecessary expense.

They don't actually add a huge lot to the overall cost when you add it all up. It's not like the component cost suddenly halves by taking out those components.

Quote
If I were designing something that had low voltage and current requirements, such as MCU devices that draw down to the uA range in sleep mode and nA normally, I would not be wasting 10's of watts of power by testing them on a bench PSU like this one.

This is a linear supply, it uses the same current as the device under test + some the power for the circuitry.
So a circuit taking say 1mA at 3.3V only takes 1mA from the input voltage as well. In this case the PSU circuit power dominates. I don't know what that is yet, but maybe another 20mA or so.

Quote
For those applications a precision PSU of 0->6V @ 0->10mA with very fine resolution would be a good investment.[/size]

That's what this supply is. A small precision 0-10V 0-2A supply with fine resolution.
0-10mA capability only would be a waste of space IMO and very niche, 0-100mA would be better but still very limiting, 0-1A makes it a very usable supply for general circuits.

Dave.
 

Offline caroper

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Re: Dave's power supply mods.
« Reply #21 on: January 09, 2012, 10:08:46 am »
I did actually intend 100mA the 10 was a typo, but point taken.  I was thinking of the voltage drop across the regulator as wasting power, but at only a few mA it is not dissipating much power at all.

I would still like to see 12->15 volts as the upper limit, but if they can be run in series it gives 20V for charging battery's etc and 10<-0->10 for driving op-amps in split rail mode so probably covers most bases.

My other problem with the external ADC/DAC is that you had to abandon through hole for them, not really the cost factor. But as you have said, it is for  precision with fine resolution so a valid compromise.
You may have to offer the KIT with those parts already mounted or you could lose a large potential market though.

EDIT:Spelling

« Last Edit: January 09, 2012, 10:47:23 am by caroper »
 

Online EEVblog

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Re: Dave's power supply mods.
« Reply #22 on: January 09, 2012, 11:08:28 am »
My other problem with the external ADC/DAC is that you had to abandon through hole for them, not really the cost factor. But as you have said, it is for  precision with fine resolution so a valid compromise.
You may have to offer the KIT with those parts already mounted or you could lose a large potential market though.

The ADC and DAC are both DIP parts, available in 10bit and 12 bit versions.
The current sense amps are the ones that are SMD.
They are only SO8, pretty trivial to solder. If I was to get just them assembled, then I might as well get the whole PCB assembled, as the cost difference wouldn't be much. Then you might as well go all SMD to lower the cost, and so on it goes...

Dave.
« Last Edit: January 09, 2012, 11:10:18 am by EEVblog »
 

Online IanB

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Re: Dave's power supply mods.
« Reply #23 on: January 09, 2012, 01:35:52 pm »
I really have no problem with SMD in a kit. It's not like soldering through hole components is actually easy. Sometimes through hole devices can be damned hard and annoying!
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Online EEVblog

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Re: Dave's power supply mods.
« Reply #24 on: January 09, 2012, 01:48:50 pm »
I really have no problem with SMD in a kit. It's not like soldering through hole components is actually easy. Sometimes through hole devices can be damned hard and annoying!

Yeah, but most people don't see it that way, SMD scares them.
And SMD parts are a real PITA to kit up for and handle and sort etc, and people lose them, or can't read which cap is what etc.
That is why I don't do the uCurrent as a kit any more.

Dave.
 


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