Author Topic: [HOW TO] Arduino digitally controlled step down buck dc converter  (Read 11950 times)

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Offline MOROZAW

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Welcome!
This is my first post on this forum!
My name is Dominik and I am from Poland!
I can't find similar topic on this forum and in a web so please help me with my problem.
Almost all topics in web not satisfy me and I am still looking for solution my problem.

I am looking for the best way to control synchronous dc-dc converter output voltage via uController.
My problem is how to control output voltage from converter.
I would like to control 4 dc converters from one Arduino.
My input voltage is 12,4V and output voltage should be from 5V to 90-100% of Vin.
My output current is up to 3A.

I have found this application note:
http://www.maximintegrated.com/app-notes/index.mvp/id/818

but I am not sure if it is the best way.
Firstly I was thinking about last option with filtered PWM, but I wouldn't like to make feedback to uC.
My second idea was to replace the potentiometer by digital potentiometer, but it's little complicated and I think little overkill.

I would like to only set voltage via PWM or voltage or other signal and "send" this information (voltage which I wanna have on output) to converter without feedback to uController. DC converter should work alone without "help" and modify them PWM signal to maintain the output voltage which I wan't.
Is this possible?
I hope You know what I mean :)

Yesterday I found this two completely different schematics and way to modify feedback loop in dc converters.
Please check the attachments. I think this is it what I am looking for. What do You think about my problem?

If this topic should be inserted into other, please merge this to appropriate topic.

Best regards,
Dominik
 

Offline Prime73

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Re: [HOW TO] Arduino digitally controlled step down buck dc converter
« Reply #1 on: March 18, 2014, 12:59:14 am »
Watch Dave's videos on his DC power supply where he covers voltage/current control using arduino. Seems like exactly what you need.
 

Offline Spike101

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Re: [HOW TO] Arduino digitally controlled step down buck dc converter
« Reply #2 on: March 18, 2014, 05:54:41 am »
I am currently trying to do the same thing.

What i found is this:
http://www.microchip.com/forums/m688260.aspx

Seems to be similar to what you found, but maybe a bit simpler to implement?

Watch Dave's videos on his DC power supply where he covers voltage/current control using arduino. Seems like exactly what you need.

I didn't know Dave covered that in a video. Do you have the video nr.?
 

Offline MOROZAW

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Re: [HOW TO] Arduino digitally controlled step down buck dc converter
« Reply #3 on: March 19, 2014, 11:09:00 am »
Thanks Prime for reply!
I will watch videos within few days  :)
Unfortunately I can't find any EE which can help me with design good feedback schematics, I have friend who can make whole PCB and finished product but he is not sure for this feedback loop so we need little kind of help.

Spike, Your link didn't work. I think Dave had in mind Power Supply Tutorial (from about #220 video).

I think schematics found by me would be the best, but I'm not sure which will be better.
Could anybody tell something more about this circuits?
Maybe somebody made something similar? :)

Greetings!
 

Offline MOROZAW

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Re: [HOW TO] Arduino digitally controlled step down buck dc converter
« Reply #4 on: March 31, 2014, 01:22:41 am »
Hello everyone!
I watched Dave's videos, but still I need some informations and help from You.
I need only to adjust output voltage using other voltage reference which is generated from uC after 2-nd stage RC filter and buffer.

After small thoughts I decided to use LDO instead SMPS for first project.
I would like to understand and learn firstly how to control output voltage before building SMPS.

I choose STM LD29150 LDO regulator. As I can see the most of the regulators use the same adjustment so this LDO is for example.

Could somebody help with this?
I would like to adjust V out from 5V to ~12V.
My Vin is ~12,2V, I have Vref from converting PWM to linear 0V to 5V.

//edit
Quote
Dave use LDO with "Single Resistor Programs Output Voltage", I have problem with converthing his CC schematics for my CV schematics. I think I cant drive voltage generated from uC directly to adjust pin in my LDO.
I know I must use op-amp with feedback, but I have problem with this.
If it is possible please help me with this part of schematics.

I have very high problem with finding somebody to help.

Any help would be appreciated.

Best regards,
Dominik
« Last Edit: March 31, 2014, 01:51:34 am by MOROZAW »
 

Online mariush

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Re: [HOW TO] Arduino digitally controlled step down buck dc converter
« Reply #5 on: March 31, 2014, 01:46:44 am »
LD29150 can only handle up to 1.5A and that's when properly heatsinked.

If you want 3A, consider using something like LT1084 (5A) or LT1085 (3A) which only have 1v dropout (so it allows you to adjust up to 11v if your input is 12v).

You could replace the resistor with a digital potentiometer or you could use pwm with a filter to get a voltage and feed that into the adjust pin .. see for example this for help: http://dev.emcelettronica.com/how-to-use-pwm-to-generate-analog-or-analogue-voltage-digital-circuits-part-2

Get some parts and practice and try stuff, don't just ask someone to do your work.
 

Offline MOROZAW

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Re: [HOW TO] Arduino digitally controlled step down buck dc converter
« Reply #6 on: March 31, 2014, 01:58:12 am »
Thanks mariush for reply!
I know how to filter PWM but I don't have any idea to interfere in ADJ pin.
1,5A is sufficient for my first apllication and project.
If it will work I would like to build another one with more Max Output Current.

I wouldn't like to use digital pot, as it was wrote at first post, apparently schematics with op-amp is this what I need, but I don't have idea how to change and use it in my application.
 


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