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Help figuring out this switching driver.

Discussion in 'General Electronics Discussion' started by PainfullyGrounded, Jan 7, 2015.

  1. PainfullyGrounded

    PainfullyGrounded

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    Nov 20, 2014
    So I picked up a few of these little drivers on ebay which are setup for constant voltage regulation. After looking at the datasheet, I noticed a few feature I would like to figure out and modify.

    Attached is the best macro I can take, but covers most of the traces aside from the input cap at the bottom and output cap at the top of the frame. The bottom of the board appears just to be gnd so all of the main connections to the IC are shown in this pic.. https://www.electronicspoint.com/at...5/?temp_hash=d1db38bfef2420f7ba91de9dadab050e

    I would like to have the ability to do the following:

    -control the soft start function / set the delay
    -set the maximum output current / preferably with an external trimmer
    -set the freq if possible to control pulsing / ^ not a priority like the above 2

    The datasheet for it > http://pdf1.alldatasheet.com/datasheet-pdf/view/551593/MPS/MP1584EN.html

    Now this driver is sold as a constant voltage source, but the datasheet indicate internal current regulation. Am I correct that changing the resistance value to pin 3 -comp- will set the current? and which pin and component would I change or alter to control the soft start function?
     

    Attached Files:

  2. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Without additional circuitry you are only going to be able to adjust the frequency (Pin 6). The other two are set internally and it doesn't seen like there are any options to modify this from the IC pin out.
    Adam
     
  3. PainfullyGrounded

    PainfullyGrounded

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    3
    Nov 20, 2014
    So there is no external components like the cap or resistors in line with pin 3 that could alter the max current? If not
    what kind of additional circuitry would be needed to at least set the maximum current?
     
  4. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    No pin 3 is for frequency compensation of part of the circuit. The simplest option for current limit is a simple resistor. But do you want just plain current limit of current scalable constant current? Tell us what you are going to be doing with this and I might be able to suggest something.
    Adam
     
  5. PainfullyGrounded

    PainfullyGrounded

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    Nov 20, 2014
    Im looking to use it as a constant current source for a laser diode adjustable from say 100mA up to the rated 3A. The issue with resistors to limit current is the vf of the diode lowers as the diode heats up and lowers its resistance. The input / output parameters of this driver are ideal for my applications I just need to find a way to set the current without altering efficiency such as using a transistor on the output which adds heat and wastes power.
     
  6. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Yep understood. Leave it with me.
    Adam
     
  7. PainfullyGrounded

    PainfullyGrounded

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    Nov 20, 2014
    Awesome, thanks for the help :D
     
  8. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    The simplest option might be something like this. You will need to read the data sheet to make sure it will do what you are after. You will need one hell of a heat sink if your running at full current. If it's a precision current source you need then that's a whole different thing. Much more to think about and often much more complex to design.
    Adam

    LT3083.PNG
     
  9. PainfullyGrounded

    PainfullyGrounded

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    Nov 20, 2014
    Thats why I want to stick with a switching circuit. Example, a diode that uses say 2A of current at 5V, the buck converter running an input of 12v will only draw 1.2A or so converting the surplus voltage to current. The higher efficiency comes in handy in that there is little heat generated by the driver. Or at least minimum when compared to other circuits.

    I have tried a few different drivers that are buck and current regulated but have issues in minimum output voltage which is an issue for diodes running 3v or less. This is why im pushing to get this little driver to work for my needs...
     
  10. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Have you considered an LED driver?
     
  11. PainfullyGrounded

    PainfullyGrounded

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    Nov 20, 2014
    I have, but for the most part they are constant voltage which leads me back to the problem I am having with this switching driver in my first post..

    This driver is ideal with only one issue which is getting current regulation out of it :(
     
  12. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    No they should be constant current, that's how they work mostly.
    Adam
     
  13. PainfullyGrounded

    PainfullyGrounded

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    Nov 20, 2014
    I have tried several and the ones that fit my criteria for minimal voltage output, with current regulation and a switching driver were always constant voltage or couldnt go lower than 3v out to the load. Ive used the AX2002 and AX2003 series, but again the minimum voltage out is not low enough.. Anything linear is too wasteful.
     
  14. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    I am thinking of using an IC not an off the shelf module. This should give you a bit more scope for what you want. I'll see if I can find something tomorrow. It won't be until later, so some of the other guys might beat me to it.
    Adam
     
    PainfullyGrounded likes this.
  15. PainfullyGrounded

    PainfullyGrounded

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    Nov 20, 2014
    Thats cool, thanks for the input. Im going to bread board this driver and tinker with it, you just never know. I have stumbled on stranger things by doing so and my fingers are crossed!

    Im still tinkering with eagle and have a couple of designs I need to finish and get to a boardhouse but im still learning the software lol At least im learning as I go.
     
    Arouse1973 likes this.
  16. ike2903

    ike2903

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    Jan 7, 2015
    Im still tinkering with eagle and have a couple of designs I need to finish and get to a boardhouse but im still learning the software lol At least im learning as I go.


    That sounds good. It is very good to people are learning the skill by themself.

    Looking forward to tomorrow.
     
    PainfullyGrounded likes this.
  17. PainfullyGrounded

    PainfullyGrounded

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    Nov 20, 2014
    Okay, so here is the other driver which I just got to checking and thinking...
    Firstly if im not mistaken, I can set the soft start on this with a cap. Yes?
    [​IMG]

    Also, could it be possible to trick the IC into sensing voltage across a resistor for its
    voltage reference?

    What im thinking is the same idea as using say a 1R resistor in series with a load
    reading across the resistor (shunt? not sure if thats the right word) and converting to mA with a DMM.
    If that voltage stays the same, would that not translate to a set current? Maybe a small separate PCB
    and circuit to enable such a function?

    Its 2:30am bare with me. Am I making any sense? resistor? lol
     

    Attached Files:

    Arouse1973 likes this.
  18. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Hello

    Ok so here is the basic idea I was thinking of. Use the voltage developed across a sense resistor (R1) to control the feedback control. The circuit here is one I added the CC control part to a device from the LT spice library. It had all I needed apart from 3 A current rating. Trying to find the right part is a nightmare with so many different options.

    So you will need to search for one that fits the bill, I would probably try and find one that had a settable Imax pin also . This design is set up for 0-2.5 Volts to control 0-250 mA using V2. I included an enable because there is no hot plug capability with this circuit, I didn't know if it was important, with a lot of lasers it is, they can be damaged quite quickly by over voltage / current.

    I think you already had this sort of thing in mind but maybe just needed an example to get things going.

    Adam

    LT1504_CC.PNG
     
  19. BobK

    BobK

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    Jan 5, 2010
    Many of the cheap switcher modules on Ebay have a current limit adjustment. These can be used as a constant current supply by setting the current limit to the desired value and setting the voltage limit at the max.

    Bob
     
  20. PainfullyGrounded

    PainfullyGrounded

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    3
    Nov 20, 2014
    Sorry for being a pain, but that just confused me a bit more lol Can you isolate the parts I would be adding, or is
    that entire circuit the 'add on'?

    I more or less was looking to get an idea how I would go about breadboarding this, and get lost if its too complex.
     
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