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    Question about MC33063

    Hello community !

    I'm an hobbyist doing some stuff at home.
    I have a question regarding this schematics coming from a commercial product.

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    I made (or I took) the same circuit at home, but I don't have 5V at the ouput but only 1,7V.

    After that I putted those value into many "online MC33063 simulator" and this seems that don't work.

    I have a doubt about the inductor type. I have chosen a 10uF 1,3A. But I don't know if there is other parameters to take in account.

    Can someone help me please ?

    KR.
    Stefan.

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    Re: Question about MC33063

    What is your input voltage? I think your inductor might be too small. Looking at the data sheet, they're using values of 170-220 uH. How did you "choose" that 10uH value?

    (And I assume you meant you were using a 10uH inductor, not a 10uF...)


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    Re: Question about MC33063

    Quote Originally Posted by barry View Post
    What is your input voltage? I think your inductor might be too small. Looking at the data sheet, they're using values of 170-220 uH. How did you "choose" that 10uH value?

    (And I assume you meant you were using a 10uH inductor, not a 10uF...)
    Hi ! thank you to take the point,

    - My input voltage is 12VDC (but may be 24 in the future...)

    - Yes, sorry for the mistake, it's 10µH :
    http://industrial.panasonic.com/cdbs...GM0000CE13.pdf
    ref: ELL6PG100M

    And fortunately I know the datasheet. But it seems the couple inductor/capcitor is calculated for each configuration, right ?

    I choose this 10µH value because, I didn't want to reinvent the wheel. It's a power supply coming from a "Commercial PIC32 dev board" . I made the same board but with the TFT/lcd plugs needed.
    My 1st link is just a screenshot of their datasheet schematics.



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    Re: Question about MC33063

    10uH is far too small, by a factor of at least 10. I would go for 220uH.
    I'm not sure what D4 does either, it will always be conducting so it serves no useful purpose.

    Brian.
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    Re: Question about MC33063

    With your chosen CT=820pF…..that gives you ton = 20us and toff = 4us.
    Generally you won't use all that on_time…you will hit the current sense reference of 300mV long before 20us….so basically, your buck is behaving as a constant off time buck converter with an off time of 4us….however, your fet may be off for more than 4us in any time interval due to the FB comparator…..so I also added a comparator feedback on the external voltage loop.
    The attached is an LTspice simulation showing you how your buck works…you can sub in inductors and loads and see what you get….look at the peak inductor current….basically your peak inductor current will be 0.3V/0.235R = 1.27A
    I have given you an effective current sense trip threshold of 300mv like in the MC33063.
    To make it more accurate…you could implement BJT instead of FET, and get the relevant on state voltage.

    LTspice is a free download from linear.com..now analog.com

    BTW i assumed your load was 2.5W...but please change it if yours is different...what is your load by the way?

    - - - Updated - - -

    to run the sim, change .txt for .asc...then open it in ltspice...then hit the running man icon.....then fill in how long you want the sim to run for, the start time, etc


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    Re: Question about MC33063

    Can I reveal here the real board ? (because it's a commercial link)
    The last revision of the datasheet AND photos seems to show us a 10µH inductor. I'm feeling better because I pointed ( I think) the good component.
    But with the results: I'm completely lost !



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    Re: Question about MC33063

    Hi,

    My recommendation: instead if using random circuits from the internet better use the datasheet and application notes from the manufacturer..
    They should give all information to make the circuit work reliably.

    Klaus
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    Re: Question about MC33063

    What is your max load?



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    Re: Question about MC33063

    Quote Originally Posted by treez View Post
    With your chosen CT=820pF…..that gives you ton = 20us and toff = 4us.
    Generally you won't use all that on_time…you will hit the current sense reference of 300mV long before 20us….so basically, your buck is behaving as a constant off time buck converter with an off time of 4us….however, your fet may be off for more than 4us in any time interval due to the FB comparator…..so I also added a comparator feedback on the external voltage loop.
    The attached is an LTspice simulation showing you how your buck works…you can sub in inductors and loads and see what you get….look at the peak inductor current….basically your peak inductor current will be 0.3V/0.235R = 1.27A
    I have given you an effective current sense trip threshold of 300mv like in the MC33063.
    To make it more accurate…you could implement BJT instead of FET, and get the relevant on state voltage.

    LTspice is a free download from linear.com..now analog.com

    BTW i assumed your load was 2.5W...but please change it if yours is different...what is your load by the way?

    - - - Updated - - -

    to run the sim, change .txt for .asc...then open it in ltspice...then hit the running man icon.....then fill in how long you want the sim to run for, the start time, etc
    Dear treez, thank you !
    I knew it was a LTSpice file since I opened it.
    It's seems to be "more accurate" as you said. I see it's an "emulation of the MC33063". I'm also not really familiar with "electronics simulator".



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    Re: Question about MC33063

    Quote Originally Posted by treez View Post
    What is your max load?
    This supply must power a µC (PIC32 at 3.3V with LT1117 converter) and (at least) a TFT at (or giving for) 300mA at 5V.
    I think 500-600mA should be the minimum for future development.



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    Re: Question about MC33063

    for information :
    https://www.olimex.com/Products/Duin...NO_AND_OTG.pdf

    How can they have this power supply working ??

    oh... unfortunately, my board is already done.
    Powering by USB is fine. That's my bad side... I know...

    - - - Updated - - -

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    My board with a power issue....



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    Re: Question about MC33063

    MC33063A is important to get exact part - also read the data sheet very carefully ...!

    - - - Updated - - -

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    here is the ckt from the data sheet - start with this I think ...



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    Re: Question about MC33063

    Quote Originally Posted by Easy peasy View Post
    MC33063A is important to get exact part - also read the data sheet very carefully ...!

    - - - Updated - - -

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    here is the ckt from the data sheet - start with this I think ...
    Good morning all !

    As I said, I know the data sheet. I mean : I know there is a good example in it. (5V 500mA, example you join here, can do the trick...)

    But the Olim** board looked like easy to reproduce.
    It seems "open-source" is not really "open".....
    I was believing a commercial board must pass tests before it can be sell....
    (maybe their forum is more appropriate to ask my question ? I don't think so, since the answer given directly by the support ...)

    If I had to design a entire board, I probably may putted a "1205" converter. (not a good choice I know)
    For this board I was thinking it was not necessary to "think all the component", as "A Power supply for a dev board" seems to be "easy" (or common...)

    Finally,
    Yes, I can replace some components to stick to the TI datasheet.
    But, that can't help me to understand "how Olim** can produce 5V with this configuration ?"



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    Re: Question about MC33063

    Do you have it working now?



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    Re: Question about MC33063

    The most likely reason it works is the schematic has the wrong value marked on it. Probably just a typo but possibly to stop people copying it. If that is the reason, it worked!

    Brian.
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    Re: Question about MC33063

    Quote Originally Posted by betwixt View Post
    The most likely reason it works is the schematic has the wrong value marked on it. Probably just a typo but possibly to stop people copying it. If that is the reason, it worked!

    Brian.
    So they even mount a false board (with value wrong value) to take picture of it ?
    if this is the case, I don't qualify this product as open source (as they claimed...)

    - - - Updated - - -

    Quote Originally Posted by treez View Post
    Do you have it working now?
    not really, but now, I know almost all value seems to be wrong...
    I believed this schematics, I had all the component at home so I decided to follow this one...
    I mean, even Microchip Datasheets of their dev board are precise, and have right values...

    "Oh my god ! they put a motor in this car !? they copy Ford !!"
    or
    "Oh my god, they put wheels on this car !? they copy an other brand !!"
    .....

    I just wanted to power this board. So don't need to re-invent the wheel as I said it.
    I have so many works to put in the µC and all the idea there is around it, that I believed I was able to pick some part...

    (think about cook and recipes... I'm not coping the person that gives the recipe...)



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    Re: Question about MC33063

    Hi,

    IC manufacturers are interested in selling their parts, thus they provide datasheets and application notes and some other informations, documents, tutorials, movies...
    ..to ensure you make it working and you are satisfied with the function..

    But other members of the internet ... are not that interested that you make it working...

    Klaus
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    Re: Question about MC33063

    Lesson learned: Always do functional simulations before mounting the prototype on breadboard. It gives you the opportunity to confirm even if there exists some detail you overlooked on your specs. Even a very simple circuit can hide some constraint that is present in the model and/or in datasheet.
    --------------------------------------------------------------------------------------------------
    Part of the world that you live in, You are the part that you're giving ( Renaissance )



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    Re: Question about MC33063

    So they even mount a false board (with value wrong value) to take picture of it ?
    if this is the case, I don't qualify this product as open source (as they claimed...)
    Doesn't is have '100' marked on the inductor in the photograph. Most likely 100uH than 10 x 10^0.

    Incidentally, that board looks remarkably like one I'm developing at the moment including PIC and ESP32 module but mine uses an MCP8403 regulator. I didn't copy it, great minds think alike!

    Brian.
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    Re: Question about MC33063

    Hello !

    ok...I will pay more attention next time... (That's the first time I use a step-down converter on board...)
    But now I have to make this board working changing the less component possible.

    Can anyone confirm this : (?)
    - (in a Simulator...) > lowering the Ct capacitor to around 220pF seems to be working with the Olim** other value (powering by 12V and putting 5V 700mA in load)

    (a little error indeed...?)



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