1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

UC3845 12v -> 24V 3A

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by arvinfx, Feb 25, 2009.

  1. arvinfx

    arvinfx Member

    Joined:
    Nov 5, 2008
    Messages:
    174
    Likes:
    0
    Hi

    Some body help me please

    I need Schematic for converting 12V to 24V With minimum 3A Current

    I use UC3845
     
    Last edited: Feb 25, 2009
  2. Ubergeek63

    Ubergeek63 Well-Known Member

    Joined:
    Apr 16, 2008
    Messages:
    1,886
    Likes:
    37
    you can start with the realization that you need a 20A inductor and a 50A FET...
     
  3. arvinfx

    arvinfx Member

    Joined:
    Nov 5, 2008
    Messages:
    174
    Likes:
    0
    20A Inducator!? how mach µH of it? 200µm is enough!

    I need Schematich for this IC uc3844-45 Boost Step-up ;)
     
  4. dave

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    -
    Likes:
    0


     
  5. Ubergeek63

    Ubergeek63 Well-Known Member

    Joined:
    Apr 16, 2008
    Messages:
    1,886
    Likes:
    37

    well it was a quick head calculation.

    12V means you are probably trying to run off a lead acid battery which drains to 10V unloaded and will be lower under load.

    the voltage ratio times the current delivered divided by efficiency equals average current:

    24/10*3/0.8=9A average

    since the inductor current is a ramp you will have at least double the average for the peak current, or 18A so 20A is not even conservative.

    Also you want to use a 3842, not a 44 since it will likely run over a 70% duty cycle.

    look at the data sheets, to make it a boost you use an inductor instead of a transformer, and a diode from the drain to the output capacitor.

    the inductor value depends on the frequency. Using a tapped inductor would allow a lower peak current rating...

    Dan
     
    Last edited: Feb 25, 2009
  6. arvinfx

    arvinfx Member

    Joined:
    Nov 5, 2008
    Messages:
    174
    Likes:
    0
    thanks Ubergeek

    But i still like use my UC3845 IC (lets try to explosion it )

    So , I not have many time and must have a schematic to finish this project.

    Do you have this one ? in datasheet not a good example for one boost output !!!

    I use the MC34063 and current is very low about 700ma Maximum power output for this IC and it not usable ...

    Best Regard
     
  7. Ubergeek63

    Ubergeek63 Well-Known Member

    Joined:
    Apr 16, 2008
    Messages:
    1,886
    Likes:
    37
  8. arvinfx

    arvinfx Member

    Joined:
    Nov 5, 2008
    Messages:
    174
    Likes:
    0
    Thanks about your documents!

    look at this is good sample?

    [​IMG]
     
  9. Ubergeek63

    Ubergeek63 Well-Known Member

    Joined:
    Apr 16, 2008
    Messages:
    1,886
    Likes:
    37
    seems reasonable. What is it rated for?

    Dan
     
  10. arvinfx

    arvinfx Member

    Joined:
    Nov 5, 2008
    Messages:
    174
    Likes:
    0
    rate of output voltage? or rate of useable?
     
  11. Hero999

    Hero999 Banned

    Joined:
    Apr 6, 2006
    Messages:
    14,902
    Likes:
    79
    Location:
    England
    He's talking about current rating.
     
  12. arvinfx

    arvinfx Member

    Joined:
    Nov 5, 2008
    Messages:
    174
    Likes:
    0
    I don`t now but must be 1 or 1.5A some one give to me and say its work ! but i now 10uH in self is very low for me!
     
    Last edited: Feb 28, 2009
  13. Ubergeek63

    Ubergeek63 Well-Known Member

    Joined:
    Apr 16, 2008
    Messages:
    1,886
    Likes:
    37
    you asked for 3A at 24V froma 12V battery. I was asking what the circuit that you posted puts out.

    If you want to use less than a 10uH you need to either reduce the frequency or the rated power, of course that is assuming that it is doing doing what you want otherwise.

    Dan
     
    Last edited: Mar 1, 2009
  14. arvinfx

    arvinfx Member

    Joined:
    Nov 5, 2008
    Messages:
    174
    Likes:
    0
    I only find upper schematic for example and it`s in accident near to my circuit ...

    about Self:

    I think high frequency provide to us low reple in output and also reduce efficiency! and i like to use bigger self in my circuit but How much uH? what is the formula ?
     
  15. Ubergeek63

    Ubergeek63 Well-Known Member

    Joined:
    Apr 16, 2008
    Messages:
    1,886
    Likes:
    37
    Sorry I did mean a larger inductance... the formulas depend a lot on how the chip runs... in general you need to get enough energy into the inductor with out saturating it to get the amount of energy you need out of the converter.

    J=½I²L and I=tV/L and if memory serves W=Jf in this case (W=J/S).

    Dan
     
    Last edited: Mar 2, 2009
  16. arvinfx

    arvinfx Member

    Joined:
    Nov 5, 2008
    Messages:
    174
    Likes:
    0
    I build upper circiut and my output is 24V and current maximum is 1.5A ! its work ,i think if my source was stronger 1.5A can be added...
     
  17. Claude Abraham

    Claude Abraham Member

    Joined:
    Mar 17, 2006
    Messages:
    197
    Likes:
    23
    Location:
    NE Ohio, USA
    You will need to add current limiting. The boost topology is not protected against a shorted output.

    Regarding the inductor current rating, if the average inductor current is 9 A, then the peak will be greater. But, not 18 A if continuous conduction mode is used. The double value occurs if boundary mode is used. With a large enough inductor value, with 9A average, the peak can be 12A, while the valley can be 6A. As the L value increases, the ripple decreases, i.e. 11A peak w/ 7A valley, etc.

    Since the duty factor will exceed 50%, instead of a 3845, use the 3843. It is identical in all respects except there is no toggle flip-flop which limits duty factor to 50%. I'd use the newest CMOS version, the UCC28C43 part. Have I helped?
     
  18. Oblong

    Oblong New Member

    Joined:
    Aug 2, 2008
    Messages:
    50
    Likes:
    0
    Why don’t you use a modern controller like TPS40210 these are only about two bucks. There are lots of online tools to use here is TI’s. For your input / output.700kHz.

    [​IMG]

    Ratings for power stage components

    [​IMG]

    Just select the external components from your preferred supplier. You can get select a better mosfet Alpha & Omega Semiconductor make nice logic level ones low Qt Rdson good prices etc and pick a better Rectifier.

    TPS40210 product folder, with online tool.Spice models etc.

    Non-Isolated Switching DC/DC Regulators - DC/DC Controllers (External Switch) - TPS40210 - TI.com

    another online tool
    Design of switch power supplies
     
    Last edited: Mar 11, 2009
  19. arvinfx

    arvinfx Member

    Joined:
    Nov 5, 2008
    Messages:
    174
    Likes:
    0
    Hi, Oblong

    Thanks about your remark, At end my UC3845 has been explosions and i buy another UC3843 it make for me about 21 volt and 2.8 AMP to! u think i must use TPS40210 and UC384x can`t handle my Load!?

    I see the sites its perfect! thanks about that too.

    AW! forget this-> IS RIGHT? : THE WATTS OF BOOST TOPOLOGY IS 150W AT MAXIMUM AND PERFECT DESIGN ?!!!!!!
     
  20. Oblong

    Oblong New Member

    Joined:
    Aug 2, 2008
    Messages:
    50
    Likes:
    0
    I’m not saying you have to use the TPS40210, I’m saying there are better controllers out there for the same price or little difference. This one has internal slope comp, has a fraction of the current sense resistor power req etc. The reason I suggested that controller is; it is well supported with spice models the online tool and a very detailed design for a boost converter in the data sheet. The part is also widely available. Ultimately your choice will depend on what you can get. I live in North America so sourcing components for me is easy. Where you live this may not be the case.

    The above was meant as an example of what’s available to assist you in your design. If you go to other semi manufacturers they usually have tools that will recommend a controller for your design parameters. You still have to apply common sense obviously you want higher voltage rated caps and some of the other components should be upgraded. I use them as a general guide,to give me a rough idea of what I'll be needing.

    The controller doesn’t set the power output, the power stage components do, unless the controller has an integrated switch.
     

Share This Page