DC/DC Convertor for LEDs

Discussion in 'The Projects Forum' started by picazzo_1982, Apr 18, 2013.

  1. picazzo_1982

    Thread Starter New Member

    Apr 17, 2013
    Hi guys
    I wondering if you finaly succeded with this project.
    And i would like to ask your help.
    I'm an electronics and computers student in sweden and this is my third year.
    I'm doing a project course where i have to dimention and build a DC/DC convertor with the following caracteristics:

    Vin 12V
    Vout 36V
    Iout 6A
    Pout 200W

    We are gonna try to drive a LED array from a 12V DC battery.
    I did notice that my project it's very similar comparing to the project you guys were working with. That's why i would like to ask you guys, specially takao21203 couse you seem to have more experience on these king of constructions.
    Can I basicly use the same circuit that you have build on LTspice with the same components?? or do I have to modify a lot and I'm misstaken all the basic theory???

    I will attach the circuit that i did build on LTspice doing some basic calcules over a basic DC/DC boost convertor circuit, this way maybe you will get a better idea about what i'm looking for.
    My teachers comments after viewing my first LTspice circuit were following:

    C2 I_ripple = 8ARMS (16A pulser), (205uF is not standard value, 220uF closest)
    I_L1 18A aprox, (how is it a 45uH 20A bobine look like? , (sounds expensive)
    M1 has 50W power loos, reducing gateresistans to 1 ohm you could reduce power loos to 45W (10%), hard to cool these power looses.
    Finally the circuit has aprox 75% efficiency, litle low.

    Well guys thank you for your time and for your help.
    I hope you read this message and are still using this web site :)
    Hope here from you soon.

  2. #12


    Nov 30, 2010
    It is requested that you start your own thread because tacking on to the end of a thread that had been dead for most of a year is generally fruitless, and it is also considered to be bad to take over another person's conversation.

    I have informed the moderators. Most of them are not on duty at this time of day, but they will move this for you when they get back.

    Number Twelve
  3. Wendy


    Mar 24, 2008
  4. crutschow


    Mar 14, 2008
    You didn't attach your circuit. When you do, post the .asc file also.
  5. picazzo_1982

    Thread Starter New Member

    Apr 17, 2013
    Thank you for the information guys.
    I'm new in this forum and i apolpgies for my mistakes.
    Here i do attach the .asc file.
    It's a basic boost converter after basic calculations i have done.
    If you can guide me it will be great!!!!
  6. picazzo_1982

    Thread Starter New Member

    Apr 17, 2013
    Hello again!

    I would like to attach the other .asc file from the project i mentioned before that i think it´s similar to my project.
    Maybe this file will help litle to find the solution to my design??
    What do you think guys, or i´m following the wrong way??
    I notice that in this booster they succeded to get Vout 30V and Iout 3A.
    I need instead Vout 36V and Iout 6A.

    Thanks again
  7. takao21203

    AAC Fanatic!

    Apr 28, 2012
    At first thank you for mentioning me.

    1. 200uF or 220uF makes no difference for such circuits.

    2. 2n3055 is not a good choice, it is slow and has very low hFE.

    3. You could use a dual channel converter. A 20A coil might be very hard to obtain. Just for the coils, you can also parallel more than one coil.

    I have done a dual coil SMPS, it's a buck and I can run it at 400W. It is based on TL494 PWM IC.

    And I recommend cooling fans. The heatsink can be much smaller.

    Attached by the way the schematic, I did not use it 1:1 but left out the NE555, as well I made many modifications.

    I use a TIP36C power PNP instead of a MOSFET, because it has a tendency to latch when approaching the input voltage.

    It is an old schematic from Thailand, but I found it very workable.

    -DTC added
    -Frequency control added
    -Many components removed
    -2x 680uH 6A coils in parallel
  8. picazzo_1982

    Thread Starter New Member

    Apr 17, 2013

    Hello takao21203!

    I did try to build a circuit taking in consideration your picture file and TL494 datasheet examples, but i did fail.
    The circuit i build is not working at all as i was specting. I'm sure that i have done many mistakes mixing the other circuits examples and choosing wrong components maybe.
    Anyway i will attach my circuit and hope that you kan help me and guide me more.
    Thank you for your help and patience.
  9. picazzo_1982

    Thread Starter New Member

    Apr 17, 2013
    Or maybe it´s better if i take this other file som base and continuo working on that?
    Even whit this circuit i could´t get the values i want.

    Vout = 36 V
    Iout = 6 A
    Pout = 200 V

    Vin = 12 V
  10. takao21203

    AAC Fanatic!

    Apr 28, 2012
    Hmm. I must say I also have read the TL494 datasheet and I made some modifications.

    Maybe try to build it small scale with real components.

    Unfortunately I have not drawn schematics. But basically I only removed the NE555 on top of the circuit.

    I added DTC and used a different reference.

    It is a buck converter not a booster but can be changed easily.

    Also I use seperate 12V supply for the TL494.
  11. takao21203

    AAC Fanatic!

    Apr 28, 2012
    You need 20 Amps or more current at the input side.
    The coil wire needs to be very thick with low resistance.
    And the core must be large enough you don't run into saturation.

    Normally a transformer would be used for these currents, not coils.

    You can use a coil, but it's difficult to calculate them for this amount of power, and buy one with the right properties or even a blank core with suitable parameters.

    I have not worked much with bridge configurations.

    The TL494 is suitable for nearly any kind of SMPS circuit.