Need Help on DC/DC

Discussion in 'General Electronics Chat' started by jesiowiec, Mar 11, 2010.

  1. jesiowiec

    Thread Starter New Member

    Mar 2, 2010
    3
    0
    Hi all!

    I have some small problem. I need to design circuit which will change 0...10VDC (form power supply) to 0..50VDC (to supply BLDC) an output current should be 2,5A. How can I solve this problem? What will be better: operational amplifier, switching regulator, voltage multipliers or boost converter?

    Regards :)
     
  2. kkazem

    Active Member

    Jul 23, 2009
    160
    26
    Hi,
    I'm a professional power supply designer with over 35 years in AC-DC (switching & linear types) DC-DC, and DC-AC Inverters. First of all, I don't know what you mean by having an input of 0 to 10 VDC and raising it up to 0 to 50 VDC. The 10V and the 50V part are no problem, but If you think you can have a regulated 50V output from a 0 to 10V source, there is no way without extreme measures. But if you mean you want a DC-DC that increases the input by 5 times, from 0 to 10VDC in up to 0 to 50 VDC in at 2.5 amperes output, it perhaps can be done, but there is one issue you must first overcome, and that's the input bias circuitry. In order to run the converter, you generally need a bias power supply (usually derived from the DC input) of around 10 to 15 VDC. If you have a separate supply for this, then no problem. But if you only have the 0 to 10 VDC input, then the converter generally cannot run until the input gets to at least 3 to 5 VDC, and that would require special low-voltage circuitry made for battery operation using two, 1.5V cells in series. But setting the bias supply question aside for now, you'll need a boost converter. It could be done with a power op-amp, or an op-amp connected to a power transistor circuit, but that would also require a bias supply of more than 50VDC in order for you to get 50 VDC out of it. If you want it to be fairly simple, it can be done with a self-oscillating circuit using two bipolars and a transformer with feedback windings for driving the bases. This requires a magnetic material with a square BH loop, like square permalloy. If you go to the Magnetics, Inc. website, http://www.mag-inc.com , you'll likely find some white papers or application notes on self-oscillating DC-DC converters. Or, you can use google to search the web for self-oscillating dc-dc converters. If you can find one, you could use a PWM IC made to run on 2each, series 1.5V battery cells, which should work down to 2.5 VDC input. However, you may need a 3-terminal linear regulator or zener diode circuit to limit the DC input voltage to the IC if its maximum input is say 5V for example. I doubt that an IC made for that purpose could also run off of 10 VDC.
    Well, I hope that helps.
    Regards and good luck. Feel free to ask me additional questions if you wish.
    Kamran Kazem
     
  3. jesiowiec

    Thread Starter New Member

    Mar 2, 2010
    3
    0
    Hi,
    By having an input in range 0..10VDC I mean I have power supply which can ensure up to 10VDC, but I have a motor which need 48VDC, because of that I need to change voltage from 10 to 48V. So I have motor and supply and then I need to build a boost converter but I don't have any idea how it should look like? And in this point I am looking for help.
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    The DC/DC converter will take more than 12.5 A from the 10 Volts powersupply.
    It will be more because of the efficiency factor of the DC/DC converter, wich will be about 80 - 90 %.
    So at 80 % it will even take about 15 A.
    Is building a seperate powersupply for the motor not an option?

    Greetings,
    Bertus
     
  5. jesiowiec

    Thread Starter New Member

    Mar 2, 2010
    3
    0
    It is a kind of solution, but I am looking for the easiest one. Because of that I am also looking for some ideas.
     
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