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inverting regulator -48V to 12V

Suraj K A1
Prodigy 40 points
Other Parts Discussed in Thread: LM78S40, MC34063A, LM5000, TPS55340, LM5576, LM5001, LM3481

Is there any way of creating a -48(-40 to -57) to 12V regulator using mc34063a or lm78s40 using some additional components? or is there a cheap solution for that? The current requirement is about 250mA

  • 0
    TI__Guru**** 164656 points

    Suraj,

    The voltage is too high for either device.
    I do not see an easy solution for this application.

  • 0 in reply to Ron Michallick
    Prodigy 40 points

    Is there any other simple solution using any other devices?

  • 0 in reply to Suraj K A1
    TI__Mastermind 35165 points

    Hi Suraj,

    You might be able to use the LM5000 or another one of the 75V input boost converters for this design in a configuration similar to what is shown in the following article. http://powerelectronics.com/power_management/converting-negative-input-voltages-positive-output-voltages-0909/

    I haven't tried it personally with these parts but I have made a negative to positive converter successfully with the TPS55340.

    Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 40 points

    Thanks. I will try it.

  • 0 in reply to Suraj K A1
    Intellectual 450 points

    Suaraj,

    I have designed the same circuit , having same requirement of course board is under design and still to test..

    below is the webbench report if you want to refere, it is designed using LM5576 - You may want to refer that.

    3312.-48V_design.pdf

    I do have some open issues in this design regarding, exposed pad and enabling function, you may want to refer following discussion on e2e

    http://e2e.ti.com/support/power_management/non-isolated_dcdc/f/196/p/210934/746751.aspx#746751

  • 0
    TI__Expert 4365 points

    Hello Suraj,

    The two devices you mention would be complicated to trick into operating correctly in this application because they have a current sense input that is referenced to the VIN input terminal of the IC. While it may be possible to use those devices it would be troublesome to debug and validate. The best choice is a boost regulator or controller that has a ground referenced current sense in the source (or emitter lead) of the low side switch. Since this is a boost derived topology it must be a current mode control method.

    Perhaps the name of this topology is called Inverting Boost-Buck or maybe just negative to positive converter. The "ground" of the boost circuit gets tied to the negative incoming rail and the input of the boost is tied to the common return line of the incoming supply. A current mirror is used across the boosted output to provide the correct feedback action.

    I just drew up the attached application schematic but have not tested it. It at least shows the approach though and will give an idea of what is required. The power components need to all be optimized and the compensation parts verifed. But schematically everything is there. Be aware that the max switch voltage of the LM5000 is 80V and this application needs 57 + 12V + 0.7V ~= 70V so there isn't a lot of margin as far as switch voltage goes. This means that the PCB layout must be very clean. Also the switch current rating of the LM5000 is 1.35A min guarateed which is larger than needed. This application could be attempted with the lower current LM5001 product but it has only a 75V switch rating so there would be even less switch voltage margin.

    An alternative device would be the LM3481 controller coupled with a 100V mosfet if you want higher switch voltage margin and a design that is scaled for 200 mA output.

    0486.5000_-48_to_+12_Schematic Prints.pdf

    Alan Martin TI - SVA

     

  • 0 in reply to Alan Martin
    Prodigy 40 points

    Thanks, Rizwan and Alan.

    I will check the circuits and let you know.