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DC to DC converter

DEVITH T
Prodigy 60 points
Other Parts Discussed in Thread: TPS40210

hi

we are designing power section for an FPGA based system :application(Medical).

Q1:        I need to convert 12v Dc voltage into both +150V DC and -150V DC ,the maximum current rating should be 0.5 A. Does any one suggest any IC based solution?

Q2:     if no IC based solution ,  Whether I have to use Inverting Buck boost topology?or Flyback?

Q3:     is any SMPS design already in this configuration by TI?

VIN=12V            Vout1 =+150V                   Vout2=-150            Iout(max)=0.5A

  • 0
    Prodigy 5 points

    Hello Devith, interesting application, thank you for posting.

    TI does not have any reference designs close to what you are looking for.

    150V,  0.5A=75W

    2x=150W

    150W / 80% efficiency =185W input

    185W from 12V = 15.5Amps average, peaks would be close to 2X that or 30Amps.

    Also 12Vin to 150Vout a boost duty cycle will be very high, too high in my opinion.

    From:

    Duty cycle =1-(Vin x Eff)/Vout= 94% , much too high.

    So a transformer is needed to help with the voltage conversion.

    Flyback or Forward converter would be best.

    185W is too much power for a flyback.

    You could make 2 flyback supplies, one for +150V 75W, one for -150V 75W.

    The negative supply would need and opto or feedback inverter circuit.

    A flyback topology could make +150V @ 75W.

    For -150V 75W the flyback could also work but use an opto isolator for feedback.

    There are many controllers that can be used for flyback.

    From this link in TOPOLOGY, select Flyback.

    PMP7127, not public, is close to what you need.

    20-28Vin, -120Vout at 600mA.

    This uses an op amp to level shift the –Vout to feed to the TPS40210 controller.

    The output can also be duplicated to make +120Vout, modify the op amp level shifter.

    These are some ideas.

    PMP7127RevA.pdf5732.PMP7127RevA.pdf

  • 0 in reply to Ed Walker
    Prodigy 60 points

    Dear EdWalker,

    First of all  ,Thanks a lot for your valuable inputs .

    i still have the confusion

    Q1: that where shold i kept a division in  choosing between Flyback and inverting Buck boost?

     

    Q2: how to invert the output of Flyback +150 to -150V?

     
    Q3:may be i'm wrong  

    1. Duty cycle =1-(Vin*η)/(Vout )=94%

    if i go with PWM with TOn=18 TOff using a 555 IC and A boost topology to get +150V and inverting buck boost to get -150V whether  this work or not?

    (say i don't want to use a transformer in my design )?

    2. say iam using a input supply of 12Vin,80A (Common supply for other blocks that's why 80 A)  and i reduced the load Current for +150V to 100mA so that  and -150 to100mA

    My new power requirement 

    P=15W*2=30W

    now whether i can go with 2 boost converters

     

  • 0 in reply to DEVITH T
    Prodigy 5 points
    Hello Devith;

    Flyback vs Inverting Buck Boost,
    Inverting buck boost will be duty cycle limited at some point.
    Just like a boost circuit, you prefer to operate at some reasonable duty cycle.
    Duty cycle affects peak currents in the power stage.
    When working the duty cycle equations, if I wind up with duty cycles above 90% then I start looking at the flyback.

    Flyback allows more reasonable duty cycles because the transformer turns ratio comes into play.


    Inverting the flyback output just requires tying Vout+ to ground and using Vout- as the output.
    As shown in PMP7127, the positive side of the output transformer is tied to ground.
    You can tie the flyback secondary anyway you want really, its just a transformer winding.


    95% duty is higher that I would like to go normally.
    You will need to evaluate the details:
    -can the IC reliably operate at 95% duty.
    -at 95% duty, the off time that current is sent to the output is very short, 5%, so the peak currents must be high to deliver all that output power in 5% of the time.
    -Inverting Buck Boost, -150V out from 12Vin, the power switch must handle 150+12=162V with headroom for spikes.
    So you are looking at a 200V power switch at least.
    -Flyback operating from 12V, a 50V power switch would work fine, its the diode on the secondary that must be rated at 200V.
    PMP7127 uses a 50V power fet BSC123N08, and a 400V rectifier.

    For +-150V at 15W each the best approach is a flyback with dual windings, center tap, regulate off the + output if your +- loads are balanced.
    If your loads will not be balanced, say heavy on + with nothing on -, and you are regulating the +, then the - will be more than -150V .
    Cross regulation would be the main concern, but it takes only one power stage, a primary flyback controller and a transformer with 2 outputs.
  • 0 in reply to Ed Walker
    Prodigy 60 points

    Dear Edwalker

    Thanks again for your valuable suggestions. Since the application is noise critical i have to think twice to go with transformer based design.

    any way from your suggestion i understood that  i can go with a power switch which can handle more than 162v with headroom spikes. With two separate power supply 

    Vout1  =  +150V using TPS42010 and power MOSFET IRFS4227pbF (VDS max 200 V VDS (Avalanche) typ. 240 V           RDS(ON) typ. @ 10V 22 mΩ        IRP max @ TC= 100°C 130 A )----Boost toplogy


    Vout2 =  -150V using TPS42010 and power MOSFET IRF9640 ( VDS = -200V      RDS(ON) typ. @ 10V  50mΩ    )------------------Buck-boost topology

     

    (i will consult your suggestion also in my team , ie one single power stage using a center tapped Fly back topology)

    once again thank you very much

    regards

    DEVITH T

  • 0 in reply to DEVITH T
    Prodigy 5 points
    I am glad to help Devith.
    Here is a tool that can help with power design:
    www.ti.com/.../powerstage-designer

    Power Stage Designer.
    It provides some basic calculations, allowing you to evaluate different topologies.