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Creating +/- 15V with each 4A power out of 24V, 14A power supply

David Michalik
Prodigy 30 points

Hey guys,


I'm searching for a way to generate +15 and -15V with each 4A power to supply two galvo motors. The voltages must be symmetrical to each other, that's why I tried to find a solution with either the same regulator or just one regulator, please correct me if this thinking is not correct. (The power supply is no problem, I will use an external 24V power supply with 14A.)


While reading through many articles I found two ways to solve this challenge.

1.) Using two buck regulators, one in the regular buck mode, the other in inverting buck-boost (IBB) mode. The challenge here for me was that I could'nt find any information on how much current I can expect when using the IBB mode of a regulator, could anybody help me here?

2.) Using a Transformer-coupled split-rail design using the step-down regulator as mentioned in a paper by Rich Nowakowski (“Techniques For Implementing A Positive And Negative Output Voltage For Industrial And Medical Equipment,” by Rich Nowakowski, Texas Instruments, How2Power Today, October 2012.). But I couldn't find a buck regulator with min. 8A and the necessary voltages.


Thanks in advance for your help!

Best regards

David

  • 0
    TI__Mastermind 35135 points

    I recommend the first option. The current can be estimated based on the duty cycle which is D = Vout/(Vout-Vin). For example with 24V to -15V, the duty cycle is D = -15/(-15-24) = 0.38. The average switch current is then Iout/(1-D) = 4A/(1-0.38) = 6.4A. This doesn't include efficiency or ripple current so the peak current could be closer to 8 A.

  • 0 in reply to Anthony F
    Prodigy 30 points

    Thanks for the replay Anthony!
    Do you have a part in mind that would satisfy these requirements?

    Thanks in advance!

    Best regards

  • 0 in reply to Anthony F
    Prodigy 30 points

    Thanks for the replay Anthony!
    Do you have a part in mind that would satisfy these requirements?

    Thanks in advance!

    Best regards

  • 0 in reply to David Michalik
    TI__Mastermind 35135 points

    Hi David,

    I don't work with any parts which would support this so I don't have a part in mind. I suggest looking for a synchronous buck controller which uses current mode control. For the inverting buck-boost circuit current mode control can be easier to compensate. In an inverting buck-boost the pole of the output filter moves with duty cycle and with current mode control it is mostly a single pole instead of a double pole.

    Best Regards,
    Anthony