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DCDC Converter Help 60V-588V Input With Fixed Output of 24V DC

Suraj Bhullar
Prodigy 10 points
Other Parts Discussed in Thread: UCC28881, UCC28740

Hello All,

I am currently working on a project and our team seems to be stumped. We are working with a large battery pack that will output a maximum voltage of 588V DC, our nominal voltage is 518V. For some of our safety boards, we require specific faults to trigger when there is 60V or greater present outside of our battery pack. We thought that it would not be very feasible to take in direct voltage for our boards, so we are attempting to find some sort of way to step down this large range of voltage: 60-588V, to a much more manageable 24V which will act as a signal of "High Voltage" presence outside of the battery pack. We are having difficulty finding solutions such as a DCDC converter or a flyback converter that has such a specific input. Does anyone have any suggestions or ideas on how we can move forward to address this issue? It would be greatly appreciated if anyone could offer some insight.

  • 0
    TI__Expert 7900 points

    Hi Suraj,

    We have many PWM controllers or regulators that can convert 60-600V down to 24V.  What is not clear is what should the circuit produce below 60V?  Most of the controller/regulators are going to try to produce an output until Vin falls below the UVLO Stop threshold.  The UVLO Stop threshold is usually relatively low, in the range 4V to 20V.

    For example, the UCC28881 is a small, low current buck regulator that is rated to 700V.  The UVLO Stop threshold is ~3.6V.

    Regards,

    Eric

  • 0 in reply to Eric Reicher
    Prodigy 10 points

    Hello Eric,

    Thank you for your response, If I am not mistaken the UCC2881 takes in AC Input and Outputs DC, our team needs a solution that takes in DC and outputs DC. Also Ideally for any voltage under 60V, we would like an output of 0V, Is there any way to achieve this?

  • 0 in reply to Suraj Bhullar
    TI__Expert 7900 points

    The UCC28881 can operate from 700Vdc.

    It sounds like you simply need a comparator and a simple, low cost way to power it.

    1) Use the UCC28881 to generate an 18Vdc rail from the 60V to 600V input

    2) Operate a non-inverting comparator (with hysteresis) from the 18Vdc rail.

    3) Set up 60:1 resistor divider from HV input.  Apply it to the comparator to detect when Vin is above acceptable voltage (80V?) and will transition low when Vin is below 60V.

    Regards,

    Eric

  • 0 in reply to Eric Reicher
    TI__Expert 7900 points

    Here is a simple INVERTING comparator with hysteresis.

    The 18V supply would come from the UCC28881.

    SIMULATION RESULTS:

    When HV is > 120V the comparator output transitions low.

    When HV is < 60V the comparator output transitions high.

    Regards,

    Eric

  • 0 in reply to Eric Reicher
    Prodigy 10 points

    what would be the maximum output current? Also, why would the comparator output be high when the input is less than 60V? For our use case we would want from 0-59V to output low, and any voltage 60-600V would output high. I assume the UCC28881 would then drop down this high output from the comparator? Also is the output of the UCC28881  variable or is it fixed? 

  • 0 in reply to Suraj Bhullar
    TI__Expert 7900 points

    The maximum output current of the comparator, or the UCC2881 regulator?  I assumed you needed a logic signal to indicate high voltage present.  Logic signals typically supply mA of current.

    This is an INVERTING comparator example.  It was simple to understand, design, and simulate.  A NON-INVERTING comparator would have the polarity you want.  Comparators are covered in detail in many text books or you can Google "non inverting comparator with hysteresis" to find design examples

    Like I said in the description, the UCC28881 (or some other small, low cost regulator) converts the high voltage input (588V) down to something to power the comparator.  I used 18V in the example.

    If you need to reduce the comparator output you can use a pull-up to the VDD pin (5V) of the UCC28881 or some other regulator.  You will need to choose resistor values based on a 5V output.

    Eric

  • 0 in reply to Eric Reicher
    TI__Expert 7900 points

    Here is a simple, low cost design to convert 50V-500V down to 18V/0.2A using the UCC28740.

    1234.18V 0.2A Flyback.pdf