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UC1875-SP: step-up/ step-down converter

Gadi Fishel
Prodigy 10 points
Part Number: UC1875-SP
Other Parts Discussed in Thread: TPS7H6003-SP, UC1875

Greetings,

Could a DC-DC phase-shift bull bridge topology controlled by the following component (UC1875-SP) be used for a step-up/ step-down converter?

Input voltages: 50VDC -200VDC

Output Voltage: 120VDC 

Power: 1500W 

Or is it only supporting step-up or step-down ( depending on the transformer)? 

If it is, could you please recommend a suitable controller for the step-up/step-down application?

Thank you!

  • 0
    TI__Mastermind 26295 points

    Hey Gadi,

    A phase shifted full bridge is able to step up and down.
    The UC1875-SP is the only space rated phase shifted full bridge controller we have available.

    If you are looking for a more updated controller the TPS7H500X-SP devices could be used to make a full bridge:
    https://www.ti.com/product/TPS7H5001-SP

    Thanks,
    Daniel

  • 0 in reply to Daniel Hartung
    Prodigy 10 points

    Thank you, Daniel!

    Does this mean the controller UC1875-SP can manage the output signals' duty cycle, not make it synchronous for step-up—step-down, or is it just dependent on a min to max ( up to 50%) Duty Cycle? 

    Thank you for the suggestion; I will also evaluate this controller option.

    Sincerely,

    Gadi Fishel 

  • 0 in reply to Gadi Fishel
    TI__Mastermind 26295 points

    Hey Gadi,

    The UC1875-SP device outputs a 50% duty cycle and then changes the phase between them to make the duty cycle of the converter.
    This controller does not generate synchronous rectification signals

    The TPS7H500X-SP devices change the duty cycle output of the controller.
    This controller does generate synchronous rectification signals.
    Note the TPS7H6003-SP also can generate synchronous rectification signals and is often paired with the controller:
    https://www.ti.com/product/TPS7H6003-SP

    A lower voltage example:
    https://www.ti.com/tool/PMP23200

    Thanks,
    Daniel

  • 0 in reply to Daniel Hartung
    Prodigy 10 points

    Hey Daniel,

    "Hey Gadi,

    The UC1875-SP device outputs a 50% duty cycle and then changes the phase between them to make the converter's duty cycle."

    It is entirely understandable, and I have an idea of how to make it for sync rectification. 

    My misunderstanding is based on the situation when the input, for example, is 50VDC, and when the input is 150VDC, the output must be stable at 120VDC.

    So, the UC1875 control loop can provide such control. I understand it will be a PWM duty cycle variation, and the same duty cycle ( just with a 180-phase shit) will apply to Full Bridge switches.

    It could work only if the transformer is designed as a 1:1 turns ratio.  Am I right?

    Thank you, and Sincerely,

    Gadi 

  • +1 in reply to Gadi Fishel
    TI__Mastermind 26295 points

    Hey Gadi,

    Im rather confused by your question.

    All the common isolated converters I know of can change their turns ratio to anything they want in order to scale up or down the voltage.

    A say flyback could have a 1:10 turns ratio, a 10:1 turns ratio or anything in between in order to produce any output voltage from any input voltage.
    There are limitations due to the input voltage variation that have to be taken into account.

    If I had a 50-150 VIN going to a 120 VOUT I might choose a 1:3 turns ratio.
    This would effectively look like 150-450 VIN to 120 VOUT converter on the output side, which is a possible down conversion for the output filter.

    If you did a 1:1 ratio a 50-150 VIN and 120 VOUT would not be possible as the output filter would effectively be a buck trying to do a boost operation.

    If you have trouble with this I suggest looking at something like Power Stage Designer which will help with your magnetics design and show you what the basic voltage/current waveforms look like:
    https://www.ti.com/tool/POWERSTAGE-DESIGNER

    Thanks,
    Daniel

  • 0 in reply to Daniel Hartung
    Prodigy 10 points

    Hey Daniel,

    I got it! You completely clarified my confusion. 

    Thank you so much!

    Sincerely,

    Gadi Fishel 

  • 0 in reply to Gadi Fishel
    TI__Mastermind 26295 points

    Welcome

    Thanks,
    Daniel