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UCC28740: 3 Ph AC to DC without Neutral

Part Number: UCC28740
Other Parts Discussed in Thread: PMP30164

Dear Team,

I want to make a design for Three phase AC to 5 VDC, so followed this reference PMP30164. Please verify the attached circuit and let me know your feedback on this. Also please clarify the below queries.

1. Will this circuit work without Neutral by feeding just 3 Phase input. If not please suggest the reference design without neutral.

2. What if any one of the phase got disconnected, will this design still converts to DC?

My ultimate aim is to design a circuit without neutral and if the phase 2 line disconnects, still the design should to DC.,

Please help me out on this.

Regards

Sagar

RIO_EXT_3184_IoT_MOTOR_CONTROLLER.pdf

  • Hi Sagar,

    Thank you for the query.

    I checked the flyback section and it is similar to PMP30164 for 5V and 2A so there should not be any concern here. I do not know about amplifier/current and voltage sensing as it uses a different IC.

    1. We do not have any readily available reference design to demonstrate this without the neutral. But ideally it should work. From your schematic my only concern is if the rectifier D50 pin 3 is floating? Also during unbalanced load condition, when one phase is disconnected, the other two phases have to carry the return current in the absence of neutral. This floating diode node can be at a higher common mode voltage which can push the Vbulk higher than required value. I also wanted to know the purpose of EGND fro your schematic? Do you plan to have it connected to this floating node?

    2. As far as PMP30164 is converned, even if one of the line disconnects, it will maintain DC across the High voltage DC side and the flyback will maintain regulation. This can be verified quickly by simulation.

    Please let us know if you require any clarifications.

    Thank you

    Regards,

    Harish

  • Hi Harish,

    Thanks for the reply.

    As per PMP310164 reference design, D50 pin number 3 connected to the Neutral for safer side provide a port.

    Please explain me more about this point 

    This floating diode node can be at a higher common mode voltage which can push the Vbulk higher than required value. 

    EGND is used to make a reference point for Voltage and Current Monitoring. 

    I hope I need to change EGND to PGND in the design. Please correct me if am wrong.

    Regards

    Sagar.

  • Hi Sagar,

    Thank you for the reply.

    The circuit will work fine. under normal operating conditions and even if one of the phase is disconnected.

    I was mentioning in my previous post that if two of the phases were disconnected in the absence of neutral, there could be an issue which I do not think is in your criteria/requirement. 

    Seeing the voltage sensing circuit, you have an isolated amplifier (where one side is referred to EGND and other side is referred to GND). So changing EGND to PGND would make sense.

    But I am not able to see isolation in the current sense signals? Do you use CTs or LEM? I_MON_P1 does not seem to be referred to GND (from the available schematic)

     Please let us know if you have any clarifications.

    Thank you

    Harish

  • Hi Harish,

    Thanks for the Reply.

    Will take a Note on changing the EGND to PGND.

    I was mentioning in my previous post that if two of the phases were disconnected in the absence of neutral, there could be an issue which I do not think is in your criteria/requirement. 

    Noted, since single phase requires Neutral

    But I am not able to see isolation in the current sense signals? Do you use CTs or LEM? I_MON_P1

    Yes we are using CT's for current measuring, planned to use EGND reference. Is it fine to use EGND? Please let me know your suggestion on this.

    Regards

    Sagar

  • Hi Sagar,

    Thanks for coming back.

    The signals from the isolated side of CT should be directly referred to your main controller GND which is monitoring these signals. So if IMON_P1 etc. signals are directly going to main MCU (i.e connector J9 is on isolated side), they should be referred to GND.

    Hope this helps. Please let us know if you have any clarifications.

    Thank you

    Regards,

    Harish

  • Hi Harish,

    Thanks for your kind reply, the given feedback solves my queries. 

    Once again thanks for the feedback and kind replies.

    Regards

    Sagar

  • Hi Sagar,

    Thank you for the feedback. 

    Regards,

    Harish