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PCB Layout Guidelines for Merging High Voltage and DC Signal in single Board.

SHREYAS S BAGI
Intellectual 400 points

Other Parts Discussed in Thread: UCC28710, UCC28742

Hi,

In our Project, we are using Input Voltage 230V line having Common mode choke, differential noise removal and filter. We are generating Voltage 24V @ 2A. From 24V ---> 5V ---->3.3V ------> 1.5V -----> 1.1V.

The voltage rails 5V, 1.5V,3.3V and 1.1V are going for Digital IC and Digital section.  

Questions :

1. PCB Layout guidelines for combining the High voltage AC and DC in a single board? Please provide resources ( layout files, schematics) for merging the boards.

2. What are the challenges and how to overcome challenges involved in " PCB Layout guidelines for combining the High voltage AC and DC in a single board"?Combination of the High Voltage and Digital Board

3. How to isolate the High Voltage and Low voltage rails in Board? The High voltage AC should add noise and disturb the Digital lines

4. How to choose the Stack up of PCB for the Merging High Voltage and DC Signal board?

  • 0
    TI__Expert 8210 points

    Shreyas

    For the AC/DC power conversion a design like PMP9041.  This design uses our offline flyback controller UCC28710 to step the high voltage AC down to a low voltage DC while providing galvanic isolation.  Please refer to this reference design for PCB layout example.  It's recommended to keep physical separation between high voltage and low voltage circuits across the isolation boundary to prevent interference.

    Below are some additional collateral we recommend reviewing to learn fundamentals of AC/DC power conversion 

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    Intellectual 400 points

    Hi Eric Faraci,

    Thanks I went through  PCB layout techniques for SMPS and flyback converters papers that you mentioned. I need information on PCB Stackup considerations for Merging the Digital circuit (Digital signal of IC like MCU and other IC's) and High Voltage (440V). I want info on how to merge the boards not information on individual topics like PCB layout of SMPS or Digital circuit. Please answer on Merging the High Voltage (440V) and digital circuit on a Single PCB .

  • 0 in reply to SHREYAS S BAGI
    TI__Expert 8210 points

    Shreyas

    We recommend that you use an isolated switched mode power supply, like a flyback with UCC28742, to convert 440V to low voltage DC.  This flyback power stage will provide galvanic isolation.  On the low voltage DC side, the voltage will be low enough to power your digital circuit and not corrupt signal quality.

    To insure that there is no coupling of high voltage signals to the low voltage side it's recommended that the PCB layout is designed in such a way where there is a physical line between HV and LV sides.  Only components that cross the isolation boundary, such as the transformer, y-capacitor and optocoupler cross this boundary.

    Best Regards,

    Eric

  • 0 in reply to Eric Faraci
    Intellectual 400 points

    Hi Eric,

    In our project, we are using an isolated Flyback converter only.

    1. Can you please elaborate and explain the statement " To ensure that there is no coupling of high voltage signals to the low voltage side it's recommended that the PCB layout is designed in such a way where there is a physical line between HV and LV sides. " ?.
    2. Please give some reference designs and reference PCB layout to understand the above statement (Point 1)?

    3. Do you think the stack-up of the PCB for high voltage and low voltage (Digital IC's like MCU, Processor) is the same ? Like, when we are talking about Multilayer board in terms of Layers, like FR4 material and Core in PCB is it same for even High Voltage also?

    4. Please tell me what is stack-up (PCB) to be considered ( in terms of layer guidelines) for merging High voltage and low voltage circuit section?

  • 0 in reply to SHREYAS S BAGI
    TI__Expert 8210 points

    Shreyas

    You can refer to our EVM https://www.ti.com/tool/UCC28742EVM-001 as an example of PCB layout.  In the user guide for this EVM https://www.ti.com/lit/ug/sluubu4b/sluubu4b.pdf?ts=1588166135987 you can see an image of this PCB.  If you look closely at the way the PCB is configured, all the circuitry that has high voltage (HV) is on one side of the isolation boundary and the all the circuitry that is low voltage (LV) is on the other side.  This physical separation protects against undesired coupling.  The PCB for HV and LV circuits can be the exact same.  The only main difference is that the HV nets need to maintain proper spacing to prevent arching.

    Best Regards,

    Eric