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MSP430F6736A: Current sensor in power monitor

Part Number: MSP430F6736A
Other Parts Discussed in Thread: MSP430I2040, MSP430F6736

Hi TI!

I am developing a power monitor and have seen the application reports for the MSP430I2040 (SLAA638) and the MSP430F6736 (slaa517).

In the application report: 'Implementation of a Single-Phase Electronic Watt-Hour Single-Phase using the MSP430F6736(A)' (slaa517f), Figure 2.1, Page 3. Attached is the image.

In my design GND is NEUTRAL. The current sensor is a small value resistor connected to LIVE, as shown in the picture.

I think the MCU is broken with the schematic shown in the picture. Because the LIVE (120/230 VAC) will be connected to the ADC of the MCU.

Am I right? The MCU is broken?

  • Hello,

    If the LIVE connection (120/230 VAC) was directly connected to a pin of the device, yes it is broken. You might have even seen some smoke come out of it. Slight smile

    A current transformer (CT) or shunt should be used to measure the current. I recommend taking a look at the full design guide here. In section 4.1, it mentions that the current inputs should not exceed 920mV. 

    Thank you

    Tim Claycomb

  • Sincerely, thank you very much!

    My problem is that I need to sense current in the live, because it is for a three phase system. I need to sense the current in each live.

    Honestly I would like to use the current sensing resistor option.

    As an alternative I have the idea of changing the polarity at the input of the power supply. Then the gnd of the MSP430 will be the live and I can put the sense resistor. Then I would need three power supplies and three MCUs. I show the idea in a picture.

    1-) Does the idea described above and shown in the picture make sense?

    2-) In case of the CT, could you please suggest me some commercial CT?
    3-) I think it is not a common component. Am I wrong?

  • Hi,

    1-) Does the idea described above and shown in the picture make sense?

    What you've drawn is a simple shunt configuration, which could work. However it is lacking any protection. It will be up to you to determine the best method to get current readings in your design

    2-) In case of the CT, could you please suggest me some commercial CT?
    3-) I think it is not a common component. Am I wrong?

    The current transform is shown in the schematic in the link that Tim sent. It is not a single device but a circuit in itself. Here it is for reference:

    Regards,

    Evan

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