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TIDA-00476 SOLAR PANEL reverse polarity protection issue

BALKRISHNA TULSYAN
Intellectual 850 points
Other Parts Discussed in Thread: TIDA-00476

Hi,

I was going with the reference design of TIDA-00476 and on page 6 of the reference design i came across line which details the protection features that is incorporated in this design. it says "The system provides protection features such as battery and panel reverse polarity connection prevention, overcurrent, overvoltage, and so forth." 

BUT nowhere in the schematic i find the reverse polarity protection instead as per schematic it looks that only reverse current to solar panel protection is included at solar panel side by using MOSFET Q3 AND BJT Q8.

Am i missing something?? Whether Q3 and Q8 are also used for reverse polarity protection of solar panel along with reverse current protection??

Can anyone guide me one this and explain as which portion of the circuit contains reverse polarity protection of solar panel???

If reverse polarity of solar panel is NOT included  then is there any reference design which has SOLAR PANEL reverse polarity protection???

I am stuck on this and really require help.

Thank you...!!

  • 0
    TI__Intellectual 2815 points

    Hi Amit,

    The panel reverse polarity protections is provided through the Fet Q3A.

    To begin with the MCU checks the voltage acrros the P+ and P- connector using the R17,R18,R26,R28 and Q6 components. Only if the voltage is positive and greater than a threshold voltage is the FET Q3A truned on. If at startup the panel is accidentally connected reverse then the Q3A will block it by default and the MCU will not turn the Q3A on as the voltage is below the minumum accepted voltage.

    You can also see from the schematic that for sensing the panel voltage the Q3A need not be turned on

  • 0
    TI__Guru 71526 points

    Hi Amit,

      Also note that Sections 4.7 and 4.8 in he Design Guide ( Highly-Efficient Versatile Bidirectional Power Converter Design Guide ) describe the Reverse Protection.

    ~Leonard  

  • 0 in reply to Ramkumar S
    Intellectual 850 points
    Hi,

    First of all thank you for reply...
    Can u please explain, why additional Q6 component is required along with R18 and R28 for voltage sensing as it can be easily done with just R18 and R28 ??? Is there any additional benefit by using Q6??
    Normally i used to sense voltage by just using a voltage divider along with a 0.1uf capacitor for stability.
  • 0 in reply to BALKRISHNA TULSYAN
    TI__Intellectual 2815 points
    Hi Amit,

    The panel voltage is "floating" with reference to system ground and hence cannot be directlly measured using a potential divider. Q6 is used to convert the panel voltage into a proportional current flowing into resistor R28 (which is connected to system ground). The voltage across r28 is used to indirectlly measure panel voltage.
  • 0 in reply to Ramkumar S
    Intellectual 850 points
    This was the point that was haunting me for so many days, as how the panel voltage could be measured as panel ground is not connected to system ground (bacause MOSFET Q3A is isolating the two, it will be connected only if MOSFET Q3A is ON). Now i got a possible solution.

    Can u please explain that what formula will fit to measure voltage across R28??

    Normally if we use voltage divider, we use a formula as R28/(R18+R28) to find the voltage across R28. But u just said that it will be proportional to current flowing into resistor R28. Can you please explain in details as exactly which formula to use in order to measure voltage.

    Thank you so much...!!
  • 0 in reply to Ramkumar S
    Intellectual 850 points

    1st-->> Only if the voltage is positive and greater than a threshold voltage is the FET Q3A truned on.

    2nd--> for sensing the panel voltage the Q3A need not be turned on

    Doesn't this seem to be contradicting. One side you said that when the panel voltage is positive and greater than a threshold voltage then only FET Q3A is turned ON. on the other said "for sensing the panel voltage Q3A need to be turned on.

    If this is the case then how come you sense the panel voltage if Q3A is not turned ON. Can you please explain?

    I hope you understand my concern...!!!

    Thank you,

  • 0 in reply to BALKRISHNA TULSYAN
    TI__Intellectual 2815 points

    The 2nd point says "for sensing panel voltage the Q3A need not be turned on".

    I hope that clarifies your doubt

  • 0 in reply to Ramkumar S
    Intellectual 850 points
    Hi,

    Yes it clarifies my doubt.

    Can u please explain that what formula will fit to measure voltage across R28??

    Normally if we use voltage divider, we use a formula as R28/(R18+R28) to find the voltage across R28. But u just said that it will be proportional to current flowing into resistor R28. Can you please explain in details as exactly which formula to use in order to measure voltage.

    Thank you..!!
  • 0 in reply to Ramkumar S
    Intellectual 850 points
    Hi RamKumar S,

    Could you please let me know the formula which will fit to measure voltage across R28?? Basically i want to know as what conversion factor i should use to covert ADC Reading into actual Panel voltage in code. So if you could write the formula used, it will be very helpful to me.

    Regards:
    Amit
  • 0 in reply to Ramkumar S
    Intellectual 850 points

    I solved the equation to relate panel voltage with ADC Readings .
    Thank you for your support...!!

    Regards:
    Amit