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LM5185: Calc-Tool shows #Value-Error if transformer ratio sec-value are higher than pri-value

Ralf Knobloch
Prodigy 90 points
Part Number: LM5185

Tool/software:

LM5185 Calc Tool - #Value Error

Hello,

I have problems with the calculation tool "LM5185-DESIGN-CALC.xlsx".
The tool works fine, when the flyback transformator "Turns Ratio" Pri-Value is higher than the Sec-Value.
When the Sec - value is higher than the Pri-value, many cells show #value  (or in the German Excel #Wert).

For example - I open the original File (Rev 3.3) with the output voltage of 16.4V and a transformer ratio from 1:1

Screenshot Original

I change the output voltage to 19V and the tool shows suggested transformer ratio of 1 : 1,19
I Select "Transformer Turns Ratio Pri : Sec" in the list the ratio 1 : 1.2 and I see the error entry #value (or #Wert in Germany) in many fields

Screenshot Problem

Does anyone have an idea what I'm doing wrong?

Thank you

Ralf

  • 0
    TI__Genius 13031 points

    Hi Ralf,

    I believe the values cells are due to the max. Rcs value on Step3 box. When decreasing Nps value from 1:1 to 1:1.2, the primary switching current increases and therefore max. Rcs value decreases. Try decreasing Rcs 20mohm to a lower value (19mohm) and the value cells shall be fixed.

    Thank you

  • 0 in reply to Manuel Alva Hernandez
    Prodigy 90 points

    Hello Manuel,

    thank you for the answer.
    I check with 19mOhm, with 10mOhm and for test with 1mOhm - same problem Worried.

    But I've found out what's causing my issue: European number format !

    The decimal separator is a comma and not a point as in the US number system.
    Excel automatically converts your sheet to the European system.
    BUT: The selection list for the transformer ratio remains with the point as the decimal separator. That is too much for Excel.
    If I switch Excel to the US number system, everything works perfectly.
    The problem is now solved - thank you for your support.

    Have a nice week - regards from Germany
    Ralf


    See: German 1:1,19 (",") and US 1:1.2 (".") separator

    German serarator and US separator

    After changing Excel to US-Format:

    After Changing