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SN6507: Poor efficiency with SN6507 with low output current

THOMAS CRAVERO
Prodigy 30 points
Part Number: SN6507


Hello, 

We are trying to make an isolated DCDC converter from 24V to 7V with wide input voltage (18V to 30V).

We used the transformer proposed in the datasheet.

We want to use this converter for low current output : between 40mA and 80mA.

When we measure the efficiency, it's very low: around 20% and 40%.

I tried to adjust the frequency to work at 600 kHz, but i still have strange measurement with very low efficiency.

Can you confirm the main component SN6507 + Wurth 750319690, are good to achieve at least 60% efficiency at low output current ?

Thanks for the support.

  • 0
    TI__Mastermind 27050 points

    Hello,

    Thank you for your question. We don't have efficiency data for all potential configurations of the SN6507, but normally at small currents efficiency will be lower. The efficiency can be impacted by more than the chosen transformer. Although the transformer is an important component, the switching frequency, chosen diodes, layout techniques, etc. can also impact the efficiency of the system. Is adjusting the frequency the only modification you have made so far?

    Regards,
    Darrah

  • 0 in reply to Darrah Merillat
    Prodigy 30 points

    Hello, 

    I tried to adjust also the duty cycle, but i have strange measures on primary side voltage.

    I tried to use other transformer also with same footprint 750319695 and 750319696.

    I'm using schottky diode and the layout is almost the same as the development board.

    WHen you are saying lower efficiency, what can we expect ? I don't need so much, but i would like to have at least 50%.

  • 0 in reply to THOMAS CRAVERO
    TI__Mastermind 27050 points

    Hello,

    The efficiency curve in the datasheet, copied below for convenience, shows what efficiencies can be expected as the load varies, you can see that as the load decreases the efficiency does as well. Although this chart does not go below 100mA we do have some data for lower loads. From this data, we see an efficiency of roughly 45% to 60% for loads of roughly 40mA to 80mA. However, this data was collected for a Vout closer to 18V so the results may differ slightly from your set up.

    Our EVM board is built for maximized emission performance and not maximized efficiency so some components may need to be changed to achieve the best efficiency. The main way to improve efficiency will be the transformer and external component selections. For the external components, diodes with a low forward voltage and diode capacitance will help maximize efficiency (BAT165E6327HTSA1 for example). Please note that making this change will result in higher emissions. However, if you are not concerned with emissions, this is not a problem

    Regards,
    Darrah