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SN6505B: Design a 23V/100mA isolation power

Barton Huang
Prodigy 20 points
Part Number: SN6505B
Other Parts Discussed in Thread: SN6505A,

Hi Teams,

We want use SN65055 to design a isolation gate driver power, the specification :

Input: 5V
Output: 23V/100mA (18V/-5V 100mA)
Isolation: 1500V

But we use Tina simulation SN6505A + 750316856 the output voltage is limited to 19.8V.

Would you mind checking what's wrong?

SN6505_5V to 23V.TSC

  • 0
    TI__Guru 52770 points

    Hi Barton,

    Welcome to TI E2E forum!
    Thank you for sharing the Tina simulation file. Please allow us to look into this and come back to you by Thursday end of day. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    TI__Guru 52770 points

    Hi Barton,

    Apologies for the delay in response.

    We have simulated the file and we also see the output voltage to be 19.8V. Although the turns-ratio of the transformer is 1:4.67, the output voltage is not expected to be 4.67 times input voltage. This is primarily due to the conduction losses in diodes and the transformer losses. You can use the equation (10) from datasheet (also copied below) to calculate the output voltage for given turns-ratio, VIN, VF and other parameters.

    I quickly changed the diodes from B340A to 1N1183 and I was able to see output voltage of 21.45V, please see below screenshot. Thanks.


    Regards,
    Koteshwar Rao

  • 0 in reply to Koteshwar Rao
    Prodigy 20 points

    Hi Koteshwar ,

    Thanks for your response.

    According to the formula, assuming the diode's Vf is 1.4V, the turns ratio of the transformer must be > 5 to meet the output requirement of 23V.
    But I can’t find a push-pull transformer with >5 turns on Wurth website. Can you recommend a transformer that meets my design requirements?

  • 0 in reply to Barton Huang
    TI__Guru 52770 points

    Hi Barton,

    Your understanding is correct. If the forward voltage (VF) of diode is 1.4V, the transformer turns-ratio needed is going to be higher. I would prefer choosing a diode with lower VF than choosing higher turns-ratio as higher VF means higher power loss and lower efficiency. It is also common to find Schottky diodes with VF of 0.5V.

    I am not aware of any existing transformers with 1:5 turns-ratio but if you request the transformer vendor of your choice, they will be happy to develop one to meet your requirements.

    There is another transformer 78931812523 listed in SN6505B datasheet that has marginally higher turns-ratio. Let us know if you have any further questions, thanks.


    Regards,
    Koteshwar Rao