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Original question:

SN6505A: 12V/12V isolation power

SN6505B: 5V to 12V

Spencer Miles86
Prodigy 70 points
Part Number: SN6505B

Is there a reference design for using the SN6505B to take 5V and turn it into 12V using a 5000Vrns transformer? Output Current from 12V will be 100mA but if the design supports more that would be acceptable to get the 5000Vrms rating on the transformer. 

Is it better to use a 5 to (slightly above) 5V transformer paired with the voltage doubling circuit or size the transformer to do the 5 to 12V?

Thanks!

  • 0
    TI__Genius 17100 points

    Hi Spencer,

    Thank you for posting, and welcome to E2E! A reference design for isolated push-pull power supplies can be found here (SLLA436).

    Although voltage-doubling configurations can be used to generate 5V to 12V isolated power supply rails with a wider selection of transformers, using transformers designed to output the required 12V is typically more efficient and requires less components; there aren't many other trade-offs between these two options.

    Below are a few transformers which can be used with SN6505B to generate an isolated 12V power supply from a 5V input supply and are specified for 5000Vrms isolation performance:

    • Wurth's 750316031, 750313638, and 750313769 may be used in a voltage doubling configuration
    • Wurth's 750343725 may be used in the typical configuration w/ LDO
    • Pulse's PH9185.013NL may be used in the typical configuration w/ LDO optional
    • Pulse's PH9185.038NL may be used in the typical configuration w/o LDO


    Efficiency varies with each transformer, but these components are all specified to handle >100mA outputs. Let us know if you'll be using a different one! We can analyze other transformers' specs and confirm expectations regarding compatibility.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 70 points

    Thanks Manuel, did I implement this correctly? My understanding is that this should generate roughly 15Vdc when 5Vdc is applied to VCC?


  • 0 in reply to Spencer Miles86
    TI__Genius 17100 points

    Hi Spencer,

    The transformers listed above intentionally supply >12V on the secondary side to both account for parasitics in the system, like diode voltage drops, and allow for the option of regulation devices (LDOs) to be used for a more consistent voltage output across loads and operating conditions.


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 70 points

    Hi Manuel,

    As long as the circuit outputs 12.25V (after the diodes) then the converter will be able to regulate to 12V after. 

    I just wanted to make sure that this transformer will provide an output in the 12.25V - 20V range. 

    Thanks,

    Spencer

  • 0 in reply to Spencer Miles86
    TI__Genius 17100 points

    Spencer,

    The schematic you shared above is also implemented as expected in the typical configuration. Minor optional improvements can be made as follows:

    • Ensure that in the PCB layout, the 10uF capacitor, C16, is placed closely to the transformer pin PS2
    • A 1uF capacitor can be placed closely to SN6505's Vcc pin
    • The CLK pin can be connected to GND
    • A 4.7kOhm resistor can be added on SN6505's EN pin to connect to Vcc instead of a direct connection

    If precisely 12V output is needed instead of 15V, an LDO can be added at node "+15V_EXT." The output voltage is expected to vary around 15V across load currents and operating conditions without one.


    Please let us know if you have additional questions.


    Best,
    Manuel Chavez