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SN6507: 12V to 24V

Rob
Prodigy 130 points
Part Number: SN6507
Other Parts Discussed in Thread: LM317A

Tool/software:

Hello,

The SN6507 is powered by 12V. I would like to obtain a voltage of ± 24VDC at the output of the transformer (750319693) 1:2.29.

1. Does the duty cycle allow to regulate the output voltage? If yes, how to determine the duty cycle to obtain ± 24VDC at the output? Because with a transformation ratio of 1:2.29, I obtain a voltage higher than 24V.

2. In the evaluation kit, there are capacitors in series with resistors (62 pF and 100R) at the input and output of the transformer. What are these components for? How to adjust these values ​​for better efficiency (fsw ± 400kHz)?

3. If I want to limit my transformer output current to 100mA/24V, should I use a 127k resistor to limit the SN6507 current to 200mA/12V?

Thanks in advance for your answers.

  • +1
    TI__Mastermind 29185 points

    Hello Rob, 

    Thanks for your interest in SN6507.

    1. The Duty Cycle Control feature is for use in applications where the input voltage is expected to vary considerably.  The additional turns would allow for 12V*2.29 = 27.5V output voltage in an ideal transformer. The actual efficiency of the transformer may result in losses that will be closer to 24V. Otherwise, an LDO (see user's guide Table 4-1. LM317A) can be used of tight regulation of 24V is needed. 
    2. The additional components are RC snubber circuits can be used to limit emissions even further. They are not needed for functionality and can be used as needed. The users guide provides an explanation in "4 EVM Configuration Options - Secondary-side snubber circuit" and "Primary-side snubber circuits"
    3. Yes, you are correct. The input current would need to be limited to allow the desired output power needed for the application.  

    Best,
    Andrew

  • 0 in reply to Andrew J
    Prodigy 130 points

    Hello,

    Thanks for your answer.

    Can I put a 120kΩ resistor on the DC pin to have a 44% duty cycle. This will allow me to have 24V output?

    For snubber circuits, can you advise me on the capacitor voltage I convert from 12V to 24V?

  • +1 in reply to Rob
    TI__Mastermind 29185 points

    Hello Rob, 

    1. The resister on DC doesn't set the duty cycle to a fixed frequency. Instead, it enables the SN6507 to actively change the duty cycle for an input voltage that varies. 
      1. See 8.3.3 Duty Cycle Control for the full feature description.
    2. The following app note shows a calculation method and test results for RC snubber circuits.  
      1. How to Reduce Emissions in Push-Pull Isolated Power Supplies (Rev. A) (ti.com).

    Let me know if you have any further questions. 
    Best,
    Andrew

  • 0 in reply to Andrew J
    Prodigy 130 points

    Ok, thanks for your help.