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Original question:

LM5100A: Two-Switch Forward Converter bootstrapped gate driver

Gate Driver IC for 2 Switch forward Converter.

abhishek moghe
Intellectual 290 points
Other Parts Discussed in Thread: TL431, UCC27714

Hi all, 

I will start working on design and development of Power supply, with continuous output power of 350W  and peak power of 550W.  ((universal input ) 

I intend to use 2 switch forward converter with Front End PFC. 

It would be an TL431 based feedback with controller Sitting on Primary side. 

Auxiliary Power supply, will be a non isolated 15V output to power up controller.  

Does Ti Recommend any Gate Driver for 2 S/W Forward converter, i do not wish to use Pulse Transformer and rest of gate driver circuit. 

Thanks 

  • 0
    TI__Mastermind 20950 points

    Hello Abhishek,

    Thank you for the interest in the TI gate drivers. There is a 600V high-side low-side driver, the UCC27714, which is suitable for this application. The datasheet can be found here:

    http://www.ti.com/lit/ds/symlink/ucc27714.pdf

    The UCC27714 VDD range of up to 17V allows for the 15V bias and the 600V HS rating allows for the typical high voltage bus in universal input PFC of 400V. This driver allows both high side and low side outputs to be on at the same time, which is required for the two switch forward converter.

    There are special considerations for the high side bias bootstrap supply with the 2 switch forward. In Figure 49 of the datasheet, a circuit is shown that ensures the HS pin will transition low to allow charging of the HB bias.

    Confirm if this addresses your questions, or you can post additional questions on this thread.

    Regards,

  • 0 in reply to Richard Herring
    Intellectual 290 points

    Hi, 

    thank you for reply. IC looks good part for replacement of Pulse transformer. i will evaluate the same. 

    Do you have any preferred part number for the MOSFETs which are required for BOOTSTRAP capacitor charging ? 

    Regards

    Abhishek. 

  • 0 in reply to abhishek moghe
    TI__Mastermind 20950 points

    Hello Abhishek,

    The switches for the bootstrap capacitor charging can be much lower current rated than the power switches since they only need to transition the switch node to allow the bootstrap capacitor charge current.

    The  STS1NK60Z is a low input capacitance 600V MOSFET that is an example of a device that will work for this application. The Vds voltage rating needs to match the power devices, the Rdson should be low enough to avoid a long time constant of Rdson and the bootstrap capacitor value, and look for low Qg charge devices.

    Confirm if this addresses your question, or you can post another question on this thread.

    Regards,

  • 0 in reply to Richard Herring
    Intellectual 290 points

    Hi ,

    Thank you very much..!

    i will now evaluate from cost/ size perspective and can decide what to go ahead with. 

    thanks for the information .

    Regards

    Abhishek. 

  • 0 in reply to abhishek moghe
    Intellectual 290 points

    Hi, 

    it looks like UCC27714 is more efficient from cost/ size perspective and i have decided to go ahead with it. 

    while reading through datasheet, it says there are different Grounds for Logic (VSS) and Driver (COM), in my case my PWM controller will be on primary side and hence there will be only 1 GND i.e  -ve of DC link capacitor. 

    hence i need to short COM with VSS. 

    Datasheet says max difference can be (-7V to 6V), with common connection will there be any issue that i need to anticipate, take care in design. 

    Thanks 

  • 0 in reply to abhishek moghe
    TI__Mastermind 20950 points

    Hello Abhishek,

    The VSS and COM differential voltage allowed is a feature to allow flexibility in the board layout. There are many designs where it makes sense to connect the VSS and COM pins together close to the IC.

    Just follow good layout advice in the datasheet especially regarding close placement of the VDD capacitor and routing of the gate drive loop.

    Confirm if this addresses your question, or you can post additional questions on this thread.

    Regards,