1. Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.
    Dismiss Notice

Offline Flyback 24V....using INN2904K controller

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Flyback, Mar 4, 2018.

  1. Flyback

    Flyback Well-Known Member

    Joined:
    Jan 5, 2007
    Messages:
    2,097
    Likes:
    34
    Hello
    We are using the INN2904K controller to make a 15W, 25V Offline 240VAC Flyback.
    We are not using the synchronous rectifier facility in the secondary side. As such, will it be allright for us to simply ground the FORWARD pin?

    The Forward pin is only rated up to 150V and with our turns ratio, the reflected voltage (+leakage spike ring) would result in the FORWARD pin getting overvoltaged if we connect it up to the switching node of the secondary side.

    INN2904K datasheet:
    https://ac-dc.power.com/sites/default/files/product-docs/innoswitch-ep_family_datasheet.pdf
     
  2. ChrisP58

    ChrisP58 Well-Known Member

    Joined:
    Apr 27, 2012
    Messages:
    1,166
    Likes:
    146
    Location:
    Provo, Utah, USA
    The first line from this paragraph on page 14 of your link implies that the FORWARD pin is part of the power supply of the controller. Grounding it might leave it kind of hungry.

    "FORWARD Pin Resistor A 47 W, 5% resistor is recommended to ensure sufficient IC supply current. A higher or lower resistor value should not be used as it can affect device operation such as the synchronous rectifier drive timing."
     
    • Like Like x 1
  3. Flyback

    Flyback Well-Known Member

    Joined:
    Jan 5, 2007
    Messages:
    2,097
    Likes:
    34
    Thanks, PI just got back to me....FWD pin is indeed used to power the secondary side of the controller at startup....this means on mains 200-285vac the transformer tunrs ratio ns/np shoudl be 1/5 or less....not what we wanted.
    I dont think we can even add some auxiliary circuitry so that we can have say ns/np = 1/2 and still work with it.
    The circuitry woudl be too extensive.
     
  4. dave miyares

    Dave New Member

    Joined:
    Jan 12, 1997
    Messages:
    2
    Likes:
    -10


     
  5. ChrisP58

    ChrisP58 Well-Known Member

    Joined:
    Apr 27, 2012
    Messages:
    1,166
    Likes:
    146
    Location:
    Provo, Utah, USA
    You could add another secondary winding just to power this part. That might be simpler than adding auxiliary circuitry. Don't know what the cost impact would be though.
     
    • Like Like x 1
  6. Flyback

    Flyback Well-Known Member

    Joined:
    Jan 5, 2007
    Messages:
    2,097
    Likes:
    34
    Thanks, you're right, i wonder what the dropout voltage of the (seconday side) internal regulator (inside the IN2904K) is though? As you know, this info is needed so that its known what to set the turns ratio to of the "auxiliary" coil.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice