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LM5015 1:1 isolated conversion

Stefano Infante
Expert 2320 points
Other Parts Discussed in Thread: LM5015, LM5160

Hello,

I am going to use an LM5015 in the 1:1 isolated configuration (data sheet, page 21), as I need a 12V isolated output from a 12V non-isolated input.

The schematics at page 21 matches almost exactly my application needs (12 V isolated output, 200 mA maximum current), so I suppose I can use all the parts and values in that schematics.

The problem is I cannot find CHSHS-3 and CMSHS-3 diodes (... typo?), and I don't know how to dimension the 1:2 transformer and 100 uH inductor which are used.

Can someone help?

Thanks in advance,

Stefano 

  • 0
    TI__Guru* 78370 points

    Hello Stefano,

    Thanks for your interest in the LM5015.  The 1:2 transformer used to verify the concept of Figure 15 in the LM5015 datasheet is Pulse PA2223NI.  Please contact Pulse engineer Mr. John Gallagher (email: JGallagher@pulseelectronics.com) for the details about the transformer.

    The 100uH inductor used was Cooper DR74-101, which can be replaced by any similar parts able to handle a few hundred mA.

    Regardign the diodes, it should read CMSHS-3 (the CHSHS-3 was a typo).

    Wish these would help.  Feel free to contact me at youhao.xi@ti.com.

     

    Good luck,

    Youhao Xi

    Applications Engineering, Texas Instruments SVA.

  • 0 in reply to Youhao Xi
    Expert 2320 points

    Youhao,

    thanks for your answer. I prefer to write to you in the forum, rather than at your email, because I always think that your answers could be useful to other people, too.

    I think to use Bourns SDR0604-101KL as the inductor, which is smaller and cheaper; it has 0.52 A Irms and 0.68 A Isat, a little lower than DR74-101, but I think it would be good for my application (only 200 mA needed).

    As for the diodes, I did not find even CMSHS-3... have you got a link? However, I looked at the diodes used in the other schematics in the data sheet, CMHD4448, and found something similar (BAS16J from NXP), but I am still looking for a smaller solution.

    The transformer seems to be the biggest issue. I wrote to Mr. Gallagher and I am waiting for his answer; I also found FCT1-90K2SL and FCT1-120K2SL from Coilcraft, but neither of them seem to be easy to find on catalog distributors (which we prefer, as our productions are small). Any other suggestion?

    Regards,

    Stefano 

  • 0 in reply to Stefano Infante
    TI__Guru* 78370 points

    Hi Stefano,

    You do not have to use 30V and 200mA Schottky in the primary side.  For your 12V to 12V application, the primary side diodes can be 20V rated, and the IF current rating of 50mA is good enough.  Note that these diodes only conduct little magnetizing current when the internal main switch turns off.  Please search the Digikey website and you would find an appropriate one.

    However, please be noted that the secondary diodes needs at least 40V, 200mA rated for your application.

    Regarding the transformer,  I believe John (@Pulse) and/or Coilcraft will help you.  If you wish, you can contact your preferred magnetics vendor(s) to make one for you. 

    Best Regards,

    Youhao Xi

    Applications Engineering, Texas Instruments SVA

  • 0 in reply to Youhao Xi
    Expert 2320 points

    Hello Youhao,

    I found RB751 (NXP), which is very small and cheap; even if it is 40V, it can surely do the job at the primary side. The secondary diodes are NSR10F40NXT5G (NXP), rated 40V 1A If, so I think I won't have any problem.

    As for the transformer, I was looking for a commercial product (something you can already find on Digikey, Mouser, Farnell or RS), but if I cannot find one, I hope the guys from Coilcraft and Pulse do help me.

    Thanks again.

    Regards,

    Stefano 

  • 0 in reply to Stefano Infante
    Prodigy 130 points
    Hi dear Stefano,
    My application is exact like to your app.
    I need the current output >=1A
    Please, Would you be so kind as help me with datasheet of PA2223NL?
    Maybe, you get other trafo?

    Thank you very much in advance
  • 0 in reply to Juan Carlos91
    TI__Guru* 78370 points

    Hi Juan,

    For your >1A application, I suggest you to consider the LM5160 in Fly-buck configuration.  It uses fewer components, too.

    Anyway, per your request through Email, I was going to attach the datasheet here but I found my copy is preliminary and Pulse's proprietary info.  So, please contact John Gallagher (JGallagher@pulseeng.com) for the info.  Please note that  PA2223 was designed for 0.3A output current, so it does not support >1A output.  Furthermore, the LM5015 primary peak current limit 1A, and the maximum duty cycle is 50%,  so the maximum load current is limited by the following:

    Ioutmax < (Vin_min x 1A x 0.5) / (Vout x Eff)

    Where Eff is the converter efficiency.

    Best Regards,

    Youhao Xi, System and Applications Engineering, TI-SVA-PPS-NPS