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Thread: Compact Aux power supply for smps

  1. #11
    .... Silvio's Avatar
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    Apr 2015
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    Quote Originally Posted by res_smps View Post
    my schematic
    Silvio, sorry I did not mean to hijack your thread, because I'm not always online to manage my own thread.
    I think you and other member can iuse this as a reference
    Its ok it is nice to share ideas among members. Now they have other choices for an auxiliary smps.

  2. #12
    Quote Originally Posted by res_smps View Post
    dear all,
    I have tried both flyback and buck using TOP224, I got up to 450mA continuous for buck converter
    please this PI's design idea (attached)
    Did you see Silvio? When using buck (flyback is not buck)(buck doesn't mean step-down) the voltage drop is big but Rds(on) is relatively small. Exactly that was my idea. res_smps tested and it gives 450mA which is good. You don't need to wind 135 windings. Just use buck for this little power.
    Last edited by expressel; 02-15-2019 at 10:16 PM.

  3. #13
    These little ICs are great. I have a parts drawer full of recovered TNY26x and TNY27x DIP8 parts. The TNY parts are just different versions of the TOPSwitch ICs. I never thought of using one as a buck converter. It's not a standard use of the TNY ones, but it should work just the same.
    As far as the normal use goes, the TNY ICs were specifically designed to be used as low power flyback converters using as few external parts as possible, and they work great. When it comes to the auxillary supply of a SMPS there is a good reason to go with the standard flyback design, and that is multiple output voltages, and the option of isolated voltage rails. The output doesn't need to be just a single voltage and it's very easy to add more secondary windings to get more rails. It's a very common use case for these controller ICs. Almost every PC power supply you take apart has a TNY26x/27x AUX supply with multiple output windings on the transformer. (Usually the +5Vsb rail which is earth referenced, and 1 or 2 mains referenced rails to run the main controller ICs.) It all depends on what type of supply you need and how much flexibility is required.
    I think the only issue with using a buck converter would be the huge voltage step. For example going from 325V down to 15V would have a duty cycle of less than 5%. Some controllers might have issues delivering full power with such a small duty cycle. You'd have to test the design if you used parts other than what was verified by res_smps.

    - Brad

  4. #14
    diysmps Member* res_smps's Avatar
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    Oct 2012
    bandung, indonesia
    tiny switch buck converter di11.pdf
    the maximum output current for the buck converter depends on the self-protection current limit of the chip (I think half of it)

  5. #15
    diysmps Member* res_smps's Avatar
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    Oct 2012
    bandung, indonesia
    Quote Originally Posted by expressel View Post
    (flyback is not buck)(buck doesn't mean step-down)
    buck is step down (voltage), flyback can be step down or step up

  6. #16
    Other options for an aux supply could be the LNK and the Viper chips.

  7. #17
    diysmps Senior Member
    Join Date
    Oct 2011
    Kuala Lumpur, MY
    i did TNY because this chip has internal protection, overvoltage, short circuit, over temp, soft start.. etc... and its very easy and its regulated, ill post pic when im get back soon, now im outstation for a week, for now i just order pcb prototype from jlcpcb because its very cheap and save my time. you can adjust the voltage only by changing zener diode on feedback thats all...

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