I am designing a PSU capable of producing 5 watts @ 5V 1A. The design will power about 12 RGB LEDs (totaling about 400mA @ 5V) and a audio class D 1.4 W amp. Space is no issue but efficiency and cost at low quantities is!

Note: I built a flyback design where space and size were a huge issue and the transformer worked about to be a very difficult problem to surpass. I ended up going with a $16 transformer... So this time around I started with a different approach after looking at transformers that are 9$ and take 120VAC to 10VAC @ 1.3A... So here where I started:

A plain and simple design

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Vout into a linear regulator and done... only the efficiency will be horrible burning between 1 to 3.3 watts in heat

Vout into a DC-DC buck converter? My thoughts are that if Vout stays well above the minimum voltage of the buck then it should function even with the large ripples.


  1. I have read a lot that flyback is the way to go in my situation but the difference between a $16 and $9 for a transformer at a qty. of 1 is huge to me. Most of the flyback designs call for a custom transformer and this is just not feasible to me. I know I am not in the norm as I plan to build between 10 to 100 of these but, am I justified in my thinking or just ill informed on this design process?

  2. Is it ok/safe to feed the Vout ranging from 7V to 13.5V @ 120Hz into the buck converter?

Vout while drawing about 1A

Vout while drawing a mean of 1A

  • 1
    \$\begingroup\$ Any reason why you don't just buy a 5V/1A switching wall wart? All UL/CSA etc. approved and you're ready to go for a song. You're correct that you don't need to worry about the ripple if the regulator is designed to work at the lowest troughs (including low line voltage and aged capacitor) at full current, as well as the highest peaks. Make sure you're well within the ripple current rating on filter cap. \$\endgroup\$ Jun 3, 2014 at 14:49
  • \$\begingroup\$ @SpehroPefhany Thanks for your response! Yes I am bound by the device use requirements to build it on a pcb...plus I enjoy this :)! +1 for the ripple current heads up. \$\endgroup\$
    – tman
    Jun 3, 2014 at 15:02

1 Answer 1


You can buck down your rippley output .Any reasonable buck converter will give you low ripple 5VDC .At these voltages and currents there are a lot of solutions .Even a cheap nasty chip will have much lower losses than the linear regulator.A good buck converter should give 90% or better efficiency .


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