Stepping down from 12v smps to 5v and 3.3v?

Discussion in 'Power Electronics' started by arnab321, Jul 27, 2016.

  1. arnab321

    Thread Starter New Member

    Jan 16, 2008
    Im a noob at power supplies...

    My project consists of a long LED strip rated at 12v 3A, shift registors working at 5v and an esp8266 working at 3.3v.

    As of now, i have a 12v 5A smps which connects directly to the LEDs, an LM317 for 5v output in parallel, and another LM317 for 3.3v output, in parallel.

    Something happened and the LM317 for 3.3v output blew up. All of them had heat sinks though. Whats actually happening, and what is the proper way to get these voltages?
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    Almost same situation- 12 V ,1.5 A for fan dropped down to 6 V for logic & LED's using a BUCK convertor from ebay. 3.2 -- 40 V in, out 1.25-- 35 V, max out 3A. Output dropped from 6 V to 5.99 V with 300 mA load.
  3. paulktreg

    AAC Fanatic!

    Jun 2, 2008
    A schematic would help?

    Are you meeting the minimum load current on the LM317 to maintain regulation?

    Is the LM317 not a little overkill for your 5V and 3V3 requirements?
  4. arnab321

    Thread Starter New Member

    Jan 16, 2008
    Okay I haven't drawn a computerized schematic ever, I googled and saw and circuitlab, but none of them had a 3 pin ic, like lm317? And the transistor symbol looked like a transistor, idk what else has 3 pins and can look like an lm317... How do u actually make that?

    The power supply circuit is simple, a 12v 5A supply, with LEDs as load, and 2 lm317s with their 5v and 3.3v loads, all in parallel.

    The esp8266 runs on an avg current of ~60mA but can spike to 1A+ during high Wi-Fi traffic. And if the power supply cannot provide that, it will just reboot.

    The shift registers take less than 40mA. Can't measure the exact now because the esp's supply blew up.

    The lm317 is definitely an overkill, that's why I started this threadd to know the proper way to do this.
  5. RichardO

    Late Member

    May 4, 2013
    No need to do a drawing on your computer. You can hand draw your circuit and take a picture of your drawing. Just be sure that the picture has good contrast so it can be easily viewed. The picture that you upload to the forum should not be too large -- usually a few hundred of KB is enough.

    Looking forward to seeing your circuit.