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Thread: Power supply question

  1. #1
    Senior Member+ Theremingenieur's Avatar
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    Power supply question

    I'm currently working on a Teensy 3.2 project which includes a pure analog backend (fed by the DAC and a few PWM signals). The PWM signals which go from 0 to 3.3V have to be filtered, amplified and shifted, so that there will be a voltage output going from -4V to 4V.

    Thus I'd need a tiny power supply circuit (similar to these which onehorse produces) which takes 8 to 12V at the input from either a battery or a wall plug adapter, and outputs +5V (up to 200mA) for the Teensy (who will then provide the digital peripherals with 3.3V through the internal voltage regulator) and the positive op-amp rail on one side and -5V (less than 50mA needed) for the negative op-amp rail.

    I could naturally design corresponding buck converters, but I don't want to reinvent the wheel. I'd prefer a simple plug and play solution in the 20$ range.

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    https://www.dimensionengineering.com/products/negatron

    Something like this? Hm its 20$... Maybe there are cheaoer sources for such a device..

  3. #3
    Senior Member+ Theremingenieur's Avatar
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    Hi Frank, Dankeschön

    but the Negatron gives me only the negative rail, while I'd still need another circuit to get the positive one which should feed the Teensy at the same time. I'd prefer a still more compact solution as follows:

    Input : 8V - 12V
    Output1: +5V ~200mA
    Output2: -5V ~50mA

  4. #4
    Senior Member Constantin's Avatar
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    This chip does not feature the wide input range you're looking for but it comes in a pretty small package, offers dual outputs fixed at 5v and has a relatively small external component count. In other words, you could put a traditional cheap VR upstream to create a stable 5v source for this device like the lm1117, for example.

    http://cds.linear.com/docs/en/datasheet/3582512fb.pdf

  5. #5
    Senior Member+ Theremingenieur's Avatar
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    I'm actually inquiring about a still more compact, ready to use power supply solution, at least when I exclude battery operation. But it would save the extra wall wart adapter : china stuff

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    Senior Member Constantin's Avatar
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    Be careful... a lot of those ac-dc boards do not feature proper anti-EMI components which then have to be sourced externally. FWIW, I am very happy with the CUI VOF-6, i.e. this unit: http://www.cui.com/product/resource/vof-6.pdf

    but it's +5V only. For a +/-5VDC with AC input solution like you seem to be looking for, I'd take a look at these two RECOM units. They offer a wide input range re: voltage, frequency, come from a known entity, etc.

    http://www.recom-power.com/pdf/Power...4-S_DC_277.pdf
    http://www.recom-power.com/pdf/Power...RAC06-S_DC.pdf

    But note how these both expect a external set of capacitors, a fuse, and a MOV on the incoming side (the VOF-6 only needs the MOV & fuse). My recollection with RECOM was that EMI resistance requires additional upstream components (i.e. a choke, some X1 caps, etc). However, these two datasheets make no mention re: such a requirement and seem to imply that the units passed an EMI test. I'd try to look that up before choosing them, just to be sure.

  7. #7
    Senior Member+ Theremingenieur's Avatar
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    Thank you, Constatin, that RECOM stuff looks great! I'll look into details. What I find very pleasing, is that there is no minimum load required. Although I doubt that their PS modules are made in the same plant than these advertised on alibaba, I feel better to deal with a renowned company and buying the stuff at digikey or mouser.

    Edit: After browsing their Application Notes, I found out that the RAC04 series have an integrated line filter (Pi-LC). Thus, things look better and better.
    Last edited by Theremingenieur; 10-27-2015 at 02:19 PM.

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  9. #9
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    +5 is easy to find, then you could add this (or similar) to get -5V.

    http://www.ebay.com/itm/LM2662-Negat...4AAOSwT6pVwcYX

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