+/- 8/10V from 5V USB power converter - diyAudio
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Old 11th January 2014, 06:03 PM   #1
RuRu is offline RuRu  Hong Kong
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Join Date: Jun 2013
Default +/- 8/10V from 5V USB power converter

I'm desiging a small PCB board as a headphone amplifier running from the PC USB 5V supply. As I'm planning to run some NJM5532 or similar OpAmp, I would like to find the cleanest DCDC bipolar converter to get +/- 8-10V in one single IC.
What are your recommendations?

Btw, I have found this headphone amp that "delivers" 130mW at 32ohm with a single supply (I believe you can use the USB 5V as a high PSRR) and no need for output caps:
MAX9722 5V, Differential Input, DirectDrive, 130mW Stereo Headphone Amplifiers with Shutdown - Overview

it looks like a highly integrated solution with very few extra components. Any thoughts on this part?

Thanks!
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Old 11th January 2014, 07:00 PM   #2
DUG is offline DUG  Canada
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Looks good.

Internally generated -5V...saves on external dc-dc.

Need a pcb though... 0.65mm pin centres.

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Old 11th January 2014, 07:28 PM   #3
RuRu is offline RuRu  Hong Kong
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Thanks!

Using the Maxim chip is a back-up option, though.

I need to get bipolar +/- 8 to 10V for the output OpAmp and as well 3.6V for the DAC.
As well, the DAC has balanced outputs so as I need another OpAmp for conveting them to Single Ended. I thought about the OPA2134, but then I need another set of bipolar supplies, another DCDC bipolar too?

I have seen integrated DCDC to take 5V USB to regulated high 4Vs in one output (for the OPA2134 for example?) and then a 3-4V output too for the DAC.

Any ICs in mind?
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Old 13th January 2014, 07:10 AM   #4
dangus is offline dangus  Canada
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There are DIP modules that convert 5V to +/- at various voltages. For the highest performance, I'd be tempted to use a higher voltage than necessary followed by linear regulators. Take a look at a Digikey or Mouser catalog under DC-DC converters. Here's one I found by filtering for +/-15V, DIP package, in stock, isolated output, 2 watts:
Isolated Module - 1W & 2W Miniature Module - DCP020515D - TI.com
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Old 19th January 2014, 01:07 AM   #5
gman76 is offline gman76  United States
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Quote:
Originally Posted by RuRu View Post
Thanks!

Using the Maxim chip is a back-up option, though.

I need to get bipolar +/- 8 to 10V for the output OpAmp and as well 3.6V for the DAC.
As well, the DAC has balanced outputs so as I need another OpAmp for conveting them to Single Ended. I thought about the OPA2134, but then I need another set of bipolar supplies, another DCDC bipolar too?

I have seen integrated DCDC to take 5V USB to regulated high 4Vs in one output (for the OPA2134 for example?) and then a 3-4V output too for the DAC.

Any ICs in mind?
I've done something similar. I built a small board (1.8"x2.8") that is USB powered that derives the +5V to generate a split supply, +/-5V. The reason for this is to avoid using coupling caps when a single rail is used. I have audio technica M35 headphones which are 65 ohms. I wanted to have a gain of 5 to boost the level from my iphone, and both intended to be powered from a computer's USB ports. Sometimes I like to crank it at work. The max output is ~2.5V rms which is close to the max allowed for the headphones, 100mW.

I tested the amp and looked at the supply rails while pushed to the max. The inverting switcher does have occasional problems under severe rock passages with heavy bass. More decoupling is needed. Also plan to use a mini USB connector instead of micro B. Also looking into seeing if the 3483 can be operated in continuous mode (runs burst mode now). While music was running, I put a scope on the output. When I saw the drops outs of the -5V rail, I was somewhat surprised how little effect it had on the sound. The rail was dropping hundreds of mV. But as you can see from the scope shot, the peaks were hitting about 3V which was very loud. Let me add, this little amp sounds very clean.
Attached Images
File Type: jpg simple-amp_schematic.jpg (122.1 KB, 105 views)
File Type: png output-rms-pp.png (40.7 KB, 99 views)
File Type: jpg simple-amp_board.jpg (177.3 KB, 102 views)

Last edited by gman76; 19th January 2014 at 01:34 AM.
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