Mixed voltage power supply for audio circuit and peripherals

Thread Starter

TrackerFX

Joined May 18, 2020
13
I need a power supply for a PCB that requires 3.3 V and 5.0 V for the MCU, LEDs and other peripherals but also requires about 10 V (positive and negative) for an audio circuit. My original idea was to bring in 20-24 V from a wall adapter and use a virtual ground circuit for the audio requirements. Reading into this, most virtual ground solutions can't handle much current and the PCB's collective power (worst case scenario ~26 Watts) must return via the virtual ground. Also, it seems that a lot of virtual ground solutions must have balanced power being drawn from the two rails to prevent the virtual ground from drifting. I looked into using multiple linear voltage regulators, but anything outputting negative voltage must also input negative voltage and Digikey does not list any wall adapters with negative voltage outputs.

Any ideas?
 

Irving

Joined Jan 30, 2016
402
This is a common problem, easily solved, but the approach to some extent depends on how much current is needed on the -10v rail? Also, do you really need 10v? What's the actual audio level?

There are 2 simple 'power supply' options, #1 is an inverting charge pump, good for a few 10s of mA, or #2, a negative buck/boost converter, as big as you like.

Option #3, less common, is to DC bias the whole audio chain at +10v using a 20v rail as AV+, a well-regulated +10v rail as AGND and the true ground as AV-. Where digital & audio mix, eg at a digital gain control, you use a simple level shifter, opto-isolator or digital isolation chip, depending on complexity, size & cost considerations. Where audio connects externally you use a capacitor to block the DC bias.

Option #4, a variant of #2, uses a dual output DC-DC converter to provide + & - AV from the raw Vin+ so your wall wart only supplies +5v regulated, or +7 - 9v unregulated. This is a good but pricy option for higher output audio channels.

Hope that helps.
 
Last edited:

ElectricSpidey

Joined Dec 2, 2017
1,156
Personally this is something I would build from scratch, using a center tapped transformer, 3 positive regulators and one negative regulator.

And yes, its linear...well because...audio.

Series pass transistors can be added if needed.
 

Irving

Joined Jan 30, 2016
402
Agreed if you're comfortable with mains voltages...

But if its just simple analog stuff it may not need a +/- 10v rail. The 5v rail and a simple 2.5v voltage follower to give a low-impedance bias point would suffice, with modern rail-to-rail opamps you can easily get 1v p-p audio for a pre-amp and 5v is sufficient for a moderate bridged 1w output stage into headphones or an efficient mini-speaker for personal use. We just don't know requirement, we only have half the story.
 

Audioguru again

Joined Oct 21, 2019
1,488
The single supply amplifier circuit I showed does not have a low impedance bias point. The + input of an opamp or amplifier is a very high impedance with a very low bias current.
 

Irving

Joined Jan 30, 2016
402
Agreed, but those bypass caps need to be good quality, high value, low leakage ones for good bandwidth and thats expensive/takes board space if you have multiple stages/channels. An active, low output impedance, bias generator soon becomes attractive.
 

sparky 1

Joined Nov 3, 2018
184
Having nice 12V can be regulated for most needs below 12V. What I keep seeing is some way to power the amplifier stage power at a hefty 24V in order to drive amplifier finals.
Since I never used this particular converter (any good I don't know) I will likely get opinions that might better serve some of the audio power supply problems people can see what converter looks like.
Too big, too noisy The description, general idea of a dc-dc step up with shielding: can it provide clean power for audio.
https://www.ebay.com/itm/200W-DC-DC-Boost-Converter-6-35V-to-6-55V-10A-Step-Up-Voltage-Charger-Power/222147971321?epid=6002950013&hash=item33b90d08f9:g:-i0AAOSwOVpXWjn4
 
I need a power supply for a PCB that requires 3.3 V and 5.0 V for the MCU, LEDs and other peripherals but also requires about 10 V (positive and negative) for an audio circuit. My original idea was to bring in 20-24 V from a wall adapter and use a virtual ground circuit for the audio requirements. Reading into this, most virtual ground solutions can't handle much current and the PCB's collective power (worst case scenario ~26 Watts) must return via the virtual ground. Also, it seems that a lot of virtual ground solutions must have balanced power being drawn from the two rails to prevent the virtual ground from drifting. I looked into using multiple linear voltage regulators, but anything outputting negative voltage must also input negative voltage and Digikey does not list any wall adapters with negative voltage outputs.

Any ideas?
Hi
I recently had the same problem and not being an electronlcs wizard came up with the following solution.
Use a centre tapped toroidal transformer and rectify the outputs to obtain dc.
For the +5v rails I used a DC/DC converter.
For +/- 15V and +/- 20V rails I built a couple LM317/LM337 power supplies which have variable outputs. All you need to do is balance the outputs using a DMM. Power output can be increased by adding a couple of transisters. There are plenty of circuits on the net. You will probably need to heatsink the regulators so leave room in your enclosure.
May be crude but it works
 

MisterBill2

Joined Jan 23, 2018
6,070
In post #10 MB provides the advice that I would offer. OR, you may possibly find a multi-voltage desktop power supply. They were sort of common in the "before the PC" era.
 
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