Electronics > Beginners

Virtual ground circuit

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Zero999:
An audio amplifier IC can be used as a very good rail splitter. Refer to the thread linked below:
https://www.eevblog.com/forum/projects/to220-rail-splitter/msg2077699/#msg2077699

I wonder how well a class D amplifier would work? That would keep losses/power dissipation to a minimum.

spec:

--- Quote from: soldar on January 11, 2019, 03:37:03 pm ---
--- Quote from: spec on January 11, 2019, 02:45:15 pm ---There are a few issues:

Most opamps will not be happy driving large capacitors.

The opamp maximum supply voltage and power dissipation limits the applicability.

None these rail splutters, provide a solid 0V. Just imagine using a class AB audio power amplifier with a rail splitter.

I am not sure how the frequency stability would work out if you did an analysis.

It is hard enough getting your 0V connections correct, even without the added complication of a rail splitter.

--- End quote ---
Well, I agree that it is better to have a split power supply and not need a rail splitter but this thread is about using a splitter for whatever reasons.

--- End quote ---
Point taken. Afraid that my fear and loathing of all rail splitters may have colored my response to your post.  But to be pedantic, the OPs question was how does the LM317/337 rail splitter work and is it any good, and having answered that, hopefully we have moved on.

spec:

--- Quote from: aheid on January 10, 2019, 10:01:44 am ---As for the cheap dual rail PSUs, any pointers for what to look for? The 19V 65W laptop bricks are readily available and cheap here, but haven't found anything dual rail that's available and not considerably more expensive.
--- End quote ---
Hmm, after a quick look, neither have I. :) But will investigate further and list any approaches that may be of interest.

[1]  SINGLE MAINS SUPPLY WITH +- 18V RAIL OUTPUTS
With this approach, the mains PSU provides stabilized +-18V supply rails directly from the mains.

This is the board that I originally had in mind, but it is only generates +-15V at 500mA:

https://www.ebay.co.uk/itm/HIFI-Single-voltage-to-positive-negative-Regulator-powerFinished-board-Low-noise/253615314877?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20170920101022%26meid%3D8b93c439f71147b7ad5c5d353e5d1c86%26pid%3D100010%26rk%3D3%26rkt%3D3%26sd%3D262381275345%26itm%3D253615314877&_trksid=p2047675.c100010.m2109

After a good search, I could not find any low-cost +-18v,  at 1A or greater, SMPSUs, so it looks like this avenue is a dead end as far as your application is concerned.

[2]  TWIN MAINS SUPPLIES TO PROVIDE +- 18V RAILS
As capt bullshot says in reply #8, two isolating mains supplies can be connected in series to generate the +-18V stabilized supply lines. This is a really neat approach and provides a good performance.

Most, if not all laptop PSUs are isolating and seem to have a fairly standard topology. I suspect that many of the laptop PSU guts are made by the same company.

If you wanted to make a tidy single PSU, you can remove the plastic cases by running a hot knife down the seams to expose the guts, which are quite compact. Then just put the two PCBs in a nice little metal case for good screening (ensure adequate heat-sinking/ventilation). With a bit of work, you could make a really professional job of it. :)

This laptop PSU is low cost and has an adjustable output voltage:
https://www.banggood.com/96W-Multi-Function-Universal-Notebook-Laptop-AC-DC-Power-Adapter-Charger-p-981672.html?gmcCountry=GB&currency=GBP&createTmp=1&utm_source=googleshopping&utm_medium=cpc_bgs&utm_content=frank&utm_campaign=pla-uk-elc2-brand-pc&gclid=Cj0KCQiAmuHhBRD0ARIsAFWyPwgEjaMVK15etZSdrOWzIJcf2mH17DD_pm715GJglHzqy1JiPcMQ4i8aArdxEALw_wcB&cur_warehouse=CN

But you are not limited to laptop SMPSUs. There are other suitable PSUs, including, board-level, wall-wart, chassis, and cased.

Here is an example from the many 18V SMPSUs available:
Output current: 4A maximum
Mains supply: international
Size: 110mmx79mmx36mm
Make: Velika
Cost: 91.84 NOK ($10.84US) delivered (free) to Norway

https://www.aliexpress.com/item/Small-Volume-Single-Output-18V-4A-72W-Switching-power-supply-Source-Transformer-100-240V-AC-DC18V/32837291241.html?ws_ab_test=searchweb0_0,searchweb201602_5_10065_10068_10130_10547_319_317_10548_10696_10192_10190_453_10084_454_10083_10618_431_10307_10820_10301_10821_10303_537_536_10059_10884_10887_100031_321_322_10103,searchweb201603_51,ppcSwitch_0&algo_expid=d54973ac-b655-42ea-9574-477d33b908af-20&algo_pvid=d54973ac-b655-42ea-9574-477d33b908af&transAbTest=ae803_5

[3}  TWIN 24V OP MAINS SMPSUs AND +-18V LINEAR REGULATORS
Here twin mains SMPSU provides +-24V which is regulated down to +-18V by a pair of complementary three-terminal linear regulators (LM317/LM337 etc). This arrangement can be made suitable for-high end audio pre amplification, but filtering out the switching hash, from the two SMPS to negligible levels, would take some doing. And the 0V line would be problematic.

Mains PSU with 24V Output
Once again, there is any number of suitable low-cost 24V mains SMPS. Here is just one example: https://www.banggood.com/4A-To-6A-24V-Switching-Power-Supply-Board-AC-DC-Power-Module-p-969204.html?rmmds=search&cur_warehouse=CN

[4]  MAINS SUPPLY AND +-18V GENERATOR
With this approach, a mains to DC SMPSU powers a board that generates +-18V supply rails.

Mains 4V to12V SMPSU
With the +- supply line generator described below, a mains to 4V to 12V, 52W min PSU would be required. There is an endless choice of suitable PSUs, especially with 12V outputs, which would be the best output voltage. An example would be the 12V, 5A SMPS from here: https://www.ebay.co.uk/itm/DC-12V-24V-5V-10A-12-5A-15A-20A-30A-Universal-Regulated-Switching-Power-Supply-/181881169501

+- Supply Line Generator
Input supply: 4V to 12V
Output supplies: +- 8V to +-18V adjustable @ 1A5

https://www.ebay.com/itm/HIFI-Regulated-Power-Supply-Single-Voltage-To-Positive-And-Negative-Power-Output/253689999076?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D1%26asc%3D20131231084308%26meid%3D50b108bfc6f043fe879ece914a932086%26pid%3D100010%26rk%3D2%26rkt%3D5%26sd%3D272417883151%26itm%3D253689999076&_trksid=p2047675.c100010.m2109

[5]  ROLL YOUR OWN +- 18V OUTPUT SMPS
This would be good fun and not too difficult to do, but more of project in its own right rather than a means to an end.

[6]  MAINS TRANSFORMER/ DIODE/ RESERVOIR CAPACITOR WITH OR WITHOUT +- 18V REGULATORS
The title is self explanatory.
This is the Rolls Royce approach that is not difficult to design and build: with the appropriate components and layout, suitable for high-end audio pre amp stages.

CONCLUSION
Which is the best approach? To me one wins hands down. :)

David Hess:

--- Quote from: soldar on January 11, 2019, 01:13:25 pm ---I cannot see the need (in general) for two OpAmps or that much complication. In its simplest form the attached circuit will do. If you need higher current sourcing or sinking then emmitter follower amplifier can follow.
--- End quote ---

With the right operational amplifier and capacitor selection that can work very well but finding the right combination can be tricky and it is limited in power handling capability unless a power part can be found.

spec:
+ aheid

I am dying to know- what is this PSU for? :)

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