How To Convert Your Dual Voltage Rail Device Or Project To USB Power

I get together with Detlef to demonstrate how to power a device that requires a plus and minus voltage supply from a USB PSU. Recorded with very little editing this is like a live jamming session between two electronics techs. Pull up a seat and join in with your comments...
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TEST METERS
ANENG AN8009 MULITIMETER
KAIWEETS HT118E MULTIMETER
VC480C+ MILLIOHM METER
MESR-100 ESR METER
XC6013L CAPACITOR METER

TM-902C TEMPERATURE METER
LCR-T4 COMPONENT ANALYZER
FNB58 USB ANALYZER
PCI POST ANALYZER
TL460S PLUS PCI_E ANALYZER
TOOLTOP ET120MC2 SCOPE
FNIRSI 1014D SCOPE
NPS3010W 30V 10A PSU
T12 STATION WITH M8 9501 HANDLE
M8 9501 HANDLE
YIHUA 982 Soldering Station C210/C245
FNIRSI HS-02 PORTABLE SOLDERING C210/C245
QUICK 861DW
PROS'KIT SS-331H

INFIRAY P2 PRO IR CAMERA + MACRO LENS
TOOLTOP ET13S THERMAL CAMERA METER
ET13S MACRO LENS
OPTICAL MICROSCOPE
TOMLOV TM4K AF FLEX
TL866 II+ PROGRAMMER
CH341 PROGRAMMER
NC-559-ASM FLUX

DESOLDER BRAID (I use size 8045)
HX-T100 SOLDER (0.6MM)
ESD-11 TWEEZERS

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Thank you
Richard

[TheEmbeddedHobbyist]

It's regulated by the +5V supply. the +5Va is being used as the regulator reference.

The problem with a virtual ground however you make it, if the 0V of your power supply is referenced to ground then you can't connect your virtual ground to any 0V that might then be connected to earth as you will short out the virtual ground (e.g. +10V).

it would be better to use a isolated DC-DC converter, I use a few recycled expensive IBEC 12ICR 6-1515-s. These provide a +/- 15V supply from a single supply rail. and the ground is fully isolated from the 0V of the powering supply.


There will a cheaper range of isolated DC-DC converters which have a range of inputs and outputs to suite what your requirements.

[marcelihryniow]

Is the power ground not connected to any other i\o connectors? If yes wouldn't you have a potential between grounds of the connected devices?

[castlecodersltd]

Great video, I'm looking forward to the follow up 🙂

[Pulverrostmannen]

You can actually make a dual voltage supply using two identical cheap buck converters by using a trick where you invert the output on one of them. this way both sides gets fully regulated and does not become sensitive for different loads. in fact the inverted side will have a bit less maximum current so it would actually be perfect for this purpose

[TheEmbeddedHobbyist]

The 7809 can not regulate if you are pulling the output upto its input. it will just try to limit the current flowing through it in order to try and get the output to fall back into regulation.
These circuits are OK for providing a form of reference by no good as a power supply.
Have a look at the internal circuit of the regulator that will show you what problem you are looking at.

[TheEmbeddedHobbyist]

looking at the circuit.
starting point.
Q16 is off
Q17 is on
Q18 is on so the line going off the sheet is at +5.6V

As the power supply voltages rise, the voltage across D13 will increase and when it passes about 11V it will start to conduct.
The current flowing through D13 and R113 will cause a rise in voltage across R113 which when it reaches about 0.7V will turn Q16 ON.
Q16 turning ON will in turn turn Q17 OFF.
Q17 while being ON was shorting out C121, but now C121 is free to charge up via R146, the time constant being R146 and C121.
Once C121 has charged up the voltage on the base of Q18 via R147 will be the same as the emitter so Q18 will turn OFF. there being a delay while C121 is charging.
The line going off screen will now fall to -5V as it's being pulled down by R148. Without knowing what else could be connected to that signal you can't say what the voltage will be but should be around -5V I'd expect.

I rest my case as it was getting a bit heavy 🙂

[perkulant]

I'd go Rich style for the price factor and I'd already have parts in drawers. Maybe even a blend Riclef style with PD in and the LDO method.

[BkR]

The 2 zeners cannot be in series, otherwise it'll be a short across the 330 ohm and diode.
A voltage divider from the output also works with the 7805 but you need caps for both halves.
And usb c is the way, one PSU runs anything and everything.

[LothyBluesCave]

You might get some ticking noise with those switching circuits. Is it quit?

[DustinWatts]

I vote for the USB C supply. The Voltge regulator has a flaw in it. What if the loads are between + and gnd and - and gnd are different. Then there will be an issue at the the GND it will change.. Edit: I watched further and you saw it yourself, sorry for that!

[Dutch-linux]

the 2 - 9 volt batteries solution we told you guys in the live stream !!!! so that was our idea not deth's to clarify things up !!!!

[SkippiiKai]

Using an inverting boost/cuk topology seems the obvious way, but since I recently got about 12 old laptop supplies from a thrift store for $2 each, all of my projects now run on them. And every supply I get immediately gets converted to 5.5mm tip+ barrel jacks. I did also find a few power bricks with a dual rail supply at the thrift store, so if I was doing it, I'd obviously just use those. And 15 years ago I once acquired a whole box of (pre-USB) left-behind cell chargers from a hotel, and I'm a little embarrassed to admit I did make a few +/-10v supplies by wiring 4 of them up in series.

[Dutch-linux]

oke at timestamp 17:40 Now I have to say Deth's idea is better !!!!

[Karthor.]

I was thinking a virtual ground / virtual zero with 2 caps and 2 resistors when you said mentioned it on livestream but maybe that would be even more unstable?

[sanderverhage]

The 7809 can only source current. Not sink any current. That’s your problem.

[Dutch-linux]

timestamp 28:28 you could use 2 regulators a negative and positive one... but all that is still more expensive then deth's solution so no matter how you look at it deth's solution is the better one

[tonypacke]

It's strange that Roland went with that connector. You can buy a PSU in the UK for £50 but not an original Roland manufactured device.

[Dutch-linux]

At timestamp 1:04 it is easy to solve take that connector out and put like a little plate from tne inside and mount a connector of your choice with a powersuply that does + and - 10 volts ...I do not see the fuzz about it or what is so interesting about it.... it is kind of a every day problem with many devices !!!!

[Dutch-linux]

Richard's idea is better.... what would be even better is combine the 2 the power suply rich dreamed up and the 2 9 volt cells.. have a switch to switch from mains to battery... and then it can operate even when there is no mains available... the only question is at this point how much current does that drum machine draw !!! so you can calculate how long the 2 cells will last.... and you should use rechargable cells.. and they are getting hard to find for 9 volts and the chargers even harder to find !!!!

[Tims_Projects]

Perhaps in hindsight, why do the diodes change the voltage?
I believe to do it using linear regulators you need to use 2 linear regulators (+) in series. (a controlling device for each rail)
Det's way is the way I did it on an old robot I have. I needed -6v-6v-, but I used two separate adjustable bucks, this way I could set any voltage.