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Most who play around with electronics would have come across an audio circuit that uses a duel rail power supply. The first time I came across this it totally baffled me – how do I get a negative charge out of a power supply? Isn’t one positive and the other ground? For some reason I had never thought that a power source such as a battery has equal negative and positive charge!

Most of the time the negative charge is grounded and not used but in some builds such as audio projects like amps and synths, you need to use the negative charge along with the positive.

Robin Mitchellover at “All About Circuits” has published a very elegant and easy way to create negative charge using only a handful of common parts that most people who play around with circuits will have in their parts bins.

I won’t go into how this works as Robin has explained it excellently in his article which can be found here.

The circuit itself is made up of a 555 timer (is there anything it can’t do!), a few caps and diodes. I wanted to make mine variable voltage controlled and portable to use and test on future projects so I included a buck booster in the design.

Step 1: Parts and Tools

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Negative Voltage Circuit Parts

1. 555 Timer – eBay 100 under $5!

2. 5.6K Resistor. Buy these as assorted on eBay

3. 47K resistor

4. 100nf Cap – Buy these as assorted on eBay

5. 10nf Cap

6. Diode 1N194 – eBay

7. 10uf Cap – Buy these as assorted on eBay

8. 100uf Cap

9. Prototype board - eBay

10. Assorted wires


To make it portable

1. Case – This one would work fine from eBay. Mines an old garage door opener I found somewhere.

2. Male and Female banana plugs – eBay

3. Various wires

4. Switch - ebay

5. 9V battery

6. 9V battery holder - eBay

7. Voltage regulator – eBay

8. Knob for a potentiometer – eBay

9. 10K Pot - eBay

10. Voltage Meter - eBay


Tools:

1. Soldering Iron

2. Pliers

3. Wire cutters

4. Hot Glue

5. Drill

6. Cone stepper drill piece (always comes in handy for drilling holes into things)

I tend to use Black for Ground (0 volts), Green for earth, Red for positive, Blue for negative.
But then you could always use two batteries if you don't need variable voltages.
vk2gwk24 days ago
Suggestion: use a different colour for the negative banana socket (like green) so you don't mix up positive and negative. This circuit won't tolerate much load on the negative. What you do is create AC with the 555 and rectify that to negative. The output power of the NE555 is not high - about 30 - 50 mA at most - and the rectified negative voltage is not stabilised so will drop on load. So this circuit is only suitable for very low load circuits.
lonesoulsurfer (author)  vk2gwk24 days ago
you are right - it won't take a lot of load but for small projects Op amps etc it works well. I've got another build I'm doing for -12v which uses AC.
I tend to use Black for Ground (0 volts), Green for earth, Red for positive, Blue for negative.
But let's face it, a PP9 battery won't supply much current for long anyway.
Gish0414X19 days ago
Nice Tutorial!
lonesoulsurfer (author)  Gish0414X18 days ago
Cheers!
MarPok19 days ago
A tip about negative voltage... there is a good IC "ICL7760". Works in the same way as the circuit with the 555 (see charge pump), but it can give a bigger current without voltage drop. I'm using it with 79L05 to get precisely -5 V.
lonesoulsurfer (author)  MarPok18 days ago
Great tip. Will look to get a few of these IC’s and give them a try
Great and useful information. I am happy that you shared this useful information with us. Please inform us like this. Thank you for sharing.



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Add a resistor in series with the push button to short the output cap, your 5.6k will do, anything over 50 ohms will be fine. Without the the resistor the momentary current through the switch will be very high and will eventually burn the switch contacts. The resistor limits this current though it does slightly slow the cap discharge (t=RC).
Thanks for the suggestion. I have updated the circuit to show the included resistor
maxhirez24 days ago
Nice work! Maybe I read through this too quickly, but did I miss the link to the original AAC article somewhere?
lonesoulsurfer (author)  maxhirez24 days ago
opps! I have added the link to the original in the intro.
Thanks dude-this is awesome! I may try the Schmitt trigger version too! Have you tried this on any Eurorack modules?
lonesoulsurfer (author)  maxhirez20 days ago
Nah - it's not really powerful enough to work on a eurorack. I am working on one however that should work a treat
abomin24 days ago
Hello! What current it could deliver?
JohnC430 abomin24 days ago
the 555 circuit with 1N914 diodes and the puny 9V battery will realistically deliver about 80mA max before the diodes get hot or the battery gets run down. in this circuit, the positive input voltage is the positive for the load (audio amp) and the output from the negative side will be the negative to the load (again the audio amp). I did not see a complete schematic in his i'ble, but i am assuming that the boost circuit will be the one to supply the LM555 circuit.
The whole idea is ok for a few opamp circuits and not for an audio power amp. but you can get much more power if you throw away the 555 and connect the 10uF cap at the output of the 555 that goes to the 1N914 directly to the boost transistor Drain. the boost is capable of much higher current. Change the 1N914 to some higher current faster diodes, e.g. https://www.ebay.com/itm/10-PCS-SR5200-SB5200-MBR5...
these are 5 amp/200V Schottky diodes, (I just checked the spec sheet) although 45Volt diodes would be better. the boost module is good for about an amp or so and this mod will give you a lot more power. make sure the 10uF cap is connected in the correct polarity, or use a 10uF ceramic cap which will work a lot better.
Very good work on the writing. But any power supply would have worked just as well. Just reverse the connections.
This statement, "...Most of the time the negative charge is grounded and not used but in some builds such as audio projects like amps and synths, you need to use the negative charge along with the positive...." is a gross misunderstanding.
Only power supplies with outputs truly floating with respect to the AC line power (such as this battery operated one) are able to have either terminal connected to ground. Many switching supply converters getting their power from 110 VAC have one of their output terminals (usually the negative) tied to the 3rd wire ground for safety purposes. If you then ground the positive terminal to try to get an output negative with respect to ground you will short out the supply.