hi people! there is a nice article that explains how to do it without building a circuit here -

carlos66ba1 year ago
Neat little circuit to solve a problem if you need some mA. For a little more $$ I'd recommend using a regulator pair 7812 and 7912. This will provide better regulation, more current and current limiting capabilities.
vricsi941 year ago
Simple circuit, but very useful. I've just built it and works great without any problems. Thanks for sharing!
Hi Harrymatic, thanks for the post. I am using this circuit as you intended (powering OpAmps) and cannot help but notice how similar it is to the so-called "Sijosae discrete split supply" borrowed from the audio world...except his design utilized 2 electrolytics (bypass caps??) whereas yours uses 1.

In his, the twin diodes make sense - 1 each to directionally force current. I am just curious, what is the purpose of 2 series diodes in your design? Could one get away with removing one?

I confess, my knowledge of BJT biasing is a little hazy, so this may sound like a really stupid question. :\ If so, I apologize!
Harrymatic (author)  BashOnABike1 year ago
Hi there! I completely admit it is similar - and I have used that circuit before; there are only so many ways of solving a particular problem! I played around with my design in a circuit simulation program until it worked best for my particular application, at which point I then constructed it. I just recommend that you play around with the circuit as well, it's a very useful exercise just to determine the effects of various component arrangements.
dog digger2 years ago
This is just like a Cmoy Headphone amp split rail PSU! I think they are mostly called voltage dividers or something like that but split rail PSU is a better name because it tells you what it does
Nope, this is not a voltage divider, and it is not like the cmoy headphone amp. It is an alternative suggested by tangentsoft, and the circuit itself is designed by miniaturization guru Sijosae.

A voltage divider however, is basically 2 resistors connected serially across a voltage difference, and a voltage between the two rails it spans over, is available at the middle tap. The voltage depends on the resistor values chosen.

this circuit is a little overkill - nice layout and everything but you don't need so much circuitry to get split rails in fact most of the time you can do it with 2 resistors and 2 capacitors - This is one I did with a unity gain buffer on stripboard too HERE
And that is okay for most applications, but assume you want to use it for something like a cmoy headphone amplifier. You might need more power that a resistive divider would allow. This basically allows you to pull more power, more efficiently :)
epierce2 years ago
I am in need of a 24 volt to 12 volt or less splitter to hande the lighting on my bike!!
Harrymatic (author)  epierce2 years ago
To be honest, I recommend you use a 7812 voltage regulator instead to do this, as you will be able to draw far more current (close to 1.5A if you have a heatsink). This circuit is really intended for use with op-amps.
TechMidden2 years ago
This circuit has a big problem in the form of its astronomically high output impedance (1kOhm). Drawing just 2mA from the +5V rail causes it to sag down to 3V. This circuit is really only going to work for micropower applications. For a split rail supply you are better off using the very user friendly TLE2426 integrated circuit. Another clever alternative is to use an LM386 audio amp. Just ground the inputs; the output self-biases to exactly half of the supply voltage. @Begradoo, please note: this is not an inverting circuit and it most certainly will not work for power amps!
Harrymatic (author)  TechMidden2 years ago
As I mentioned in the second paragraph, this circuit is designed with op-amps in mind. I've used it in various small audio projects such as headphone amplifiers and I have never had any problems. Furthermore, the point of this circuit is how cheap it is - the parts cost me less than 50p to make it, whereas the TLE2426 would set me back about £4. Nevertheless, thanks for explaining the shortcomings, and that LM386 hack sounds really interesting - I'll have to try it out.
raaymaan2 years ago
Can I ask what the diodes are for? Thanks.
For what it is worth... allegedly:
BC549 = NTE123AP
BC559 = NTE159
How serendipitous!
I have been working with some power amp circuits that require an inverting power supply. This is a great help.