There is often a need for a dual voltage supply when dealing with audio (op amps often require dual supplies for example) but there may not be a suitable one at hand. There is, however, usually a single supply, a wall adaptor, bench supply etc. and, at its most basic, all that is required to ‘convert’ the single supply into a dual is a resistor divider circuit. In the past I have knocked together virtual ground split supplies on a breadboard but I thought it would be useful to have a decent, permanent, adjustable dual voltage supply for testing circuits. There are various solutions to this problem; you could purchase a ready-made bench dual supply (expensive); you could build a complete supply yourself or adapt an existing one.
There are a number of sites detailing such circuits including offerings from ESP, Reed Research and Tangentsoft. As ever, circuits are a series of trade-offs and the pros and cons of the different approaches are summed up nicely on the Tangentsoft site. The image below shows two breadboarded circuits, the one on the right, connected to the bench PSU, is an op amp based circuit from ESP and to the left is a simple TLE2426 circuit from Tangentsoft.
As I already have an adjustable 30VDC bench supply with a display, I decided to build a permanent DC splitter to hook up to this. I ended up with something that is likely overkill, but the cost is still very low. The circuit as shown is from Tangents site and uses a TLE2426 rail splitter to keep the voltages balanced, a cheap LM741 op amp to keep the impedance low and a BUF634A wrapped in the op amp feedback loop to maximize current. The buffer is the new SOIC version of the BUF634 which is much more affordable than the DIP8 version (c.£2 compared to £10!) and can output up to 250mA of output current. The combination of these parts provides a stable voltage split, low output impedance and high current output. The maximum input voltage of this circuit is governed by the BUF634A and is therefore restricted to 36V for +/-18V.
The board was designed using Kicad and sent to JLCPCB for fabrication. I used a cheap stomp box type enclosure and added some banana plug sockets for connecting to the bench PSU and the circuit under test.
The image below shows the completed, enclosed DC splitter. 30V DC is supplied from the bench PSU to the input jacks at the rear of the splitter and a steady +/-15V is delivered out of the front jacks.
Gerber files for this project can be downloaded here.
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