When I started UBZR1 I re-used a power supply I already got - a compact switching power supply of +-12áV at 1.5áAáeach. It can generate additional voltages by extender modules.
I added two 5áV extender modules. One to generate +5áV for digital circuitry and another one for -5áV for some analog stuff.
It turned out I needed to trim the 12áV up to 12.5áV because I had OpAmps going up to 10áV output only if power was +12.5áV.
However, this switching power supply's output voltages are quite noisy, especially if you draw only a small fraction of the maximum current. I measured that only from about 600ámA the noise would decrease substantially. But UBSR1 needs only about 250ámA which is far below the 1.5áA the power supply can do and also far below the "minimum" load this switching power supply needs.
Hence I decided to design and build my own power supply. To keep it quiet I went for a classical analog non-switching design.
This module feeds all the UBZR1 modules with stabilised DC voltages of +12.5áV, +5áV, -5áV, -12.5V.
The voltage current requirements of UBZR1 are as follows:
I am using a standard toroidal transformer to go from mains 230áV voltage to 2átimes 12áV AC. I wired this as 24áV with centre tap. I put three rectifying circuits with corresponding electrolytic capacitors:
As the currents drawn from +−5áV are relatively low, I decided to spare a separate transformer and accept the additional power loss by getting it out of the 12áV AC.
The circuit is built as three separate assemblies
I took the idea to generate auxiliary voltages by separate rectifiers from an old Elektor article about improving the efficiency of an LM723 based circuit from 1978.