Low-Cost PSU

To feed modular system, you need bipolar power supply giving voltages from ±9v to ±18v depending from used system. Additional power lines might be needed. Eurorack standard suggests symmetrical ±12v line and additional +5v line which is useful for MCUs and some another digital ICs. It is possible to use computer power supply for modular systems, but PWM supplies have quite unstable voltage in fluctuating environment. Because of that, tune and volume of the synthesizer powered by PWM supply may have undesirable modulations. In some cases it can be used as artistic effect but to get completely predictable sound you need traditional power supply that uses a transformer.

Here is the example of such kind of supplies — Low-Cost PSU intended to work with external ±12v AC power adapter or external transformer.

The idea was to design power supply that is small, light, not so noisy, cheap and easy to build. This supply can be used as test supply in a lab or as a PSU for small, portable cabinet.

Schematics. The circuit is based on half-wave rectifier. AC splits in two lines and virtual ground with D1 and D2 diodes. The positive voltage is sustained by electrolytic capacitor C2 and ceramic capacitor C4, which is more fast. Then it goes to positive voltage regulator U2, followed by filtering capacitor C7, and protection diodes D3, D5. Minimal load and indication is provided with R2 resistor and D8 LED. The value of the resistor is to be selected manually to obtain comfortable brightness. I used 15K. The negative voltage bus is similar with different polarity and different regulator. The +5v bus is even simplier and utilize low-current regulator, 78L05.


Low-Cost PSU: принципиальная схема

The Board. The whole circuit including heatsinks, seven 16-pin IDC-connectors and mounting holes, can fit on one 37×24 holes stripboard. Because of simplicity of the circuit, there is very few cuts and jumpers needed.


This is how it looks inside 3U rack chasis.
Low Cost PSU: фото

Creative Commons license
This circuit is published under Creative Commons «Attribution-NonCommercial-ShareAlike» 3.0 license.
Any use beyond this license must be discussed with author.

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