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Modular Modular Synth Power Supply
quad VCO
dual VCF
dual VCA
power supply

see bigger image
working circuit with nice LED glowing
same thing but with heat-sinks mounted
Power supply mounted in modular synth case.

After 5 years of modular making I came to the point when my old power supply was just no good. I used it so long because I hate doing power supplies, but finally it became too small and unreliable. This one is my first decent power supply ever made. Sadly enough I made 2 very stupid mistakes on PCB (like reverse powering an opamp) so you can see kynar there too.

four outputs:
+15V, -15V, +5V, -5V
current limit:
1.4A at 15V, and 100mA at 5V
load regulation:
3.5mV/A for +15V, less than 1mV/A at other outputs
line regulation:
about 1mV/V for all outputs



The heart of the system is Analog Devices voltage reference REF03, but other chips with standard pinout fit there too. 15V regulators use common opamp (741 for now as I had only those at hand) and darlington transistor as power element. Current limit uses common scheme of current sensing resistor and additional transistor. There's significant drop at +15V when working under heavy load, but I will work on this.
5V supply is taken from stabilized +/-15V output, and uses precision opamp OP249 and smaller transistors. 5V are used only as a reference, and 100mA current limit is more than enough. They are trimmed by multiturn trimmers with small range of changes, so setting them with 100uV accuracy is no problem. The limit is accomplished simply by powering regulator transistors via 100ohm resistors.
All outputs are available at screw terminal strip at the edge ot the board (2 points for each voltage) while ground terminal strip sits at the ground star point in the middle. Another board is used to distribute the power to 20 modules.

Power supplies deal with high voltage and may kill you if you're not carefull. Don't attempt to build this circuit unless you know what you're doing. If the schematic didn't resolve any of your doubts, that means it's not safe for you to even start building it. I take no responsibility for any harm caused by building a power supply.

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© 2004-2006 Roman Sowa
Last revised May 9, 2006