Does anybody know the designer of these Eurorack Busboard , Power Supply and Distribution Cables ? according to info he/she is from France
The PSU looks a bit like the MFOS one. but hey this could be useful for really small cases
but 100mA without heatsinks it not much
The MFOS version is an easy build and might work better. I built two, use one in my Anushri bento box and the other is just a spare.
Power output is dependent on the wall wart you power it with (AC WALL WART, very important) but if you use a 1A wall wart, you can get nearly 1A out of the power supply.
it looks a bit like (but not identical) to the one from razmasynth: http://www.bend-electronic.com/Razmasynth/MiniPower.html
No clue if it is any good, but looks useful for super small cases.
I’m David, the designer of the Mini dual power supply and the Compact bus board. I’ll try give you further informations about my designs.
The power supply is effectively based on the idea developped by MFOS. I think Razmasynth’s power supply is also based on the same idea. The base principle of this kind of power supply is the “double half-wave rectifier” : one half off the AC wave for each rail.
MFOS power supply can deliver more power than mine. The reason is the number of capacitors. Each capacitor has a limit on the current it can store and release in a given time (the ripple current). Putting several capacitors in parallel allows you to rise that limit. MFOS Wallwart power supply has 6 capacitors, 3 per rail. My power supply has only 2 capacitors, 1 per rail.
I designed it that way because I needed a very compact and low power PSU in several personal projects.
What could happen if your capacitors can’t manage the ripple current: a ripple voltage occurs on the input pin of the regulators.
The second limit is the heat sink. When I say “100 mA max without heat sink” well, it’s because you really don’t want to burn your fingers.
Given the voltage dropout on linear regulators, usually 2 volts minimum, at 100 mA, you get a power consumption of 0.2 Watts, minimum.
Now, if you supply the regulators with a plug pack delivering 18 V, the dropout will be 18 - 12 = 6 V. With 100 mA, the power consumption will be 0.6 W. Ok, let now consider the thermal resistance of a TO220 case:
The “Junction to Case” thermal resistance is 4 K/W. The “Case to Air” TR is 50 K/W.
At 0.6 W, the temperature rise is 54 x 0.6 = 32.4 K. If the ambiant temp is 30°C, then the case is 30 + 30 = 60°C.
With the same wallwart delivering 18 V, if you draw 200mA, the power consumption is (18 - 12) x 0.2 = 1.2 W, case Temp rise is 50 * 1.2 = 60 K, and finaly your regulator case is 30 + 60 = 90°C.
30°C is not a very high value for a closed synth case. Imagine your synth box, painted black, no air vent, in the sun, in a heated room and with a lot of components heating…
Using heatsink allows you to draw more current without danger for you or your components.
Finally, the wallwart itself is a big limitation on how much current you can draw. Those transformers tend to have a high series resistance in their secondary winding. The more current you draw, the more the voltage will drop, the more ripple voltage will occur.
Razmasynth’s power supply is quite similar to mine but there’s in addition a +5 V rail.
Well it’s usefull for prototyping and when you need to build a simple project.
I think it needs some improvements, more ground traces for example, in order to reduce the number of wires (I hate wires
Just to clarify why I mentioned a plug pack delivering 18 V :
I measured yesterday the output of a “13 VAC” unit, and I got a peak voltage of 21 volts! Often, those wallwarts have higher voltage output values than expected. The output tends to drop when you draw current. So, in order to provide the rated voltage with a charge connected, the manufacturers tend to overdimension their transformers.