It has adjustable output voltage from 0 to 30V and adjustable max output current from few miliamperes to 3 amperes.
As it turns out there are serious flaws in it, but in the forum in that site it was thoroughly discussed and the member audioguru proposed an improved schematic, in which all flaws were addressed. I used his schematic to build my new power supply.
|This small heatsink is only for test purposes and in the final product|
there will be a much bigger heatsink and maybe also a fan.
After I built it and did some testing I made two changes: first, I added 24V zener diode + resistor to stabilize supply voltage on IC1. This is especially important because when there is high load and supply voltage drops by few volts reference voltage on pin 6 also changes significantly.
Second, I removed 10k trimmer resistor RV1 - there isn't any need for it.
Here is the final schematic:
The two trimmers are for adjusting the max output current and the max output voltage.
And some shots of the second PCB and assembled board:
My plans are to make 2 pieces in two separate chassis and when I need dual voltage supply or voltage higher than 30V I will use both of them.
There will be digital panel meters on the front of the chassis which I already ordered from eBay.
Update (13.03.2012) :
Finally, over a month after ordering, the two transformers are ready. They are capable of delivering 30V/4A.
The panel meters also arrived from Hong Kong.
As you can see, I have replaced 0.47 ohm/10W resistor with two 0.68ohm/10W resistors in parallel, because the former generated too much heat.
The front panel is also ready, later will post a picture. What is left to do is to make a little board with a fan controller.
Here is the link for downloading archive with project files in PDF format: LabPS.rar
The first one of the two PS is ready!
Here is puny board of the fan controller:
And there is power supply itself:
Here is the schematic of the fan controller:
The schematic may be supplied with AC or DC voltage but not both simultaneously. If the supply voltage is DC, then B1, C2 and J3 may be omitted. With different R7 value we can control the speed of the fan. Adjusting switch-on temperature is made with TR2.
And here is the link for downloading: FanControl.rar
The PCB is different from that shown on picture above, because I made some improvements and rearrangements.
Use it on your responsibility.
P. S. There is even smaller version here: FanControl2
The second unit is almost ready. Here one shot from inside:
The fan is secured to the bottom with double sided adhesive tape.
It's done! Dual adjustable laboratory power supply :)
Update: December 29, 2015
I was asked couple of times how to connect center tapped transformer to the power supply. It can be done according to the schematic bellow. The bridge rectifier is replaced with two diodes. The negative voltage come from one of the windings. It is rectified by D3 and smoothed with C3. D1 and D2 must with high current rating - at least 5A (diodes in the schematic bellow are just for illustration). C3 must be with 50V or 63V rating. R1 and R2 must be 2W power resistors. There can be added a capacitor (100uF) between -V and GND for extra smoothing the negative voltage. If the negative voltage is bellow 1.3V, the value of R1 and R2 can be decreased a little. Bear in mind that I haven't tried this schematic, just simulated it, so be careful.