Although having made more than enough power supply’s, there where still some boards in my storage that I bought from a fund raiser at Circuits Online. These are a dual 0-34V 2,5A PSU with tracking. It would be a waste to have the boards and not build them.
(Above pictures are from CircuitsOnline because I forgot to take pictures myself)
As with the previous PSU build kit (Lab Power Supply 0-70V 0-3A) I was not completely happy with the specs (/wanted to make it more of a challenge) and decided to change them to 2x 0-48V 0-3A. This would mean the transistors had to dissipate a lot more heat. To counter this I used a switch mode power supply instead of a normal transformer. This switch mode power supply I modded so It can be controlled by a 0-1.5mA signal to give 20-60V on the output. This way the voltage on the transistors is limited to 20V max. I made a circuit to keep te input voltage about 10V higher then the output voltage.
This circuit I build using 1 of the op-amps on the main board and a small piece of pcb added fixed to a unused connector.
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- Schematic
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- PCB
After this the power supply needs to be changed. Some components can not handle the larger voltage, some resistors need to be adjusted to increase the range and some other modifications have to be done.
Now that the PSU works, it was time to make an enclosure. I could not really find what I was searching for, so I decided to 3D print the entire enclosure. This way it is exactly to size and I can add custom features, like the front is on a big printed hinge, making it easier to work / measure on the boards.
On the bottom are 3 power supply’s (2x modded 48V SMPS, 1x 12V for the fans), 4x 12V transformer for auxiliary voltages of the supply circuits.
Above this level are the heat sinks, for this I used old processor coolers, where the transistors are clamped on with a metal sheet. The fans on these heat sinks can be PWM controlled, so I used a simple dev board (the blue one in the centre) to read out 2 temperature sensors and drive 2 fans.
In the front are the 2 lab PSU boards, and on the front panel the display/pot PCB’s:
The end result:
On the equipment shelve:
Dutch 
