While firmware M2 is under heavily construction (managed by my colleague) I spent some time to summarize observations and obstacles found in the latest revision of the hardware part and see to which extent (and that is limited with lack of knowledge and resources) is possible to include it into the next revision. The following things asks for some attention and improvement:

• The power supply (or just PSU) has two channels and their PCBs are mounted on two level using eight 50 mm spacers. Such construction does not allow access to the lower section (channel #2) when everything is assembled and e.g. we are willing to conduct some measurements on that channel.
• Each channel is connected with digital control module (Arduino shield) using 10-wire flat cable (SPI-bus) and 2 x 2-wire cables (power output and remote sense input).
• Each channel (indeed) require dedicated heatsink (two separate or one shared by both channel)
• Both Arduino Mega2560 and Due boards are supported, but Mega’s price/performance looks pathetic in comparison to the Due. Support for Mega costs us 6 level shifters.
• Two different type of digital isolators is used: 2- (input) and 6-channel (output). Such “careless” selection require additional two ‘125 logic buffers (one extra IC)
• Using 4 mm binding posts for remote sense inputs looks attractive and robust but that’s “too bold” and many professional models use much smaller connectors. Additional obstacle is their location in between power output. Therefore no standard 750 mil (19.05 mm) distance between positive and negative posts was provided (that is recommended when e.g. BNC to 4 mm adapter has to be used).
• Software triggering will be added into one of the following firmware releases, but it could be also interesting that some functions are triggered with external signal.
• Similar to the previous one: there is no possibility to perform tracking functionality based on external signal. That is called “remote programming” and it could be helpful to use the PSU as a “smart” pre-regulator during development and testing with all additional features such as current limitation, OVP, OCP and OPP managed by the MCU.
• The enclosure is fully packed: six PCB’s (+ piggybacked Arduino board), big main transformer and two heatsink are mounted outside the box. But still, is it possible to make it smaller with smarter organization and still without using mains voltage “pre-regulation” that can remove huge transformer from the scene?

The quest for the better solution was initiated with rearranging of the PCBs. Once again it’s started with selecting of suitable enclosure that has enough room for not less then two channels. This time an enclosure from the different line of the same manufacturer comes to mind (Galaxy Maggiorato) that comes with 1, 2, 3 or 4U (40 to 165 mm) height. The current enclosure is 115 mm high therefore 3U (120 mm) looks as good replacement. But such dimension is mainly dictated with the size of the Arduino shield PCB (200 x 105 mm) and that is result of vertical placement of the TFT display. Existing PCB is pretty crowded, but with smaller remote sense inputs, removing of 6 level shifters (Sorry Mega), no ‘125 logic IC (better digital isolator’s selection) and minimizing output protection to only TVS (MOV and SAR are going out) we can rotate TFT and lower the PCB’s height below 80 mm. In that way even 2U (80 mm) enclosure starts to be a real candidate for the next revision!

Such reduction in volume (about one third) require new location of channel’s power modules (pre- and post-regulator PCBs). They could be eventually merged into single board but more importantly is to change their form factor that is suitable for mounting them not any more near the rear panel but on the side supports (one channel per each side). Above mentioned enclosure comes with 10 mm aluminium profile that possibly could safely dissipate up to 15 W (per side).

Moving channel’s PCB to the new position remove additional cabling from the picture (10-wire digital, 2 x 2-wire analog). Now we can plug power modules directly to headers located on the opposite ends of the redesigned Arduino Shield (of course here we must take care about rotation of pins because PCB’s are turned “face to face” and we don’t want to end up with “left” and “right” channel PCB variants!). 20-pin connector should be enough to carry all required signal and power lines.

It’s obvious that next revision is not a trivial one. In that case adding more stuff like what is mentioned in the last two bullets (digital trigger and remote programming) makes sense. An open question is where to locate input terminals for them: on the rear panel (that is quite usual for many professional models) or at the front panel? I think that for the bench power supply that is not mounted and forgotten somewhere in huge laboratory rack, front panel sounds more handy.

I tried to draw a new proposal using the FreeCAD, this is my first encounter with it so not many details are on the drawing that follows:

You can see that AUX power supply is now moved on the rear panel. There is also enough place to add 60 x 60 mm fan. The AUX power supply PCB with minor changes could be used for mounting (vertical) USB and Ethernet connectors. One important thing that should not be skipped are limited ability of enclosure to dissipate a heat. That calls for more efficient solution and with currently used pre-regulator that is not a case. That topic will be discussed in one of the coming posts.