I did not add much capacitors on any of the boards simply because they take to much space + I wanted a separate capacitor board to be able to scale up/Down and be more flexible about mounting them due to their size.. I found some very nice sized 10,000uF/50V that I am using that have a decent size to them. We need to add one of these on the out step (before the out relay) to make the PSU capable of dealing with nasty behaviour from test equipment. I also wonder if I might need some caps between the relay board and the regulator to smooth input voltage changes – will see.

The TVS diode should clamp down on ca 45V to protect the 50V capacitors in case we deal with spikes caused by 360W of fun.

What I will do next is to review the full PSU and adjust for assembling of the entire PSU. That include looking into a project box and HMI solution.

to be continued …

In part 1 I created an analogue linear regulator that can be used stand-alone as is. But, the drawback with a linear regulator is that it regulate by splitting voltage out between the load and the transistors. This means that if you short-cut the load you have 36V * 10A = 360W heating up the transistors. That is a lot of heat to dissipate and this is the main drawback with linear regulator techniques.

To improve on this I want to use 3 x 12V DC-DC and a few relay’s to connect in 12V, 24V or 36V as it is needed. Adding a MCU I can autosense the output voltage and if voltage out is 10V I switch in 24V etc. This means that my maximum voltage drop is 14V giving 140W to dissipate. It is much better.

I also need a separate 5V for the MCU, Display etc, so I grab a smaller 2A DC-DC for this and add a classic 7805. By doing this I also isolate MVU power from the Lab PSU which is good. The MCU I chose is my own STM32F030 breakout board. This leaves us the option to replace this with an Arduino or whatever we want to use later – freedom of choice.

This is an early 3D model of the Relay/MCU Board- again I use hole through Technology only. The DIP14 Circuit is ULN2003. I decided to use this because the relays need ca 6V-14 to hold + having the ULN2003 between the coils and MCU adds protection.

To improve our heat dissipation further we implement temperature sensors and fan’s. I have available 12V/600mA ports and ADC’s anyway so implementing 3 of these are easy. I will add schematics and BOM lists later.

to be continued…

I desperately need more lab PSU’s and I have a bunch of LM723 and TIP3055 transistors that are excellent for creating an old-fashioned Linear PSU module. Thinking a bit ahead I want to create the analogue regulator as a small, separate module with knobs on the front, heat-sink & transistors on the back and connectors on the side.

The 3D model above is an early draft on 70 x 75mm. I am using hole througt Components on this one to enable hobbyists to grab a PCB and solder them up themselves to save cost. Adding a Voltage/Ampere meter is easy because I just use a module like this one (or similar):

They cost less than 5.- USD and they work well. I add no other led’s or display, but I add two power switches – one for input and one separate for output.

I am also using 2 x TIP3055 that technically enable 30A together, but PCB lanes and current limit is scaled for max 10A. The following block diagram show the complete PSU.

The mains are basically a 36V/10A DC-DC regulator. These comes at a decent cost with CE/FCC approval that is needed for 48V and higher. What is remaining is to find a project box and we have a nice Lab PSU.

to be continued…