I fancied testing my MC4X15A motor controller as the driver for a PSU. The code is very simple as I bit-bang a PWM with 50% duty and use filter consisting of a 100uH coil and 1000uF capacitor.
The result was quite good. I did however notice some input ripple. As I also scoped the Lab PSU output I saw a much, much smaller of the same ripple. Replacing the cables the input ripple improved. What happens is that due to wire resistance we get a power drop as we start drawing current. The drop was actually 1V before I changed cable.
My home made little PSU actually worked quite well. I would have needed a better filter, but output ripple was not horrible and if I had put a decent driver and wiring it probably would have disappeared.
I used 100uH, but a real PSU would use something like 10uH to get a lower power drop in the filter. My motor controller hold it’s ground at 1A, but temperature on HEXFET’s started to rise at 1,2A. I need to work on cooling obviously.
This scope pic is from the 3.3V on my MC4X15A – Universal Motor Controller. The MCU is running and I have the 0.33F Supercap mounted. Ca 200mV point to point ripple is to much for my taste, but it works and this is far better than I have measured out of the Lab PSU’s. I am also using the DPS5005 in this case just to see if it worked at all.
This started as a small experiment as I wanted to see the effect of swapping out the inductor on my LMR14206 – I obviously need to revisit my lab PSU design. The lab PSU and scope is located next to each other on the shelf and I only need to switch it on to introduce noise – I don’t even need anything connected. I obviously have introduced a noise source in my lab that I need to figure out.
This is a set-back because I have been extremely happy with DPS5005 before this.
Returning to LMR14206 I seem to be stuck with 200mV point to point ripple. I am also puzled to as why I see the same ripple on 12V and 3.3V, but I will get some help investigating that. The actual reading on the scope pic is much higher, but that is the external noise. The ripple signature will differ a bit from using DPS5005 versus Thaoxin as they introduce different noise pictures. The small spikes you see above is the 1.25Mhz switching frequency of LMR14206 – and just for the record – it’s no problem adding a filter on the 12V and remove this ripple, but that add PCB size and complexity – part of the objective here was small space.
I decided to test my LMR14206 based DC/DC again and replaced the 15uH inductor with a 47uH inductor on the 12V design. The scope pictures was a shock:
This first scope picture show what I saw as 12V out. It is 12.2V, but look at that ripple picture of several voltages. To compare I scoped what I got out of my PSU and what a shock – I saw the same signature in and huge spikes & ripples out of the DPS5005 based PSU.
This is with no load and it show the same noise signature. The Scope above have different time scaling. Replacing the DPS5005 with the older Thaoxin I also instantly saw a different ripple signal from LMR14206 as can be seen below:
This is a bit better as we have 12.2V and +/-100mV ripple out. But, I need to go back and open my DPS5005 to figure out where the ripple noise is introduced.
This litle Servo about 3 x 3cm is far from a wimp as far at current usage goes. A single Servo have no problem dragging a 10A PSU down – actually I think it’s the current regulation that is predictive, meaning it drops out because current raise is to fast – but, anyway – the only PSU I have that can manage this is a 80A battery.
I connecting 4 of these to my ESP32 Utility Driver and some of my dodgy wires burned up.
Looking at the scope I observe a small Voltage drop as the Signals pulse in. As I add servo’s it become worse. I think I need to alter my algorithm a little to spread the pulses out in time and avoid 12 servos that pulse at the exact same time. I also think I need to buy a 6V battery and ditch the 12V to 5V regulator as it most likely is this that dip a bit.
The ESP32 Utility Deriver does however work well. I am a bit puzled over my DPS5005 PSU’s. They seem to use a predictive aproach to regulating current.
The DPS5005 contains a USB/RS485 interface so both PSU’s can be remotely controlled. I want to use this option to create a Wifi based PSU. ESP-Wroom-32 do have 3 UART’s, so we can still keep UART0 for programming and use UART1 & 2 for each board. I do however notice on the original USB board that the vendor used photo couplers and I think that is a good idea. I would otherwise struggle with ground between the two PSU units that needs to remain isolated from each other.
The only concern here is that the opto coupler’s have limited data rates, but DPS5005 comes pre-programmed with a fixed baudrate anyway. The schematics above is just one I found and modified in Powerpoint of all things. I am not sure ESP32 is capable of driving an opto-coupler directly, so we might need transistors. I obviously also need a separate PSU as I can’t feed from any of the main ones. The signal from DPS5005 include a 5V PSU to feed that side, so we will be using 3 separate PSU’s on this board.
This shows the assembled PSU. Only one of the DPS5005 modules are mounted as I am still waiting on the 2nd. You can see the driver stage mounted inside. The black painted front turned out quite nice.
This is the back side with the mains connector, fuse and switch. I have to wait a few weeks for the 2nd module, but I am quite happy with this PSU. Actual max voltage out is 34.75V as input is 35.75V. Current limit is +/- 0.005A according to the build in meter.
I recently bought a DPS5005 which is a 5A variant of the larger 20A DSP5020 I wrote about earlier. This module can deliver 0-50V/0-5A and have all the electronics inside the display module. Testing of this proves to be very good and it’s a good match for the 36V/5A driver module. As it all also fit well within a low-cost metal cabin I decided to build a dual Lab PSU.
The picture above is the HMI module. The larger DPS5020 have a separate regulator board while the smaller DPS5005 have the regulator board inside this module which makes it very size optional. Both modules are with USB. Basically I just wanted the RX/TX and Modbus in place so I can expland the Lab PSU later.
One of the things I really like with this HMI is that turning the knob by accident changes nothing. You actually have to press A or V first. You also get to adjust out power before setting it out. In fact the HMI does not look like much, but it is very impressive and clever design.
This picture show the 230VAC to 36V/5A driver module available for ca 10.- USD. DPS5005 can deliver 50V out, but as this module is limited to 36V it delivers only 35V out. This is however more than sufficient for basic needs.
This is the 17.- USD box that I use. The plates are steel, so it’s a bit of a job drilling holes etc. But, it is sufficient room for fuses and mains connection, 2 x driver modules, 2 x displays and 2 x PSU connectors. Making the holes went a bit messy. Basically the plate ended up bent around my drill, so I I had to hammer it back out and decided to change color. Was not too found of the blue in the first place.
This shows the all-in-one mains connector, fuse and on/off switch. The only drawback is that I end up with the on/off switch on the back, but I can live with that.
The last component is this female banaa plugs in front, one for each PSU. The table below show the BOM and the ca total cost of the PSU. All these parts are avaiable on www.aliexpress.com
A single PSU 0-30V/0-5A is usually around 100.- USD with P&P. A dual PSU (cheap) would be ca 150.- USD++. This is a programmable, dual PSU. It will cost me anoth 50.- USD to add the ESP32 and HMI later, but once that is done you have a PSU that normally cost several times more.
The LMR14206 ripple was a bit much for my taste. It worked, I had 12V out, 3V3 out and the MCU ticked. But, it’s not a design I can live with. For now I continue on a different board and avoid mounting the DC/DC because I also realized that I could not really bypass it they way I had set up the jumpers. I decided for a 78M05 in TO252 format that gives 0,5A. But, for now I will use 12V directly.
This will work for now. I will return to DC/DC later, but looking at other peoples postings and the lack of LMR14206 popularity I get the picture.
The supercap in the schematics works well, but I probably need to add a bit of circuitry like I did on on PLC Com module. I use a 0.33F due to the size.
LMR14206 with 12V output to a LM1117 3.3V regulator. This is the 3.3V – 350mV ripple – not good. I need to work on that a bit. This is from my Motor Controller with MCU ticking.
I probably need to add another coil on the 3.3V, but that add a lot of space, so I am starting to think that a 7812/317 regulator is a better shoice. Will see how much is needed to fix this.
Regardless a bit impressed over my DS1054 Rigol Oscilloscope. I have an expensive Techtronics at work and to be honest I would gladly replace it with my Rigol costing only 10% of the price for a Techtronics.
I was finally able to test this on a pro lab with full 20A throughput. The small Fan started moving at ca 10A, but was still silent at 20A. We shorted and let the module take a bit of beating with no effect – it continued to behave. This turns out to be a very good programmable Lab PSU module. Well done.
A minor comment is that the module lack a calibration option. Both Voltage and Current are close, but we noticed a 0.3V difference to calibrated instruments. This could easily have been calibrated in software.