Category Archives: PSU

PSU Ripple

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 PSU Ripple

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.

DPS5020 Review 3

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.

PSU 36V / 5V

I purchased this for < 12.- USD and tried it as a driver stage for DPS5020. It works fine. It is small and perfect for a 0-35V / 0-6A “bread & butter” lab PSU. The DPS5020 have a cut-off setting that I set to 6A. It cut’s the PSU if you by mistake allow more than 6A out to protect the driver stage. The driver is also short-cut protected.

  • Driver PSU : 12.- USD
  • DPS5005: 25.- USD
  • Box : 17.- USD
  • Mix: 10.- USD

That is 64.- USD for a single 0-35V / 0-5A and 101.- USD for a dual. And this Lab PSU will have far better spec than any of the “cheap” ones. Also keep in mind that DPS5005 is much smaller than DPS5020 as it hide the PSU inside the HMI unit.I notice that Input Voltage to DPS5020 variates with +/- 0.05 as I use the Driver at 5A. I will put a oscilloscope to see if I have ripple later.

I had to abort the test yesterday after ca 10 minutes because my load started to melt 🙂 – we have some awesome Lab PSU’s coming up. DPS5020 do have a small fan, but it has been silent so far.

Adjusting Voltage/Current on these modules are a joy- Just select V or A and turn the knob. Push the knob to change digit you adjust. With a MCU using ADC’s we have an accuracy on ca 0.02ich – which is pretty good compared to analogue PSU’s.

What we have not discussed so far is output filtering. With some of these giving 50V – 20A we will be giving 1KW out. That is 1KW that will spike back as 1000V with 1KW energy if we have coils/motors connected. We need to ensure that the PSU can protect both itself and the equipment we are testing.

DPS5020 Review 2

The interface on the UART is Modbus RTU. I managed to translate the document from Chinese to English yesterday, so it is uploaded on the download page. Running the top-side app was straight forward on Windows 10. I had a bit of issues with antivirus installing it, so had to switch that off. The graphs are cool, but the window scale is a bit short and it only update once a second. Testing current under load was however a beauty. Using 36V in (3 x 12V/10) I had no problems with 10A out – or more correctly my load and test wires did get hot.

DPS5020 Protocol Specification 1.2 can be found on the download pages here.

Using UART/Modbus as interface it will be straight forward to create a custom HMI module to add buttons and display graphs on the box without a PC.

PSU Driver

The diagram above show the minimum needed for any mains PSU. We need a On/Off switch and a fuse. This can be purchased as a single unit. The 2nd is the PSU itself that is available in numbers on the net in nice modules.

A 12V/10A module cost < 10.- USD and they can be connected to create more current or higher voltages. Using 5 modules you can create 60V/10A at a cost of < 50.- USD. Using multiple modules like this can save some cost, but it usually require more space. As illustrated in an earlier entry the Driver stage is actually more expensive than the DPS5020.

Please check the regulations of your country before connecting anything to the mains.

Programmable Lab PSU 0-50V / 0-20A – DPS5020 Review

I received a DPS5020 module yesterday, well packed. This is the 0-50V/0-20A Lab PSU module I mentioned earlier. Assembling and switching this on was straight forward, and using it was a very positive surprise. I was initially concerned about it’s HMI, but I am actually impressed by the cleverness of this design.

This first picture (sorry for the quality) show what you receive. A small user manual, cables and the two main modules. What surprised me a little is actually how small this is, but I need to remind everyone that you need a 6-60V DC supply in front here. I applied 30V and get an output from 0-29V. The HMI sence the input and adjust on Voltage range accordingly. I will see if I can do the same on current (manually set upper limit)

This picture show the HMI module opened up. The display is small, but sufficient. The entire module is quite simple and could easily be replaced with some hacking – it has a separate LCD and Keys cable, but I have no info about their pins jet. My initial plan was to replace this, but after having used it a little I am not so sure I actually want to.

This is a picture (from the net) showing the HMI in use. The Green/Yellow/Purple text in the middle is showing actual output. On bottom (cyan) you see voltage in, on top(cyan) you see Voltage and Current setting. Notice that Voltage out show actual voltage out, not the intended setting. You will actually see a +/- 0.01 variance in this.

Operating this is straight forward – press V and turn the knob to set Voltage, Press A and turn the knob to set Current limit. Once you are done you press Set and get a confirm screen. After that you press the On/Off to enable this out. This took me by surprise because it is not just about turning the knob to change voltage – you actually have to press V button first. This is very good because it is nice to know that your PSU don’t change by accident. You can adjust voltage both on-line and off-line this way. The second issue is the capability to adjust setting before you enable it out. The knob is a standard encoder with a push switch used to change what digit you adjust. Seriously it took me around 60 seconds to learn this interface. This is far, far better than I actually expected.

This is the PSU module itself (above). Input at left, output at right. On the front you see a LQFP48 holding a STM32F100C8. I ordered the USB which is a familiar CH340G operating on an UART. That is the small 4 pin connector next to the MCU. I will get back to using this, but it basically means you can remotely connect to this using USB, Bluetooth or simply hacking the UART. I believe the protocol is described.

This is the included top-side HMI that can be used to operate this from a PC. I have yet to test this. You need to downoad this from their site – this pic is actually from the 15A module. My comment here is that this is all fine, but I need my PC screens for different purposes. I would however like the graphs, so I am considering hacking the UART and connect a Graph display on the PSU + adding Ethernet/Wifi capabilities.

Next I will get some load tests done to see how this wonder behave under heavy usage. Not bad for 45.- USD P&P included. Transport was under 3 weeks, but this is only pure luck.

Programmable Lab PSU

Starting at left with 230VAC input we need a classic rectifier and filter that will produce high voltage DC out. This is input to a PWM driver that will use HEXFET’s to generate a MCU controlled PWM into the isolation transformer. The duty of the PWM decides the output voltage. If we have 400VDC and a duty cycle of 10% we will have 40VDC in average out. The 2nd rectifier ensure we got all positive voltage out and the end Filter (illustrated below) convert this to a stable DC out. To Control this we use fast ADC’s to read output voltage and current into the MCU that control PWM duty.

The core of any PWM driven PSU is the prinsiple that we provide a PWM in where an output filter consisting of a coil and capacitor force this back to a stable DC. Voltage out is a simple average calculation, meaning that we control voltage with setting PWM duty.

Building a 0-50V/0-20A Lab PSU

I ordered a DPS5020 (50v/20A) Lab PSU for 45.- USD with USB connector. I intend to hack that serial port and extend the HMI with my own interface, but my primary challenge is finding an affordable AC/DC that will deliver 60V/20A as input. I did find some interesting alternatives:

This is 36V/5A and well suited as input stage for a 0-30A/0-5A Lab PSU. It is also quite small. I ordered one of these because it only cost ca 11.- USD P&P included. A 20A PSU is a monster needed for motors, but a 0-30V/0-5A is a “bread & butter” PSU that you need several off.

The best priced single 60V/20A unit I found is this that actually is 25A at 124.- USD. You have to be aware that both voltage and current will drive prices a bit, but as I know that higher currents are the worst to deal with I looked for 60V/10A units and found the one below.

This cost ca 30.- USD if you order 10 units so I need to think about that. You can also buy them single units for ca 36.- USD. To achieve 20A I would need 2 of these that require some size, but the advantage is that I make 20A wires myself which makes each driver PSU cheaper. This gives me a cost of a driver stage around 70.- ++ USD which is decent.

Getting a box for the largest 50V/20A Lab PSU will cost around 100.- USD sadly. Adding 70.- for a driver stage and 45.- for the module + an estimated 30.- for extra bits I will land on ca 245.- USD for a 0-50V/0-20A Lab PSU.

The “bread & butter” 0-30V/0-5A Lab PSU is easier. We can pack 2 modules into the 16.- USD Blue box I showed you before and with 2 x 30.- + 2×10 and some 20.- in extra parts we should have a small, dual PSU for ca 116.- USD (of ca 58.- USD each).

Both those are decent options taken into account what the spec of these PSU’s will be – that said I want to receive the units and do some testing before I invest more time and Money on this.

0-50V/0-20A Programmable Lab PSU – DPS5015 & DPS5020

DPS5015(0-50V/0-15A) and DPS5020(0-50V/0-20A) are DIY modules available for ca 40.- USD. It exist several of these. Notice that input here is 60V DC, so you need a AC/DC converter in front of this.

I have looked at these for a while as I plan to build some Lab PSU’s.  It is an interesting option. The USB/Bluetooth adapter with the software below is very interesting. The module uses a UART With Modbus RTU – the protocol doc is in Chinese, but I hope someone will translate this to English.

One can never have to many lab PSU’s ….