JLM Electronic Load, 0-30V, 0-4A, 1mV/1mA resolution

[JeanLeMotan]

[edit: updated the links]

This is the 3rd revision of the load first discussed here: https://www.eevblog.com/forum/projects/programmable-electronic-load-0-5a/
As pointed out by several forum members, the previous revision had some issues:

- The PWM ref voltage was unstable as it relied only on the stability of the AMS1117 LDO - which is not great
- The MOSFET was not good for a load. A linear one gives way better performance, both in therms of max continuous power but also because it has a DC region specified in the datasheet SOA
- The reverse polarity was not ideal as the MOSFET went into the linear region at low voltages and heated up considerably
- The opamps (TL071) were too noisy for this application
- Several other smaller issues - like the screen being too small and hard to read, lack of SD card for saving the data, incomplete schematic (opamp voltages were generated outside, no fan mosfet on the PCB) etc

I've been working on an improved version during the past month and I finally managed to get something working.
Specs:

• 0-4A (it was 5A in rev2, dropped now due to shunt de-rating)
• 1mA, 1mV resolution. Accuracy should be similar if calibrated
• 0-30V
• 100W continuous with the recommended heatsink & FAN
• 3D Printed case
• Reverse polarity protection (opamp driven, improved from rev2)
• 2 & 4 wire measurements (rev2 had only 4 wire)
• Autoranging for both V&A using the ADS1115 PGA to get the max resolution/accuracy I can get from that part
• Temperature sensing
• Fan control (mosfet on pcb this time)
• Fully programmable: it can execute a programmed sequence of operations and output the data through serial
• SDCard for data saving (a csv per session)
• 320x240 Touchscreen
• Proper linear power MOSFET (IXTQ 42N25P)
• Voltage reference REF3120AIDBZR (rev2 used PWM for this)
• Precision DAC DAC8571IDGKR (rev2 used PWM)
• Digital section on the PCB (rev2 PCB had no room for the esp32)
• USB Powered (rev2 needed 3v3 input and +/- 12V for the opamps)

The software has the following features (some are WIP)

• Voltage/Current/Power/Resistance display
• Energy - both Wh and Ah
• Graphs for the whole session
• Constant Current/Power/Resistance Modes
• SD card data saving
• Time/Energy/Voltage limits

I had to switch to a 4-layer PCB for rev3 in order to fix the esp32.
Possible improvements for a rev4:

• Better shunt, double the current capability
• Use a raw esp32 module instead of a devkit, to cut BOM costs
• 2-3 power mosfets, each with load regulation for way more power

I made a video with it in action: https://youtu.be/jkzM7wHbVtE
Schematic: https://easyeda.com/jeanlemotan/jlm-electronic-load
Github project: https://github.com/jeanlemotan/jlm-electronic-load


Let me know what you think.
I plan to do some more videos analyzing the schematic - including TINA sims for the load regulation and so on. I'm a SE, not an EE and I don't want to spread false info so your scrutiny is appreciated.

[Edit]
Second video here with the PCB & Schematic and details about the load regulation.
https://youtu.be/gcrGE7rbWiY
Hopefully I haven't made any embarrassing mistake

[Dubbie]

Can you post some photos of your board?

[thm_w]

Links got cut off:
https://easyeda.com/jeanleflambeur/electronic-load
https://github.com/jeanleflambeur/electronic-load

Looks like some good improvements.

[trinhvanthien]

Hi JeanLeMotan,
When i try compile the electronic-load project had failured.

[exe]

When i try compile the electronic-load project had failured.

Looks like it actually succeeded and uploaded. Those yellow lines are warnings, not errors.

[JeanLeMotan]

Links got cut off:
https://easyeda.com/jeanleflambeur/electronic-load
https://github.com/jeanleflambeur/electronic-load

Looks like some good improvements.

Thanks, I corrected the post.

[JeanLeMotan]

Can you post some photos of your board?

Definitely, as soon as I get 1h I'll post some high res photos of the insides.
Are you interested in something in particular?

[Dubbie]

Not really, I just like to see how others do things.

[JeanLeMotan]

It took a while but I finally uploaded the second video with the PCB and schematic. I go over the load regulation a bit - hopefully it's relevant for someone.
In the next video I plan to go over the voltage reference section and how to get a negative voltage for the bias required to cancel the input offset voltage.
https://youtu.be/gcrGE7rbWiY

[JeanLeMotan]

I'm thinking to do a next video about dummy loads and I have a few options:

• How to create a voltage reference for the load regulation: filtering a PWM signal or using a proper voltage reference and DAC
• Reverse polarity protection: diode, mosfet, opamp + mosfet
• Breadboarding the load regulation from the prev video and showing how it works, preventing oscillation etc
• Making a new PCB from scratch, double layer vs 4 layer
• Simulating a dummy load in Tina-TI, stability, gain & phase margins
• ESP32 programming in PlatformIO vs Arduino IDE
• Making a pretty and ergonomic UI on a small screen
• Getting 100 FPS on the ESP32 with a SPI screen (ili9431)

Which would be the more interesting topic?

[trinhvanthien]

Hi @JeanLeMotan
Your project sometimes runs very unstable, ESP32 normally runs but the screen is not displayed.
I checked the display is good with Arduino.

[JeanLeMotan]

Hi @JeanLeMotan
Your project sometimes runs very unstable, ESP32 normally runs but the screen is not displayed.
I checked the display is good with Arduino.

In what way unstable? Does it crash or reboot?
Double check that the display is connected correctly - check the schematic for that.
Also - are you using the same display? This will only work with 320x240 ILI9341 displays.

[trinhvanthien]

In what way unstable? Does it crash or reboot?
Double check that the display is connected correctly - check the schematic for that.
Also - are you using the same display? This will only work with 320x240 ILI9341 displays.

Thanks so much for your replay.
It does not crash or reboot but is not displayed, I use Display 2.8 "TFT and connected correctly as diagrams.
Link: https://www.aliexpress.com/item/2-8-240x320-SPI-TFT-LCD-Serial-Port-Module-With-PCB-Adapter-Micro-SD-ILI9341-5V/32889801161.html?spm=a2g0v.10010108.1000001.11.16c17dc9EDKcL9&transAbTest=ae803_4&ws_ab_test=searchweb0_0%2Csearchweb201602_7_10065_10068_10547_319_10059_10884_317_10548_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536%2Csearchweb201603_52%2CppcSwitch_0&algo_pvid=dc7332f9-fb71-47b6-be6b-7a42c4b5aa04&algo_expid=dc7332f9-fb71-47b6-be6b-7a42c4b5aa04-1

[JeanLeMotan]

Thanks so much for your replay.
It does not crash or reboot but is not displayed, I use Display 2.8 "TFT and connected correctly as diagrams.
Link: https://www.aliexpress.com/item/2-8-240x320-SPI-TFT-LCD-Serial-Port-Module-With-PCB-Adapter-Micro-SD-ILI9341-5V/32889801161.html?spm=a2g0v.10010108.1000001.11.16c17dc9EDKcL9&transAbTest=ae803_4&ws_ab_test=searchweb0_0%2Csearchweb201602_7_10065_10068_10547_319_10059_10884_317_10548_10887_10696_321_322_10084_453_10083_454_10103_10618_10307_537_536%2Csearchweb201603_52%2CppcSwitch_0&algo_pvid=dc7332f9-fb71-47b6-be6b-7a42c4b5aa04&algo_expid=dc7332f9-fb71-47b6-be6b-7a42c4b5aa04-1

You need to double check your display connections according to the schematic.
Can you post a few photos of your setup?

Can you run any other ILI9431 demos to see if they work with your wiring? Make sure you configure whatever demo to your actual pin mapping.
Another thing to do is use an oscilloscope to see if the clock and data signals look ok.

[JeanLeMotan]

I just saw your photo: you have to connect the LCD Led and Reset to VCC for the screen to work.

[trinhvanthien]

..... and Reset to VCC for the screen to work.

Great! it worked

[JeanLeMotan]

..... and Reset to VCC for the screen to work.

Great! it worked

Great!
What will you be using for the case? If you have a 3d printer you could try the one that I use, it's uploaded on github.

[trinhvanthien]

Great!
What will you be using for the case? If you have a 3d printer you could try the one that I use, it's uploaded on github.

thank you for the suggestions....I will try.

[Rerouter]

Possible suggestion. If you divide the load voltage into the dac vref pin. You end up with a constant resistance mode with a few 10s of KHz bandwidth

[trinhvanthien]

To @JeanLeMotan
I have 2 problems:
1 - Fan does not run when temperature reaches 70 degrees
2 - The value is not saved to the memory card...

[trinhvanthien]

@JeanLeMotan
Did you stop developing your project ??