Hey folks,
I would like to present you the current status of my electronic DC load and would be very grateful if you could have a look at the schematic and tell me what you are thinking about this design.
My rough requirements were:
• Max. input voltage: 60V
• Max. input current: 20A
• Max. power: 300W
• DUT input isolated from digital control
• CC/CV/CR/CP mode
• Reverse polarity protected
• External setting input
• External trigger input
• External sensing inputs
• Slew rate control
• Touch display control
• Powered from mains
My project is splitted into three parts, the digital, analog and 230V part. I'm splitting this because I'm doing my first design in Altium and it could easily be possible to screw some things up in the first revision. Not only regarding the design but also regarding the Altium toolchain. Also the analog part will be a quite large PCB (20x6cm) (I don't need so much space for the components, but the heatsink is quite large) and I don't want to put everything on one board because newer revisions would be very expensive looking at PCB costs.
Digital part:This part is equipped with the MCU (Arduino Due), Isolation (SI86xx), 3,5" Nextion touch display, watchdog, EEPROM, buzzer, RTC, rotary encoder and off course the power supply for the digital part.
The schematic is mostly finished, but I decided to finish the analog part first, test it and afterwards go on with the digital part.
The digital board gets and sends information about voltage, current and some other things through an isolated SPI (Si8651).
230V part:This part exists only of a transformer with the bridge rectifier and bulk caps. 2x +15V are generated on this board. The analog and digital part are powered isolated from each other from this board.
I have not started with the design of this board yet. It will be the last one because I can test the digital and analog part with my power supply which delivers also several isolated outputs.
Analog part:This part is equipped with its power supply, the DUT input, sense measurement, AUX setting, external trigger, slew rate control, two identical current control circuits, ADCs, DAC, reference voltage, SPI IO expander and two LM35s. The schematic of this part is in the attachment.
I’m quite unsure about the input snubber network. After some simulations I came along with very big resistors and capacitors. Is this really necessary or am I overengineering here?
Also my current solution for the slew rate control is changing the time constant of a RC filter by adding capacitors in parallel through the analog switchs U6&U7.
I'm not going to get a nice straight rising and falling edge because I'm not charging the capacitors with constant current. The edges will look like normal charging curves, but that is sufficient for me.
Your feedback is highly appreciated!
Thank you very much in advance!
Kind regards