Making modules to create Voltage power Supply based on Rasberry Blog #2

RE: Making modules to create Voltage power Supply based on Rasberry Blog #2

GustavoMorales — Wed, 07 Jun 2023 16:56:52 GMT

Awesome I was thinking during these days about your feedback, I would have had all of this before in order to change everything on my board I made it to the PCB manufacturers (don't want to say names to avoid problems) I am thinking on everything that was said about changing transistors and all stuff necessary to work at this point I am kind of concerned on how to fix everything on time, maybe as Michaelkellet said considering on making some extra effort using another controller to work on the analog part, I did not consider the missing ADC and that was a really big mistake I am now working on another schematic that works with an analog controller changing mosfets and keeping in mid voltage that can be tolerated by the rasp and finally making a user interface with the rasp.

As I said I really wanted to have some physically made on time and my PCB I ordered about 3 weeks ago has not arrived and if I change everything now it will be late at the end. Maybe what I can do is simulate in any software to check the status and at least present the user interface since there is not enough time to get new PCBs on time. And another thing is that some THT components are not sold in my country so I can try it on a breadboard that is another challenging thing I will do my best to present something that can be done in the future and keep on working with everybody help

RE: Making modules to create Voltage power Supply based on Rasberry Blog #2

michaelkellett — Tue, 06 Jun 2023 12:58:02 GMT

I see you have already had some good feedback about this design.

The Raspberry Pi is just the wrong type of controller for power supply.

Power supply control is usually described as a "Hard Real Time" software problem, which means that not only the values of the computed outputs are significant but that they must be ready in a specified time interval (Real Time) and the interval is short compared with the operating system (if any) latency. The Pi (as a Linux computer) just doesn't work well in this space.

There are many micro controllers with peripherals designed for this type of application. They have fast ADCs, PWM timers with emergency stop and programmable dead time and other useful features. They are cheap and available on dev boards which are easy to use (eg ST Nucleo boards.)

A much more satisfactory system architecture would be to use the Pi for user interface and high level stuff, talking to the micro controlling the power supply via UART, SPI or I2C.

You may be wondering why the control loop needs to be fast - consider the situation where your load is drawing a large current, the feedback loop will adjust the PWM to compensate for the losses in the components due to that current. If the load suddenly reduces its demand the PWM must respond very quickly (within a small number of switching cycles) to change the PW or the output voltage will rise to possibly destructive voltages.

RE: Making modules to create Voltage power Supply based on Rasberry Blog #2

shabaz — Mon, 05 Jun 2023 21:30:02 GMT

Hi,

For the MOSFETs, the schematic shows P-ch (indicated with the yellow arrows below), but I think they need to be N-ch:

What do these buttons S1 and S2 do? They are connected to a single GPIO, is that intentional, or should they be going to separate GPIO? The single GPIO could distinguish the different buttons if it were configured as an analog input, but I don't know if there are any ADC on the Pi.

For the FeedBack resistors R5 and R6, with the values in the schematic, the output will be 5V, but the Pi can only accept 3.3V maximum, so those resistor values need modifying. However, is there a reason such feedback is needed, and from this point in the circuit?

I also didn't understand the current sensing circuit. The output goes directly to the Pi, but the Pi doesn't have an ADC: