Electronics > Projects, Designs, and Technical Stuff
USB-C PD laboratory power supply
MaTkEOxjC:
--- Quote from: bloguetronica on February 16, 2019, 05:55:40 pm ---
Well, that was a war that I once fought and lost. I went looking for chips to do flyback isolated DC-DC modules/converters/designs, and the solutions commercially available didn't satisfied me. I went for a module that was readily available and worked as well as promised. If you don't need isolation, I'm sure there are plenty of chips out there. But, as I and others suggested, you should go for an isolated design (unless you are building a battery charger, exclusively, and that depends).
--- End quote ---
Woops, I meant topology wise. I'll probably implement the regulator in software or at least partially in software. But I'm not going to invent another exotic topology (as one of my Professors at the University does xD) Currently reading "Leistungselektronik" (Power electronics) from Franz Zach, German book.
--- Quote from: bloguetronica on February 16, 2019, 05:55:40 pm ---Well, you don't need two micro-controllers. Actually, if you use the CP2130, you can get away with none. You don't need to upgrade the firmware unless you need to change the PID/VID or other descriptors. Anyway, the CP2130 provides an API, and if you use Linux, you can easily do away with libusb. You can always check my FAU200 or FAU201 projects to see how I've implemented some power supplies using this chip. They are isolated, by the way.
P.S.: Added the schematics attached.
Kind regards, Samuel Lourenço
--- End quote ---
I really appreciate it. Took a look at your website and schematics, looks very nice!
But I'm more of a hardware (and Linux) guy, so enabling the hardware for easy software updates (and more features) is something I'd really like, as design choice.
Having the controlls on the board is probably the better choice because USB is not real time. If have a hardware that can measure output voltage and current, I can easily implement features as "trip current" or similar.
MaTkEOxjC:
Quick and dirty design mockup
Voltage measurement after the DC/DC to adapt for the linear stage. Linear stage makes final filtering. Afterwards output voltage and current are measured.
Errors:
* Control data from micro to DC/DC on top is missing.
* after the isolated 5v or 3.3v converter a LDO is probably a good choice, for better ADC/DAC performance
* power to data isolator is missing
bloguetronica:
--- Quote from: MaTkEOxjC on February 16, 2019, 06:58:28 pm ---...
I really appreciate it. Took a look at your website and schematics, looks very nice!
But I'm more of a hardware (and Linux) guy, so enabling the hardware for easy software updates (and more features) is something I'd really like, as design choice.
Having the controlls on the board is probably the better choice because USB is not real time. If have a hardware that can measure output voltage and current, I can easily implement features as "trip current" or similar.
--- End quote ---
Thanks! Yes, in that case, you don't want to be dependent on a software that runs on your host PC. You will definitely need local and realtime control, and that only can be implemented by the use of a micro-controller. Still, you can reduce that to one micro, that communicates with the USB via SPI. That micro would also read the voltages and provide local control. It would be located on the isolated side (if you wish to implement isolation).
Kind regards, Samuel Lourenço
David Hess:
--- Quote from: MaTkEOxjC on February 16, 2019, 05:19:49 pm ---Microcontroller on primary and feedback via optocouplers:
I need voltage and current. Isolated ADCs are pretty expensive. With optocouplers I need some kind of A-to-D conversion on the secondary side. Normal adc/dac and isolators might be an option.
--- End quote ---
The microcontroller which controls the output voltage and current is on the output side with the ADCs, reference, current shunt, and output connection. The linear optocoupler bridges the isolation barrier to control the switching controller on the input side. I would rather have two microcontrollers than have to bridge the isolation barrier with voltage and current measurements. Having the microcontrollers communicate over a separate isolated link for USB PD status and control is not costly.
--- Quote from: MaTkEOxjC on February 16, 2019, 06:58:28 pm ---I'll probably implement the regulator in software or at least partially in software.
--- End quote ---
At most I would rely on the microcontroller for detecting a fault in the analog control loops. Under normal conditions, I would generate analog voltage and current signals for the analog control loops to use and get feedback of actual voltage and current. Inserting the microcontroller into the control loop is a hazard, extra complexity, and potentially limits performance.
MaTkEOxjC:
--- Quote from: David Hess on February 16, 2019, 09:03:39 pm ---The microcontroller which controls the output voltage and current is on the output side with the ADCs, reference, current shunt, and output connection. The linear optocoupler bridges the isolation barrier to control the switching controller on the input side. I would rather have two microcontrollers than have to bridge the isolation barrier with voltage and current measurements. Having the microcontrollers communicate over a separate isolated link for USB PD status and control is not costly.
--- End quote ---
What's bad about bridging the voltage/current measurements? I thought about an ADC with SPI/I2C isolation.
Two microcontrollers seems like it rises complexity and cost; flashing firmware via USB will be difficult, having two USB connectors is not really what I wish.
I'd like to control over USB full speed, so isolating USB full speed is not really an option (cost wise). Isolating USB PD should not be a problem.
--- Quote from: David Hess on February 16, 2019, 09:03:39 pm ---At most I would rely on the microcontroller for detecting a fault in the analog control loops. Under normal conditions, I would generate analog voltage and current signals for the analog control loops to use and get feedback of actual voltage and current. Inserting the microcontroller into the control loop is a hazard, extra complexity, and potentially limits performance.
--- End quote ---
That's actually quite a good safety related consideration.
So I need some sort of analog mux, to either re-direct the analog signal from voltage or current measurement to the DC/DC controller.
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