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| USB-C PD laboratory power supply |
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| MaTkEOxjC:
USB-C PD is quite nice and will become more and more available. Some people have already played around with it. (e.g. https://hackaday.io/project/20424-pd-buddy-sink) Wouldn't this be an interesting basis for a minimalist laboratory power supply? * output voltage range could be dependent on PD profiles (design choice), 0-30V would probably be preferable (I'd like to include a usable 24V range) * dedicated port for power and usb controls * use a dc-dc converter followed by a linear regulator to smooth out the ripple * isolated design would be nice but increases complexity * implementing features in software (CC, CV, current trip...) would be nice As target audience I'd expect EE students and similar people (I'm one myself in my masters study). So certification should not be needed (sell it as development), BOM cost should be less than 50€ What are your thoughts about this? |
| David Hess:
I was thinking about this the other day in connection with designing a smart charger for AA and AAA cells. --- Quote from: MaTkEOxjC on February 14, 2019, 12:53:27 am ---* output voltage range could be dependent on PD profiles (design choice), 0-30V would probably be preferable (I'd like to include a usable 24V range) --- End quote --- If a switching converter is used, then the PD profile could set the maximum output power instead of voltage or current. --- Quote ---* use a dc-dc converter followed by a linear regulator to smooth out the ripple --- End quote --- This is usually a waste of time if the switching regulator is designed for low noise unless fast transient response is required. --- Quote ---* isolated design would be nice but increases complexity --- End quote --- I would not do it without isolation. |
| alex-sh:
@MaTkEOxjC I have this USB-PD Buddy sink, which I am using to charge my laptop on a go from a 28650mAh power bank. I have used it to power little projects, but there are a few drawbacks: - In order to change voltage, you have to enter DFU mode by rebooting the module. - Putty or other program has to be used - you cannot power the module and monitor parameters without PD Buddy Wye Basically, this has been designed to "set-up-and-forget-it". To have a proper PSU, it has to be completely designed in my view. Personally, I think unless you explicitly use USB-C PD (laptop? power bank?) to power the project, there is no benefit using it. Voltage cannot be more than 20V (Personally I'd rather have 24V max) or less than 5V and there are many other limitations. I have another small power supply on LM2577, which I can power from a battery, PSU, USB port and I see very little benefit developing anything based on USB-C PD. A good filtering is not a big deal - darlington pair, LC or Pi would do job very nicely. |
| MaTkEOxjC:
--- Quote from: David Hess on February 15, 2019, 02:55:29 am ---I was thinking about this the other day in connection with designing a smart charger for AA and AAA cells. I would not do it without isolation. --- End quote --- How would you suggest the isolation? At the moment I can only think about on the USB data lines or with an isolated ADC, both options are quite expensive. I need to get the voltage and current on the output. Two µC with isolation in between is kinda lazy. Or how are you doing the feedback at your charger? |
| David Hess:
--- Quote from: MaTkEOxjC on February 16, 2019, 12:31:40 am --- --- Quote from: David Hess on February 15, 2019, 02:55:29 am ---I was thinking about this the other day in connection with designing a smart charger for AA and AAA cells. I would not do it without isolation. --- End quote --- How would you suggest the isolation? At the moment I can only think about on the USB data lines or with an isolated ADC, both options are quite expensive. I need to get the voltage and current on the output. Two µC with isolation in between is kinda lazy. --- End quote --- Well, that is where it gets interesting. There are a number of transformer isolated switching regulator topologies which are suitable for a general purpose power supply. Most come down to following the transformer with a buck inductor and these might be considered a buck converter with an additional impedance conversion which allows a higher output voltage from a lower output voltage. They of course have the usual problem of having to support discontinuous conduction mode at low output currents unless synchronous rectification is used but some designs drive the synchronous rectifier across the isolation barrier so that is not completely infeasible. If you can come up with a suitable non-isolated design, then you can always add a transformer to it and get a free impedance transformation as well. Having a microcontroller on either side of the isolation barrier would not bother me at all but I think this depends on where the control circuits for the switching regulator are. I would tend to use one microcontroller to negotiate the USB PD and another for everything else because this allows for an integrated USB PD solution if it exists. If the switching control circuits are on the primary side, then the usual arrangement of optocoupled feedback is the usual control method. Higher performance will require a switching preregulator and linear output stage. --- Quote ---Or how are you doing the feedback at your charger? --- End quote --- I mean I would not do a power supply without USB to output isolation. For a battery charger, no isolation is needed unless it has a data output like serial or another USB port. I am not very happy with the user interface on my MH-C9000 smart charger so I occasionally consider how I would design something better from scratch and being about to use a USB PD source (or power over ethernet?) might be a nice feature. |
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