This is a placeholder topic for “5V USB-C Dual Supply - Dual Ideal Diodes” comments.
Power USB-C devices from two USB-C power sources! Where does power go? Power from each USB-C input (A/B) connector goes via a MOSFET “Ideal Diode” to the…
Read more
1 Like
Would you guys consider making a variation of this product, but with the voltage just a bit higher so you could power a pi 4 with it, that would be an awesome kit
2 Likes
Hi Patrick,
Good news, this unit will almost certainly work fine at 5.1V. 5.1V is within the USB spec for 5V, and the “Fixed at 5V 3A” comment is just saying it doesn’t support reporting as a lesser source/sink due to the pullup configuration. See the deep dive docs here:
https://www.st.com/resource/en/technical_article/dm00496853-overview-of-usb-type-c-and-power-delivery-technologies-stmicroelectronics.pdf
2 Likes
Hi Patrick
This looks like a variation of a classic “diode OR” supply configuration but using Mosfets instead of diodes. Mosfets have the advantage of lower forward voltage drop when switched hard on. You will never get more out of it than what you put in. In other words if you want a higher voltage out you need to put a higher voltage in.
If used as a load sharing set up both power supplies need to be exactly the same or very close. If not the higher voltage will supply all of the demand until the output voltage is forced to drop to the lower level when the lower supply will pick up some of the load. Under these conditions the higher voltage supply would be operating at something like maximum output all the time with only a little help from the other unit. Not an ideal situation with one supply possibly being over stressed and prone to failure. If they are both the same or very close the load sharing will be a lot closer. This is easier to achieve with adjustable supplies.
If used for redundancy both power supplies should be capable of providing the total load requirement. The higher voltage one will prevail but in the event of a failure or “brown out” of this supply the hot standby supply will be in use.
This device would be particularly useful where a device needs to be connected to and communicate with a computer where the computer USB port will not provide enough current. I see data is transferred to the output via input A. Connect your computer to this port then have another larger supply (to provide the required current) connected to input B. Make sure the supply connected to B is slightly higher voltage than A and this supply will provide all of the required current.
I note the term “ideal diode” used. Personally I don’t think this device exists but a hard on Mosfet will probably be as close as you will get. The “ideal” device is sometimes used in the initial simulation of an idea or concept and fine tuned later with a “real” device. In other words it is imaginary, like √-1.
I also note the absolute absence (that I can find anyway) of any specs or really useful information like some sort of circuit for this device so one could make some sort of decision re usefulness for a specific task. Sadly this seems to be the norm these days so personally I would tend to use a couple of schottky diodes (where information IS available) and allow for or put up with the bit of extra voltage drop. All the above comments would apply.
Cheers Bob
2 Likes
Hi Bob,
Thanks for sharing your insights, it is a shame the design is closed source for this product so we don’t have a full schematic.
I think a lot of newer battery management modules will now embed most of the features of this design into their products so you can have battery managers that have the battery ready to go for redundancy, but not continuously loaded down and burning through the battery life cycle by being fully loaded.
1 Like
