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USB PD for older device (piefed.social)

submitted 4 weeks ago by SorryImLate@piefed.social to c/askelectronics@discuss.tchncs.de

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I have an older electrical device which I would like to switch to charging with a USB C cable and a standard USB power supply. The device's power supply unit supplies 14V and 400 mA, so 5.6 W. The device documentation certifies it for 12V with 2 Ah.

I found a useful answer on stackexchange about the Source Power Rule for USB 3.1. This implies to me that my device is not compatible with 3.1 because at a power draw below 15W, PD 3.1 defaults to 5V.

According to Wikipedia, a USB4 DFP is required to supply at least 7.5W Type-C current, which is above the power requirements for my device.

Based on this, it seems to me that the power supply of my device is too non-standard to be supplied by a standard USB power supply. Have I understood this correctly?

Thank you for your help.

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[–] cmnybo@discuss.tchncs.de 1 points 3 weeks ago

It must be the PD trigger chip that does that then. With every PD trigger module I've used, I get a lower voltage if the requested one is not supported. It doesn't stay at 5V unless that's all the power supply supports.