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USB isolation schematic

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teslinius:
I have a stm32 uc am i am using DP/DM pins for usb communication. But i want to make it isolated. I don't want to use specific ic's because they're too expensive for my taste. So i have come up with a circuit using optocouplers and isolated DC/DC converter. So my question is would this circuit work?

ataradov:
Apart from a non-functional idea of the schematic, PC817 has a cut-off frequency of 80 kHz. Even USB LowSpeed uses 1.5 MHz signalling. No, this will not work at all.

It is virtually impossible to do optical isolation for USB using traditional LEDs. The best you can do is laser link with modulated signals. But this is far more complicated than ADuM isolator.

Benta:

--- Quote from: teslinius on July 30, 2022, 08:34:55 pm ---I don't want to use specific ic's because they're too expensive for my taste.

--- End quote ---
I think you'll find that optocouplers up to the task are far more expensive than the required ICs.

NiHaoMike:
Probably the cheapest option would be to use something other than USB, especially if the bandwidth requirements are low. For example, Wifi using an ESP32.

Benta:
Dunno which STM32 the OP is using, but if it's got Ethernet, RJ-45 sockets with integrated isolation/magnetics are dirt cheap. Needs a TCP/IP stack of course, but I'm certain that it's in the STM32 library.

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