Two diodes or one, is there a difference?

Question

Do it yourself

I connected the gamepad from the xbox 360 (wireless) to the computer, and when the receiver was soldered, the instructions said that the VBUS (usb +) wire must be soldered through 2 diodes connected in series. It became interesting why exactly 2? Although it also works with 1 (again, the question is, why doesn’t it work without a diode? It seems that the wire just supplies power). Can anyone clarify?

Answer 1

The voltage drop at the PN junction of the diode is ~.6V (Russian textbooks call this figure = .7V). Thus, two diodes connected in series provide a voltage drop of 1.2V.
Probably, such a drop is due to the peculiarity of use. And it works for you most likely because the voltage level + 5V on USB is already underestimated (or while the piece of iron suffers overestimation). Better - put a voltage regulator and do not worry about such inaccuracies and diodes ...

Answer 2

the diode reduces the voltage by 0.3 volts if the memory does not change.

Answer 3

Voltage drop to 3.3 volts. Standard bydloresheniye of shit and sticks. You put LD1117-3.3 there and forget about the problem. And there also go atmega on VUSB :)