simple usb protection against reverse polarity - need help

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silkyre6xtenz

Joined Jan 8, 2018
15
usb.JPG Hello guys, i got this schematic diagram. This is some kind of box which is connected to external source by +5V and GND terminals. Mosfets are IRLR7843, resistors are 100k pullups. X1 is used to connect this box to external source, X2 is used to discharge batteries inside powerbank. So, the mosfets must work as low-loss diodes. Will it work? Are 100k pullups necessary?
And after all - will it work if voltage is reversed (5v os GND, GND is 5V)
 
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Bordodynov

Joined May 20, 2015
2,397
The transceivers will protect the circuits of the left side if the poles of the source are reversed from the right (there will be a reverse polarity). The voltage drop across the transistors is small (with the correct connection). Resistors are not needed. These resistors will only discharge the batteries when there is no voltage on the right.
 

crutschow

Joined Mar 14, 2008
23,361
Here's an LTspice simulation of the circuit.
As you can see as the supply voltage (green trace) goes from +5V to -5V, the load voltage (red trace) only goes from +5V to 0V, as desired.

upload_2018-2-12_10-17-43.png
 
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