USB Reverse Voltage Protection  Module - Page 1
Forum section: electronics / beginners

author: Dark_Nathaniel
author_rank: Newbie
timestamp: April 09, 2024, 06:00:05 am
content: In the past I damaged some components connected my PC by using the USB power for a 5V source when I connected a device backwards, so I built this circuit out of spare parts left over from other projects.My goals which I succeeded at was:1) Protect the USB power source from reverse voltage2) Prevent the device connected to the output terminals from experiencing reverse voltage3) Have at least 4.9V at the output terminals4) Have a 1A fuse to prevent the circuit from pulling more than 1A in the case of an overload or short circuit5) Not spend any money, only use parts I already haveMy goals I did not succeed at was:1) Protect the USB power source from short circuit of the 5V output terminals2) Drain any left over power in the circuit once disconnected (as it is, once I disconnect the USB power input, if there is nothing on the output connection, there is still about 2.2v in the circuit)I verified that if I connect a device expecting 5V in reverse to the output terminals, the USB power source is safe, and the BLUE LED becomes dimmer. If i measured the output test points, voltage drops to about 3.3V while a device is connected in reverse.I am very happy that it is working this far, but I still want to solve the goals I did not succeed at (protect from short circuit at the output, and add a resistor to drain the leftover power)What should I modify about my circuit to meet the goals I did not succeed at? How would you change the circuit to make it simpler & more effective?Thanks for your help.(Edited at 11:22PM PST: Realized i made a mistake on the schematic; fixed now)

author: Dark_Nathaniel
author_rank: Newbie
timestamp: April 09, 2024, 09:03:53 am
content: I am thinking maybe the blue LED circuit is what is really doing any of the work here and thus here is my proposed simplified schematic which will also be able to mitigate a situation where the outputs are shorted together.

author: Zero999
author_rank: Super Contributor
timestamp: April 09, 2024, 10:43:55 am
content: Neither of those circuits will work.Just use a fast blow fuse and a diode, with a much higher current rating, compared to the fuse.Another option is a MOSFET, but you still need a fuse for over current protection.https://kc9on.com/ham-radio/station-accessories/reverse-polarity-protection/

author: Dark_Nathaniel
author_rank: Newbie
timestamp: April 09, 2024, 11:18:41 am
content: Will this work?It seems like it'll handle the reverse voltage and short circuit scenario, but maybe i'm wrong.The fuse + diode solution you provided looks nice and simple though, so I don't mind going with that.Also, thanks for your help.

author: Zero999
author_rank: Super Contributor
timestamp: April 09, 2024, 11:39:50 am
content: Quote from: Dark_Nathaniel on April 09, 2024, 11:18:41 amSorry, that circuit is meaningless because it doesn't show which is the input from the USB and output to the load.

author: Dark_Nathaniel
author_rank: Newbie
timestamp: April 09, 2024, 01:17:51 pm
content: Thank you again for your help. This is what I did. Hopefully it's right, but if it's not I am hoping to rectify it.The input is by 2 pin headers and there are two sets of pin header outputs so that i can monitor that output with a DMM while i have something attached to the output terminals, that's why there are some wires going around.

author: xvr
author_rank: Frequent Contributor
timestamp: April 10, 2024, 10:36:11 am
content: Protect USB powered device from plug IT in reverse direction impossible (in general). There is no any reliable way to say which way of connection of DUT is right one. You lucky that your device draw extra current been plugged in reverse. Another device can just die silently (and without any current surge) be plugged in reverse.And another one - fuse as protector in your case useless. DUT could be (and would be) sensible enough to blown up first, just to protect fuseYou need current limiter circuit. Simple incandescent lamp for 5V in series cold be used (it's rated power should be order of magnitude more, than planned power consumption of DUT)