How to protect 5v supply from 5v sensor connection?
How to protect 5v supply from 5v sensor connection?
(OP)
I have a board that has a 5v rail for microcontroller (and other electronics). I also have an external sensor that I need to provide 5v to. I am concerned, that if I connect the 5v from main rails directly to the sensor, the entire board will go (in case of fault/short). Previously I have "solved" this by deriving another 5v supply and using only for the sensor (obviously this is crud, expensive and not needed). My question is, what type of circuit can I have, that will allow me to power the sensor from the same main 5v rails, but protect the main board if the sensor supply is shorted?





RE: How to protect 5v supply from 5v sensor connection?
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If we learn from our mistakes I'm getting a great education!
RE: How to protect 5v supply from 5v sensor connection?
Or any more-complicated, more-modern, solid state functional equivalent.
But I'd just use a fuse. Someone needs to repair the shorted sensor and/or wiring anyway. So they could replace the fuse at the same time.
RE: How to protect 5v supply from 5v sensor connection?
Hi ScottyUK. OK, sorry. I am using a LM2575-5 for the 5v and the sensor does not require much current (I don't know how much, but not much, it is a Hall Effect device). So regardless of budget for a moment, do you advocate adding another regulator? Or would you be comfortable using the same 5v supply as the board?
RE: How to protect 5v supply from 5v sensor connection?
If the sensor is only inches from the board in a benign electrical noise environment you need nothing.
If you want something to protect your supply use a PTC resistor that will operate and limit current if a short occurs. This would require a board power down and up to reset the PTC. (Much better than a fuse hunt!)
If you fear noise entry, include an RF choke(bead) followed by a 0.01uf ceramic cap to ground.
Twist all the leads to the sensor.
Use shielded cable. Ground it only at the board.
Keith Cress
kcress - http://www.flaminsystems.com