Hello I have a circuit for a 1wire device that operates without any problems, but once in a while the R3 resistor shown in the image fails open and 1wire communication stops. Any help ideas info will be appreciated. I was thinking maybe it is a ground loop problem, not sure yet.
Resistors are generally very reliable, so for R3 to fail you would have to have a lot of current. I'm not sure what the two wires are connected to, but there must be something for the 1-wire device to work. It would help if you could post the rest of the circuit.
The resistor is not used as a fuse, it's just a standard 5% 1/4W 1210 SMT resistor.
The two wires simply go to a DS2431 1024-bit 1-wire device.
The voltage across the resistor is about 70mV which is not enough to cause a high current to damage it.
This is an intermittent problem and really rare to see the problem, I've tried many things to recreate it and have not been able to do so.
There is also an LED in series with R3 not shown but it's a 24VDC----->1.5K 1/2W Resistor----->LED 2.6Vf------>R3 4.7OHM (shown in circuit).
That's why I'm thinking there is a ground loop issue where the current from A ground is going through R3 and into Earh ground.
When you say R3 "fails open" does it mean that it become an open circuit?
does this happen in various configuration?
if i was you i would search the problem outside your circuit, which seems OK to me...
The DS2431 would fail at a far lower current than a 4.7 Ω 1210 resistor. Therefore the current that is blowing the R3 must be coming through D2. That means that there is some voltage appearing between the point A and "Earth Ground". That in turn probably means that there is a problem with the power supply.
What sort of power supply are you using? For a properly floating power supply, I would normally connect ground to the negative of the supply.
The DS2431 would fail at a far lower current than a 4.7 Ω 1210 resistor. Therefore the current that is blowing the R3 must be coming through D2. That means that there is some voltage appearing between the point A and "Earth Ground". That in turn probably means that there is a problem with the power supply.
What sort of power supply are you using? For a properly floating power supply, I would normally connect ground to the negative of the supply.
I think this is exactly what's happening. there is no reference between A GND and Earth Ground. I'm using a transformer to an LM317 without any reference to earth ground. Maybe I'll add like a 1M resistor from Earth Ground to A GND to keep them at the same potential and see if that helps. I was not able to measure any voltage between the two grounds, this is an intermittent problem that happens once in a while and have not been able to recreate the failure during troubleshooting, but it happens once in a while when I'm not looking for it.
Actually there is a common failure of resistors to an open circuit state, which mainly occurs when they are operated near their max voltage (ie >100v or >200v). I would not call that failure a burnout as it does not need significant currents.