I had an issue with a U3V40F12 that I just installed and I need some advice on the application in case I have misinterpreted the user info.
The input voltage I just used was 8.4V, and I had the magic smoke expel from the regulator.
The leads to the regulator are around 2.5” long and the leads after the regulator on its load are 1” long.
The constant load in service is around 5/6W.
Before this I have been running 7.2V and 11.1V during by building and config stage of this small rc plane. Powered up many times and seen the expected 12V output.
The last 5 /6 power ups I have had a 4.5W (electrical power consumption not radiated power) video transmitter connected with no other significant loads connected.
I have just monitored the output voltage from the regulator and it is now input=output as expected.
May I have advice on what I could do better with my application?
I do not see any obvious issue with the power draw expectations you posted. Could you post pictures that show all of your connections? A diagram or schematic might be helpful too.
What was your system doing when the regulator smoked (e.g. as soon as the system was powered up, running the motors at high speed, sitting idle). Did you add or change any connections just before it happened?
I removed /bypassed the reg and used a 3 cell lipo battery to check the functionality of everything else.
Nothing changed from previous power ons apart from fully charging the 2S battery, though I had already tested it with 11V.
It happened as soon as I plugged in the battery.
I discussed with another person the possibility that I shorted the balance connector +8.4V or 4.2V against the antenna connectors which are a common ground. They are the only ‘exposed’ conductor, so I don’t want to rule out that possibility.
That would have been Vin shorted to ground on power on if that was the case.
Would you expect that the happen to the component if Vin was shorted down.
I have ordered two more of the regulators to fit another next week.
I do not see any obvious problems with your diagram. It might be possible that the potential short you mentioned could have caused the problem depending on the path that the current took. However, it is hard to say for sure; you might have just been unlucky with something like an electrostatic zap that damaged the regulator.
By the way, since you mentioned connecting a 3S LiPo, please note that when fully charged, a 3S LiPo can be reach higher than 12V, and in this case, the higher voltage will show up on the output, which could potentially be dangerous for your connected load and could also damage the regulator.
Two arrived yesterday, so I can get one wires back in for flying.
That’s right, the plane is a little 250g 2S wing. I use a lot of 3S packs for other bits that are often at storage voltage, under 12V and use them for testing. I made sure not to connect anything over 12V!
Will keep an eye on it and hopefully it doesn’t happen again. Will also print a little balance connector clip so that flying lead with 8.4V on it isn’t loose in the fuselage.
It is wired as above, apart from this time, no VTX is connected, no servos, gps or receiver, only the flight controller.
I’m at a bit of a loss, I’m not sure if there could be a batch issue?
Though one might say, don’t power cycle it quickly, the reason I have done this is that the XT30 connectors and short cables are quite springy/ easy to fumble.
I expect the first failure I had was a pair of power ons in quick succession. I was able to repeat it twice this evening with new regs.
I am sorry to hear that your new regulators were both damaged as well. We test every unit, and have not heard of anyone else having a problem with them, so it is unlikely to be a batch issue.
When you power cycle it, are you toggling the power on and off from the supply side or the load side? That’s the kind of damage I would expect from an LC voltage spike, but it seems strange since the 100μF electrolytic capacitor you added to be enough to mitigate it. Also, it shouldn’t be as much of a concern at your operating voltage and with short wires.
If you try again, you might try monitoring it closely with an oscilloscope to get a better idea of what’s going on.
