How to properly snub transient spikes from a transformer and prevent switch mode power supply burn out

Posted on Feb 5, 2014

The leads from the transformer to the circuit are quite long (>5m). Apparently the 110V side of the transformer was switched off somewhat frequently lately which likely caused a spike on the secondary (24V) side. The input pin of the LTC3631 has a visible mark where the blowout occured (gas escaped). The LTC3631 is protected upto 60V on it`s power

How to properly snub transient spikes from a transformer and prevent switch mode power supply burn out
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-in. I doubt that the failure is due to an over-voltage situation. Maybe it might be better to sit-back and wait for reasons without 2nd-guessing the possible cause. Hey it could be exactly what you say but, there may be other factors you haven`t mentioned that makes you sure it is this. This info would be needed to give a decent answer to your question. Andy aka Apr 5 `13 at 20:32 @Andyaka the only other information I have is that I read a little over 28Vac from the transformer which translates to 39. 5Vdc just below chip`s normal tolerance. It`s possible that it was being too close to it`s normal limit. I`m not sure if that would cause the physical blowout. The chip is not overloaded and runs quite cool normally. MandoMando Apr 5 `13 at 20:58 @dext0rb no, I haven`t seen any spikes, just a blown chip. The handheld meter reads the input at about 28Vac. It was installed last week, so didn`t live long at this location regardless. MandoMando Apr 5 `13 at 21:01 The easy solution is adding some clamping on the primary side of the transformer to limit any surge energy coming in - a MOV from line to line will shunt any high voltage energy away from the transformer. A small series resistance would also help limit the surge energy, and wouldn`t be excessively lossy since the regulator draws such a low current. Safety-rated X-capacitors from line to line may also help with smaller surges (also sometimes called `fast transients`) -...

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