# DC DC Converter Failure Modes

If a DC-DC converter (say 48V input to a 5V device) fails, is it possible for it to send the raw input voltage (48V) into the 5V device? And, if warranted, could anyone elaborate further as to common failure modes for DC-DC converters and how those might impact the output side? I'm not an electrical engineer, so please understand I'm a noob at all this and have no expertise whatsoever. Thanks in advance for understanding.

Background: I'm powering an Android tablet (5V) with a 48V->5V DC-DC converter. I've seen a couple tablets eventually get fried with no warning (just running for several months). They literally smoke and burn a hole in the case near a transistor where the power comes into the tablet. I've examined a less-than-ideal scope plot with the converter in question's output side... the amplitude on the output is nearly 500mV, and there's even an oscillation to the amplitude (there isn't with some other converters I've tested)... it varies from 200mV to 500mV. The other "good" converter I've tested is pretty steady at about 200-250mV amplitude.

My guess is that either the tablet's charging circuitry is getting worn out by the dirty power of the DC-DC converter, or the converter itself is failing and shunting through 48V to the tablet. Curious what others more knowledgeable might think.

Note: I tried researching before posting (and found the following posts), but these are way over my head, and probably not really what my situation is...

• Yes, just think about a buck converter and short the top MOSFET. Commented Feb 26, 2019 at 18:26
• @winny, thanks for your input. Also, I'm a software engineer and have very minimal expertise in the details of how a buck converter actually works. Commented Feb 26, 2019 at 19:03
• Please look up buck converter on Wikipedia or similar. Commented Feb 26, 2019 at 19:33
• Update from learning... a non-isolated buck converter couples the input to the output. If the input MOSFET fails in shorted mode, the input voltage may feed into the output. Sound right? Commented Feb 26, 2019 at 21:09
• Can you link the particular model of DC-DC that was involved? Commented Feb 26, 2019 at 21:16