Electronics > Projects, Designs, and Technical Stuff
Case Study: SMPS fails at elevated voltage
T3sl4co1l:
I remembered this case from a little while back, and thought it might be useful food-for-thought.
An engineer brings you a (failed) PCB, noting: the SMPS fails at elevated voltage.
More specifically, it's a POL buck converter:
- Nominal 24V input; the regulator is rated to 50V
- The load is modest and stable: MCU, LEDs, super basic device-control stuff; well below the regulator's current rating
- Input current is also as expected
- Failure occurs as soon as input voltage is raised to, say, 27-28V
- Nothing gets hot (or, well, I suppose the chip might've briefly when it failed, we'll never know)
As your response, give your immediate follow-up questions -- what you think is the minimum additional information required to reach a confident conclusion. Additionally, if you think you have the solution, give it.
My response: having access to.....a bit more information than listed here -- I pondered for a few minutes, then provided a single component solution. The engineer applied the fix and found it a complete success.
Tim
ConKbot:
Go check it out myself because my coworkers have a knack for doing no troubleshooting at all even at the highest level. "Xyz peripheral isn't working" examine the board and see a BGA regulator knocked off from rough handling. So yes, said peripheral isn't working, nor is any other peripheral, just the micro core supply. :palm: I'm not asking for full troubleshooting just a voltage rail check before it shows up on my bench.
PeteH:
Regulator itself fails... What's the boost voltage rating, where is it being fed from, output voltage? (If applicable)
Assuming it has temperature shutdown.... Leads to it being EOS failure....
Monolithic?
If it's a controller, are the FETs appropriately rated?
Is it synchronous? - diode rated for current and voltage? Is the diode breaking down?
Inductor saturation is something ... But not likely if you're not already getting heating at 24V due to the ripple...pk to pk doesn't change much at 27 unless it's a knee, unrealistic hard saturation....
Input was continuously raised to 28 or set to 28V and hot plugged? Undamped input ?
Assuming that you had to ponder for a solution for a few minutes eliminates most obvious problems...
WattsThat:
OP has the ultimate advantage. You were handed the board in question. We know only what you tell us.
You’re asking for assumptions. Foul. I cry most foul.
I guess I could play along and imagine it is an interview question. But then I’ll be 65 this year. My brain refuses to go into that mode. :=\
oPossum:
Enable input tied to converter supply in rather than logic level (or whatever it's allowed maximum is).
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