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Smoked a 5V Regulator S10V4F5


Not a support question, but a note for others to be able to search for later.

I had a S10V4F5 regulator stepping-down a 12v supply to feed an Adafruit Feather board via the USB pin. The first time a battery was plugged into the Feather but no voltage was applied to the regulator’s Vin, the magic smoke was released and the regulator died. (The Feather’s battery voltage is available on the USB pin.)

As best I can tell, the regulator won’t tolerate voltage only on its Vout pin.



While connecting a voltage to the output of a regulator that is not on is not generally good practice, I would not expect exposing the output of that regulator to 5V to immediately damage it like that. Could you tell me more about the circuit it was in? Was the voltage on the output pin 5V? Could you post a picture of how everything was connected?



Hi Claire -

Thanks for responding. :slight_smile:

Agreed that it’s not good practice; for some reason, I had assumed that the Feather isolated the USB pin from the battery pin, which wasn’t the case. My error.

The Feather was a 32u4 Basic Proto model; https://www.adafruit.com/product/2771

The connections were:
3.7v LiPo --> [JST connector] Feather [USB pin] --> [VOut] S10V4F5 [VIn] --> 12v power supply (but switched off).
The ground lines of the Feather, regulator and power supply were all connected.

With the power supply on and the battery disconnected, the circuit operated as expected.
With the power supply off, as soon as the battery was connected, the converter smoked.
(I didn’t get a chance to test both power supply and battery connected.)

The voltage on the output pin was therefore coming from the LiPo battery, so would have been ~4.1v.

The failed part appears to be the IC marked BH00 (Semtech SC4503?). There’s a small volcano-shaped hole above pin 1 on that chip now, and I’m pretty sure that was where the smoke came from.

I rebuilt the circuit, but can reconstruct it if a photo would be useful. Let me know?

Thanks again!



Did you have USB connected at any point?



Not while the regulator was connected up.
(I had previously connected USB to the Feather to program it, but soldered the regulator into the circuit later.)



I am not sure what damaged your regulator, but if you would like to try again with a modified setup, please send us an email at support@pololu.com with a link to this thread and your order information and I can see what we can do to help with a replacement.

By the way, if you haven’t already, I recommend testing your feather board throughly to make sure it was not somehow damaged as well.