DPS3005 Buck Converter/Power Supply: Blown MOSFET - Page 1
Forum section: electronics / repair

author: xraj
author_rank: Contributor
timestamp: December 12, 2017, 02:43:42 am
content: I managed to kill my DPS3005.I tracked down the fault to a N-Channel Power MOSFET (part marked AO4264E) located right before the supply ground terminal. Upon unsoldering the SOIC package, it fell apart into two pieces (shown in photo).For those that don't know, these things have four terminals marked in sequence (Vin+, Vin-, Vout-, Vout+). I've attached a diagram of the portion of the circuit in question. I think the mode of death was probably creating a short through Vin- and Vout- (too many test leads with the same color)What I'm confused about is that the MOSFET is hooked up "backwards". My best guess is that the MOSFET is being used as a sense resistor for the current shunt? I thought MOSFETs weren't very good for this kind of use?

author: floobydust
author_rank: Super Contributor
timestamp: December 12, 2017, 08:21:00 pm
content: Thought they added battery-charging protection to the DPS lineup, I think they used to blow up if powered down (no Vin) yet Vout is present due to a battery.As an output-disconnect switch... but the body-diode is still there? It doesn't make a lot of sense to me, either way.R4 looks discoloured in pic.

author: xraj
author_rank: Contributor
timestamp: December 13, 2017, 01:09:14 am
content: Actually, the drain/source orientation does make more sense as reversed supply input protection. They might want to add idiot protection as well.I'll test the resistance of R4 when I get home tonight; however, if I dickered it the way I think I did, voltage was applied directly across Vin- and Vout-. I wouldn't think there would be any significant current through that bit.I also found that the unit will turn on if I connect Vout- as current return to the input supply --which makes sense given the diagram. Obviously, I'm not hooking it up to a load this way.

author: xraj
author_rank: Contributor
timestamp: December 13, 2017, 01:14:53 am
content: Quote from: xraj on December 13, 2017, 01:09:14 amNo wait. I take that back. It still doesn't make sense.

author: wraper
author_rank: Unknown
timestamp: December 13, 2017, 01:28:12 am
content: Quote from: xraj on December 13, 2017, 01:14:53 amWhy not, it makes perfect sense for this application.

author: wraper
author_rank: Unknown
timestamp: December 13, 2017, 01:32:42 am
content: Same circuit, just on negative rail.

author: xraj
author_rank: Contributor
timestamp: December 13, 2017, 05:23:37 am
content: Quote from: wraper on December 13, 2017, 01:28:12 amI guess it makes sense for reverse polarity protection for the input. Previous poster was taking about protection from the load turning into a supply (e.g. charging a battery).

author: xraj
author_rank: Contributor
timestamp: December 13, 2017, 05:33:52 am
content: Quote from: xraj on December 13, 2017, 01:09:14 amMeasures at 5.8k.

author: floobydust
author_rank: Super Contributor
timestamp: December 13, 2017, 06:02:03 am
content: R4 is OK, lettering is 6k02 and kinda hard to roast one. It must be just another brand with darker markings.How did you kill the DPS?AO4264EMOSFET 60V 10A rated...

author: xraj
author_rank: Contributor
timestamp: December 13, 2017, 06:40:19 am
content: 12V lipo as power source.