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Topic: Need Help In MOSFET Substitution--SOLVED (Read 5459 times) previous topic - next topic

SteveOr

Apr 20, 2013, 09:12 pm Last Edit: Apr 21, 2013, 06:24 am by SteveOr Reason: 1
I'm attempting to replace a blown MOSFET in an RC Logger Eye One mini quadcopter's flight control board.  I believe there was too much current flow due to a defective motor.  In a forum it was suggested to use a 20V, 6.3A, IRLML6244TRPBF MOSFET   http://www.irf.com/product-info/datasheets/data/irlml6244pbf.pdf.  However, they are out of stock at Mouser, Jameco, Digikey, etc. with stock times months away.  I don't know much about electronics so I need help in evaluating if there are alternatives that will work.  A discussion on the matter stated that the critical factors are the Rds(on) resistance, the switching speed and gate voltage. Would this MOSFET http://www.mouser.com/ProductDetail/Diodes-Inc/DMN2041L-7/?qs=tiksPeNXt0LSbn3jTreVOg%3d%3d match some of the critical parameters?  

Any elementary assistance in evaluating these types of components would be greatly appreciated.

Erdin

It turns on at a very low gate voltage and has a very low Rds(on), so it should be okay.

oric_dan

Max current is still the same though, might be worth it to try to find something more
robust. Is there enough room to mount something a little larger than SOT-23? Eg,

http://www.digikey.com/product-detail/en/STB60NF10T4/497-7951-1-ND/1883514

MarkT

But which MOSFET are you trying to replace??  Without knowing that we cannot guess the values of the "crucial parameters"...
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

SteveOr


But which MOSFET are you trying to replace??  Without knowing that we cannot guess the values of the "crucial parameters"...


Unfortunately I don't know the specifications of the MOFSET it is replacing.  The original has AKPV and 10 on its side.  In forum discussions about its replacement, no one was able to identify the original nor get info from the manufacturer.  If anyone can provide insight on this, I would really appreciate it.


Max current is still the same though, might be worth it to try to find something more
robust. Is there enough room to mount something a little larger than SOT-23? Eg,

http://www.digikey.com/product-detail/en/STB60NF10T4/497-7951-1-ND/1883514



The footprint only allows something like the SOT-23.  Although I have a little flexibility in this as one of the pads was burned away.  I think the configuration of the STM MOFSET is too big.


cjcj1949

We need the circuit or as much description as possible. I fly helis and we have a lot of problems with escs failing. Unfortunately most escs do not control their max current and just rely on things working as normal, but in fault conditions the current can go to very high values. Is the motor brushless or brushed. If brushless you will probably have other fets that are damaged as they are connected in three bridge circuits.

MarkT

what makes you think its a MOSFET?
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]

SteveOr


what makes you think its a MOSFET?


I base it on other people fixing theirs with the IRLML6244TRPBF MOSFET; ie this RC Mini Quad Rotor thread post in which the guy has success in soldering on a new one.: http://www.rcgroups.com/forums/showpost.php?p=24308094&postcount=1448


We need the circuit or as much description as possible. I fly helis and we have a lot of problems with escs failing. Unfortunately most escs do not control their max current and just rely on things working as normal, but in fault conditions the current can go to very high values. Is the motor brushless or brushed. If brushless you will probably have other fets that are damaged as they are connected in three bridge circuits.


I wish I could describe the circuit but my electronic skills are rather limited.  The craft uses brushed motors.  From my examination of the PCB it appears each motor has its own MOSFET.  The thing only costs $70 but I just want to try and fix it rather than buying a whole new quad or pitching it.  

SteveOr

A photo of the blown MOSFET.

oric_dan

Quote
The footprint only allows something like the SOT-23.  Although I have a little flexibility in this as one of the pads was burned away.  I think the configuration of the STM MOFSET is too big.

I figured the footprint was SOT-23 or 223, but that might not mean the replacement
has to be soldered in exactly the same way. Eg, mount it up a bit and solder 3 wires,
etc. Jury rigs aren't always pretty, especially if they replace a marginal design with
something a lot better. The MOSFET I cited is tiny in comparison to a TO-220.
It was just a thought.

Recently somebody didn't like that the mega boards use a ceramic resonator instead of
a real crystal, and ended up proposing someone build a complete D-I-Y mega clone
with xtal. I'd have just gone in with my soldering iron and exacto knife and surgically
altered the darn thing.

SteveOr


...that might not mean the replacement has to be soldered in exactly the same way. Eg, mount it up a bit and solder 3 wires,
etc. Jury rigs aren't always pretty, especially if they replace a marginal design with
something a lot better. The MOSFET I cited is tiny in comparison to a TO-220.
It was just a thought.


A great idea only the one you suggested seems too big if I comprehend the data sheet correctly.  But as you say I'm not committed to putting it exactly where the last one was.  Since my board was burnt up I really have nothing to lose trying another size as long as it works. 

My other issue is that up until a few days ago I didn't even know what a MOSFET was or how they work.  So I don't know how to evaluate if the new one will totally screw up the flight control despite its ability to withstand a higher current. 

SteveOr

I was just notified on the manufacturer's web forum that it is an AO3418 from Alpha Omega and in stock at Digikey.  Woo hoo!

Thanks for everyone's help all the same.

oric_dan

Quote
My other issue is that up until a few days ago I didn't even know what a MOSFET was or how they work.

Hey, last week I couldn't even spell "injanear", and now I are one, LOL.

And ... try not to burn up the new one! And always buy a spare, in any case.

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