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Can't identify a FET on 180qx Quadcopter

RedMongoose

Mar 21, 2015
3
Joined
Mar 21, 2015
Messages
3
Hello all,

Shorted a motor FET on a quadcopter today at the park, and my donor board is out of spares. Annoyingly, I can't figure out what they actually use, parts wise. I'm pretty sure it's an N-channel SMD FET but as for it's exact specs, it's a mystery. Here's a picture from me working on it (ignore the text, I was reverse engineering it):

2015-03-20%25252020_15_53-SANY0023%252520-%252520Windows%252520Photo%252520Viewer.png


If you look just to the right of the text (1:00 position), you'll notice the "G23 AB (8 maybe?)" FET. The one that shorted is in the top right corner under the white motor connector, and has the same text. I've looked around and couldn't find anything on it. I ordered some other ones before, which turned out to be PNP (5ACSA?), or as the description says: "5.4 amp 8v SOT23-3 MOSFET Upgrade for Blade MCPX"

I'm kinda stupid when it comes to FETs - the 180qx I exploded and who's board is visualized above uses bigger motors than the MCPX, so i'd assume the amperage rating would be around the same? I found a hit on "G23 fets" but it just says "TRANSISTOR 500 mA, 55 V, 7 CHANNEL, NPN" - http://www.datasheetarchive.com/g23 SMD Transistor-datasheet.html

Any idea on how to further crack into this? All of the RC hobby forums seem to be just as confused as to what goes on these boards.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
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25,510
That hit you found is not relevant. It refers to a 16 pin device.

You're also confused a little in your terminology. Mosfets come in P Channel and N Channel. Bipolar transistors come in PNP and NPN. In view of the size of this component and the fact that it seems to be controlling power for a motor it can really only be a mosfet.

If you can determine whether the motor connection which is NOT connected to the mosfet is positive or negative, we can determine if the mosfet is more likely to be N channel or P channel.
 

RedMongoose

Mar 21, 2015
3
Joined
Mar 21, 2015
Messages
3
That hit you found is not relevant. It refers to a 16 pin device.

You're also confused a little in your terminology. Mosfets come in P Channel and N Channel. Bipolar transistors come in PNP and NPN. In view of the size of this component and the fact that it seems to be controlling power for a motor it can really only be a mosfet.

If you can determine whether the motor connection which is NOT connected to the mosfet is positive or negative, we can determine if the mosfet is more likely to be N channel or P channel.

Yep my point exactly - NFI about what exactly i'm looking at. Micro electronics scare me for this reason. I tested the component, and here's what I found changed voltage when I throttled up (which was otherwise 0.0v at throttle cut):

2015-03-21%25252001_17_28-Can%252527t%252520identify%252520a%252520FET%252520on%252520180qx%252520Quadcopter%252520_%252520Electronics%252520Forums.png


Does this help identify it further?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
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25,510
I saw that too but I thought the motor current was likely to exceed 200mA.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
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Messages
25,510
Red, the motor terminal that is NOT connected to the mosfet. Which power supply rail is it connected to?
 
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