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Old Aug 07, 2012, 12:11 PM
Crash and learn
United States, PA
Joined Dec 2011
1,605 Posts
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MOSFET - The thing that drives our motors

MOSFET

Yes, MOSFET - Metal Oxide Semiconductor Field Effect Transistor.

In the beginner section, one should not abbreviate. Spelling out what MOSFET stands for only makes it worse.

In the case of the DH9116, they are power transistors that are controlled by an electrical charge on the "gate". Put zero volts (ground) on the gate and the transistor turns off (turns very off, like it isn't there). Put +5 volts on the gate and the transistor turns on (turns very on, like a direct short). The gate only needs a voltage and no current, so the power needed to control the MOSFET is practically zero watts.

Fantastic devices. The two MOSFETs on the DH9116 printed circuit board can switch (I seem to recall) 80 amperes to turn the main and tail motors on and off.

A short circuit dissipates no power. An open circuit dissipates no power. The MOSFETs only dissipate power during switching, the transition between a short and an open.

But voltage spikes from the motor's inductance during switching will kill a MOSFET. So, across the main and tail motor connectors are "snub" diodes to short motor spikes.

Enough electronics. MOSFETs are such a mystery to RC helicopter pilots, but are as vital as the LiPo batteries.
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