Artbyrobot
!!Cd/+jXhVZy7
11/8/2025, 1:50:35 AM
No.2956055
Couple updates:
An audience member redid my brushless DC motor schematic in the traditional commonplace formatting which for most is easier/quicker to read and understand due to familiarity. So I'm reposting it. It looks mostly accurate although I have since added a 100nF ceramic capacitor between the gate and source of the highside mosfets to reduce ringing issues. Standard practice according to chatgpt. I also changed the LED color to orange because chatgpt said blue would show through the silicone skin more and add a cold inner glow and we want it to look like real skin so no blue.
As to why the highside mosfets get a 100nF ceramic gate capacitor but not the lowside, here was how chatgpt explained it to me:
-High-side MOSFETs:
Their source pin moves up and down with the motor phase (it’s not at a fixed potential).
During switching, the drain and source both move rapidly, and the gate voltage must track that movement precisely — any ringing or inductive noise can momentarily over-stress Vgs.
That’s why we add the small capacitor across gate and source: it tames that high-frequency ringing and helps hold the gate steady relative to its moving source.
Low-side MOSFETs:
Their source is solidly tied to ground, so the gate always swings relative to a fixed, quiet reference.
They don’t experience the same “floating” gate drive or large dv/dt transitions on the source pin.
So, the gate is inherently more stable, and you don’t need that extra 100 nF G–S capacitor.
An audience member redid my brushless DC motor schematic in the traditional commonplace formatting which for most is easier/quicker to read and understand due to familiarity. So I'm reposting it. It looks mostly accurate although I have since added a 100nF ceramic capacitor between the gate and source of the highside mosfets to reduce ringing issues. Standard practice according to chatgpt. I also changed the LED color to orange because chatgpt said blue would show through the silicone skin more and add a cold inner glow and we want it to look like real skin so no blue.
As to why the highside mosfets get a 100nF ceramic gate capacitor but not the lowside, here was how chatgpt explained it to me:
-High-side MOSFETs:
Their source pin moves up and down with the motor phase (it’s not at a fixed potential).
During switching, the drain and source both move rapidly, and the gate voltage must track that movement precisely — any ringing or inductive noise can momentarily over-stress Vgs.
That’s why we add the small capacitor across gate and source: it tames that high-frequency ringing and helps hold the gate steady relative to its moving source.
Low-side MOSFETs:
Their source is solidly tied to ground, so the gate always swings relative to a fixed, quiet reference.
They don’t experience the same “floating” gate drive or large dv/dt transitions on the source pin.
So, the gate is inherently more stable, and you don’t need that extra 100 nF G–S capacitor.