So I'm in the process of trying to reverse-engineer a hobby brushless ESC. Above is the schematic for a single half-bridge drive circuit.
VIN is 11.1V
D1 is an unidentified diode; all that I've been able to glean so far from it its orientation and that it has a forward voltage drop of around .54V. Suggestions on obtaining more info about it are welcome
T1 and T2 are NIKOS P75N02LDG (logic-level enhancement mode N-FET)
T3 is LMBT3904-LT1 (general-purpose BJT)
HIGH and LOW come from a 5V micro. LOW is also pulled-down (forgot to show that here. 10K to GND)
Haven't been able to measure C6, could possibly be 10uF-22uF (1206 package, my bet)
My questions are as follows:
- Why does the high-side FET need to be driven with the BJT circuit and the low-side FET not?
- What is the purpose of the diode in there (D1) (forward voltage drop of .54V, not sure about what part# it is)? Is it to keep momentary dips in the VIN line from affecting how T2 is driven?
- As near as I can tell, HIGH is not pulled up or down. When the uC is not configured, this will leave the base floating, which will cause T3 to not conduct (right?), which will cause the gate of T2 to go high, which will cause VIN to go out on the motor line, right?