# Brushless motor ESC circuit

I want to build myself a basic ESC, but I have some questions after watching this video (ESC electronic speed controller with arduino ALL EXPLAINED - YouTube).

a) At around min 11, he shows the circuits with the mosfets. I dont understand why he uses n-channel mosfets instead of
p-channels combined with n channels. Dont you have to apply a higher gate voltage if you use n-channel mosfets, because Vsource = Vgate - Vth ?

b) Im also confused with the mosfet drivers. I've never used them and i only want to supply around 12V (doesnt really matter for now, just high enough) at the gate. Do mosfet drivers need an external supply or they convert your arduino 5V signal into 12V.

And by the way, how to I calculate the value of a capacitor. For example, motors have peak current so I never know what value the capacitor should be and where to place it. Thanks guys!

a) and b) are related.

In MOSFET and IGBT bridges modern practice is to only use n-channel. This is because they have
3 times the efficiency (3 times less on-resistance), for the same silicon process - its a no-brainer
decision basically for high-current applications.

However to do this you need bootstrapping gate drivers to drive the top-side MOSFETs - the
video shows that IR2301 drivers are used, each controlling one "arm" of the bridge. Look at
the datasheet for the IR2301 for details - an external diode and capacitor are typically used
for the bootstrap circuit.

Incidentally the designs misses a trick, you can get a complete 3-phase MOSFET bridge driver in
one chip, such as the FAN7388 or HIP4086.

Using gate drivers means many useful features can be incorporated without extra expense, such
as low-voltage cutout, dead-time (shoot-through prevention).

Most gate drivers require +12V supply, but the motor supply can be completely independent
of this, either below or above, the circuit topology has the nice property that you can power
down the motor supply or the driver supply independently and nothing bad happens.

icedgoal:
a) At around min 11, he shows the circuits with the mosfets. I dont understand why he uses n-channel mosfets instead of
p-channels combined with n channels. Dont you have to apply a higher gate voltage if you use n-channel mosfets, because Vsource = Vgate - Vth ?

The gate voltage is boosted by the bootstrap circuit of the ir2301 to always keep the gate voltage above source voltage for the nfets. The explanation of gate drive voltage is kind of confusing in that video.

I normally use a 5 volt buck regulator to bring down battery voltage to supply the MCU and then use a boost converter to supply the 12v for the mosfet drivers. This way the battery voltage can go down to 6 volts and the mosfets still get full voltage at the gates.

I have a bunch of designs here if you are interested, some with the fan 7888, I have made a few speed controllers with the ir210X drivers too but I like the simplicity of the single chip.

The power capacitor choice will depend on a few factors, The motor, current, voltage, wires and battery, the type of switching and the tolerance of the rest of the system to power fluctuations. take a look at some off the shelf esc’s rated for a certain sized motor and you can see the size they use. I use a low esr 470uf cap on most of my esc’s for the 10-30 Amp range (8-20v), this is enough to keep the power rail steady.

Ok I got most of it! Thanks