An Arduino Nano Electronic Speed Controller (ESC) — Part 3

In Part 1 we introduced our Arduino based ESC and followed this in Part 2 with an explanation of the power stage and MOSFET drivers. Part 3 focusses on the bootstrap capacitor which is part of the driver circuit used to turn the high-side MOSFET hard on.

Figure 1. IR2110 Dual MOSFET Driver Connections

7.0 The Bootstrap Capacitor

The bootstrap capacitor is placed between the VB and VS terminals on the IR2110 (Figure 1). It is there to satisfy the requirements of driving the gate of the high-side MOSFET hard ON, namely:

1. The gate voltage needs to be 10–15V higher than its source voltage to turn the MOSFET fully on and minimise RDS. However, with the drain of this device connected to VCC, the gate voltage needs to be higher than VCC, which is often the highest voltage rail available.
2. The MOSFET driver is controlled using TTL logic referenced to ground (i.e., VDD) and the control signals must be level-shifted to the source of the high-side power device (VBS).
3. The power absorbed by the gate drive circuitry should be minimal.

The IR2110 is designed to be used in bootstrap mode and can operate in most applications from frequencies in the tens of Hz up to hundreds of kHz.