1. Introduction One of the most widely used methods to supply power to the high-side drive circuitry of a gate driver IC is the bootstrap power supply. The bootstrap power supply consists of a bootstrap diode and a bootstrap capacitor; this circuit is illustrated in Figure 1.

　　This method has the advantage of being both simple and low-cost. However， the requirement to refresh the charge on the bootstrap capacitor may result in limitations on the power converter’s duty-cycle and the power switch’s on-time. Proper capacitor and bootstrap resistance selection can drastically reduce these limitations. The maximum voltage that the bootstrap capacitor （VBS） can reach is dependent on the elements of the bootstrap circuit shown in Fig. 1. The voltage drop across RBOOT， VF of the bootstrap diode， the drop across the low-side switch （VCEON or VFP， depending on the direction of current flow through the switch）， and if present， the drop across a shunt resistor （not shown in Fig. 1） placed between the low-side switch’s emitter and the DCrail， all need to be considered. The intent of this document is to develop the bootstrap sizing theory and practice， while focusing in particular on topologies where the gate driver IC features the integrated the bootstrap “diode”1 。