H-Bridge Boot-Strap Concept
Category: Miscellaneous
Designer: RANA MUHAMMAD ADNAN KHALIL
Notes
This circuit is designed in Proteus 8.2. It is recommended to use the latest version of Proteus. This is a simple circuit of H-Bridge. The main interesting part in this circuit is bootstrap concept. In this simulation you will learn how to drive H Bridge with bootstrap concept. The lower side of the MOSFET is very easy to drive because source of the lower MOSFET is directly connected with ground and normally power supply is available with respect to ground. To turn ON the MOSFET we have to provide voltage with respect to source, so it is easy to drive lower side of MOSFET. But the MOSFET (NMOS) which is connected at high side of the H-Bridge is difficult to drive. There are three possible ways to drive upper side of MOSFET. a)Use PMOS at high side instead of NMOS, because it is easy to drive at high side as it will turn ON at zero-level. b)Use seperate isolated supply whose ground (negative terminal) is common (connected) with source of high side MOSFET (NMOS). c)Use bootstrap technique to drive high side MOSFET (NMOS). In bootstrap method a capacitor is charged with respect to source of upper MOSFET (NMOS) using diode clamp, and reverse current (and voltage) will be blocked by diode (in reverse bias mode). The bootstrap capacitor is calculated (selected) according to switching frequency and gate charge of MOSFET. Just download this simulation to learn how bootstrap and H Bridge works.