Functionality of IR2101 driver
IR21xx driver series are used to drive bridges when both UP and LOW switches are N-channel Mosfets. In this case, driving the Up Mosfet is a challenging job because the voltage of Mosfet's Source is floating. So, the solution used in IR21xx ICs is this: when the lower Masfet is on, the cap (between Vb &amp; Vs) is charged up to (Vcc - 0.7v) where Vcc is the supply of IR2101 and 0.7v is the voltage drop of diode. After that, when the lower Mosfet is turned off and the Upper Mosfet is going to turn on, the voltage stored in the cap will be used to supply and drive the circuitry (inside IR2101) which is responsible to drive the upper Masfet. This procedure will happen at every cycle.