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Please explain how the bootstrapping circuit help in driving both the mosfets connected to IR2101 driver.Please explain this by taking an example of any voltage so that I can understand easily.Explain how the capacitor charging and discharging during this procedure and the use of diode and resistor connected. It will be really helpful for me if someone explain thisenter image description here

anmol kumar
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  • the diode and the right side capacitor look like a part of a voltage multiplier circuit – jsotola Oct 20 '20 at 20:16
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    Does this answer your question? [Functionality of IR2101 driver](https://electronics.stackexchange.com/questions/506472/functionality-of-ir2101-driver) – Marcus Müller Oct 20 '20 at 21:08

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Suppose u r going to drive a mosfet bridge (half or full) with all n-channel mosfets. Obviously there's no problem driving the low side mosfet, because its source is connected to GND and u can simply drive the gate pin with a 12v signal. But the challenge is how to drive the high-side mosfet, since its source is not connected to GND and is floating, and u have to apply a 12v on gate-source pins. For example with a bridge voltage of 100v, u need a 112 volt on its gate to drive it.
The solution is "bootstrap". In this technique, as can be seen on schematic, a diode with a cap is used. When the low-side mosfet is ON, the cap is charged through diode and the ON mosfet. If Vcc of IR2101 is 12v, the cap is charged up to 11.3v (0.7v drop because of diode). Then the low-side mosfet is turned on and it's time to drive the high-side mosfet. In this case, we have a floating voltage supply of 11.3v stored in the cap which will serve the driver circuitry inside IR2101. So, the voltage on the minus pin of cap is 100v and the voltage on its plus pin is 111.3v (and the diode is in reversed bias). This voltage is used to apply on the gate-source of high-side mosfet.
This "cycle" continues over and over. The bootstrap cap is charged during low half-cycles and serves (and of-course discharges) in high half-cycles.

Hamid R. Tanhaei
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  • And what is the use of diode given in the circuit – anmol kumar Oct 21 '20 at 10:30
  • The diode charges the cap in the first half-cycle (when low-side mosfet is on), and allows the voltage on positive tap of cap to go above the IR21 Vcc in second-half cycle (when high-side mosfet is on), if a wire were instead of diode, the cap voltage cannot go above IR Vcc and discharges into the IR Vcc. – Hamid R. Tanhaei Oct 21 '20 at 10:39
  • I want to know how HO is calculated i.e when the drain of low side mosfet is connected to the VS terminal and from their we take the output for load .Let say 48V battery connected such that positive terminal of battery is connected to drain of high side mosfet and negative terminal of battery is connected to source of low side mosfet.Use this voltage value to explain the HO value. – anmol kumar Oct 27 '20 at 18:42