LTspice Help needed from those proficient in it


Joined Mar 14, 2008
If you are trying to determine the value of the bootstrap capacitor, It depends upon the actual MOSFET you use, since it is determined by the particular MOSFET's gate charge.
That capacitor value is not critical, and normally is just made more than large enough to provide the gate charge with little voltage droop during the MOSFET's on-time.

Thread Starter


Joined Jul 18, 2013
Yes I just wanted to get a close ball park number.
Too bad that Silicon Labs took down their on-line calculator pgm for the most optimum value based on the Mosfet and frequency, which I had been using up till now.


Joined Mar 14, 2008
Below is the sim using a MOSFET model in LTspice with 108nC gate charge, so that should be very close to using IRFP460.

I modified the sim some--
I removed the gate to source resistors since they are not required when using a push-pull driver such as the IR2110 driver.
I used the .step function to simulate with C1 capacitor values of 50nF, 100nF, 200nF, and 400nF to determine the optimum value.

The sim shows the increase in M1's gate source voltage, V(VGH,Vload), as the capacitance is increased, and there is not much increase above a C1 value of about 200nF.
Of course a higher value for C1 will be fine as there is no particular upper limit.



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