bootstrap capacitor calculation for h bridge configuration for varying pwm duty input

[renga92]

I am planning to use IR2110 to drive H bridge configuration. I was going through the formula for the Bootstrap capacitance and it had a factor of time period of the high pulse which will vary in my case as my PWM width will vary to provide different output ac voltages. So what should I do ?

Briefing on my application I am planning to vary a constant 400 VDC power source and generate varying AC voltages by varying the PWM duty cycle.

Thanks in advance
Renga

 

[FvM]

The formula is for minimal bootstrap capacitor (an inequality in mathematical terms), so the answer in case of a variable time period should be clear.

 

[renga92]

Thanks FvM. I didn't look at the formula clearly. Had another thought when I was looking at the formula.Is it what the designers use to calculate the cap value every time or is there any thumb of rule to make our lives easier.

 

[crutschow]

Since it's a minimum cap value, you can just use a value much larger than that.