I had a question about the ir21xx gate drivers if anyone has had any experience with them. I know the high side boot cap need to be kept charged so the base of the cap must be periodically turned low.
How should the pwm be applied to the driver to make this happen properly,
To PWM the high side while keeping the low side (opposing) on)? Will this bring the boot cap base low enough to charge during the pwm off time?
or should i be applying an inverting pwm on the high then low side while keeping the opposing low side on?
This seems like it would create a motor brake during pwm off where both low sides are on?
or should i apply inverting pwm to one side and also pwm the opposing low side? So the cap can charge to full and then a motor can freewheel on pwm off?
How can i implement an inverting pwm on two different pins?
You can arrange (given suitable shoot-through prevention circuitry) to just pull the low-side
high every ms or so for a few us. Without shoot-through prevention circuit you'll need to coordinate
the low-side pulses with the high side yourself.
Some drivers have continuous charge pumps (like the HIP4081) which obviates the need to prime
the bootstrap caps explicitly.
Thanks , that would be the easiest for me to work into existing code for brushed motors too, I have blown enough mosfets to ask first now.. getting jumpy..
If i were using it for a brushless motor would the commutation speed be enough to keep the bootstrap charged? If the motor was turning 10,000 rpm, or 166 rev/second. That would be a 6ms period per revolution and many commutation steps per revolution.
I would be using pwm on the low side. ( or hope too because i wired it this way but can change it)
I have used the hip4081 and think its great, but its winter and i have some ir2110's i was going to used to drive some big mosfets for a sensored brushless motor to learn with.
The problem with the brushless motor is that it has to get from stationary to 10kRPM, and that is when
the bootstrap cap would droop and cause issues - so no its not going to help (though you could switch
modes at speed to get maximum performance)