I agree with Matt, a fast turn off is only important to creating higher voltage
from coil discharges and both turn off and on quickly to allow and disallow
current is mainly for reducing the power dissipation in the switch. And too
fast of a turn on or off can cause unwanted ringing ect. Sometimes we may
use a gate resistor to slow down the turn on and off or suppress ringing at
the gate.
With the cap dumping, I look at it two ways, the way I used in my posted
setup was to dump a relatively small capacitance at higher frequency and
not fully discharging the capacitor, this is mainly to hasten the desulfating
process with low input power, pinging the battery with short high current
spikes.
Then there is dumping a large capacitance relatively slowly and totally
discharging the capacitor to get high surge currents through the battery.
In the later case the turn off time is unimportant in any way except maybe
to save time so the cap can be recharged sooner, maybe.
This video shows some wave forms and stuff from a boost converter
powering a cap dumper/desulfator.
Note the groups of step discharges of the dump cap towards the end of the video..
https://www.youtube.com/watch?v=7ZBE4i5UR58
..
from coil discharges and both turn off and on quickly to allow and disallow
current is mainly for reducing the power dissipation in the switch. And too
fast of a turn on or off can cause unwanted ringing ect. Sometimes we may
use a gate resistor to slow down the turn on and off or suppress ringing at
the gate.
With the cap dumping, I look at it two ways, the way I used in my posted
setup was to dump a relatively small capacitance at higher frequency and
not fully discharging the capacitor, this is mainly to hasten the desulfating
process with low input power, pinging the battery with short high current
spikes.
Then there is dumping a large capacitance relatively slowly and totally
discharging the capacitor to get high surge currents through the battery.
In the later case the turn off time is unimportant in any way except maybe
to save time so the cap can be recharged sooner, maybe.
This video shows some wave forms and stuff from a boost converter
powering a cap dumper/desulfator.
Note the groups of step discharges of the dump cap towards the end of the video..
https://www.youtube.com/watch?v=7ZBE4i5UR58
..
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