On Friday 01 November 2024 03:23:03 pm Derek Koonce wrote:
For all ICs, one should look at the output drive capability. Then look at the load being driven. If it is a small MOSFET with low input gate capacitance, one can drive directly. However, if using a larger MOSFET, such as a DPAK / TO220 size, the gate capacitance is high and thus a high initial current could stress the output drive of the IC.
I believe that based on the specs that he mentioned in some of those videos that it was indeed a TO-220 cased device He also did a couple of other videos, one on assorted MOSFET drivers and one on high-side drivers, though for the third alternative in that one he used a chip made for the purpose.
I can see where it'd be easy to look up the drive capability of a 555 chip on the one hand, but for a given capacitance of a given part, how do you know what it's gonna take to drive it?
In the video posted, they used a 10 Ohm resistor to limit the in-rush current into the MOSFET gate. Drawback is that this will slow down the turn-on of the MOSFET, and, in some cases, burn out the MOSFET due to not saturating the MOSFET drive quickly, and current through the MOSFET to the load. It comes down to design check that one should do for every design - it is the engineering thing to do. ;-)
Somehow I don't think that 10 ohms is going to slow things down all that much, and in some of those videos he actually looks at turn-on and turn-off time and MOSFET power dissipated, with comments about some alternatives in there. I've seen a fair amount of stuff where much more resistance was used, say in a bunch of the reverse-engineered schematics that Big Clive posts pretty regularly for one example.
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