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Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
When planning my 12V mini sstc I realized that it's really difficult to get any gate drive chips here in Finland. I thought about different solutions. This came into my mind:
So just a totem pole of two darlingtons. Would this be powerful enough to drive the IRFP240 at 2.5MHz with good rise/fall times? Is the 220R resistor fine or should it be bigger?
Registered Member #89
Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145
Spark, emitter follower does not amplify voltage and your input is limited to 5V for HC version of IC.
To drive from 5V logic I would add one class A preamplifier stage consisting of a BS170 mosfet and 100ohm pullup resistor to drive voltage - this worked well for me up to few Mhz. (note that this inverts your output, though!)
Don't use darlingtons, they are usually slow and that much amplification is usually not needed! BC237/307 should work very well, for more power go for 2N2222/2N2907.
You should also remove the 220ohm base resistor you are using and use a low value, 2-5 ohm resistor on the output to carry the power dissipation burden instead of transistors.
Put the driver circuit as close as possible to mosfet and use decoupling caps - if you do it properly you can actually make it work better than UCC's.
Registered Member #952
Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388
Could I then use just BD179/80 for the totem pole? And does the transistor on the amplifying stage have to be a mosfet or would 2n2222 do the job? I have plenty of these available.
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Discrete MOSFET gate driver with Darlingtons?
