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Top left circuit:
Simple CMOS setup..... but look at the current meter in orange there !
In the very short time that one Mosfet opens with the other Mosfet closing, there is a brief crossover
whereby a short-circuit occurs passing extreme current from top to bottom.....it is called Shootthrough and is likely to blow a Mosfet....This circuit is inadequate for the task.
Bottom right circuit:
Bottom left Nmos acts as a Level Shifter with the resistors and diode to set the left CMOS in action as before.
The 1MΩ resistor between the two CMOS drains however, greatly reduces any crossover shootthrough current.
The CMOS on the right now has very restricted μA shootthrough seen in the green meter there.
Values can be varied as reqd. It's the overall structure which we are looking at to reduce shootthrough, whilst enabling an equally balanced available power final output. (at 30v either side of zero here).
All Mosfets used are standard with 3v/-3v VTO
Note1...
I had to place a tiny resistor with the amp meter in the top left circuit to prevent EC locking out with infinite shootthrough. See how even such a tiny resistor placed on that Source side prevents the full action of the Mosfet bar.....Keep the Source connected directly to supply (often a zero, but -30v here).
The 3v VTO is fine, but remember that the Mosfet there will start to conduct when the gate volts reach -27v .......heading from its -30v on its journey towards zero......and will continue in that conducting mode through zero and +ve direction....Again, that tiny resistor will have a large volt drop with extreme shoot through current....and that will shift the V in an unstable manner at the Source, producing a dynamic 3v gate Vth (Hence the gate v there in the top left circuit not swinging beyond -27v towards -30v as needed for that Nmos bar to close off....in fact, the -30v at Source there is shifted into a + value so the gate v is only seen as 0 to an accumulation of approx +40v...all because of that tiny Source resistor with a high current).
That problem does not occur in the bottom right circuit where there is no Source resistor.
Note2....
The 6.8kΩ and the 680Ω resistors are set here so that the gate swing across both Mosfets is suitable, and not greater than the usual datasheet +/- 20v recommendation. Take care with the cap choice, since a bad selection can change the final shootthrough drastically!
Altering these resistors gives you personal scope to alter the Mosfet bar timings to your choice here on EC eg as per your datasheet Vth, rather than blowing a Mosfet by trying to do so on a board.
Click on the green amp meter to see the μA bottom right circuit shoot through value compared with the extreme kA shoot through of the top left circuit.
Rds is not discussed in this article....it is a different issue.
The above article is my viewpoint and discussion is welcome.
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