An error in my haste to transcribe onto a clean piece of paper, Change "VDD" to "VDD-VF" ...Jim Thompson
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Depends of device, the Si4666DY has a very narrow spread.
I don't rely on capacitance, remember my commenting that QG is the best parameter to hang your hat on.
Funny how "spicing" is preferred or denigrated, depending on how you want to twist things.
Time to grow up, little boy. ...Jim Thompson
Post the math that derived the values in your original post. You claimed, on the
7th, that you had calculated those values.So, show us how you did that.
Well, they're both just common-drain amplifiers. The distinction with the high-side switch application is that the gate has a much larger swing. Namely, the high-side switch's gate has to swing well above Vdd, whereas the follower's doesn't. So, Cdg matters more.
Yes, that was my original point. Jim could probably pick an inductor current that works decently over a range of part-to-part variations, but the gate drive voltage would be part and Vdd-dependent. He'd have to make sure that's okay.
Yep, and I still like overkill inductor drive + clamp. Easy, solid, cheap.
James
Wastes current... though, albeit, not a lot. A mental exercise not worth the effort.
This thread is herewith abandoned. Students and engineers wishing details, derivations, etc., should go to my website...
and utilize the envelope icon to request technical information.
All requests are cordially invited.
I also invite you to partake of the LTspice list, where true technical discourse still exists. ...Jim Thompson
Good one! Thanks, Spehro.
John S
OK, you give up on showing the calculations.
Because they never existed.
Yes, there are a lot of capable and smart folks on that list and this is an interesting topic.
Unfortunately this isn't axactly LTspice specific so this subject would be put to a stop there, sooner rather than later.
boB
I didn't realize that mattered, since the circuit wastes the entire resistor current whenever it's idling 'OFF'. But, you're right, of course.
I looked up Jim's FET--
To a first order, the reverse transfer capacitance Crss amounts to about Cgs/10. Multiplied by dVgd/dVgs of ~2 (if Vdd=12v, Vgs(ON)=12v) means it changes (lowers) Vgs(ON) by ~10%, all things said and done.
So, not a big deal with these parameters and this FET.
It wasn't supposed to be controversial, just mentioned offhand as a factor. Five minutes' worth of checking, that's all.
Maybe we could discuss it on USENET? I hear they've got electronic discussion groups over there. :-)
Cheers, James Arthur
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