mosfet driver needed for logic-level mosfets?

Not there, but here:

and here:

and here:

which references this excerpt from a book:

This all came by searching on "speed up bjt switching with negative base drive" -- there are probably other fortuitous combinations if you wish to exercise your Google-Fu.

I think there was more than that, but dangit, I can't remember.

Fred Baker was doing that. We had these plasma panels that had a complex waveform and had to refresh the things at 15KHZ horizontal rate just like NTSC TV (back in the 70's) ~1/2 million pixals... X-Y diode steered addressing lines, I forget how fast the transistors were working but it was way beyond anything that this guy's PWM might encounter.

One beauty of the panels (that we took advantage of) was that it didn't require memory, light up a pixal on the screen and it stayed there until you changed it, due to some magic in the power supply - some kind of stepped waveform. My memory isn't up to describing the whole system...

Or something simpler. Isn't that what the Schottky transistor does? It uses a single Schottky diode between the base and collector. Since the Schottky diode forward voltage is lower than the Vbe voltage it limits the collector voltage and keeps it out of saturation. But now there is no diode blocking the current path to turn off the base and drain the charge.

That sounds similar to what they did in WWII radar sets where they drove the grid positive with respect to the cathode to drive more current to the plate. The grid would conduct significant current, but since they were generating pulses with a relatively low duty cycle the grid didn't melt.

There are class-B amplifier tubes that are designed for that even with continuous-wave or audio service -- but they need to have grids that are capable of withstanding (and dissipating, I think) the extra heat.

That's kinda old. Actually, very old. There are some milliohm mosfets around now.

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. Is this the article you were referring to?

ied MOS as this suits their technology) but in terms of equivalent on-resis tance and silicon efficiency, the low voltage bipolar device has no equal. For example, the ZETEX ZTX849 E-Line (TO-92 compatible) transistor exhibits a RCE(sat) of 36m?. This can only be matched by a much larger (and expensi ve) MOSFET die, only

Oh nice!

From the datasheet, Vgs,th,max = 1.1V. This should work fine as a logic- level mosfet, then?

In general, for PWM at 1-2A, 12-18VDC, are mosfets preferred (lower resista nce, cheaper) than BJTs?

Thanks,

Michael

AFAIK FETs have pretty much taken over any space where BJTs were once useful as switching power devices. Once you get above the convenient operating voltage of FETs, you start seeing IGBTs and SCRs. There may be some fringe applications, and some older circuits that are still being shamelessly copied (photoflash units come to mind), but by and large I think that the BJT has had its day for this.

I know a variation of Forth that uses color for syntax. There are modes of execution of the code. Some code is executed by the editor, some by the compiler and some is run time. They are all distinguished by color (along with some other categories like comments).

Oddly enough it is called... ColorForth (written with "color" in red and "Forth" in green).

Eeew.

If you have 2.5V of gate drive, that makes

It would be a nightmare for those of us who are moderately color blind :)

I can barely tell the yeasts apart on page 12.

Michael

Cool! Thanks!

Michael

Forth is a nightmare no matter what your vision.

Yeah, there's supposed to be some way of getting around that, but I don't recall. It was written by one person for himself, Chuck Moore.

From someone who doesn't program. Forth is easy to learn, but you have to learn it. Funny though. Programming in Forth requires you to start with the basics (it doesn't have arrays built in for example, but they are easy to create, very easy) but can be very powerful opening the full potential of the system you are running on. That strikes me as analogous to the way JL does analog. I guess when it comes to things he doesn't understand he expects it all to have been done for him.

maybe just stick the right capacitor in parallel with the base or with most of the base resistance.

This doesn't sound like a very critical application. So it might be overkill, have you looked at the TC4420 series of FET drivers.

Mikek