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Millenium 2 and positive gnd effects

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5/24/2000 4:06 AM
Bob S II	Millenium 2 and positive gnd effects Does anyone know of a suitable p-channel mosfet that will work in the millenium 2? I'm having a hard time coming up with one. Thanks, =Bob

5/24/2000 2:04 PM
R.G.	I use the BS270P. Mouser, Digi-Key, etc. Works. Or use Zachary's trick of just substituting in parts at random until something works and you achieve your own beautiful understanding of how things work, free of the intimidation and repression of any formal learning...

5/24/2000 7:01 PM

quote:
"Or use Zachary's trick of just substituting in parts at random until something works and you achieve your own beautiful understanding of how things work, free of the intimidation and repression of any formal learning..."

give it a rest. do us a favor and leave your personal grudges out of your answers.

5/25/2000 4:24 PM

quote:
"I use the BS270P. Mouser, Digi-Key, etc. Works."

Thanks R.G. I've been unsuccessful in locating the BS270p anywhere yet, but I did find another number, BSS110, that looks as though it should do the trick. It's rated at 170 ma (vs. 500 or so for the BS270), but I can't imagine that being an issue in this circuit. If you want to give it a look, the data sheet is at http://tmxnet.com/BSS110.pdf

In the mean time, I ended up using the original millenium circuit with a J176 p-channel jfet. I had to decrease the value of the resistor in parallel with the LED to get it to turn completely off, otherwise it's as you drew it it. One thing I found interesting is that there's no delay or "fading-in" of the LED - it comes on instantly, although I have no idea why.

Anyway....thanks again for putting this stuff out there - it makes life a whole lot easier for those of us who *don't* know the math. Yet.

5/25/2000 9:08 PM

quote:
"BSS110, that looks as though it should do the trick. It's rated at 170 ma (vs. 500 or so for the BS270), but I can't imagine that being an issue in this circuit"

You're absolutely right. Very, very few P-channel MOSFETs *won't* work in this circuit. They only have to be able to handle the LED current, and fully saturate with a 9V change on the gate-source.

You know, the P-channel device you can get to inside a CD4007 will work too... as will a CMOS inverter. They're clumsy because you have to stick the whole DIP in, but they will work.

quote:
"I ended up using the original millenium circuit with a J176 p-channel jfet. I had to decrease the value of the resistor in parallel with the LED to get it to turn completely off, otherwise it's as you drew it it. One thing I found interesting is that there's no delay or "fading-in" of the LED - it comes on instantly, although I have no idea why."

Hmmm... no fading? Wow. Must be a *very* low Cgss JFET. I did some computation on all the ones I've measured, and the voltage fade-in is within measurement error of the diode leakage charging the gate capacitance. Maybe you got a really high leakage diode - like maybe 100nA instead of 10nA.
That could do it. Try swapping for another diode or diode type and see.

Hey! Great! Serendipity on the hoof.

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