2N7000's Hfe :1200 ?

[JFX09]

hello,

I'm checking out the features of my new DMM and I thought i'd try out the transistor tester thinghie. Tried it with a couple of different transistors and now this 2N7000 is reading 1200, is this possible ?

jf

[R.G.]

Actually, it's seriously low.

Hfe is the **current gain** of a transistor. The 2N7000 is a **MOSFET**, so its base is a connection to a layer of very pure glass about 20volts thick. The input current to the 2N7000 is so small that it's seriously difficult for a very well equipped lab to even measure as different from zero. The "current gain" of a 2N7000 is nearly infinite, because the input current is nearly zero.

Which is another way of saying that current gain has almost no meaning for MOSFETs.

The devil is always in the details.

[JFX09]

Ah, I see. I've been doing a lot of swapping of just about everything I have at hand, as long as It had 3 legs but I thought I'd get a little bit more methodic and keep track of what I tried and what works. Since I've been reading the "Technology of the Fuzz Face" (almost reciting it as a mantra, to sink it in) I was puzzled by the numbers since you talk about 80-110.

Thanks for the clarification.

jf

[WGTP]

I did the same thing when I got a DMM and the highest I got was around 900hfe with a MPSA-18 with the 2N5089's almost that high around 700-800hfe and the 2N5088's were almost that high.  Most 2N3904 types were around 200 - 300hfe.