a break from disease

Looks almost use-able as a voltage-controlled resistor with a reverse beta of ~4 over 5mA

Did you try the transdiode connection - C to B shorted?

It is what the analog guys like for precision diode.

I don't understand the last two sets of data (with base supply negative)

- is that because Ib is now part of Ic flowing into the base voltage supply - can one say it has beta then?

piglet

It is sometimes difficult to decode your uA from you mA. Try printing better or use a sharper point on your pen.

Where are the units not obvious?

That was me... I guess I should try and measure the gain at ~1 MHz and 10nA to 1 uA.. or something like that.

So silly question; Are your graphs at what I would call reverse bias? Collector negative wrt emitter.(and base) Well the second one Vb-e you've left the collector floating?

George H.

Really low-current beta would be interesting.

The reverse-beta one was. The fA leakage graph goes both ways.

Yes. That's just to characterize the b-e junction and emitter resistance. I was wondering at what current the b-e diode would go ohmic, but it's past my last 10 mA point. I've been doing some Spice sims that may not agree with real life. Maybe my model needs tweaking. Needs more work.

But, that doesn't tell you the emitter resistance; it tells you Rbb, the base spreading resistance. There's not much Rbb contribution when the collector is taking most of the current, it's collector-connected-to-base that tells you the emitter resistance.

Cheers

Phil Hobbs

The base-emitter curve is exponential to 10 mA, which means that the emitter resistance is low enough that I don't have to worry about it in my current application. I guess I could try to resolve the two resistances somehow.

It's an amazing diode. Maybe half a pF, a few fA leakage, pretty low series resistance. C-B is similar but good for more voltage. It's miles better than a PAD-1.

Small schottkies are mostly ohmic at 10s of mA. There's a zero forward TC point there, too.

That was the same chip in SOT-143 wasn't it? Long gone.

The BFG and BFU series are/were faster but otherwise similar. The BFG25A/X was an improved drop-in replacement for the venerable and beloved MRF9331.

The regular BFG25A came in the normal SOT23, iirc.

Cheers

Phil Hobbs