Hi all, We make this low noise power supply. (~ +/- 12V up to ~100mA) A voltage regulator followed by a cap-multiplier. The first bunch I made had an output noise of ~>1.5 nV/rtHz. So I wrote a spec of 2nV/rtHz. Then a new batch of transistors (2N4401) and the noise was worse... ~3.5 nV/rtHz. I had a bag of the older npn's and just put those in. Now I've run low and ordered a bunch of them (200) from several different suppliers. These are in now and some of them test just fine. (transistors from the same batch seem to be very similar) And I was wondering if the difference in noise is related to a difference in Beta. (Can I do a DC measurement and ID the good ones?) So I'm looking for a simple circuit to measure transistor beta. This looks like a good start,
The noise is highest at the highest currents, so I'd like the current source to ~100 mA. I guess that's simple enough.
Other ideas? Thoughts? Thanks.
George H.