Germanium transistors, new?

[kalee20]

I'm interested too - particularly the 30μA consumption! That'd be a challenge for Ge unless it's for an outside location in Iceland!

I can't (not allowed to) post the circuit but it is a standard "volts developed across a resistor turns on transistor to turn off big transistor". The only current I need apart from leakage (well spotted kalee20) is to turn on the MOSFET pass transistor.

As they (new Ge) aren't made and the leakage problem which I didn't remember was awful for Ge devices. I must admit it was a step too far, the boss will have to accept 0.6V.

I suppose what I want is a 0.1V turn on low leakage transistor!

Thanks all.

[mhennessy]

So like I discussed in post #14...

At circa 3uA, I'm amazed that there's enough collector current in the sensing transistor to give it enough gain to do its job, but it presumably meets the spec (which we don't know) for current stability. I normally expect to put at least 1mA in that first transistor if I want a current source with decently high output impedance, and that's on top of whatever current the second transistor requires if it's bipolar. You said it's a limit rather than a source, so I guess that's how you've got away with it...

Just to add to the "fun", Ge leakage is highly temperature-dependant.

[emeritus]

In the 1970's a US company called Germanium Power Devices took up manufacture of Germanium transistors after they were discontinued by the big manufacturers. I see that the company, now called GPD Optoelectronics, still exists, but they only seem to make Germanium infrared sensors nowadays.