whiteboard lights

So driving home I did the series inductance multiplier, (which has certainly been done before.)

So I_+* to collector, and to R_cb. And also at base, inductor to emitter L_be

--+---\ />----+--> I out | --+-- | | | | +-Rcb-+--L_be-+

Does that work?

George H.

ps

These ~10-100 mH inductors come in groups where the L/R time constant is about the same, one group with 1/3 milli-H/ohm and then

Geo

Right, and turn it into an inductor... does anyone use such a thing? Unless I've got some high gain transistor I need a big L.. oh a Darlington inductor multiplier?.. I need to check my (rather thin) inductor parts drawers.

George H.

Oh, and a series resistor between the emitter and the cap will help stiffness and reduce the shot noise contribution. We make a way-sub-Poissonian laser driver in a similar way.

Cheers

Phil Hobbs

That actually looks capacitive. ;)

The transistor works like a gyrator.

Cheers

Phil Hobbs

But the transistor is off!

Well, a cutoff transistor is capacitive. ;)

I was assuming that was the AC equivalent circuit.

Cheers

Phil Hobbs

Oh, very fancy. I have a Rohde&Schwarz UVM Microvoltmeter. Very pretty design but I hardly have use for it anymore:

Huh, too many inversions on my part maybe?

OK so a good cap and the right resistor, that does make more sense.

I will say the modulation looked like a decent sine wave, which does make things much easier filtering-wise.

I'm not anywhere near shot noise.. just getting rid of ~40 dB at ~0.1 A. Anyway I'll give it a go. Series is easy in this case.

George H.

Right, sorry, my mistake. I've got a lot of good capacitors, so for me it's a good mistake. :^)

GH

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Hi Phil, so a tip31 with R_bc=500 ohm and C_be = 100uF worked like a ch arm. I could add one in series to my diode laser drive! Thanks.

I'm confused by the series resistor between cap and emitter. (Oh maybe I put it in the wrong spot!) So this,

--+---\ />--R_e--+--> I out | --+-- | | | | +-Rcb-+--C_be----+

and not this, (which I drew first)

--+---\ />----------+--> I out | --+-- | | | | +-Rcb-+--C_be--R_e--+

George H.

The top one is what I had in mind.

Cheers

Phil Hobbs

Wouldn't an inductance multiplier rather look like this?

----+---\ />------> I out | --+-- | | +-Lcb-+

... with the L between C and B, and with no R whatsoever?

Dimitrij

Ahh, OK. The resistance is the base-emitter 'resistance' plus the coil R. (I want to guesstimate the time constant.) I_c average ~200mA (for the led thing.)

George H.