wimpy diode

John Larkin · 2015-12-07T19:47:48+00:00

I need a wimpy diode, with lots of forward drop at a few mA, to bias up an e-phemt. Thought I'd try a small-geometry NPN transistor. Looks good. The b-e and b-c junctions look symmetric. The middle config looks like the classic 60 mV/decade-current, and the others are maybe a little ohmic. We pay 2.4 cents each for these, so I don't mind wasting the transistor action. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com

Dec 07, 2015 41 Replies

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Phil Hobbs 10 years ago

I'm using one in that super low cost TIA (with the LM324). It's in parallel with a 200M feedback resistor, to give a logarithmic overrange indication.

Your plot has the transistor in normal bias for the inverted configuration (collector negative), which probably helps the log conformance a fair amount.

Cheers

Phil Hobbs

Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net

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John Larkin 10 years ago

Yeah, too many voltage regulators. About 100, of all kinds, including switchers.

Most of those 3e6 parts are resistors and caps on reels.

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