eight dollar 0805 resistor

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John Larkin         Highland Technology, Inc 
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John Larkin
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Wow, and here a few weeks ago I was complaining about those $3 0805 resistors you were using.

Just goes to show that once you start downhill, it's hard to stop. ;)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Phil Hobbs

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It is one GIG-Ohm, that has to be a bit tricky. Just breathe on it and it woun't be a gig Ohm anymore. I have no idea how well it does after SMT reflow and cleaning. Also, if you just buy 100 of them, they are ONLY $5!

Jon

Reply to
Jon Elson

I've designed circuits for customers with 50G SMT resistors. You need to put a slot under them to prevent water-soluble flux from destroying their performance. Sufficiently thick top copper combined with an unplated hole underneath can allow you to clean adequately between the resistor and the board, but a slot is better. Once you get it right, they're nice and reliable, but it doesn't happen by accident.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

1G is easy.

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Just don't use water-wash flux.

I have some samples of an 0805 1T resistor.

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John Larkin         Highland Technology, Inc 
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John Larkin

snip

I remember needing a 68M resistor for a timing circuit in my youth when I didn't know how to do it any better but what needs 1T? Isn't that the same as an open circuit? :)

Reply to
John Smith

I went to its catalog page and there was a 25 G ohm one! That's hard to get my head around. For example, wouldn't the air between the terminals be less (much less?) than 25G?

Bob

Reply to
Bob Engelhardt

A clean PCB will have fA leakage. 25G is perfectly usable.

Here's an ugly rosin-flux-glopped, bare-finger-handled PCB.

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Pins the needle on the 1e14 ohm range.

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John Larkin         Highland Technology, Inc 
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John Larkin

Den mandag den 12. oktober 2015 kl. 23.31.54 UTC+2 skrev John Larkin:

just be glad minimum order isn't a reel with 5000 ;)

-Lasse

Reply to
Lasse Langwadt Christensen

I just did a current source with five 1 Meg's in series. Above ~1 Meg precision resistors disappear.

We pay about $3 for TH 1 G 1%. Big blue things, fat leads.

George H.

Reply to
George Herold

Pretty good for a 11kV SMT part. That's less than 100u$/V.

Reply to
krw

In LTspice you'd have to have 10 open circuits in series to get there. ;)

For TIAs at really low currents, you win by using a capacitor as the feedback element and fixing it up afterwards.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Phil Hobbs

On Mon, 12 Oct 2015 18:00:48 -0400, Phil Hobbs Gave us:

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Yes. And even then, it is nearly impossible to get repeatable performance from them. Even an epoxy dipped planar types change value when environmental effects get applied.

In the HV lab, we used to call it "coffee breath".

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Very difficult. We also used to place slots under our SMT HV diodes and caps on our miniature HVPS designs.

Still a quite susceptible realm at those form factors.

Reply to
DecadentLinuxUserNumeroUno

...and stay MILES away from "no clean".

Reply to
Robert Baer

** One app is externally polarised condenser microphones.

Two IG ohm resistors are needed, one to supply charge to the capsule and another to feed bias voltage to the gate of a FET or grid of a triode acting as the first preamp.

The large value allows the puny 20 to 100pF capacitance of the capsule to work down to 20Hz PLUS bypass and eliminate nearly all the resistor's thermal noise voltage.

... Phil

Reply to
Phil Allison

Your meter is broke ;)

Reply to
John S

Did you think of re-arranging the circuitry so only ONE resistor is needed (for both) functions?

Reply to
Robert Baer

They seem to charge by the ohm.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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John Larkin

Cheaper but bigger, 1% tolerance, good to 1.5kV:

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Cheaper but bigger and good to 3kV:

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Reply to
Chris Jones

It's them thar Texans: ohm, ohm on the range...

Reply to
Robert Baer

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