I had the experience of looking at a circuit board with a resistor marked 50G, indicating 50,000 Megohms. One of the resistor leads was mounted on a teflon pad since the resistance of the board would probably be a good portion of 50 Gigs.
Any idea what application would make use of a resistor so high?
-Bill
To work with small currents, of course. I have resistors to 1T in my inventory. When using these I find that air is better than teflon.
Sometimes one has to replace the resistor with a capacitor, if you get my drift.
I agree
One application is a feedback resistor for a transimpedance amp for a photodiode.
Steve Noll | The Used Equipment Dealer Directory: |
Hello Win,
And after turning it on, don't breathe :-)
Regards, Joerg
Wouldn't that be more than the resistance of air?
I think your reading it wrong. I think the highest resistors only make it to 10's of Meg, and not 1000's
15M, occasionally 18M is usually the highest readily available value. Anything higher I'd count under boutique parts. Might be needed for highly specialized measurements but should not be used in day to day designs IMHO.
Regards, Joerg
** Wrong:
Condenser microphones typically use 1Gohm resistors to bias the capsule and FET preamp.
......... Phil
In article , Steve Noll wrote: [... 50G ....]
I can imagine a situation where you'd want one that high on a transimpedance amp. Consider an op-amp with a 1nA bias current.
50E9 * 1E-9 = 50VThat's more offset voltage than the Vcc limit of most op-amps.
Nah, 50G is not all that high.
Best regards, Spehro Pefhany
In article , Phil Allison wrote: [...]
I know one design uses quite a bit more than even that.
Are there distributors who carry either of these guys parts?
"Ken Smith"
** How mysterious .........What does it take to get you to spill the beans ??
....... Phil
I've built photodiode transimpedance amps using as high as 100G-ohm resistors before. It takes some care, but is definitely do-able. It's interesting and dramatic to watch the offsets decrease when the box containing the circuit is flushed with dry nitrogen.
Steve Noll | The Used Equipment Dealer Directory: |
But you can look! 1V/1Tohm = 6 Millions electrons per s. Your eyes are sensitive to a few hundreds photons per s. For a particle physicist 1 Tohm is shortcut.
Punny!
Of the more common hi-R resistors, note that DigiKey and Mouser carry the various Ohmite series; to 5,000Megs and 20KV rating at 1% and 5%. ...and Ohmite is not the only maker...
22 meg was readily available in the old carbon comp days in 5%, 10% and 20%.
Meggitt electronic components, do 0805 SMD cermet resistors, in a range from 15M, to 50G. Maybe even further than this, but this is the highest I have used. The tolerance, is only 30% on the higher values, and with slightly worse than normal temperature coefficients, but readily available (at least in the UK - both RS, and Farnell do them).
Best Wishes
"Spehro Pefhany" schreef in bericht news: snipped-for-privacy@4ax.com...
And if that isn't enough, you can always put a bunch in series ;)
Have something to add? Share your thoughts — no account required.
Ask the community — no account required