🚀 go-pugleaf

In article <5170101@hplsla.HP.COM> tomb@hplsla.HP.COM (Tom Bruhns) writes:

Thanks to Tom and to others who replied in this newsgroup. I also 
received several replies by email. The summary is 
that, from data books, and from theoretical calculation, the 
impedance is better than a few megohms. 

The leakage current is, according to one email response I got, 
25nA max at 20 volts, 5000 at 75 volts (from a National Semi databook)
Assuming a linear slope, the dynamic impedance is 55V/5uA = 11 Mohm. 
The actual dynamic impedance will be better because the exponential
curve will lie below the straight line approximation. 

The capacitance of the reverse biased junction, according to one posted 
response, is 1.5 pF at 2.5V. In that case, Xc is 5.3Mohm, for 20KHz.
Actually I only care about telephone line bandwidth (4KHz, max),
so the impedance is greater. 

In my application there are 2 of these reverse biased diodes, in 
parallel, sharing voltage with a 220K resistor. So it seems that the
parallel combination of two 1N4148's is negligible compared to 220K.

Thanks again, 

/ Jon Sreekanth

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