David wrote:
So collector-base junctions make good low leakage high voltage diodes
although they are slow
I guess it depends on what one means by "slow" and "fast."
The B-C junction of an MPSH10/MMBTH10 or 2N/PN/MMBT5179 switches on in
<1nS and off in <2nS, which is comparable with Schottky microwave mixer
diodes such as the Agilent HSMS282x series and better than "ultra-fast"
silicon switching diodes such as the FD700 and 1S1585. (I did my
switching tests at 20mA.) (Note that the silicon and Schottky switching
diodes have reverse leakage currents from several hundred to tens of
thousands of times higher than the B-C junction of an MPSH10/MMBTH10.)
The gate junction of a 2N/PN/MMBF4117A JFET switches on in <2nS and off
in <4nS.
The cheapest guaranteed low leakage diode is probably some variety of
4117/4118/4119 n-channel JFET.
If the 5pA reverse leakage current of the MPSH10/MMBTH10 is too much and
one must, must, must get leakage down to 1pA, the 2N/PN/MMBF4117A is the
best inexpensive choice that I'm aware of.
Best regards,
Charles
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