High off-resistance diode

Discussion in 'Electronics Resources' started by rachelgl, Apr 5, 2011.

  1. rachelgl

    Thread Starter New Member

    Apr 5, 2011
    5
    0
    Hi!

    I'm looking for a schottky diode (Vd<0.5V) that has a high "off-state" resistance (in the range of 10GΩ). I need this because I am passing a AC signal through a diode at low frequencies and charging up a small capacitor (≈1pF). The AC isn't rectifying through the diode as the capacitor is too small for the low frequency signal and it discharging through the diode during each cycle. I cant increase my capacitor value so I'm thinking I'll change the charge time RC and increase R. Is there any such diode that exists commercially?

    Thanks

    Rachel
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,144
    1,790
    I don't think so. All diodes have reverse leakage currents in the micro amps range at pretty low voltages which puts them pretty far away from the range you are looking for. I think you're SOL
     
  3. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
    300
    Schottkys are not renowned for low leakage. Ordinary silicon PN diodes are available with lower reverse leakages down to 1nA typical at 25C, e.g. 1N3595, but their forward voltages are a bit more than 0.5V at room temperature.

    Just as important is the diode self-capacitance. Most run-of-the-mill silicon types will have more than 1pF (1n3595 is ~8pF, 1N916 is 2pF) . Actually, this may be the real reason for the failure to rectify: The AC can be coupled straight through the diode self-capacitance, without any need to consider reverse leakage, so that the circuit functions as a capacitive divider.

    If you are trying to rectify a low frequency, what is the interest in having such a low capacitance in the first place? If the load capacitance can be increased, the diode requirement may become more reasonable.
     
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