A capacitor after the diode will sort out the impedance issue, it doesn't need to be particularly large as the impedance is only relevant for higher frequencies - 100nF would probably be enough. Add a zener across it to prevent it charging up too much and changing the bias voltage.
BTW, 3.3V tranzorbs ARE available, NXP, Vishay and ST all do them.
Last edited by Nigel Worsley; August 5th, 2008 at 06:17 AM.
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