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Old August 5th, 2008   #7
Senior Member
Join Date: Jan 2008
Posts: 102

Originally Posted by Nigel Worsley
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.
I did look for tranzorbs but their breakdown voltage was not good enough at over 4V for most of them. The absolute maximum in my system is 4.0V for the processor.
I will check again.

The diode is the correct way to go here in my opinion, if we can make it work.

So we have 3V3, diode(a-k), pullup, dataline+.
Did you mean the capacitor needs to go from the 3V3 to gnd on the diode a side? How will this work if the diode is reverse biased?

Or do you mean the capacitor should go across the diode, providing an ac path to 3V3?

Kind regards

Last edited by berntd; August 5th, 2008 at 06:01 PM.
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