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Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
I have a problem with some non-intuitive behavior from a zener diode.
When connected "forwardly" with 13k of resistance upstream and a 12V supply, I see 11V at the diode. I would expect 0.7V, the "standard" silicon diode forward voltage.
Registered Member #146
Joined: Sun Feb 12 2006, 04:21AM
Location: Austin Tx
Posts: 1055
Well, that is weird... all my my zeners are around the typical 1V Vfwd range. Do you have a part number on that diode? And uhh, you are sure you have it the right way around, yes?
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
Ok, here are some more details:
Its a 1N4568A connected to a ~13V supply through 13k in series. In the "normal" direction I measure 6.4V (yay!). In the "backwards" (forward) direction, I measure 11V. I'm sure this diode is "good".
Curve trace shows knee in the forward direction at 10.8V.
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
A single junction zener/avalanche reference diode usually has minimum dV/dT when the reference voltage is in the 4 to 5 volt range, I'm not sure, but I suspect that the 1N4568 is composed of more than one junction a common 'trick' is to use a zener of about 5v6 in series with a forward-biased diode the zener would have dV/dT of about +2mV/degree, cancelled by the diode's -2mV/degree so maybe that's what's inside the device?
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Zener diode forward voltage problem
