On 7/22/2011 9:21 PM, IVP wrote:
> My understanding is that a TVS clamps *above* its rated voltage
> and would not be effective below that, including -ve excursions,
> rather like a zener. I believe a TVS has no Schottky region. I've
> done a quick Google for 'under voltage protection device' but what
> I saw were generally slowish protection circuits for PSUs etc, not
> fast components like a TVS
A TVS is basically a zener from a 'mental picture' of it...

And unless I'm missing something...  a zener/TVSS tied to ground/vdd=20
will clamp at it's rated voltage, and a couple of volts or less below zero.

That is, Unidrectional TVS'es basically have a Vf of a few volts or=20
less, just like a zener.   And a breakdown voltage in the reverse=20
direction of a lot larger voltage.    So a positive voltage won't be=20
clamped to say dozens of volts, and a negative voltage across the diode=20
will be clamped at a fairly low Vf voltage.

Bidirectional TVS'es have the larger voltage breakdown in both=20
directions - my understanding is that they consist of back to back=20
unidirectional TVS diodes.  Which leads me to believe that a=20
Unidirectional diode would work just fine for my application.

FYI, see=20
http://www.littelfuse.com/data/en/Data_Sheets/Littelfuse_TVS-Diodes_P6SMB.p=
df

-forrest


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