I'm using a derivitative of bob's circuit to produce a rail to clamp to.

That is, two forward diodes and a transistor arranged as in bob's=20
schematic to produce vclamp.  The second diode is to compensate for the=20
additional drop...  I use BAT54S'es as clamps, so I just use a single=20
54S ignoring the center pin to get the two diodes....

Then a whole bunch of bat 54S'es used as normal clamps to my vclamp rail=20
and ground.

-forrest

On 9/6/2011 2:09 PM, Marcel Duchamp wrote:
> On 9/6/2011 9:38 AM, Bob Blick wrote:
>> Hi Matt,
>>
>> Attached is a circuit that I have used many times. This one is for eight
>> inputs and protects against positive swings. It will work for +5 or
>> lower, just attach the diode anode to the same supply as the micro.
>>
>> Cheerful regards,
>>
>> Bob
>>
>>
>>
>>
> I like your idea, Bob.
>
> It might be slightly improved by using 9 transistors instead of 8 plus
> the diode in order to better match the Vbe.  And if possible, a
> transistor array would probably have very close Vbe matching.  None of
> this usually matters though.

--=20
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