[sdiy] Protecting an input from overvoltage

[Seb Francis]

Doh!  .. of course a better solution that (b) is to use schottky diodes 
from the power rails to the inputs.
But I'm still concerned that this will introduce distortion for normal 
signal voltages.

Seb


Seb Francis wrote:
> Hi,
>
> I'm trying to work out the best (hi-fi) way to protect the input of a 
> CODEC chip from overvoltage.
>
> The datasheet recommended input configuration is this:
> http://burnit.co.uk/sdiy/balanced_input_stage.gif
>
> Basically AIN+/AIN- on the CODEC chip need to be kept >=0V and <=5V.  
> I thought of a couple of solutions, but both seem to have drawbacks:
>
> (a) Run the input opamps from power rails of 0V and 5V.
> Drawback:
> I want to be able to drive the CODEC near FSR (5.6V ptp AIN+ - AIN-) 
> even when running from an unbalanced source (i.e. the AIN- input 
> grounded).  My preferred opamp OP275 won't go anywhere near the power 
> rails.
> Maybe there's another more suited opamp also with excellent audio 
> performance?
>
> (b) Use 2 sets of series zener & signal diode to clip any overvoltage.
> Drawback:
> I'm not sure the diodes will be fast enough acting to protect the 
> CODEC input.
> I'm concerned the leakage current of the diodes will distort the 
> normal signal.
>
> Any comments, other ideas?
>
> Seb
>
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