On Tue, Sep 6, 2011 at 5:32 AM, RussellMc wrote: > An extremely good alternative to zener diodes is a clamp regulator > such as a TL431(which I tend to recommend to all and sundry). The > lower voltage TLV431 has some advantages. > > This has a much sharper "knee" than a zener and can be obtained in > 0.5%, 1% & 2% accuracy versions. "Programming" requires 2 resistors. > If you are committed to an existing PCB then a small add in PCB could > be made to insert where the zener no longer is. > I really like the TL431. It's dirt cheap. The TL431 datasheet says that it needs a minimum of 1mA cathode current. This might mess up A/D accuracy if using a higher value series resistor. The TLV431 is more acceptable, at ~55uA cathode current. These values probably vary slightly depending on manufacturer. --=20 Martin K. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .