> I don't know if i'm saying something completly stupid, but don't you > think that the Zener shoud be after the transistor? and actually I think > you don't need the transistor at all. if your power supply could give > you more then 100mA, use just a resistor and a Zener. No, the transistor is there for good reason. In a pure shunt regulator (like what you described), the shut has to handle the max power supply current when there is no load. This is inefficient and most easily obtainable zeners like 10mA to 20mA, not 100mA. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu