It looks to me like those circuits work simply by having a transistor which is kept OFF by the base-emitter (or gate-source) resistor until the zener conducts enough current to cause enough voltage drop across the resistor to turn the transistor ON. I don't think these will be as accurate as a zener can be by itself because the turn-on voltage/current characteristics of the transistor and the resistance of the resistor will all affect the clamping voltage. On Thu, Mar 5, 2015 at 10:13 PM, Robert Dvoracek wrote: > This reminds me of the zener booster circuit. > I have no idea how this works. > > http://www.dissident-audio.com/Yves/Z-Booster.gif > > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .