At 03.38 2011.09.17, you wrote: >On Fri, Sep 16, 2011 at 9:20 PM, Dwayne Reid wrot= e: > >> At 05:53 PM 9/16/2011, V G wrote: >> >I want to be able to generate a low current isolated supply (for drivin= g >> my >> >solid state relay MOSFETs) gate-to-source. I googled and found this: >> >http://www.maxim-ic.com/app-notes/index.mvp/id/1932 >> > >> >1. How does this circuit work? I'm guessing the 74HC14s give a sharp >> signal >> >to U1 whose outputs oscillate signals into high pass filters C1 and C2.= At >> >that point, I'm guessing the signal looks more like a sine wave which >> passes >> >through the full wave rectifier comped of those 4 diodes and the >> capacitor. >> >Tell me if I'm wrong. >> >> Nope - you are pretty much bang-on. However, the signal coupled >> through the capacitors is a square wave, not sine. >> >> You can think of the coupling capacitors as high-pass filters but >> that is NOT their intent and might cause confusion at a later >> date. Rather, they present a low impedance at the high switching >> frequency used, and therefore couple most of the energy to the load. >> >> The coupling capacitors present a fairly high impedance (~13k) at >> line frequency (60 Hz). >> > >1. How do you calculate the impedance of a capacitor at a particular >fequency? It's called capacitive reactance (XC), and it's obviously measured in ohms: XC =3D 1 / ( F*Hz*Pi2 ) Where F is Farad of the capacitor, Hz is the frequency for which you wanna know the impedance, and Pi2 is roughly 6.28 Cheers, Mario --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .