Hi Hans. You wrote, amongst other things..
< My power supply intends to use a printed wiring spark-gap for transient/lightning protection.> Not a good idea... Mains transients and lightning etc. have a very low source impedance. If the volts get high enough to switch on your spark gap, you won't get a little blue spark accompanied by a 'tick' sound, you'll get a very big red flash that will effectively conduct a few thousand amps until your little fire ball takes out the local HRC protection device. When the flames eventually go out your 'spark gap will be a highly conductive black hole in the PCB about an inch diameter! PCB spark gaps are great on high impedance/current limited devices such as TV tube bases, where the current can't exceed a few microamps, and where the spark current drops the circuit voltage to the ionized air volt drop of the gap (say 60V), but if you try to drop your mains supply to the ionized volt drop of a 4mm gap, you'll need a lot more amps than your building will supply. MOV's don't have this problem, nor do proprietary gas-gaps which are already ionized by the addition of a radioactive material inside (that is the dust you see inside a gas gap, dispose of carefully). Serious lightening protection is achieved by stuff like the Phoenix Contact TRABTECH products, serious spike and surge protection is still achieved by MOV's. Of course, if you are intending to place your PCB spark gap as a 'component' before the mains get to your mains powered PCB, then you are proposing a sacrificial protection device, but you're still better off with a MOV. Just a thought or two. Chris Dupres Surrey, UK.
