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dxAce wrote: wrote: Thanks for the info and advice Pete. I recently saw a comment that standard 1N4002 type (60 Hz) diodes are actually good replacements for the PIN diodes on the front-end band pass switching networks. Have you heard of this? It's supposed to be the higher voltage parts in that series, (the 1N4007). Whatever happened to all those Schottky Diode mods that seemed to be the rage years ago? Would this be something similar? Semiconductor-wise, they're pretty much the opposite. A Schottky diode uses only one type of semiconductor and the junction is silicon-metal. (The modern version of a cat's wisker detector). Their feature is that they don't store a cloud of electrons or holes inside their junction so that they don't have a feature called "reverse recovery". (Executive summary, they don't look like a short circuit for a few nanoseconds when the current switches direction). Reverse recovery causes all sort of problems in switching power supplies, and is also the cause of RFI from regular old transformer/rectifier power supplies. A PIN diode uses both P and N type doping in the junction, but in addition there is a layer of Intrinsic (neutrally doped) silicon in the middle. This causes a bunch of stored charge to hang around in the middle of the junction, so that for high frequencies it doesn't look like a diode anymore. They're used for switches by forward biasing them to turn them on, or when reverse biased the stored charge eventually gets swept out of the junction and they look like an open circuit (or really, a capacitor). As I understand it, there's a tradeoff between storage time (and switching speed) and capacitance. The designer would like as much storage time (sets the low frequency response) and the minimum capacitance. Mark Zenier Googleproofaddress(account:mzenier provider:eskimo domain:com) |
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