ssave@ole.UUCP (Shailendra Save) (03/05/91)
What are surge suppressor diodes, and how do they work? What configuration is used? ie, are they in series with the power supply? Or are they like zeners and in parallel? Pointers to device physics involved and technical reading appreciated. Shailendra
whit@milton.u.washington.edu (John Whitmore) (03/06/91)
In article <1837@ole.UUCP> ssave@ole.UUCP (Shailendra Save) writes: > > What are surge suppressor diodes, and how do they work? What >configuration is used? ie, are they in series with the power supply? >Or are they like zeners and in parallel? There are all kinds. Some are pairs of Si rectifiers to clamp a signal near ground (telephone 'varistors' are of this type), some are Si zeners (aka TransZorbs) with ratings for high surge currents (and relatively loose voltage specifications). Some are not doped Si at all, but largeish chunks of semiconductor with contacts on two sides (aka MOV, metal-oxide varistors, ZNR). This last type sometimes looks like a disk capacitor and is usually the type found in surge-protection devices. I have seen data sheets for yet another type of surge protector, a 'breakover' type which integrates a zener and an SCR: it has the breakdown voltage of the zener and the clamp voltage (when 'full-ON') of about 1V. And there are some exotic devices; neon bulbs are a VERY good clamp, and some radioactive-electrode gas-filled tube surge suppressors are available (or used to be) that combined extremely high current capacity with very low stray capacity and negligible leakage current. For higher voltages, a simple spark gap (like the neon light, only with nitrogen/oxygen...) is effective and cheap. Your color TV probably has a half dozen of these around the CRT neck. Usually the big surge protectors are placed in the AC line (because that is presumed to be the source of surges) for any plug-in-the-wall item. Because an input capacitor is a pretty good surge snubber, many manufacturers think they needn't put in any other device (so people in some parts of the country have to get a lot of TV repair after a thunderstorm). An input transformer, like in a linear power supply, is a pretty good surge suppressor in its own right; it'll absorb a LOT of high-frequency energy in a quick spike, and a longer spike will saturate the transformer (well, at least the OUTPUT won't burn up...) Of course, no one uses big input transformers these days. In various forms, diode clamps for surges are ubiquitous. After the first year of manufacturing 7400 series TTL circuits, it was found that the logic lines would 'ring' in some configurations, and that this would degrade the input transistors. Since that effect was found, TTL circuits have ALL had input protection diodes (shunt to ground). I have also seen some op amps (LM308 for example) with protection diodes to keep the input transistors from becoming saturated. John Whitmore
eugene@locus.com (Eugene Hu) (03/07/91)
whit@milton.u.washington.edu (John Whitmore) writes: > And there are some exotic devices; neon bulbs are a >VERY good clamp, and some radioactive-electrode gas-filled tube So does this mean that all the stuff I have plugged into power strips with neon pilots is surge protected? -- Eugene Hu lcc!eugene@seas.ucla.edu, eugene@locus.com {uunet,turnkey,att,alphacm}!lcc!eugene
whit@milton.u.washington.edu (John Whitmore) (03/08/91)
In article <eugene.668308225@fafnir.la.locus.com> eugene@locus.com (Eugene Hu) writes: >whit@milton.u.washington.edu (John Whitmore) writes: >> And there are some exotic devices; neon bulbs are a >>VERY good clamp, and some radioactive-electrode gas-filled tube > >So does this mean that all the stuff I have plugged into power strips >with neon pilots is surge protected? No; those pilot lights are connected with a 100 kOhm resistor, and will not really absorb surges. If you connect the pilot light WITHOUT the resistor, it will happily burn up a 15A fuse. I've seen it happen. Neon lights are actually Ne/He (the helium lowers the breakdown to about 70V); other gases and geometries can be had with a wide range of breakdown/breakover characteristics. Once ignited, the plasma can pull a LOT of current, so the limiting resistor is necessary. John Whitmore
erk@americ.UUCP (Erick Parsons) (03/08/91)
>In article <17958@milton.u.washington.edu> whit@milton.u.washington.edu (John Whitmore) writes: >In article <eugene.668308225@fafnir.la.locus.com> eugene@locus.com (Eugene Hu) writes: >>whit@milton.u.washington.edu (John Whitmore) writes: >>> And there are some exotic devices; neon bulbs are a >>>VERY good clamp, and some radioactive-electrode gas-filled tube >> >>So does this mean that all the stuff I have plugged into power strips >>with neon pilots is surge protected? > > No; those pilot lights are connected with a 100 kOhm resistor, >and will not really absorb surges. If you connect the pilot light >WITHOUT the resistor, it will happily burn up a 15A fuse. I've seen >it happen. > Neon lights are actually Ne/He (the helium lowers the >breakdown to about 70V); other gases and geometries can be had >with a wide range of breakdown/breakover characteristics. >Once ignited, the plasma can pull a LOT of current, so the limiting >resistor is necessary. > John Whitmore How about using two or three neon bulbs in series ? These things are cheap. This would effectively clamp the line to 140-210 Volts. -- -------------------------------------------------//------------------------- (ames att sun)!pacbell! ----> sactoh0!pacengr!americ!erk Multitasking, ucbvax!ucdavis!csusac! --/ // Never leave uunet!msac! -/ Erick Parsons \Sacramento Ca Home Without it --------------------------------------------\X/-----------------------------
danr@ais.org (Daniel Romanchik) (03/14/91)
In article <erk.1516@americ.UUCP> erk@americ.UUCP (Erick Parsons) writes: [[stuff about using neon lamps deleted]] > >How about using two or three neon bulbs in series ? These things are cheap. >This would effectively clamp the line to 140-210 Volts. > While neon lamps are good clamps, I don't believe that they will react fast enough to make good surge suppressors. Some surges are very fast, and the neon lamps will not turn on fast enough to protect equipment. Have fun, Dan (danr@irie.ais.org)