You are completely misinterpreting the specifications. What it is saying is that .8 of the specified current of 800 microamps. 640 microamps, the device will drop 1.35 volts across it. There should be a chart that shows that at low voltages, under 1 volt, the device acts like a resistor, and at higher voltages the VI curve bends over and ends up almost horizontal. So once you get above 1.35 volts, you will be getting 80% of the rated current, and as you increase voltage the current will increase slowly until reaching the 800 micoramps. The 1.35 would be referred to as the knee voltage.
600 mW is plenty, if you have 100 Volts, and 800 microamps, that will be only 80 mW, so you will exceed it's maximum voltage long before you exceed it power rating. See http://www.semtexinternational.com/Semiconductor_Div_/Semiconductor_Product_Line/Current_Regulator_Diodes/Current_Regulators.PDF for a listing of all these devices. For complete mil specification on these devices see: http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-PRF-19500/prf19500ss463.pdf The Motorola specification sheet though is the best place to start: http://www.physics.ohio-state.edu/~cms/cfeb/datasheets/1n5297.pdf this last one shows the curve and knee I am talking about about half way down. Marshall ascottsil...@aol.com wrote: > Hi Steve, > > I checked out the data sheet but I don't understand it. At the top it > says the device will dissipate 600 mW. That's good. But there is a > parameter called "Limiting Voltage." It is described as Vl x Il = .8 > Ip. and says it is 1.35 volts for that device (1N5297). I read it as > the load voltage time the load current (wattage) is equal to 800 > microamps. That's bad. Can you drop more than 1.35 volts across the > device before it becomes hot and doesn't work anymore? Thanks for your > help. > > Andy > >> >> From: "S &J Young" <you...@konnections.net> >> To: "Silver List" <silver-list@eskimo.com> >> Subject: CS>Simple Current Limiting CS Generator >> >> Fellow CS brewers, >> >> Not well known is the fact that for about $5 you can easily convert >> your >> constant voltage CS generator (e.g. a three nine-volt battery setup) >> to one >> that limits the current to assure small particle production and >> prevent >> current "run-away". Thus your unit would then function the same as >> the >> better "constant current" commercial units. I will try to describe >> this in >> non-technical terms so many can take advantage of this. >> >> There is a device called a silicon FET current regulator diode that >> does the >> trick. This is really a small integrated circuit, shaped like a >> small >> rectifier diode, that limits current flow to a set value. The >> regulator >> diodes are small cylinders with about a 1 inch wire coming out of >> each end >> of the cylinder. One end of the cylinder is marked with a band >> around it. >> >> The part numbers are the series 1N5283 through 1N5314, with the >> current >> limits in the range of 0.22 ma thru 4.7 ma, respectively. Probably >> the one >> of most interest to us is the 1N5297 that limits the current to 1.0 >> ma. One >> manufacturer is Central Semiconductor Corp. Go to >> www.centralsemi.com and >> search for 1N5297 if you want to see the specifications and a >> drawing of the >> device. >> >> Using them is super simple. For example, for a three nine-volt >> battery >> system, just cut the wire between the minus terminal of the battery >> and the >> silver electrode. Connect the wire from the battery minus-terminal >> to the >> "banded" regulator diode wire. Connect the wire from the silver >> electrode >> to the other "non-banded" regulator diode wire. One can use 2 small >> wire >> nuts, available at any hardware store, to make the connections, >> alligator >> clips, or solder and tape them. Congratulations - you now have a >> sophisticated constant current CS generator! >> >> When brewing a new batch, the current will start out very small as >> before -- >> a few microamps--depending on water purity. As silver production >> proceeds, >> the current will rise until it reaches the value set into the >> regulator >> diode. Then it will stay constant (e.g. at 1.0 ma for a 1N5297) for >> the >> remainder of the brew time. It is impossible for the current to >> "run away" >> and increase beyond the "set point", even if the electrodes >> accidently short >> together. >> >> These regulator diodes are rated to a maximum of 100 volts. That >> means one >> could use a higher starting voltage (e.g. 54 volts from six >> nine-volt >> batteries) and reduce the brew time (it will take less time for the >> current >> to reach 1.0 ma). Again, the higher voltage is perfectly safe as >> the >> current cannot "run away" because of the current limiting effect of >> the >> regulator diode. >> >> These devices are not widely used so they are not available from >> many >> sources such as Radio Shack. One source that sells them is Mouser >> Electronics. Go to www.mouser.com and search for the part # 1N5297 >> and you >> will see the information. When I checked recently, they had about >> 1,500 of >> them in stock for a price of $4.29 each. I suppose they have a >> minimum >> order, so it would be a good idea for someone to volunteer to order >> a batch >> of them for those that express an interest in a group buy. (I don't >> have >> time to do this - sorry). >> >> I believe the use of a 1N5297 along with a few nine-volt batteries >> is by far >> simplest, goof-proof way to make a constant current CS generator. >> If you >> give it a try, please let us know how your results. >> >> --Steve Young > > >
