When selecting a power adapter it is good to understand a few things about how they work. Power adapters are either of the unregulated or regulated type. Within the regulate type there are two basic designs. The three possibilities are listed below:
Unregulated Silicon Steel Transformer Type -- This type employs an old fashioned 50/60 Hz transformer who's output is rectified and filtered into DC. This vary simple design has the limitation that the output voltage is very poorly regulated. The output voltage can be 1.5 times the rated voltage for very low output current. As the output current increases the output voltage drops and becomes close to the rated voltage at the rated output current. Also the output voltage is strongly effected by variation of line voltage (it is proportional). Because of this lack of regulation devices that use this type of power adapter usually have internal regulators. The silicon steel transformer makes these units heavy and the lack of line regulation means that different adapters must be used with different line voltages. Regulated Silicon Steel Transformer Type -- This type is the same as described above but with a linear regulator tacked on. The linear regulator works for both line and load variation and may provide short circuit protection. This type solves the regulation issues at the expense of efficiency. Regulated Ferrite Transformer Type -- This more complex design creates an unregulated 160VDC (assuming 120VAC mains) by rectifying and filtering the line voltage. Then a switching mode regulator circuit converts this DC voltage into high frequency AC which drives a ferrite transformer that creates a regulated output voltage. This type has the advantage of high efficiency; a smaller transformer and filter capacitors and the ability to function with a wide range of line voltages. I have an unregulated 12V power adapter here that puts out 17.3V with no load. A similar 24V unit would put out 34.6V. Clearly a 24V power adapter like this would not be a good choice for a device with a maximum input rating 28V. One danger is that it is common practice to plug a working adapter into a device. When this is done the device is briefly subjected to the high unloaded output voltage of the adapter. This can damage a device even if the adapter is not plugged in because the adapter's output filter capacitors can store charge for long periods. Because the net5501 has an internal regulator there is nothing fundamentally wrong with using an unregulated type of adapter. But, under all line and load conditions, that output voltage must be within the 28V rating of the net5501. -- Gavrik On Jan 17, 2008 11:28 PM, Niels Ole Staub Kirkeby <[EMAIL PROTECTED]> wrote: > > > Niels Ole Staub Kirkeby wrote: > > > >> I'm planning on getting power for the net5501 from a PLC (Siemens or > >> Allen-Bradley) 24VDC power supply. Has anyone > >> had > >> any experience with that kind of configuration ? AFAIK the PLC power > >> supply delivers at least 24 CDV while the > >> net5501 > >> has a max of 28-30 VDC (25 VDC recommended, right ?). > > > > I run mine from 12V DC just because I have an old Netgear hub power > > supply around. > > > > Soekris website says it will run on 6 to 25 volts, max draw 20 watt. > > Or you can bypass the internal regulator and supply a regulated 5 volts. > > > > - Martin > > > > Yeah, i know. All during my test phase i had been using a 12 VDC, a PSU from > Cortex Systems. This was the first > time we connected the net5501 to 24 VDC and it became toast ! It could be a > bad component ofcourse but .... :-) > > Niels Ole Kirkeby > > > > > _______________________________________________ > Soekris-tech mailing list > [email protected] > http://lists.soekris.com/mailman/listinfo/soekris-tech > _______________________________________________ Soekris-tech mailing list [email protected] http://lists.soekris.com/mailman/listinfo/soekris-tech
