Matthew T. Russotto wrote:
In article <47deee6f$0$6737$9b4e6d93@newsspool3.arcor-online.net>, Linards Ticmanis <ticmanis@gmx.de> wrote:glen herrmannsfeldt wrote:Many switching power supplies don't like to run without a load.In the sense of "they won't put out the right voltages in that case" or in the sense of "they'll be damaged"? I thought it was only the former?What the Apple ][ Reference Manual calls a "no load" condition on an Apple power supply is a short. In that case the supply will shut down, start back up, shut down, start back up, etc, and make a clicking noise while it's doing it. If you run it with the outputs open, I think it just won't regulate right. Easiest thing to do is to put something like a headlamp bulb across the 5V output.
It actually says that if the power supply is disconnected from the main board, the power supply will sense this "no load" condition and respond by "short circuiting" its +5v output (with a "crowbar" SCR)-- because the output voltage is trying to exceed the rated voltage limit. The unloaded condition is unusual for an Apple II power supply, but the "clicking" mode of repeated crowbar operations should be safe. When forming the line-side supply capacitors, the clicking won't even start until the voltage has been increased a few times. And I'd worry a little about the supply straining to regulate to a dummy load when its input voltage is well below rated levels. But if you'd prefer to avoid crowbar mode, putting a load on the +5 supply that does not exceed 2.5A should be OK (might be worth checking how much current your chosen bulb draws--they tend to have very low resistance when cold). -michael NadaPong: Network game demo for Apple II computers! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."