Hi All, Do any of you know where one could find a Motorola or equivalent MC3420 or MC3520? I know there are some suppliers of obsolete I.C.s but have lost access to the sources I used before retiring. I need one for a power supply. Thanks, Al _______________________________ Al Allworth W7PXX On the Beautiful Southern Oregon Coast ________________________________ ----- Original Message ----- From: "S-T Morrissey"
To: Sent: Wednesday, July 12, 2000 12:44 PM Subject: constant voltage transformers > > Regarding constant voltage transformers, or CVTs. > > I have been using them for over 30 years, and have always found > a sinewave output. There are some better designs that use a > larger high voltage AC capacitor for the resonant circuit that > are "harmonic neutralized" and regulate to 1% over a +,- 20% > input change. These cost about 10% to 20% more than the 3% regulation > "line conditioners", which DO put out a sinewave, but with higher > distortion. The very nature of CVT design is that it is a true > transformer (total isolation of the input from the output), that > only passes a sinewave to the output winding at the resonant > frequency of the high voltage secondary/capacitor circuit. > > If you play with one with a variac (variable transformer) input, > you can see this: as you increase the input, there is little > output until there is enough voltage (about 45 volts AC) to resonant > the high voltage secondary, at which point the output jumps to within > a few percent of the regulated level. As you drop the input voltage, > to as low as 20 VAC, the output remains near 110V as long as the > transformer resonants (test with a moderate load, like a lightbulb). > > SOLA is a major manufacturer, and they claim that their standard > conditioners (MCR series) will output a sinewave with 3% THD (total > harmonic distortion) with a square wave input. I use a 120 watt CVT > with my large frequency controlled converter in my field van to > convert the square wave to a sine wave for electronic loads. This > is similar to common marine use for AC operated electronics. > > Since CVTs are passive, they last a long time; the main problem being > the high operating temperature of the transformer core that eventually > cooks the insulation, and the high voltage (660 volt) AC capacitors that > eventually fail causing a voltage drop. The capacitors are replaceable. > > Since CVTs ONLY pass a completely isolated sinewave, I have always > used them as a primary protection of the AC line from lightning. They > always work, except in one case when the lightning arced thruout the > case to the secondary line. I have had one at a shared tower facility > where lightning has frequently smoked the varistor-based line protection > of the other equipment, while the seismic station and transmitter were > never harmed. They are an expensive ($350 for 250 watts) but permanent > solution for protecting AC loads. > > Regards, > Sean-Thomas > __________________________________________________________ > > Public Seismic Network Mailing List (PSN-L) > > To leave this list email PSN-L-REQUEST@.............. with > the body of the message (first line only): unsubscribe > See http://www.seismicnet.com/maillist.html for more information. __________________________________________________________ Public Seismic Network Mailing List (PSN-L)
Larry Cochrane <cochrane@..............>