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Author Topic: N3 IREM Rectifier Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 07-22-2003 02:08 AM                     It looks like the diodes are in backwards. The cathodes of the diodes are grounded and the center taps of the star winding are connected to the anode of the xenon bulb. Are my eyes failing me or my mind? Or, am I missing something? Or, is the bulb polarity a missprint?  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 07-22-2003 11:51 PM                     If this is the rectifier I'm thinking of... all diodes are reverse polarity. nothing is grounded, the heatsink is isolated. The circuit is unusual to our non-Italian minds but it works quite well. I have much more trouble trying to understand the boost circuit!  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-23-2003 12:35 AM                     Uh....please forgive the ignorance, but how can a diode be reverse polarity? I've been trying to figure this circuit out for days, and I just can't understand how it can work with the diodes drawn the way they are. (I have a Big Sky manual in my possesion, and the Irem manual is on this site.)  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 07-23-2003 01:49 AM                     Dave, on that boost circuit....Join the crowd. I never did figure that thing out. As far as reverse polarity on the diodes, that may be true. But the cathodes are all grounded in the IREM roadmap I was looking at, including the bulb's anode. The center tap of the star was feeding the positive side of the bulb. I think either the doides are drawn incorrectly or the polarity of the bulb is reversed for some reason. I wonder if the Italians used the theory that current flows from positive to negative...as some colleges teach. [ 07-23-2003, 08:53 AM: Message edited by: Paul G. Thompson ]  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-23-2003 02:53 AM                  I'm confused as to why yous are confused. By looking at the N3 schematic on this site, it is a straight-forward "negative" power supply. The center taps are the "+" terminal and the diode anodes are the "-" terminal. The diodes are shown correctly. BTW: The boost ckt is also correct. I agree that most PS are a "positive" configuration, but there is nothing wrong with the schematic. >>> Phil  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 07-23-2003 08:43 AM                     Many apologies....My tri-focals have deceived me. When I orginally glanced at the schematic of the N3G3 IREM, somehow I saw the cathodes of the diodes tied to the cathode of the xenon lamp. I am still wondering how I saw that incorrectly. Bad eyeballs strike again. The diodes and the bulb are correct in that schematic.  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-23-2003 02:45 PM                     Paul, I am glad you understand how it works, but I still do not! Please help!  |  IP: Logged Sam Hunter Jedi Master Film Handler Posts: 779 From: West Monroe, LA, USA Registered: Jan 2002 posted 07-23-2003 03:01 PM                     Ken, just think of it as a SERIES circuit and that current flows in one direction meaning that it doesn't matter which side the diode is in as long as it gives you the correct flow of current. Personally I like my rectifiers and pass transisters on the plus or supply side myself as I have trouble understanding some of those backwards circuits myself.  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 07-23-2003 05:56 PM                     Ken, maybe this will help. Remember there is phase reversal from one side of the secondary with reference to the other side. The center tap is common to them both. Above is basically what IREM is doing, now all you have to do is add the other 4 doides and secondary windings of the star transformer. The capacitors across the diodes are RF suppression capacitors. As you can see, the power supply is not referenced to ground. The capacitor on the negative end of the bulb is a .022 mfd at 1500 volts. It is another RF suppression capacitor, and not a filter capacitor. The filter capacitor is not shown on my diagram. It is connected across the RA unit as the schematic shows in the manual. The circuit designation of the filter capacitor is C7. Remember the diodes do not conduct when the cathodes are driven positive with respect to the anode.  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-23-2003 06:36 PM                  Below is what I earlier emailed Ken, While not as elegant as Paul's diagram…yous get the gist. It's a simple 1/2 - wave explanation. The arrows represent "conventional current flow." Also, Sam's suggestion is excellent. >>> Phil  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 07-23-2003 08:33 PM                     Ken, I think Phil's explanation will also help you. If you still have problems understanding it, please let us know.  |  IP: Logged John Pytlak Film God Posts: 9987 From: Rochester, NY 14650-1922 Registered: Jan 2000 posted 07-24-2003 07:37 AM                        Links to some on-line tutorials on power supply design: http://www.tpub.com/neets/book7/index.htm http://www.tpub.com/neets/book7/27.htm http://www.tpub.com/neets/book7/27b.htm http://members.aol.com/_ht_a/RAdelkopf/rect.htm http://www.eleinmec.com/article.asp?18  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-24-2003 01:27 PM                     Thanks for the links, John. I think I am beginning to understand it. I learned about half-wave, full-wave, and bridge rectifiers back in school, but we did not study negative supplies. Below is a diagram of a full wave rectifier similar to that shown in my text book. So I guess the only difference between that and what Irem is doing is that the Irem supply is negative? Am I correct? So now I still don't understand something: why are the center taps connected to the bulb? In the circuit above, the center tap is grounded. That is the only use of a center tap that I am familiar with.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-24-2003 01:39 PM                     The centre tap does not have to be grounded. But it is the low reference to the two outside windings But it doesn't have to be actually grounded  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-24-2003 04:35 PM                  Ken, in your diagram: 1) Draw a line between the xmfr center tap and the bottom of the load resistor. 2) Erase both "ground" references. 3) Replace the load resistor with a xenon lamp…ANODE at the top. That's a basic " positive ", full-wave, xenon supply. Remember the "grounds" indicate a common connection, not necessarily an earth or chassis ground. NOW: 1) Reverse the diodes. 2) Invert the xenon lamp... CATHODE at the top. That's a basic " negative ", full-wave, xenon supply. >>> Phil  |  IP: Logged

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