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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 07-24-2003 06:39 PM                     Very good explanation, Phil. I'll bet that will make sense to Ken without any problem. Now, a question I have: Can you explain the theory of operation of that damned RA unit? I never understood how that worked. Apparently, some others are in the same boat. I know it has to be simple, but I am just missing a key. Thanks  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-24-2003 07:01 PM                  Paul, it's a bit of a joke on my part...sorry. There is no separate "boost" circuit. The power supply relies on a high no-load open-voltage for the "boost". Thus the boost circuit is also correct since it's the same as the main ckt. (It's all in their excellent transformer design & saturation) That RA crap is nothing more than an automatic surge protector to limit the charging current to the filter cap. >>> Phil  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 07-24-2003 11:18 PM                        We had actual "boost circuits" installed on some of our FP30Es. I am not familiar with the details of the circuit, unfortunately. A friend of mine came up with the idea because he wanted to try using welding rectifiers. The experiment wasn`t too successful though.  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-24-2003 11:41 PM                     Paul: You are correct; Phill's explanation helped greatly. Phill, Like this: ? Pretend, of course, that the resistor is a xenon bulb. When I run this simulation and connect a scope, I only see a half-wave rectified signal. Why?  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-25-2003 12:08 AM                  Ken, it sounds like you are referring to circuit simulation in software rather than a "breadboard"? Either way, the scope connection "dots" are located in the wrong place.... that would indeed only give you a 1/2-wave ckt and waveform since the bottom diode is not included in the scope-monitoring point of the load. You are looking at the voltage across the bottom diode.... The scope should be connected across the load resistor. Mike, yes as a result of low line voltages in the field, many had a "real" boost ckt to ummm... boost the initial voltage. >>> Phil  |  IP: Logged Sam Hunter Jedi Master Film Handler Posts: 779 From: West Monroe, LA, USA Registered: Jan 2002 posted 07-25-2003 12:09 AM                     Because the diode acts as a one way valve and that there is no filtering of the rectified voltage. The simplest filter is just a large value capacitor connected between the rectifier out and return . Nominal values are anywhere between 50-100000uF depending on the design and use of the supply. The filter cap smoothes out the half wave waveform. Due to my late night memory fog I have deleted the incorrect portion of this post and hope that FT will forgive my oversight [ 07-25-2003, 11:50 AM: Message edited by: Sam Hunter ]  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-25-2003 12:19 AM                     Yes, I am using Electronics Workbench. The dot to the lower left was not a scope connection, it was a connection for a grouding point. I removed all the grounds as you said, but when I went to run the simulation, a box popped up that said the circuit requires a grouding point for simulation. So I added one, without giving much thought as to its location. I moved the ground to the bottom of the resistor, and now I get a full-wave rectified signal.  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-25-2003 12:39 AM                  But Ken, your scope is ground referenced so the left dot was indeed the scope monitoring point... So, in that case you were looking at a 1/2-wave ckt...and got the correct waveform for it >>> Phil  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-25-2003 12:49 AM                     Phill, now to make sure I fully understand how the circuit works, I followed your second suggestion and reversed the diodes. Indeed, I got a negative full-wave rectified signal. So I can see that it does work. But I still don't understand how it works. I return to my original question: As the current leaves the transformer, how can it get past the dioes if they are facing the way they are?  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-25-2003 01:14 AM                  Remember, the transformer "takes in" the current as well as put's it out. It has to in order to form a complete, closed circuit. (God forgive me for saying this... Kirchoff's Law) So, in the case of a positive supply, the diodes only allow current to flow "from" the xmfr. The center tap is the "into". In the negative supply, the diode only allow the current to flow "into" the xmfr. The center tap is the "from". The circuit is closed and complete only while a diode is conducting. >>> Phil  |  IP: Logged Sam Hunter Jedi Master Film Handler Posts: 779 From: West Monroe, LA, USA Registered: Jan 2002 posted 07-25-2003 12:10 PM                     Please refer to my last but anyway on a center tapped full wave only one diode cunducts at a time as the ac between the center tap and the two other ends are 180 Deg out of phase. Refer to my somewhat better drawings for a visualization of current flow and phase relationships. P.S. Phil, its been a while but I remember this shit and corrected myself  |  IP: Logged Daryl C. W. O'Shea Film God Posts: 3977 From: Midland Ontario Canada (where Panavision & IMAX lenses come from) Registered: Jun 2002 posted 07-25-2003 11:19 PM                        Jerkoff's Law! You shall never be forgiven, Phil. You know this is probably one of the best uses of the upload feature so far... I guess you're forgiven then.  |  IP: Logged Ken Lackner Phenomenal Film Handler Posts: 1907 From: Atlanta, GA, USA Registered: Sep 2001 posted 07-26-2003 12:43 AM                     Wachu got against Kirchoff's Law?  |  IP: Logged Paul G. Thompson The Weenie Man Posts: 4718 From: Mount Vernon WA USA Registered: Nov 2000 posted 07-26-2003 12:49 AM                     How you define Kirchoff's Law depends on your frame of mind and whether or not there is a full moon.  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-26-2003 02:22 AM                  Daryl: That sound's like a character from "Flesh Gordon". Ken, if your referring to me, I was merrily interjecting some humor cuz of my reference to "text-book" stuff. I hope all the time that many of us have spent in trying to help you out, did. >>> Phil  |  IP: Logged

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