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Joined: Jun 2007
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Silly me, I didn't see the discussion link until after I sent a PM. Oops!
Anyway, here's how I think it works:
The diode connected to the switch is the key. When the circuit to this diode is completed, the current flows across the diode and effectively bypasses the lamp, diode and capacitor due to the other diode being connected backwards in respect to the diode on the switch. Without the diode connected to the lamp, the light would glow dimly. With the diode blocking the other half of the AC waveform, the lamp will only see the 0.7V or so dropped across the diode, not nearly enough to light a 120V bulb.
The polarized cap is probably to prevent flicker. I don't think it would be wise to screw in a CFL into this contraption!
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Joined: Nov 2005
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The caps were optional. The diodes were mandatory. Joe
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Joined: Oct 2002
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That's easy. It's magic...
Seriously though, in my head I can make it work if the switches are DPDT and configuired in sort of a "three-way" set up, but each switch would affect the other switch. Let me put it to paper...
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Joined: Nov 2005
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Joined: Oct 2002
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That was my next guess. The question throws you off if you're thinking in AC terms.
The Capacitors seem needless though. Lamps don't usually require much supply smoothing, unless I'm missing their intended purpose in the circuit?
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Joined: Oct 2002
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Oops, I didn't read back. The capacitors are in fact optional.
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Joined: Jun 2007
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Not only are they optional, but I think they are there solely to throw you off. I took another look and each lamp receives the full AC wave, so those polarized caps would go BOOM anyway. It might be CFL safe after all.
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Joined: Nov 2005
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You probably ought to take a third look at it HWG. I didn't put the caps in there to blow up or throw off, but to smooth out. If you still can't make sense of it, say pretty please with silicon on top, and I'll draw it up a little more clearly. Joe
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Joined: Jun 2007
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Yup.... sure enough, the cap would work just fine. Man, this is a devious little puzzle.
Now I want to make one of these, put it in a nice Lexan box and confuse others. I have the pars laying around in the junk pile. I'll probably use neon bulbs instead of incandescents just too keep the contraption small.
I'm going to laugh if my professor puts this as a bonus question on a test in my Circuit Analysis & Design class.
I have seen some lamp designs that have a full wave rectifier and cap to reduce flicker but I honestly haven't had a noticeable flicker issue with incandescent lamps. The filament never has time to cool durning the tiny amount of time the voltage drops to zero in the sine wave.
How is it possible that a little circuit like this is so hard to understand? It's probably because I have never seen anything so weird! Is this a purely theoretical circuit or was a commercial design based on it?
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Joined: Feb 2002
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The neons may give it away - only one electrode will glow, so people will know that there are diodes involved.
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Posts: 404
Joined: March 2007
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