Gunrunner, Please take another look at the drawing. Each LED acts as a rectifier for the other, in this case a shunt rectifier in stead of a series rectifier. That is to say that the LED will clamp the reverse voltage of the other LED to what ever it's forward voltage is. The resistor limits the current for each half cycle of the applied AC.
Dale, I have not made a technical study of the charistics of LED's but leakage current would not suprise me especially with cheep LED's. These LED's normally are connected in just such a series parallel arrangement with a single resistor in series with the whole string. I know this as I have taken them appart. I have used this circuit for many years without trouble. The only problem I have had is with LED's that have very different forward voltage drops and different forward current ratings. This causes a problem with brightness. Years ago when LED's were just starting to become popular I read an article that recomended using a diode in the shunt rectifier mode for LED's instead of the series mode as this would provide better reverse bias protection. Yes I have used these to light passenger cars and they work very well. Yes they blink and yes they vary in brightness with voltage BUT SO DO LIGHT BULBS. If this is objectionable then by all means go the full regulator and filter route, but if this is not a concern then this methode is quick and cheep.
One other problem this avoides, although it is not a problem in this application, is the question of 3 versus 4 terminal power supplies. In most train applications we use 3 terminal power supplies. One power input point, one power output point, and one point that is common to both. If you use a bridge rectifier, as is recommended in most projects, you create a 4 terminal supply. One point for the input, one point for the output, one return point for the input, and a seperate return point for the output. The input and output return points can no longer be connected together. Why is important? You cannot use a bridge rectifier to power an accessory and then trigger the accessory from the track without isolating the accessory completely from the track.
Al
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