In December RR Model Craftsman there was a flicker free LED circuit schematic that is probably copyrighted and can't be shown here, but was basically a bridge rectifier paralleling three in series super caps , feeding into a 3.3 low dropout voltage regulator. The regulator output then fed three or more paralleled LEDs. One configuration had individual current limiting resistor per LED. The other circuit had all the LEDs paralleled and used a pot as current limiter doubling as a dimmer control.
The article says the 14VAC DCC voltage is rectified and charges the three series 5.5V super caps (16.5V max). Unless I am wrong 14V* 1,414 is about 19V for bridge with capacitor output. So is DCC voltage not a real 14V rms or something much less so that the bridge voltage is less than the 16.5 VDC across the supercaps?
Second thing that puzzled me was the three un-resistored LEDs depending on one current limiting resistor. As I remember diode theory the diode with the lowest Vf will light and others may be dim or off. Experimentally I paralleled three LEDs from same manufacturer and batch and one lit brightly and others not so much. I looked up the LEDs in Mouser and the devices don't seem to have any built in current limiter. Of course more LEDs draws more current thus changing voltage drop across the resistor which could account for dimming.
Obviously the circuits work for them but something seems off in my thinking. What am I missing, or have I been out of school too long and forgot formulas and textbook theories?
