@Professor Chaos posted:I'm curious if the electrical gurus have an opinion on the need for R1 in the design: a 33 ohm 1/4 watt resistor to limit the inrush current when the capacitors are recharged.
How important is having such an inrush limiter? Is it for the sake of the circuit itself, or is it important to limit the load on the transformer?
A big spike would very likely be more than the DB107 bridge rectifier limit, but would only be a split second so not likely of consequence. What I can tell you from playing with the circuit quite a bit, is the recharge time for even 4700uF caps is well less than 1 second, so there is no big time penalty by having it. The 33R size was Dale's suggested size in his original circuit sketch, and I simply chose to stay with that. There have been no issues with either the bridge or the 1/4 watt resistor. The instantaneous current flow is just over 1/2 amp with 18VDC at the bridge output, and the 33R resistor. So it is well within the DB107's 1 Amp capability.
It is worth noting that Dale originally suggested a large 5 or 8 amp bridge feeding as many CD circuits as needed. This would make the wiring simpler if you were hand wiring a bunch of these. In designing the board (because building each using a board is quite simple) I chose to use a small bridge on each so that commonly available AC layout power could be used for any number of them. Once the cap is recharged, there is no current flow except for the tiny amount to light the led. So the total power draw on a transformer is of no real concern IMO. 
Rod
