Z
z_jdp298
Guest
This would be my first post to CPF.
I have a hub-dyno rear standlight of my own design, which without drawing the diagram, is a bridge rectifier, 5.5V 1F supercap, then an LM317 regulated to 2.1volts, fed across 1 red LED.
Its not the only rear standlight, I have a BM tophat or whatever they call it. The circuit works just fine and the supercap from Maplin seems to cope with whatever comes its way. On test I used a Hornby controller and it didnt even get warm at 7v. Admittedly the load was minimal at that point. the Bridge Rectifier holds the dyno voltage down, as does the ohmic resistance of the cable from fwd to aft.
Given the LED needs 2.1 volts, the supercap will drive it until it shows about 2.8v, at which point it can't squeeze through the LM317 and it fades. I had reckoned to use a PNP transistor, opening up when the output of the LM317 went low, thus connecting the supercap straight through for a bit more power, but that's not effective, nor can I make it work. Is there some voltage regulator IC or circuit design which can drag some more power out of the supercap for me?
Jon, near Swindon
I have a hub-dyno rear standlight of my own design, which without drawing the diagram, is a bridge rectifier, 5.5V 1F supercap, then an LM317 regulated to 2.1volts, fed across 1 red LED.
Its not the only rear standlight, I have a BM tophat or whatever they call it. The circuit works just fine and the supercap from Maplin seems to cope with whatever comes its way. On test I used a Hornby controller and it didnt even get warm at 7v. Admittedly the load was minimal at that point. the Bridge Rectifier holds the dyno voltage down, as does the ohmic resistance of the cable from fwd to aft.
Given the LED needs 2.1 volts, the supercap will drive it until it shows about 2.8v, at which point it can't squeeze through the LM317 and it fades. I had reckoned to use a PNP transistor, opening up when the output of the LM317 went low, thus connecting the supercap straight through for a bit more power, but that's not effective, nor can I make it work. Is there some voltage regulator IC or circuit design which can drag some more power out of the supercap for me?
Jon, near Swindon