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Leds Answered

New to site not sure this were to post this.

Led's for ac powered model railroading, to replace incandescent bulbs.  Voltage to track varies from 5 to 17 volts AC.  Leds will light up, but what is it doing to them. They do not pop like a flash bulb at top voltage. I've rectified some to dc voltage for lights in cars, the variable voltage seems to power them.

Ideally a circuit that put out a constant 3.2 DC volts, with a variable 5 to 17 volt AC input.  Or maybe would a constant 3.2 volt AC out would function?

I found that with HO DCC control, a white led with a 1k resistor will function, have not ran them for more than few hours though.

Prewired rectified leds go for around $3.00  each, 5 passenger cars, 2 bulbs each, gets pricey with 4 sets of cars.

Surly someone has gone through this.



5 years ago

Bit too lazy to do the calculations right now but there are several option to overcome the problem without sacrificing the lifetime of the LED.

A simple resistor wth a diode will work if the resistor is set for the highest voltage that your system puts out, but it also means the LED will react to changes in the supply voltage like a dimmer.

Especially for moving trains this in not wanted.

A Zener diode parallel to the LED with a normal diode in series to the power will provide constant brightness from about 3V to full.

For example a 3.3V Zener for a LED rated in the same range.

Obviously a current limiting resistor is still needed if you use sensitive LED's like these miniature 2mm white ones.


5 years ago

So what it is exactly that you wanted to ask? there are no question