Diode sggestions, please

Started by Wild E, August 08, 2010, 03:15:07 PM

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Wild E


I need to block 14.5VDC so I can get 3 colors from a 2 color LED. (ckt1, ckt2, bypass) I have the schematic in my head but I don't know which diodes I should use. Any help would be appreciated.

Earthscum

4148's, or a zener stack to add up? You need the diode itself to block the voltage? Or are you using the diode to extract the voltage? or using it to drop 14.5V down to the LED's req's (or everything to the LED except the 14.5)?

4148's can handle (I believe, without looking it up) about 200mA. They have a Vf of around .6-.7V.

4001-7(?) can handle varying degrees of current, and have about the same Vf as the 4148's.

Ge's have even lower Vf.

Zeners have all sorts of flavors.
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Wild E

From what I've read you can get a third color from a two color led by lighting both colors. I want to keep it from feeding back into the unused anode when in single color mode. This will take 2 diodes in my design. D1 & D2 anodes to "both" V+, D1 cathode to color1 anode & ckt1 indicator V+ and D2 cathode to color2 anode & ckt2 indicator V+

Earthscum

if this is the 3-lead LED, then yeah, should be easy to do. One is common, and the other 2 will just get resistors hooked to them to bring them into the right current range. When you do that, your voltage for each LED diode will be different, depending on the current drop through the resistors.

If it's the 2-lead LED, then you will have to probably just use a single resistor and vary it until you find the right color. If it's one color or the other at exact voltages, then you are looking at building some kind of circuit to create AC signal to vary between the 2 at a fast enough rate that the colors "seem" to blend to your eyes.
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Earthscum

Use this to figure out resistor values, if you haven't found a calculator yet (or aren't as lazy as me and figure out your own math, lol).

http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

You should be able to just use 2 diodes for directing the current, an drop resistors. IMHO, you shouldn't need anything more than the LED, a resistor or 2 and maybe a trimpot, but I dunno... there's so many different kinds of LED's these days.
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